Question about duplexers

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wb3cez
Posts: 39
Joined: Sun Mar 21, 2004 11:11 am

Question about duplexers

Post by wb3cez » Fri Dec 27, 2013 10:06 pm

I have a Yaesu FT-100 transceiver which covers 160 meters thru 6 meters plus 2 meters and 440 mhz. It has two pigtails for RF output. Pigtail #1 is for 160 thru 6 meters, and pigtail #2 is for 2 meters and 440 mhz. I have 4 separate antennas for these bands. I am guessing I will need 2 different diplexers in order to connect all 4 antennas. Are their any two diplexers available that will cover this frequency span? I have not been able to locate one the covers 160 thru 6 meters only. Also, here is perhaps a stupid question.....why do I need diplexers at all? Why can't I use a coaxial "T" for each pigtail? Thanks for any help.
Last edited by wb3cez on Sun Jan 12, 2014 1:04 am, edited 1 time in total.

k9yli
Posts: 223
Joined: Fri Aug 12, 2005 11:35 pm
Location: northwest wisconsin

Re: Question about duplexers

Post by k9yli » Sat Dec 28, 2013 3:55 pm

Somewhat depends on the 4 antennas and what they cover.
But if you use a T connector between 2 antennas, you may have the radio input impedance to be at
25 ohms if both antennas are at resonance and are 50 ohm..
Now if you have a resonant 2 meter antenna and a resonant 440 antenna connected to the 2 m /440 pigtail
you may get away with that as one antenna may appear to be a very high impedance at the opposite frequency.
"Effectively 'not there'// or because they are harmonically related, they both may radiate effectively.

on 160 thru 6 meters you need a coax switch to change antennas,, A diplexer to seperate 7 bands is just not practical.

Antenna impedances add or divide, just like resistors in series or parallel circuits.

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