Multiband Vertical Antenna Design.....

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marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Multiband Vertical Antenna Design.....

Post by marty_wittrock » Wed Feb 27, 2008 11:39 pm

Howdy,

I'm looking for a design for an all-band (80m - 6m) vertical antenna design much like the Comet CHA250B. I have a station at home where my antenna 'farm' is located on the lower roof of my house about 40' off the ground - not very radial-friendly. I'd like to build an antenna that's similar to the Comet CHA250B since it's a vertical capable of operating 80m - 6m and has no radials needed. I currently use a Hustler 4 band trapped vertical (40m, 20m, 15m, and 10m) and use an autotuner to tune out the VSWR issues on 80m, 75m and the WARC bands - but that leaves a lot to be desired.....hence the reason I'm looking for a new antenna that's broadband and vertical to work with my FT-100D (for 80 - 6m) and TS-140S. I have a discone I use for 2m and 440MHz that works great for what I have to ping locally on V/UHF.

I'm looking for constructive discussion on this issue since other multiband antennas (read here dipoles, beams, etc) are out of the question for my setup (it's a compromise to keep peace in the family HI HI). Comet makes an antenna that fits the bill for me, but $400 bucks seems a little steep for aluminum, brackets, a connector, and wire when it can be built for less.

Anyone with any details or links on designs please post here. TNX es 73's
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Well, finding info was easier than first thought......

Post by marty_wittrock » Sat Mar 01, 2008 6:49 pm

I went about 4 days without any answers but had a lot of readers, knowing that this would be somewhat of an interesting topic, not to mention the fact that I needed an antenna that was fairly broadband to work ALE. Well, I found the golden nugget at the following website:

http://www.vk5zdb.com/CHA250BXII.htm

This fellow fell into a mishap with his Comet 250B that could not be overcome by events - water was leaking into the 'mystery load' and caused the antenna to fail shortly after it was purchased (incredible for a $400 antenna). Taking matters into his own hands, he opened up the matching network and took photos of it. The actual design is not very descriptive, but it does offer you some insight to what's in there and the antenna's overall basic design. From what I saw and read, doesn't look too challenging - - and it's going to save me about $300 for what's been reviewed as a marginal performance broadband antenna - but for ALE it's an attractive alternative.

I'm going to try reproducing it within the next couple of weeks and will try to report back with my results. I have an old Hy-Gain antenna that will be the basis for this new antenna, so I have a foundation to start from (read here: brackets and main antenna base). Stay tuned.........
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Even more info.....take a look......

Post by marty_wittrock » Sun Mar 02, 2008 6:46 am

I corresponded with the fellow in Canada that dissected his Comet 250B and he sent me back links that proved to be even more valuable. As it turns out, many other hams are now cloning this balun and antenna design and have had very similar successful results. Here are some of the links I was sent:

http://www.vk5zdb.com/CHA250_Notes.htm

http://g8jnj.webs.com/cometcha250b.htm

http://g8jnj.webs.com/broadbandhfvertical.htm

If this doesn't start a prairie fire of interest in building broadband vertical antennas, I'm not sure what will. I know I'm building mine starting next week once the ferrites arrive.

More to follow - stay tuned.
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

I've built it and here are the results.......Excellent!

Post by marty_wittrock » Mon Mar 10, 2008 4:08 am

I wanted to write back and let those who have been checking in know what the results are of this antenna. Here is my own running history:

I got on the web and ordered ferrites from two different sources: Digikey and Newark. I ordered the ferrites on Sunday night and the Digikey order showed up on Wednesday afternoon of that week and the Newark order showed up on Friday afternoon of the same week. Here are the order details:

Digikey: QTY 6 732-1528-ND 0.92000 $5.52, QTY 2 732-1563-ND 2.94000 $5.88

Newark: 1 98K8790 Each 15 $0.51 $7.65 ($15.00 shipping direct from United Kingdom)

The ferrites I ordered from Newark were the same ones that were used in a design by a fellow in the UK. So I ended up using those first in the design since the others that I bought from Digikey were 'close' to the same parameters (and I was almost certain it would take longer to ship from the UK - funny how that turned out). I bought 15 since I knew 6 were used in the design - so I could build a couple of these antennas and have extras around for experimenting with the matching transformer later.

I built the matching transformer to specs in the article:

http://g8jnj.web.com/61balun.htm

I used the same 1/2 " soft drawn copper tubing (straightened) and then fashioned 12ga copper wire for the ground side of the copper tubes, slipped the ferrites on, and then finished the wiring to make the transformer. I used 12ga stranded wire for the tranformer windings (at first I used solid 14ga wire, but it was too hard to work with for the single loop - stranded worked much better). I had an old antenna that was wrecked from a storm a few years ago and I salvaged the mount from it. I used 2" diameter schedule 40 PVC pipe to enclose the transformer assembly and fashioned a mount on the antenna mount to encase the bottom of the PVC and SO239 connector connections from weather. The top of the 2" PVC I found a PVC that allowed a 3/4" threaded copper fitting to be screwed to the top and then used 3/4" copper pipe as the base for the antenna. I used another PVC collar to insulate the copper base from the top of the antenna mount. Used 3/4" and 1/2" copper pipe to finish the vertical element (not cheap, but here in Iowa aluminum pipe is almost nonexistant).

