Re: [Elecraft_K3] Integration of External Band Pass Filters

Dave Hachadorian

Here’s another thought.  There is a carrier-operated relay on the Rx ANT IN connector.  If the signal is high, the relay disconnects the Rx antenna.  Maybe it also reconnects the main antenna?
It could be that the second harmonic of the 20 M transmitter is overloading the COR, causing it to reconnect the main antenna, which is not protected by the bpf?
To reduce the second harmonic of the 20M transmitter, an 11’ 6” closed stub could be attached to the 20M feedline.
Dave Hachadorian, K6LL
Yuma, AZ


From: aa3b.bud@... [Elecraft_K3]
Sent: Monday, January 15, 2018 1:39 PM
To: Elecraft_K3@...
Subject: [Elecraft_K3] Integration of External Band Pass Filters

I am experiencing an issue with band pass filters (BPF) here that I don’t understand and I am hoping that someone can help me work through it.


I have been experimenting with BPFs to eliminate interference while doing single operator two radio contesting (SO2R).


My K3 includes the KRX3 sub receiver, KAT3 ATU and KXV3 option.  The BPFs are 100W units manufactured by LPS.


My experiment tested two configurations as follows:


1.  BPFs connected in series with the coax going to the rear panel Antenna 1 connector.

2.  BPFs connected between the rear panel connectors RX ANT IN and RX ANT OUT.  The RX antenna was activated from the front panel.


I transmitted a 500 CW signal on 10M and the K3 was receiving on 10M.


Configuration 1 worked fine with no interference heard on 10M.   Configuration 2 did not work – strong interference was present and I got a “High Signal” warning.  I would have expected similar performance in both configurations. 


I really would like to use Configuration 2 as a permanent solution but it appears not to work.  Any advice?




Bud AA3B

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