[ARC5] AN/GRC-109 antenna clamping diodes CR1, CR2

[Kenneth G. Gordon]

On 19 Feb 2019 at 6:03, Fuqua, William wrote:

> I was testing the GRC-109 and found that the TR switch in the transmitter was 
> not passing any signal.

Actually, the "T/R switch" in the GRC-109 is the CW hand-key.

> I suspect CR1 and CR2 HD2172 diodes are bad. What would be a good 
> substitution for these? I can't find any data on them.

As has been said, 1N34s are a close match.

> The receiver works well down to less than a uV on CW with the signal applied 
> directly to the antenna terminals.

The receiver is pretty hot, all right. I really like mine.

BTW, the "suck out" from that T/R circuit when the TX and the RX are on the same 
frequency is greater than -30 dB. This is why the manual states than when the two are used 
on the same frequency it is better to use separate antennas.

"Suck out" is caused by the transmitter's high "Q" final tank tuning circuit being in close 
relationship to the receiver's input circuitry.

In field use in Vietnam, the transmitter and the receiver were almost always on different 
frequencies, sometimes widely separated, so this "suck out" issue never occurred in that 
use.

As I have mentioned here, although I do have one NIB 1L6 ($50.00) left, I have substituted 
a solid-state version of that tube in my R-1004 so I can save my 1L6. The improvement in 
operational results is quite amazing.

I'll have to look at Breck's relay mod asap.

Ken W7EKB