Help with a 100 watt amp for fm broadcasting

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Help with a 100 watt amp for fm broadcasting

Post by sonicdrive » Thu Mar 06, 2008 1:28 am

i have a board that i know very little about can anyone help me i know it is a milli volt to 100 amps output board it runs around 146 to 178 mhz i want to use it for 88 to 108 mhz and i cant get the board to fire up please help ... 264118.jpg ... 264114.jpg ... 264109.jpg ... 264108.jpg ... 264105.jpg

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Post by k9yli » Thu Mar 06, 2008 3:32 pm

To move a 150 mhz amp down to say 90 mhz would take a complete retune from end to end.
possibly replacement of some components, coils or caps.
And if you have an FM broadcast license, then you should know someone
who normally does your engineering if
you can not do it yourself.
And if you do not have a broadcst license, then hams are not likely to help you as we frown on lawbreakers anywhere in the radio spectrum.
If that offends you , your original post did not fully explain your position on
needing/using an amplifier in the broadcast band.

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Post by sonicdrive » Fri Mar 07, 2008 12:52 am

it isnt the law that im trying to break it the fact of doing it it is the fact of taking this old amp and making new life in to it
seconded thing im sick of people telling me im breaking the law because i want to experiment with this board yes i will broad cast with it but to tune it in and make it work i wont be using it to break the law hell if i wanted to do that then i would just put up about 1k and have a 100 watt amp and transmitter combo and then i can do it very easily i just wanted help with getting it going stop making assumptions about people that you dont even know (k9yli)

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Tell it like it is.....

Post by marty_wittrock » Fri Mar 07, 2008 5:16 am

If you're *not* going to do anything illegal by using an amplifier within a band that is typically constrained to commercial broadcasters, then what's the intent? Honestly, when you post a message about taking a VHF amplifier that's not intended for 88 - 108 MHz and say you're going to use it there, then what do you take us for? We're not stupid. No one on Earth would ever ask a question like that unless you were going to *experiment* on the commercial FM bands.

If you're going to broadcast music on FM, then go out and obtain the license (that's about $25K), get the real FM gear to broadcast (that's about $900K), buy the land to put up the tower (that's about $100K), buy the tower (that's about $50K), get your approvals for the land use (that's about $5K), hire your staff (there's about a $60K layout per year - they work cheap) and finally pay for the power to run all that (that's about $50K/year) and then you'll be ready to put that amplifier to use legally! WOW! But then, you'd have to *experiment* to get it to transmit there and frankly, it's a lost cause to convert that amp because the matching networks are all wrong for it to work in the FM band along with all the tuning end-to-end (that's already been discussed).

If you want to experiment, then get a ham license like the rest of us did, go out and buy gear to drive that amplifier legally on 2m, and have fun doing this hobby and meeting new hams. What's wrong with that?

Start studying......
de Marty (KN0CK)

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Post by k9yli » Fri Mar 07, 2008 3:11 pm

"yes I will broadcast with it..."

that sounds illegal to me..
You do not say you will run it into a dummy load, which could still cause interference to a legal broadcast station.

and Marty, you forgot the possible $11k for a fine for illegal use of a radio transmitter..
Ham radio, where you asked the question , is a selfpolicing operation and everyone is a policeman. Hense everyone should be telling you not to break the law.
Laws were passed to be obeyed, not as some kind of puzzle that its your job to try and find a way around.... so that more laws have to be passed to cancel your way around the first one,,,,,,,, and on and on...

Appearantly your parents and grandparents did not tell you often enough,
" thats not the kind of people we are, we don't do that in this family.....
thats unacceptable behavior i this family ,,,,, etc. ""
Well you will hear it from us,
breaking the law is unacceptable behavior anywhere. ..

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Post by k9yli » Sun Mar 09, 2008 3:27 pm

I read something more in sonics message.

I made an assumption he wanted to do something illegal even though I don't know him.

HELLO. You wanted to put a measly 100 wat amp down on the FM broadcast band.
Seems totally obviously that would not make a viable licensed station amp.
Therefore since you don't seem to have the engineering expertise to
make the needed adjustments to modify the amp in question and do not have an oncall engineer, that your aim is patently illegal.
It doesnt take a 'rocket surgeon" to figure that out.
With the attitude you seem to have about 'rules' I don't think you would make a good ham operstor.
What does the FCC say about moral and upright standing or something to that effect.

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Post by sonicdrive » Sun Mar 09, 2008 6:42 pm

so you show to be the god of law tell me sir when will you cast the first stone when will you walk in to heaven never to have been touched by sin lol come on man yes i will prob break the law to run my experiments prob wont get in to trouble let me ask you this speeding down the road is illegal and so is throwing out your smoke when you drive all are illegal so don't freaked preach to me saying that i Will break the law when you have in your day just to let you know this i am not going to run it 24-7 it is just to say i did it i built this and all i was looking for was a latter diagram to work on it when im done then i will use it for parts or sell it lol so stop getting your panties in a bunch and relax this isnt rocket science

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Post by WA9WVX » Mon Mar 10, 2008 2:38 am


Perhaps you chose the wrong web page for advice, here's one that might answer some of your questions regards FM transmitters / amplifiers:

The other thing to keep in mind regarding your solid state 100 watt amplifier is it isn't a good deal when you would need to completely redesign the VHF Land Mobile RF Amplifier from 146 MHz down to 90 MHz. That's a 50 MHz change in frequency and the two RF transistors are designed to operate primaryly between 136 MHz up to 175 MHz. The devices have parameters that will cause a -3 dB to -9 dB roll off below and above the VHF High Band frequency range.

Transistor devices used on commercial FM broadcast are a MOSFET and/or LDMOS design which display charteristics of a high impedance similiar to a vacuum tube and provide more stable power output being driven at Class "B" for continous duty. These LDMOS and MOSFET devices are not inexpensive when purchasing. Refer to the web link provided and you'll need Adobe Reader for a few files: ... quency.htm

I would recommend using a commercial 50-Ohm Dummy Load while proto typing any RF Transmitter or Amplifier to provide a known good load for the output. All transistors display the same operational charteristics if not properly connected ... they turn into a three legged fuse and there's no forgiving using a solid state device unlike a vacuum tube.

I don't think there's a Law on the books regarding experimental research for building a project or product but using it on a Commercial Broadcast Band is another subject because the FCC has Type Acceptance Standards to be met before connecting a RF unit to the antenna.


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Re: Help with a 100 watt amp for fm broadcasting

Post by n5wrx » Mon May 12, 2008 12:07 pm

Yet another ham turned FM radio pirate.

The FCC busts several of them each year and here is this guy standing in line to be next.

What is the attraction of being a pirate radio operator?
it seems to be all risk and no real gains.
The movie PUMP UP THE VOLUME glamorized the FM pirate operator and for a while it seemed like every high school kid wanted to be a pirate radio broadcaster.
In the real world getting a $10,000 fine from the FCC is not very cool.
I can somewhat understand a kid wanting to do it but a grown man with a ham ticket ... that is hard to understand.

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