Assembled the rest of the antenna (the veritical element was only 22' long - the other piece of 1/2" copper made the top to gangly that it was hard to set it up. So I opted for 22' of copper for now - it would have been 32' - a 1/4 wavelength at 80m). Oh well. Connected up the coax, got back into the shack and checked the following frequencies for VSWR:

1.90 MHz = 3.1:1
3.80 MHz = 1.5:1
3.90 MHz = 1.5:1
7.00 MHz = 2.0:1
7.125 MHz = 2.0:1
7.250 MHz = 2.3:1
10.125 MHz = 1.6:1
14.0 MHz = 2.3:1
14.125 MHz = 2.3:1
14.30 MHz = 2.3:1
18.150 MHz = 1.15:1
21.0 MHz = 1.1:1
21.125 MHz = 1.1:1
21.250 MHz = 1.1:1
21.45 MHz = 1.1:1
24.430 MHz = 1.2:1
28.0 MHz = 1.1:1
28.25 MHz = 1.1:1
28.50 MHz = 1.1:1
28.750 MHz = 1.1:1
29.0 MHz = 1.1:1
29.25 MHz = 1.1:1
29.4 MHz = 1.1:1

So, as you can see, the VSWR looked pretty good for a boradband antenna. I really needs to be tweaked for length to get it to 1/4 wavelength on 80m - and that will happen by next week. Receive-wise, it seems to receive better than my vertical antenna that I had setup in its place. I could receive more of the lower bands (40m and 80m) than I could before - matched better than my HyGain vertical. I ran it on ALE for more than 3 hours, sounded on all bands (160m to 10m) and worked excellent - never saw the VSWR higher than 3.0:1 on 160m - all the other bands appeared to be either 1.1:1 or no higher than 2.0:1. I haven't tried it for QSO'ing yet - but expect to over the next couple of days.

Stay tuned.......
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

More about performance now.....

Post by marty_wittrock » Wed Mar 12, 2008 3:56 am

Okay - more data points on the broadband vertical antenna....read on....

I've given the antenna a pretty good workout on a number of bands (80m, 40m, 20m for now) and was given signal reports of S-6 and S-5 with this current design (22' vertical element - not optimal) on all those bands. I was heard well on groundwave here in the state of Iowa on a local statewide 75m net (3.970MHz) and was able to hear most everyone who checked into the net, too. Although the signal reports aren't stellar compared to my 18AVT and long wire, I'm banking on that the efficiency isn't quite there yet (more on this later).

One thing that I've learned is that while my VSWR is in good shape for this broadband antenna, there are definite drawbacks of this design because of the matching transformer (no great surprise there). There really seems to be a delicate balance between the (now) 6:1 transformer design and the length of the vertical element (and I really need to get mine to 32'). So I'm working that issue out now and will report back with what I have later this weekend (3/16). One thing I've also found out is that since my vertical element is not optimal for the lower bands, the transformer can heat up on 80m @ 100W quickly, and as a result the VSWR rises sharply. So the focus will be placed on improving the electrical length for a little more efficiency and getting a better transformer out of this.

On the flip side, this antenna receives like a magnet!! I can hear DX as good as if I were on a beam antenna - it draws signals out that I couldn't hear with my 18AVT trapped vertical and my 120' long wire.

Back to the transformer inefficiency: I discussed this issue with Martin (G8JNJ) and he suggested that I use a 7:1 transformer design. I'll rewind my transformer this weekend to that design and see where it leads me (along with the longer vertical element). I've also posted questions to him about base loading a coil on this antenna or spiral winding the vertical element with wire (to cut down on the weight). More to follow on this, soon, too.

Iain (VK5ZDB) wrote me back today and mentioned that he'll be posting pics of my antenna on his website (http://www.vk5zdb.com/CHA250_Notes.htm). So be looking for those soon. My antenna is based on common building materials (PVC and copper pipe).

Eventually we'll get an efficient broadband antenna out of this - it may take time and some may think it's impractical against other antenna designs, but someone will benefit from this info. I'm doing it so I can operate HF ALE over the operational bandwidth.

Stay tuned......
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

More data from discussions with G8JNJ......

Post by marty_wittrock » Thu Mar 13, 2008 2:41 am

More data points on the broadband vertical design, especially on the topic of electrically longer elements through wire-wound techniques.

I discussed the issue of electrically lengthening the vertical element through base loading for winding a new vertical element and here is what Martin (G8JNJ) had to say about that:

"There is a problem in adding any form of loading as it introduces varying impedances at other frequencies. A loading coil or trap which is introduced to improve performance on the LF bands will have an impact at the HF end. The least problematic method would be to add a loading coil towards the top of the radiating element and / or capacitive loading. See Petlowany loading:

http://www.n0lx.com/petlowany.html .....or....

http://dt.prohosting.com/hacks/antenna/petlowany.html

If you use a ‘lazy’ helical winding for the radiating element, say up to 4 turns per metre length it should be OK, however this technique tends to introduce unpredictable secondary resonances which could put ‘lumps and bumps’ into the frequency response.

The basis of the antenna is that it is NOT resonant on any of the desired frequencies. It is designed so that the impedance presented by the radiating element on wanted frequencies is close to the secondary impedance of the transformer for maximum energy transfer. The use of a 7.1m radiating element is not accidental. It’s intended to present a manageable impedance on the desired amateur bands, whilst not being too long (under 5/8 wave) for effective operation on 10m and 6m.

