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[aprssig] Re: Duplexer or Diplexer

tvsjr tvsjr at sprynet.com
Tue Sep 6 03:47:49 UTC 2005

>You won't "fry them".  You will only overload and temporarily block the 
>receiver of one radio while the other one is transmitting.  In the case 
>of the APRS radio transmitting, that means you will get a one second or 
>so hole punched in your 2M voice RX whenever the APRS radio beacons.    
>[ I have THREE antennas attached to radios capable of transmitting on 2M 
>and 450 (Kenwood TM-742, TM-D700 and Yaesu FT-100) within 3 feet of each 
>other on the roof of a Passat wagon with no problems other than receiver 
>blocking. ]

Don't be so sure. I think I'm OK to comment here... I've got 15 mounts on
the roof of my Expedition, and just installed 20 today on the roof of my new
truck (actually, in the topper). I have fried an amateur radio (D700) and
the preamp in an Optoelectronics Scout connected to an external antenna with
a high-power (110-watt) Motorola VHF Astro Spectra.

>o     Spend thousands and thousands of dollars each for high-end 
>professional land-mobile radios that have much greater spectral purity 
>on transmit and much better receiver overload immunity on receive  than 
>"civilian" ham gear.

No reason to spend thousands and thousands of dollars. Since the analog
Spectra has been EOLed, you can pick them up sub-$200 (Astro P25 radios are
quite a bit higher, but that's another story.) The Spectra is arguably the
best commercial radio ever made.

>o     The only TOTAL  solution is to conduct voice operations on another 

High-power commercial radios will often block hammy rigs across multiple


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