[Elecraft] K2 - signal loss in band-pass filter

[Geoffrey Mackenzie-Kennedy]

Are,

Do you have anything attached to J13 (Xverter Interface)? If not a 
resistance measurement between pin 7 of one of the relays K1, K2  etc and 
ground with the K2 switched OFF, and W6 removed, should read a very high 
value, I would expect > 1 Megohm.

There is also the remote possibility that one of the relays is stuck with 
its pin 7 connected to its pin 8, something which could be checked with a 
resistance measurement with the K2 turned off.

73,
Geoff
GM4ESD


Are, LB3SA, wrote on Saturday, May 17, 2008 6:44 PM

> I recently completed my K2 and everything seemed to work OK. All tests are 
> ok
> with exception of a slightly low 8V regulator output (7.59V).
>
> The sensitivity seems low however (my KX1 is much better at this point).
> Tracing the receiver revealed that sensitivity is top notch at certain
> points. This is where it gets weird...
>
> When I inject a signal on the north side (according to schematic) of C7
> (40m), C15 (80M), C24 (20M) and the same on all other bands, the 
> sensitivity
> is great. But when I inject the signal on the other side of these 
> capacitors
> (pin 8 on the relays), the level drops  (at least 20db) to the same as 
> what
> it is at antenna, W6, W1,D2/D3, D3/D4 and all other points along the 
> signal
> path.
>
> I removed W6 and RFC7 to isolate the problem and to see if anything in the
> T-R switch or Low Pass filters could pull the signal down but there is no
> change. I still only hear a weak signal when I inject a signal at pin7 or 
> 8
> on the respective relays. But as soon as I touch either side of C6 for 
> 40m,
> L7 for 80m, C22 for 20m etc, it is as strong as it should be.
>
> I have measured all the relays for potential shorts but they seem to be
> fine.
>
> Any ideas out there?
>
> 73,
> Are - LB3SA