The big problem is managing the impedance presented by the radiating element on the LF bands. For example a 7m long wire over an average ground plane on 1.9MHz is typically 10 – J1310 and on 3.6MHz 10.5 –J640. As you can see the resistive element is very small in relation to the transformer secondary impedance and the reactive component is very much greater and capacitive. With my transformer design I have tried to roll off the impedance ratio at the LF end to get a closer match to the radiating element but it’s still a long way out. From this I hope you can get a good feel for what design parameters can be traded, and those which will remain a compromise. The ideal efficient broadband antenna is a ‘holy grail’ for antenna designers, and I’m sure there are a lot more qualified persons than myself who haven’t found it yet.

If you are not too worried about the performance on these HF bands you can lengthen the radiating element to improve performance on the LF bands. However you need to use lengths which will not present an impedance of greater than 1k on any of your desired frequencies. suggested lengths would be 9.2,19.4, 22.8 or 34.3m long for amateur bands.

Use the LVD programme on this website

http://zerobeat.net/G4FGQ/page3.html#S301

to give an estimation of feed impedance. And see my notes relating to auto-tuners

http://g8jnj.webs.com/usingautotuners.htm

If you can’t get the full length as a vertical other options would be to try using the transformer to feed an inverted L antenna or something like a 60m dia horizontal loop, which would also improve your need for NVIS coverage on the LF bands.

I’m interested in what you are comparing your Comet clone against, and on which bands. For example I would expect it to perform fairly well against your 18AVT on the HF bands, however it will not work anything like as well as your 120ft wire on the LF bands. I estimate 8 to 10dB worse on 80m and 20 to 30 dB worse on 1.9MHz. The only fair comparision would be against the same radiator and counterpoise, but fed with an auto-tuner in place of the matching transformer, as this would represent the best performance you could achieve in this configuration. This is how I measured my antenna performance and the standard I judge it against. By it's very nature the transformer version will be worse than this ideal, but it may be worth trading a few dB of additional loss to obtain broadband operation.

The perceived loss of performance may be due to several factors excluding the the poor impedance match. One is that it’s a lot shorter so the actual ‘aperture’ of the radiating element is much less, another is that being a vertical it has very little upward radiation, so it is a poor performer for NVIS coverage on 1.9 and 3.6MHz. Hence once you get outside the ground wave coverage there is nothing until past about 500 Miles so it’s very poor for semi-local contacts. Now you would expect that if you can hear stations you should be able to work them, however as you noticed, the lower noise floor on receive means that you can sometimes hear stations on the LF bands which would otherwise be masked by QRM on larger antennas. In summary the signal level is lower but the signal to noise ratio is much better."

Based upon this I'm most likely going to replace my (otherwise) heavy copper vertical element and replace it with a spiral wound one on smaller diameter (1" gray) electrical PVC and keep the height to 20', yet try to wind the antenna to have a length of 9.2m as Martin suggests (there are a number of multiples: 9.2m, 19.4m, 22.8m, etc.). By keeping the vertical electrical length to 9.2m I think I can contain it within 20' and have something that more closely approximates a 1/4 wavelength at 80m. Martin did mention that while winding the antenna may provide the compactness I'm looking for, it's at the expense of it being broadband since the windings introduce reactance that any well make the VSWR response curve look 'lumpy'. So that's going to be a trade off. As well, the reactance may not play well with the transformer and may cause it to heat up in certain bands where the wound vertical element is less efficient with the transformer - but that remains to be seen this weekend.

As always......stay tuned for more info......
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Chasing the design some more......and some data....

Post by marty_wittrock » Mon Mar 17, 2008 12:21 am

I've been chasing the design for the past couple of weeks and did a lot of thinking about what direction I wanted to go - wire wound vertical element or more length in the vertical element. I ended up taking the latter to make one change at a time. Read on....

With a side business trip to Omaha on Saturday, I found 8' aluminum tubing at a reasonable price - that was the major motivation for me to lengthen the vertical element and not pay the price of decreasing the bandwidth of the antenna (making it more inefficient - who needs to compound that problem with this design). So I bought 4 lengths of aluminum tubing (1 - 1" ID, and 3 - 1/2" ID) at a local Menard's store in Omaha and didn't have to unload my pocket to do it. The whole bill for that came up to $40.00.

On Sunday (just about an hour ago as I write this) I assembled all the aluminum elements together to make a 32' element - close to what I needed for 1/8 wavelength on 80m. I tried putting it up vertical, but the length and the weight of the vertical element by itself wasn't enough to keep the vertical element very upright - it was pretty gangly. So, with a lot of regret, I shortened up the vertical element to 24' and decided that it was a little better than where I was last week (22'). I also had the means to push the antenna up a little bit since the 1" aluminum fit real nice over 3/4" copper. So I pushed the vertical element up about 12" more to get about 25' in the air and tightened up the clamps that held everything together. I also noted that the antenna was a little more straight that the one last week (lighter). I must admit that 24' of aluminum was a lot easier to setup up on my mount than 22' copper was.

Back in the shack, I checked the VSWR and the following was noticed:

1.90 MHz = 3.1:1
3.80 MHz = 1.2:1
3.90 MHz = 1.2:1
7.00 MHz = 2.2:1
7.125 MHz = 2.2:1
7.250 MHz = 2.2:1
10.125 MHz = 2.0:1
14.0 MHz = 2.0:1
14.125 MHz = 2.0:1
14.30 MHz = 1.9:1
18.150 MHz = 1.0:1
21.0 MHz = 1.2:1
21.125 MHz = 1.2:1
21.250 MHz = 1.2:1
21.45 MHz = 1.3:1
24.890 MHz = 1.2:1
24.990 MHz = 1.2:1
28.0 MHz = 1.2:1
28.25 MHz = 1.2:1
28.50 MHz = 1.2:1
28.750 MHz = 1.2:1
29.0 MHz = 1.1:1
29.25 MHz = 1.2:1
29.4 MHz = 1.2:1

The VSWR that was 'dogging' me last week was 80m, but this week I had it down to 1.2:1 for the first time, and the other bands (with the exception of 40m - it was still a little high) were improved or not eroded much from my other vertical element length.

