[MRCA] [Milsurplus] RS-6 Set. Oddity

[Tim]

Roger all....
The relay in the RS-6 simplifies all that, but at the expense of a relay
and associated complexity. LOL
Yes the RS-1 and GRC-109 system receivers have a compromise design in the
RX antenna routing.  There is an 18 pf RX antenna signal coupling capacitor
in the circuit that is too small to permit significant signals to get to
the receiver at the lower frequencies (during Key Up), but it is too large
in that it is in parallel with the output variable loading capacitor (upon
Key Down) thus limiting impedance matching range with that fixed value.  18
pf was a compromise value in trying to attain both with QSK ops..

Yes, the GRC-109 TX pi network and tube are in a parallel branch circuit to
ground on receive so they form a low impedance path for some receive signal
to "get lost".  "suck out" if you will.  Mostly a problem on the lower
freqs with a common antenna.  However I think (and in Vietnam MACV-SOG
operations for sure). operational TX and RX were on separate frequencies -
mainly bypassing the problem.
Also, getting the message OUT from a team was higher priority than getting
a message IN to a team, so RX system performance may have been compromised
a bit with the selection of that 18 pf capacitor during the design phase.
Plus they were listening to  URC-32, GRC-106, GRC-26 or some other high
powered TX. "Plenty of signal"...... My speculation on that part...

I just use a separate 50 foot random wire on the receiver and it works
great, plenty of sensitivity.  Usually a dipole or Inv L on the TX.  Good
comms.
73, Tim
N6CC

On Sun, Nov 22, 2015 at 2:34 PM, Al Klase <ark at ar88.net> wrote:

> You guys are trying to confuse me.  (That's my job.)
>
> Yes, both the RS-1/GRC-109 and the RS-6 ground the receiver antenna
> connection with the key, as a form of TR switching..  You'll notice that
> the rest of the keyed circuits in the TX are isolated from the receiver
> antenna by RF chokes.  The RS-1/GRC-109 definitely have a suck-out problem
> impacting the receive signal strength, because the RX antenna is connected
> to the TX output circuit all the time.  They were obviously trying to get
> away really cheap.
>
> The RS-6 adds a TR rely to solve the suck-out problem.  It's not straight
> forward, as the TX idle current holds the relay in the actuated (receive)
> position when the TX is NOT keyed.
>
> Al
>
> Al Klase – N3FRQ
> Jersey City, NJhttp://www.skywaves.ar88.net/
>
> On 11/22/2015 1:28 PM, Tim wrote:
>
> Hi guys - yep, that's it.  Receiver muting/front end protection.  The RS-1
> and GRC-109 sets use the same technique.  Simple and effective.
> 73, Tim
> N6CC
>
> On Sun, Nov 22, 2015 at 8:18 AM, WA5CAB--- via MRCA <mrca at mailman.qth.net>
> wrote:
>
>> Receiver mute.  According to the manual:
>>
>> "When the key is closed, the terminal labled REC ANT is grounded through
>> C115 (.01) to prevent the transmitted signal from paralyzing  the
>> receiver.".  Saves a relay contact.
>>
>> Robert Downs - Houston
>> wa5cab dot com (Web Store)
>> MVPA 9480
>>
>> In a message dated 11/22/2015 07:12:48 AM Central Standard Time,
>> arc5 at ix.netcom.com writes:
>>
>> Tim, N6CC has a web page dedicated to the RS-6.
>>
>> http://www.n6cc.com/the-rs-6-radio-set
>>
>> Scroll down and you will see a schematic of
>> the transmitter.  Odd-  Why is the "REC ANTENNA"
>> terminal connected to the keying buss via a .01 cap??
>>
>> 73 Dave AB5S
>>
>>
>>
>>
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