[Elecraft] Deaf KRX3 on one band ...

[Ron D'Eau Claire]

Joe, the only element in the receiver dedicated to 160 meters is the input
bandpass filter. It's the top one on the attached schematic (sent direct to
your personal e-mail). 

Note that this filter covers both 80 and 160 and relay K2 changes two
capacitors to tune it for each band. It seems like that K2 is not switching
or that C81 or C82 (the two capacitors switched in to tune 160) are no
longer in the circuit. It may be a problem with the switching command from
U2. 

I'd start as follows:

Open the K3 and exercise the connectors on the SUBIN and SUBOUT boards that
connect the KRX3 module to the main K3 RF board. I'd do that first to ensure
the module is fully plugged in and all the pins of the connectors is making
good contact. The SUBOUT interface is particularly vulnerable to being
dislodged since it's farthest from the supporting bumper on the back of the
loudspeaker. 

If that doesn't do it, I'd switch the KRX3 to 160, power down and open up
the KRX3 enclosure to see if both sides of C81 and C82 are grounded. Those
are the two caps that resonate the filter on 160 meters. One side is always
at ground through the inductors in the filter. The other side goes to ground
through the relay when you switch to 160. If one or both are not grounded,
Relay K2 is not switching. Either it's defective or it's not getting the
proper switching signal from U2. 

73,

Ron AC7AC
 

-----Original Message-----

My KRX3 is deaf on 160 meters ... and only on 160.  I had not done
any significant split on 160 since getting it (that one was off-line
for a while until I replaced a heat sensitive VFO B encoder and made the 
updates).

Yes, I've checked the antenna <G> ... it's on same antenna as the
main rx.  On every other band, signal levels are the same in both
receivers (balance is centered when the receivers are tuned to the
same signal) but on 160 there is almost nothing from the sub Rx ...

It does not appear to be related to roofing filters as I've checked
signal levels with both the 2.8 KHz and 400 Hz filters.  I've also
rechecked the receiver gain alignment ... although those should also
effect the higher bands and operation is normal other than 160.

Any suggestions where to start looking - signal levels are normal
on80 meters and higher as well below 1700 KHz (high end of the AM
broadcast band - both receivers have BPF3 installed).

73,

   ... Joe, W4TV

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