I did a check using ALE to see if I could contact the pilot stations and get a reading from them on my signal. On the first try, I did a sound and was heard by NJ7C (Sierra Vista, Arizona from my station in Belle Plaine, Iowa) and was heard as a BER of 30 (excellent quality) and a SIG quality of 8 (clear and readable). I was also heard by WD8ARZ (South Bend, Indiana) as a BER of 24 and SIG of 4 (moderate with some signal noise) on both 80m and 40m. Later in the afternoon, NJ7C heard me as a BER of 28 and SIG of 4 (excellent, but with some noise in signal) on 20m. So from all the signal reports, it was clear to me that increasing the vertical length did me a favor instead of treading water like I thought may happen. I also eliminated the transformer heating that was happening on 80m before - that problem appears to be gone now.

What's next? At this point I think I'm going to solidify the 25' section in the design and then work on the 7:1 transformer mod next weekend and see what happens to my efficiency in the other bands where my VSWR is high. I'm also going to take Martin's (G8JNJ) advise and add four short 15 ft (5m) radials to the design to see if I can lower the radiation angle of the antenna and help increase my range a little more with what I have. For now, as the antenna is designed, it would be a perfectly adequate antenna for ANYONE to put up if you're looking for a broadband antenna that doesn't have radials. You won't work 5 band WAS or make the DXCC with it (unless you have a lot of time and patience) but what you WILL get is an antenna that works well with the broadband demands of ALE from 80m to 10m (160m is another matter entirely).

It's not quite over yet. There's a little more fiddlin' with the design to do........so stay tuned......
de Marty (KN0CK)

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Multiband Antenna - The Final Chapter.....

Post by marty_wittrock » Mon May 05, 2008 1:19 am

Okay - it's been awhile since I've reported back and I must say it's been a fairly hectic spring here in Iowa and I've rebuilt my antenna at least twice since the previous time I wrote - - but keep reading, the info is pretty different from my previous experiments.

I had to rebuild the antenna twice since strong spring breezes and t-storms took their toll on the antenna. I started out with a fairly strong (aluminum) bracket that I scrounged off of an older broken ham antenna and figured that the 24' of aluminum I was using and the overall PVC construction was enough to be bullet-proof.....well, not so. I quickly found out one breezy spring day that JB weld, PVC, and a fairly beefy aluminum bracket coupled with the lever action of 24' of 3/4" (soft) aluminum tubing can be mangled and laying in a nearby tree if the wind was blowing strong enough. The second time I used more PVC and real end caps instead of wimpy end caps. I also fastened a strong strip of sheet metal formed into a strip onto the transformer compartment (a 2.5" PVC tube with the aforementioned end caps) to hold the whole transformer assembly to the antenna bracket better than before. I also removed 8' of aluminum tubing to make a more compact antenna (knowing there would be compromises in the antenna performance at the lower bands).

When it was all over I truly thought I had a 'bullet proof' antenna. I even fashioned the main element to be removable - I used 3/4" copper fittings at the transformer compartment such that the main element was screwed onto that assembly and allowed maintenance, if needed. I was really proud of it. Then I set it up on (yet another) breezy spring day. My.....was I surprised to find out how much leverage 16' of aluminum has when it was all locked down on the mast and looking pretty bowed against the wind. Disgusted, I added 3 threads of nylon fishing line to the top of the main element and 'guy wired' the main element of the antenna to three strategic points on the roof of my house to keep the element sturdy. It worked. It was straight as an arrow and the breezes can blow as hard as they want now - it wont bow anymore. Lesson learned: DON'T USE SOFT ALUMINUM WHEN BUILDING AN ANTENNA. I think Texas Towers sells all sorts of aluminum that is reasonably priced and is harder stuff than what I found at a local Menard's building supply superstore. Anyway.....

Before I launch into the final data set taken on this antenna, a couple words about the antenna length, VSWR, and performance:

I tried making this antenna optimal by cutting the (then copper) antenna element to 21' like the rest of the experimenters had done. The VSWR is posted above, but the performance was 'okay'. I wasn't particularly thrilled with the VSWR in a couple of spots in the lower bands (160, 80, and 40m). So I tried lengthening the antenna element to a 1/16th wavelength at 80m (about 33') giving me a 'wet noodle' at 160m, 16th at 80m, and 1/8th wave at 40m, 1/4 wave at 20m, ect. Tried it, saw the performance using it with stateside ALE stations (which was, again, okay), and promptly saw the wind take the antenna down (it was a copper/aluminum hybrid). Shortened the antenna to 24' (all aluminum) going for a compromise did the same thing (tried it on ALE with stateside stations on the network) and, again, the performance was 'okay', but nothing stellar. Had the wind take that one down, too. Finally, I rebuilt the antenna to 16' (for the final time - again, all 3/4" soft aluminum) tried it with the same stations and......you know what......it's actually a little better, I think. There really isn't that much difference no matter what you do with the length. It may seem optimal to use 21', but at 16' this antenna has the same signal strength to all the stations I sounded on ALE to as it did the previous 3 attempts. So, in effect, while the length 'may' matter (recall, physics plays a part in this) in actual hard practice it makes no difference - - and I'm living proof because I actually tried all the combinations and didn't see a HUGE difference. We're dealing with a transformer-coupled antenna here, you know....!

