[MRCA] MK-456/GRC, Retransmission Cable

[Gene Smar]

All:

     After a bit of reading in my TM for the PRC-77 I see that the 
CX-4656/GRC cable assembly uses Pin E in one radio's connector to pull to 
ground the PTT line in the opposite connector when the first radio's squelch 
opens.  Pin E becomes active in this way when the -77 (and -25, I assume) is 
placed in retransmit mode.  The cable assembly includes a box that has small 
capacitors to ground and steering diodes for the PTT lines, plus 
inductors/chokes in series with all lines (audio and control.)  Should all 
be easy enough to fabricate if one wanted to.

     There is one issue with using this assembly with two -77's in 
retransmit mode:  The two antennas and their TX freqs must be far enough 
apart that desense is minimized.  The TM recommends a minimum channel 
separation of 3.5 MC (physically, the units with their antennas are to be 
placed 50 feet apart - the length of the cable.)  For us to be able to use 
this technique at Gilbert or elsewhere we would need one freq just below 54 
MC (say, 53.90) and another at around 50.40.  This is permitted by FCC Rules 
but it eliminate 51.00 from possible use.

     That's enough for tonight.  G'night, all.


73 de
Gene Smar  AD3F


----- Original Message ----- 
From: "Gene Smar" <ersmar at verizon.net>
To: "Pasquale Lombardi" <pasquale.nj at verizon.net>; <MRCA at mailman.qth.net>
Sent: Sunday, August 30, 2009 9:36 PM
Subject: Re: [MRCA] MK-456/GRC, Retransmission Cable


> Pat:
>
>     Thanks.  That helps a lot.
>
>
> All:
>
>     The cited web page is a pretty complete explanation of how
> retransmission with two -77's works.  The key component is the CX-4656/GRC
> patch cable (p/o MK-456/GRC) that connects between the two audio jacks on
> each radio and utilizes the connection via Pin E that goes to ground when
> the respective radio is in retransmit and hears incoming, unsquelched 
> audio.
> The CX is 50 feet long - long enough to reduce somewhat the potential  for
> desense between the two -77's/-25's.
>
>
> 73 de
> Gene Smar  AD3F
>
>
> ----- Original Message ----- 
> From: "Pasquale Lombardi" <pasquale.nj at verizon.net>
> To: <MRCA at mailman.qth.net>
> Sent: Sunday, August 30, 2009 9:20 PM
> Subject: [MRCA] MK-456/GRC, Retransmission Cable
>
>
>>
>> For the Retransmission Cable Kit MK-456/GRC
>>
>> http://www.prc68.com/I/Mk456.shtml
>>
>> Pat in NJ
>>
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