Two Radios one Antenna, Duplexer??

[darrenster]

Hi All,

I have two mobile radios; the ft8800 and icom-f1020 and one Larsen NMO2/70b antenna. The 8800 will be used as "regular" ham radio and the icom will only be used for APRS traffic. I'm looking for the best way to use both of these radios on a single antenna. I been getting mixed answers on antenna duplexers. I'm hoping that someone could point me in the correct direction.

Thanks!

 

[W5LZ]

How close to 144.390Mhz will that FT-8800 be used? The closer those frequencies of use, the 'better' those duplexers will have to be for using only a single antenna. Hang on to your wallet! The simplest/cheapest answer is to reconcile yourself to using two antennas. If this will be in a mobile, just where do you think you will put those duplexers (yes, more than just one probably, depends on frequency separation). Also, in a moving/vibrating environment, count on retuning those duplexers fairly regularly, unless you do a really good job of shock-mounting them.
Lots'a fun!
- 'Doc

 

[darrenster]

interesting. I guess this wasn't as easy as i thought. After looking more closely at the duplexers that i thought would work, it turns out that they are more along the lines as band pass filters, one lead being the low pass and the other being the high pass. Does a duplexer that allows the full band pass to two radios on one antenna exist? It doesn't matter to me if both radio happens to be able to pick up the 144.390MHz; only one would be tuned to it though.

I'm not really sure I want to mount a 3rd antenna on the car. I've got the Larsen NMO2/70b for the ham and a Larsen 27B for the CB.

 

[wavrider]

Darren,

Good questions, without going into a lot of detail take Doc's advice, two antennas are way better than a duplexer.

I have seen first hand what happens when a duplexer fails, results are nasty burned up electronic parts. Of course the tax payers paid for the repair as it was a government piece of equipment.


Two antenna's are the best way to go. If to many antennas are the question on the mobile, that is up to you to decide.

 

[WR0220]

Since the Larsen is a dual band (2m/70cm) antenna and both radios operate on those bands why would you need a duplexer? Couldn't you just put a 2 into 1 antenna switch inline and swap between the radios using it?

 

[darrenster]

my goal is to be able to use both radios at the same time on one antenna.

 

[WR0220]

Ahhh...I didn't realize you wanted to use the radios simultaniously. The only device I know of that allows simultanious operation is the "DX Doubler" but it also requires the use of a computer.

 

[VA3ES]

The bottom line is that you'll need two antennas.

A duplexer will not do what you want. A duplexer will filter out RF 1 or more octaves away from a signal. Unless you wish to order a a rather expensive cavity duplexer tuned to 144.390, you will have problems with excess RF getting back into your other rig, unless you use the non-APRS rig on UHF only.

 

[g4ilo]

Sell the two radios and buy a Kenwood TM-D710. That will do APRS and "regular" ham radio in the one box, using one antenna.