Back to the REST of the story.....

Built a length of RG-214 for this new antenna (since I would be using it for ALE full time - I'm a Pilot Station on HFLINK), coupled it up to my FT-100 and gave it the final-final-final VSWR test. Here are the results:

1.90 MHz = 2.5:1
3.50 MHz = 1.3:1
3.80 MHz = 1.3:1
3.90 MHz = 1.5:1
7.00 MHz = 1.6:1
7.125 MHz = 1.5:1
7.250 MHz = 1.4:1
10.125 MHz = 2.3:1
14.0 MHz = 2.0:1
14.125 MHz = 1.9:1
14.30 MHz = 1.9:1
18.150 MHz = 1.8:1
21.0 MHz = 1.3:1
21.125 MHz = 1.3:1
21.250 MHz = 1.3:1
21.45 MHz = 1.3:1
24.890 MHz = 1.5:1
24.990 MHz = 1.5:1
28.0 MHz = 1.1:1
28.25 MHz = 1.1:1
28.50 MHz = 1.1:1
28.750 MHz = 1.1:1
29.0 MHz = 1.1:1
29.25 MHz = 1.1:1
29.4 MHz = 1.1:1

So, as you can see, the VSWR really isn't that much different than the previous 3 attempt. And on the lower bands it's actually better. I need to get some more 'stick time' with the antenna to see how it performs on the lower bands, but the cursory signal reports I did at 80m and 40m shows that it has good performance. Above 40m this antenna works great! My signal reports from the ALE stations were excellent (BER of 30 with S/N of 7 to 8 meaning that the data was solid to the stations and there was no noise in my signal).

That's it, crew. I'm done monkey'ing with this antenna. I'm just going to use it from now on and keep you tuned in as I go along here. Bottom line is: GO OUT THERE AND BUILD THIS ANTENNA IF YOU WANT SOMETHING PLAIN-JANE AND HAS REAL NICE WIDEBAND PERFORMANCE TO IT. Read the threads above for the details and get out of mode of being restricted to certain bands because the antenna you have now can't hack it. This one does 80 - 10m (and even 6m is pretty good, too) and it performs admirably in the continental US. As I've said earlier, don't expect 5 Band WAS, DXCC, or mega-station performance. Just know that you, too, can make a wideband antenna that will work decently and provide you with an alternative when the going gets tough.

Now, go make it happen. So long, for now.....
de Marty (KN0CK)

n5wrx
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Joined: Sat Jun 10, 2006 5:00 pm
Location: Corpus Christi, Texas
Contact:

Post by n5wrx » Sat May 10, 2008 2:45 am

A big dummy load at the base of a vertical.
What is new about that?

I would think a tuner like the AH-3 mounted at the base of a vertical work much
better.

William Lee N5WRX

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Well not really, Bill.....

Post by marty_wittrock » Sat May 10, 2008 4:22 pm

Bill,

Thanks for posting. This antenna really isn't "...a big dummy load at the base of a vertical...". There's nothing resistive about it. It's more a matching transformer than it is some lumped resistance to fool the rig. The matching transformer is certainly there to pick up any VSWR from the electrically shorter vertical element and may absorb power as a result, but you get the same effect from a tuner located at the base of the antenna, too - - there's no difference there. Both have different ways of accomplishing the same objective: matching the load to the rig's impedance and the attached feedline.

The major point of my posts was to get hams, like you too, motivated to think, move, and build antennas again. It's a lost art. Too often we grab the plastic out of our pocket, call up a radio shop, and order a new antenna. With a few bucks of common building materials and some torroids I ordered from Newark, I made an antenna I'm actually using on ALE and it works great! I learned something in the process, and I actually experimented with the design. In the end, I knew the antenna's shortfalls, but it's strengths far outweighed the shortfalls and I applied it to my station. Now I'm heard 80 - 10m with no fear of any one band not being there to transmit on - they all work acceptably.

So go out there and experiment, Bill - that's my challenge to you. If you do, then you'll be providing your input to this forum to keep the art of antenna building alive.
de Marty (KN0CK)

sean_anderson
Posts: 2
Joined: Sat Aug 29, 2009 3:35 pm
Location: northern indiana

homebrew version of the comet ch250

Post by sean_anderson » Sat Aug 29, 2009 3:49 pm

Marty,
I found your information last night and was going over it today. I was wondering if you ever considered using a stainless steel whip on the end of the antenna to achive your goal of 32 feet? I see that MFJ sells these for $26.95 for a 108 inch length (MFJ-1966). I'm going to order the ferrites and whip this week and try my luck at building your version of this antenna! I'll be sure to pass along my findings on where or not this whip will work or not.

73
Sean Anderson kc9llx

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

Re: homebrew version of the comet ch250

Post by marty_wittrock » Mon Sep 21, 2009 2:12 am

Sean,

Sorry for the incredibly long delay in getting back with you. I check into QTH.com all the time, but I haven't checked the posting in awhile until this evening and saw your comments. Please read on....

