[Elecraft] K3 Strange Power Output Problem

Mon May 14 02:57:47 EDT 2018

Hi Bob, 

Thanks, I'll try your ideas. We have a year to get ready for our next 
NSS operation... 

NSS was a Field Day style operation with AB-577 towers, all of the 
NSS towers and buildings were demolished 20 years ago except for 
three 600 foot towers that are all in the red zone of a firing range! 
Because its a Field Day style operation, we don't have enough time 
to install separate receiving antennas despite our 500+ acre NSS site... 

Our objective is to transmit on our assigned MARS frequencies outside 
the ham bands (e.g., 9448 kHz) and listen inside the adjacent ham band 
(e.g., 10128 kHz). We don't need to listen to both frequencies at the 
same time. 

Our K3 main receiver and KRX3 subreceiver share the same antenna 
and the transceivers have KBPF3 bandpass filters installed in the 
main receiver only . 

Before we began NSS operations on Saturday morning we had no idea 
that the K3 could not perform out of ham band split operations without 
using the KRX3 sub receiver. When we realized that our transmit 
power output was severely reduced by using wide split (e.g., 
9448 / 10128 kHz) we started to search for a solution... 

We were not successful using the K3 transceivers with a wide split 
so on those bands with wide splits (e;g., 9448/10128) we removed 
the K3 transceivers and substituted our old FT-1000MPs instead. 
They worked very well and were very easy to use. The K3 is far 
from easy to use in this application! 

As was suggested, operation of the K3 transceiver to meet our needs is 
much easier if we install a KBPF3 in each KRX3 subreceiver, since 
K3 operators almost always use their KRX3 sub receiver with SPLIT 
enabled, which forces the transmitter to transmit on the sub receive 
frequency. But a KRX3 sub receiver with no KBPF3 installed 
can't listen outside the ham bands where we transmit. So the 
commonly used SPLIT operation with the KRX3 can't meet our needs 
with our K3 transceivers with no KBPF3 installed in our KRX3 sub receivers 

If I had known not to tap SPLIT as I've always done when not transmitting 
on MARS frequencies, I may have been successful since we would then 
have been transmitting through the Main Receiver KBPF3 on the 
VFO A MARS frequency, and listening to the KRX3 sub receiver 
in the ham bands. 

I'll try split operation on 9448/10128 well before next year by not using 
SPLIT and listening on 10128 with the KRX3 sub receiver... 

Thanks Bob, 

73 
Frank 
W3LPL 

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

From: "Bob Wilson, N6TV" <n6tv at arrl.net> 
To: "Frank Donovan, W3LPL" <donovanf at starpower.net>, "Elecraft Reflector" <Elecraft at mailman.qth.net> 
Sent: Monday, May 14, 2018 12:34:36 AM 
Subject: Re: [Elecraft] K3 Strange Power Output Problem 

On Sun, May 13, 2018 at 5:17 PM, < donovanf at starpower.net > wrote: 

Its hard to devise a solution without this knowledge! 

Frank, 

It's also hard to suggest a solution without a clear understanding of the problem, which seems different than N3CW's original question. 

It's not clear to me what you need to achieve at NSS. I think you are saying you want listen to both widely-separated frequencies at the same time, using different antennas, one for the MAIN, one for the SUB? Or maybe you want to use the TX antenna for both receivers? Or maybe a separate RX antenna for both receivers? 

The SUB listens to either what is selected by MAIN (RX ANT or TX ANT) or to AUX, which is a totally separate RX ANT input that seems to bypass all the filters in the MAIN. With the SUB on, hold RX ANT to switch the SubRx to listen on AUX. This is a perfect input if your RX antenna is miles away from your TX antenna, which I assume is the case at NSS. 

Otherwise, if you want to listen to the TX ANT with both receivers, feed RX ANT OUT to both RX ANT IN and to AUX via an external 50 ohm splitter such as the Mini-Circuits ZFSC-2-6 , and now both receivers are listening to the same antenna, but with totally different receive paths. 

If you want to listen to a dedicated well-separated RX antenna in both receivers, instead of listening on the TX antenna , use an external splitter to feed the RX antenna to both RX ANT IN and to AUX. 

Repeating, do not use SPLIT mode, just tap SUB to TX on A, receive on both A and B, or just receive on B (CONFIG:L-MIX-R B B), whatever you require. 

73, 
Bob, N6TV 

On Sun, May 13, 2018 at 4:45 PM, < donovanf at starpower.net > wrote: 

<blockquote>
Hi Wayne, 

The MARS to ham band K3 cross-band problem affects every band, 
but it was extremely severe on 30 meters because the NSS assigned 
frequency -- 9448 kHz -- was almost 700 kHz from our typical 
10128 kHz receiving frequency. 

Since switching between the K3 bandpass filters and the KBPF3 
band pass filters at T/R rates isn't a workable solution, how about 
this external BNC cable solution since my K3 transceivers have 
KRX3 sub receivers? 

If I understand the K3 internal receiver antenna switching correctly 
a single external BNC jumper cable allows the K3 to transmit and 
receive on VFO A on MARS frequencies and listen to any amateur 
band on the sub receiver: 

- Connect the RX ANT OUT connector to the RX ANT IN connector 

- Tap the main RX ANT button which connects ANT 1 to the RX ANT OUT 
connector and switches the input of the main receiver to the RX ANT IN 
connector (connected by the external BNC cable to RX ANT OUT) 

- Tap SUB to turn the sub receiver on 

- Hold BSET and tap ANT to set the sub receiver input to MAIN. This 
allows the subreceiver to listen on the RX ANT connected to the main 
receiver. 

I'm sorry I didn't think of this yesterday... 

tks 

73 
Frank 
W3LPL 
</blockquote>