Using a 9' steel whip instead of aluminum tubing should work fine - in fact, it's a lot like what I did for the mobile version of the same antenna (just look for other posts with my userID for that post on the results). I found that there was no noticeable difference using a whip on top of the transformer than the aluminum tubing I used on the base antenna I did a couple of years ago (almost), but it's going to be more optimal 40m and up than 80m and up when doing so. Seems that if there's a 16' section available it will work better at 80m. I have a somewhat modified version of the same transformer coupled antenna up in my attic of my new house (in a restrictive covenants neighborhood) and run a 16' chunk of wire horizontally in the attic with this antenna. I also have a 100' long wire antenna (that hugs the black roof on my house) that I gauge performance against and I can tell you that the wideband antenna in that configuration is MUCH better on receive than the long wire and quieter, too. I hear signals on it that I cannot hear using the longwire on an autotuner. And I have worked MANY WSPR station with the wideband antenna in the attic - some in Europe - without any issues on 30m. PSK31 and other digital modes I run are also achievable on this antenna with great stateside results. When the band is noisy, I always switch to this antenna to see what's really happening in the background - it always helps me pick sigs out of the noise. Really impressed with the performance.

I'd be interested in knowing what you find for VSWR on your antenna variant of this design. I would think that 40m to 6m it would run great. So please write back and let us all know.

73's for now and keep the antenna building going out there! That's why we experiment......

de Marty, KN0CK
de Marty (KN0CK)

sean_anderson
Posts: 2
Joined: Sat Aug 29, 2009 3:35 pm
Location: northern indiana

Update on CH250B clone

Post by sean_anderson » Tue Nov 10, 2009 1:31 am

Hello everyone, Here is an update on my progress regarding my version of the CH250B clone. I used 15/32" brass tubing and 10ga stranded wire for my transformer, otherwise everything else is the same as others have tried. I also tried something different for the vertical element. I used a 10' piece of 1/2" EMT conduit and a 102" stainless steel whip from Radio Shack. The whip has a 3/8-24 stud on the end which threaded into the 3/8-24 nut Iwelded into the top of the conduit. Overall length is 18'-6" with 6" slid down into the PVC base.

I mounted it last night (11/8/09) and tested my "master piece". Below are the results I measured using a MFJ-874 SWR/Wattmeter with my ICOM IC-706MKIIG power level set on "L" (3 watts). I measured both ends and the middle of each band to see if there was any significant changes.

I'm not sure if the steel conduit was a good choice over copper. The steel seemed to be more rigid when compared the the same 1/2" heavy walled copper but it seems like Marty's aluminum performs better.

SWR Results using 3 watts of power:

1.80 MHZ= 1.8:1
1.90 MHZ= 1.8:1
2.00 MHZ= 1.75:1
3.60 MHZ= 1.85:1
3.80 MHZ= 1.9:1
4.00 MHZ= 1.95:1
7.125 MHZ= 1.7:1
7.20 MHZ= 1.7:1
7.30 MHZ= 1.8:1
14.150 MHZ= 2.5:1
14.250 MHZ= 2.5:1
14.350 MHZ= 2.4:1
18.110 MHZ= 1.85:1
18.139 MHZ= 1.85:1
18.168 MHZ= 1.8:1
21.200 MHZ= 1.85:1
21.325 MHZ= 1.85:1
21.450 MHZ= 1.85:1
24.930 MHZ= 2.5:1
24.960 MHZ= 2.4:1
24.990 MHZ= 2.4:1
28.300 MHZ= 3.2:1
29.000 MHZ= 3.2:1
29.700 MHZ= 3.0:1
50.100 MHZ= 4.5:1
52.000 MHZ= 4.7:1
54.000 MHZ= 5.0:1

I contemplating changing the steel to copper for the vertical and also checking to see if i'm getting a good ground in my tower. I scrapped to bare metal for my grounding fastners but i'm wondering if the all the joints in this old tower are making good contact.

Any input from yourself or other hams is always welcome!

73
Sean Anderson
KC9LLX
kc9llx@yahoo.com

K9FW
Posts: 39
Joined: Wed Jul 15, 2009 3:28 pm

Extra length

Post by K9FW » Thu Nov 12, 2009 8:52 am

I've found if you need sturdy(long lasting) 16-18' of vertical height, use a 20' fiberglass fishing pole, with a wire taped to it. also tape the joints and coat for uv protection. You can even leave a 12-18" of wire out the top. These work great in the wind-super flexable, can almost touch tip to bottom of pole. I used these for extra length when we had up 3 full sized 1/4 wave 80m vert ant in phase-worked great.
Al

K9FW
Posts: 39
Joined: Wed Jul 15, 2009 3:28 pm

Fishing poles

Post by K9FW » Thu Nov 12, 2009 8:55 am

Forgot 1 thing, put a wooden dowel rod in bottom of pole and weather proof. use hose clamps to attach to main vert ele.
Al

marty_wittrock
Posts: 31
Joined: Sun Feb 24, 2008 6:32 pm
Location: Iowa

More about the Multiband Vertical Antenna....

Post by marty_wittrock » Mon Nov 16, 2009 2:49 am

Sean,

Nice work! Glad you're out there experimenting with the design - you'll keep finding that some materials seem to work better than others. I did the same thing when I was playing with this antenna and found that using 3/4" rigid (blue letters) copper was better than the softer (red letters) copper pipe that you can find in any building supply place. About 8' of 3/4" and then tapering to 1/2" copper in a 8' or 10' length will do well. While I thought steel would have been optimal (being even more rigid) you can't do much better than copper for conductivity. I was wondering about the whip when I first saw your post, and not sure if it's looking a little inductive as compared to the pipe I used in all the designs. Even with the two dissimilar metals (aluminum and copper) I used in one of the designs gave me pretty good results. So I'm thinking hard why the whip doesn't perform similarly....

All I can say is: keep trying. Never give up experimenting when it comes to antennas. You can never learn the physics of antennas by not playing around with a design - and you've done just that. Designed, found the results, and gained something in the process - valuable experience.

73's for now, Sean - keep at it!
de Marty (KN0CK)

Caleb
Posts: 1
Joined: Tue Jan 14, 2014 10:00 am

Re: I've built it and here are the results.......Excellent!

Post by Caleb » Thu Jan 16, 2014 9:34 am

marty_wittrock wrote:I wanted to write back and let those who have been checking in know what the results are of this solar panel. Here is my own running history:

I got on the web and ordered ferrites from two different sources: Digikey and Newark. I ordered the ferrites on Sunday night and the Digikey order showed up on Wednesday afternoon of that week and the Newark order showed up on Friday afternoon of the same week. Here are the order details:

Digikey: QTY 6 732-1528-ND 0.92000 $5.52, QTY 2 732-1563-ND 2.94000 $5.88

Newark: 1 98K8790 Each 15 $0.51 $7.65 ($15.00 shipping direct from United Kingdom)

The ferrites I ordered from Newark were the same ones that were used in a design by a fellow in the UK. So I ended up using those first in the design since the others that I bought from Digikey were 'close' to the same parameters (and I was almost certain it would take longer to ship from the UK - funny how that turned out). I bought 15 since I knew 6 were used in the design - so I could build a couple of these antennas and have extras around for experimenting with the matching transformer later.

I built the matching transformer to specs in the article:

http://g8jnj.web.com/61balun.htm

I used the same 1/2 " soft drawn copper tubing (straightened) and then fashioned 12ga copper wire for the ground side of the copper tubes, slipped the ferrites on, and then finished the wiring to make the transformer. I used 12ga stranded wire for the tranformer windings (at first I used solid 14ga wire, but it was too hard to work with for the single loop - stranded worked much better). I had an old antenna that was wrecked from a storm a few years ago and I salvaged the mount from it. I used 2" diameter schedule 40 PVC pipe to enclose the transformer assembly and fashioned a mount on the antenna mount to encase the bottom of the PVC and SO239 connector connections from weather. The top of the 2" PVC I found a PVC that allowed a 3/4" threaded copper fitting to be screwed to the top and then used 3/4" copper pipe as the base for the antenna. I used another PVC collar to insulate the copper base from the top of the antenna mount. Used 3/4" and 1/2" copper pipe to finish the vertical element (not cheap, but here in Iowa aluminum pipe is almost nonexistant).

Assembled the rest of the antenna (the veritical element was only 22' long - the other piece of 1/2" copper made the top to gangly that it was hard to set it up. So I opted for 22' of copper for now - it would have been 32' - a 1/4 wavelength at 80m). Oh well. Connected up the coax, got back into the shack and checked the following frequencies for VSWR:

1.90 MHz = 3.1:1
3.80 MHz = 1.5:1
3.90 MHz = 1.5:1
7.00 MHz = 2.0:1
7.125 MHz = 2.0:1
7.250 MHz = 2.3:1
10.125 MHz = 1.6:1
14.0 MHz = 2.3:1
14.125 MHz = 2.3:1
14.30 MHz = 2.3:1
18.150 MHz = 1.15:1
21.0 MHz = 1.1:1
21.125 MHz = 1.1:1
21.250 MHz = 1.1:1
21.45 MHz = 1.1:1
24.430 MHz = 1.2:1
28.0 MHz = 1.1:1
28.25 MHz = 1.1:1
28.50 MHz = 1.1:1
28.750 MHz = 1.1:1
29.0 MHz = 1.1:1
29.25 MHz = 1.1:1
29.4 MHz = 1.1:1

So, as you can see, the VSWR looked pretty good for a boradband antenna. I really needs to be tweaked for length to get it to 1/4 wavelength on 80m - and that will happen by next week. Receive-wise, it seems to receive better than my vertical antenna that I had setup in its place. I could receive more of the lower bands (40m and 80m) than I could before - matched better than my HyGain vertical. I ran it on ALE for more than 3 hours, sounded on all bands (160m to 10m) and worked excellent - never saw the VSWR higher than 3.0:1 on 160m - all the other bands appeared to be either 1.1:1 or no higher than 2.0:1. I haven't tried it for QSO'ing yet - but expect to over the next
couple of days.


Stay tuned.......
Awesome thanks for sharing outcomes.. I would love to build similar antenna pretty soon and share my own experience.

vu2sij
Posts: 1
Joined: Fri May 22, 2015 6:09 am

Re: Multiband Vertical Antenna Design.....

Post by vu2sij » Fri May 22, 2015 6:14 am

Hi Marty,
I am in the process of building this antenna .
Do you have any pictures of your antenna to share ?
73
Sanjay Joshi
VU2SIJ

E73M
Posts: 1
Joined: Sun Sep 20, 2015 1:07 pm

Re: Well not really, Bill.....

Post by E73M » Sun Sep 20, 2015 1:28 pm

marty_wittrock wrote:Bill,

Thanks for posting. This antenna really isn't "...a big dummy load at the base of a vertical...". There's nothing resistive about it. It's more a matching transformer than it is some lumped resistance to fool the rig. The matching transformer is certainly there to pick up any VSWR from the electrically shorter vertical element and may absorb power as a result, but you get the same effect from a tuner located at the base of the antenna, too - - there's no difference there. Both have different ways of accomplishing the same objective: matching the load to the rig's impedance and the attached feedline.

The major point of my posts was to get hams, like you too, motivated to think, move, and build antennas again. It's a lost art. Too often we grab the plastic out of our pocket, call up a radio shop, and order a new antenna. With a few bucks of common building materials and some torroids I ordered from Newark, I made an antenna I'm actually using on ALE and it works great! I learned something in the process, and I actually experimented with the design. In the end, I knew the antenna's shortfalls, but it's strengths far outweighed the shortfalls and I applied it to my station. Now I'm heard 80 - 10m with no fear of any one band not being there to transmit on - they all work acceptably.

So go out there and experiment, Bill - that's my challenge to you. If you do, then you'll be providing your input to this forum to keep the art of antenna building alive.
PLEASE READ ALL INFORMATION ABOUT THIS ANTENNA FROM http://www.vk5zd.com/CHA250/CHA250_Measurements.aspx

it is DUMMY LOAD antenna!!!!! Don't you see that VK5ZD measured loss in transformer at the link above stating a loss , -3.6db on 80m and -10.9dB on 10m.

To translate it in plain terms.... out of 100W fed into this antenna less than 10W will be radiated on 10m and less than 45W on 80m (best case).

You and many others are misleading a HAM population with such posts, claiming that it is same as tuner at the bottom of same vertical, IT IS NOT!
Many don't mind to spend $300 or more on these CHA-250 and clone antennas, just to make any contact. But here, you are propagating bad design which is intentionally made with high loss transformer in order to present LOW SWR over all HF spectrum.

Everything will radiate some power and you will make a contact, even with resistor at the end of the coax.
N6BT made great article about feeding a light bulb at the end of of his coax and making contacts. (QST July, 2000)
So let's replace all our antennas with bulbs and analyze how far it will propagate :)

73 Danny N4EXA aka E73M

http://www.vk5zd.com/CHA250/CHA250_Measurements.aspx

Frequency R X Vin Pin(mW) Vout Pout(mW) Loss(db)
3.60 43 27 0.601 8.4 1.110 3.7 -3.6
7.10 57 17 0.626 6.9 1.070 3.4 -3.0
10.10 60 10 0.628 6.6 0.986 2.9 -3.5
14.00 61 5 0.648 6.9 0.870 2.3 -4.8
18.10 60 6 0.670 7.5 0.727 1.6 -6.7
21.20 56 10 0.677 8.2 0.646 1.3 -8.1
24.95 50 11 0.688 9.5 0.573 1.0 -9.8
28.50 45 11 0.680 10.3 0.525 0.8 -10.9
51.00 53 20 0.671 8.5 0.485 0.7 -10.8
Daniel "Danny" Horvat, N4EXA aka E73M
http://www.E73M.com & http://www.MyAntennas.com

g8hul
Posts: 1
Joined: Mon Jan 25, 2016 11:20 am

Re: Multiband Vertical Antenna Design.....

Post by g8hul » Mon Jan 25, 2016 11:33 am

Hi

That is a somewhat misleading post. The results that you quote with the high loss are with the matching unit terminated with a 300ohm resistor. This does not represent the working conditions. Subsequent tests show significant losses in that test set up so there is a lot of ambiguity.

However, the test That I would like to see is 2 matching units back to back, then, as a first approximation, the loss for a single Matching unit would be half of the measured total.

73
Jeff G8HUL

KJ4RWH
Posts: 8
Joined: Thu Apr 01, 2010 11:18 pm
Location: Virginia

Re: Multiband Vertical Antenna Design.....

Post by KJ4RWH » Fri Mar 04, 2016 7:41 pm

I'm somewhat green in the hobby, what does ALE stand for?

n5wrx
Posts: 80
Joined: Sat Jun 10, 2006 5:00 pm
Location: Corpus Christi, Texas
Contact:

Re: Well not really, Bill.....

Post by n5wrx » Thu Sep 08, 2016 12:11 pm

marty_wittrock wrote:Bill,

Thanks for posting. This antenna really isn't "...a big dummy load at the base of a vertical...". There's nothing resistive about it. It's more a matching transformer than it is some lumped resistance to fool the rig. The matching transformer is certainly there to pick up any VSWR from the electrically shorter vertical element and may absorb power as a result, but you get the same effect from a tuner located at the base of the antenna, too - - there's no difference there. Both have different ways of accomplishing the same objective: matching the load to the rig's impedance and the attached feed line.
The simple task of an transmitting antenna it to radiate the RF that is fed to it.
If 100 watts goes in and 10 watts gets radiated then I would not call that a very good antenna.
If you are happy wasting 90% or more of your RF and effectively running a QRP station then all these "wonder antennas" will work for you.
It is a well known fact that a shortened version of any antenna is a compromise.

A field strength meter and an antenna test range will not lie and is the simplest way to test the efficiency of an antenna design.

A fella years ago designed and sold an "Solid State Automatic Antenna Tuner" that was touted to load up a dipole on any band.
It was a sealed box with a connector for the coax and two connector studs for the antenna wires.
(used like a balun on a inverted vee)
It was very expensive.
So ... where is Sonny Irons and his magic "solid state antenna tuner" today?
Something that dont work will not survive the test of time.
Oh ... it did work ... you could make contacts on all bands with a very low SWR but the problem was it had extremely high loss.
You were much better off with a common Dipole antenna and a QRP rig.
To put it in simple terms ... It was just another version of a dummy load with a radiating element (or elements).

Your metal rain gutter around your home and a good tuner combined with a little work and ingenuity will make you a useable stealth antenna if normal antennas are not allowed where you live. Just dont expect it to perform as well as a standard inverted vee up 15 foot.

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