K3 - External RX Mute
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In the recent WAE CW Contest, we had two K3s on the same band, one as
the live transmitter, and the other either tuning the band or listening on the running frequency to assist the run operator. While listening on the run station's frequency, even though we used an Acom 2S1 to ground the antenna line and thus protect the RX front end, the run station's signal was very loud in the spot radio's RX. Is there a way to configure the K3 for variable muting during PTT active times on the other K3? I'm wondering if the run station's PTT line could be used to variably mute the spot RX somehow. Full muting is not the goal, but rather a way to keep the RX "on" but keep the S meter down to S9 or thereabouts, to allow the RX to recover very quickly. Even with AGC-F, often the first character of the caller's callsign would be missed due to the recovery time. Plus it hurt my ears! OTs may remember that the Collins 75S3B had a "Mute" jack on the back, to be used with the 32S3 transmitter. In those days, we could accomplish a variable mute of the RX by putting a large resistance pot (50K maybe) across that jack, and switch it in and out with a reed relay following keying. Can this be done with the K3? 73 - Dave N3RD ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Dave, How is the signal reaching the "spotting" K3 during transmit from the "run" radio? Have you checked the signal level with the antenna completely disconnected from the run radio? If the problem is coupling through the 2S1 and primary antenna input you could build a pin diode operated attenuator (or even reed relay switched attenuator), install it in the RF IN/OUT loop of the spotting radio and control it with PTT from the run radio. 73, ... Joe, W4TV On 8/17/2010 8:37 PM, Dave Hawes wrote: > In the recent WAE CW Contest, we had two K3s on the same band, one as > the live transmitter, and the other either tuning the band or listening on the > running frequency to assist the run operator. > > While listening on the run station's frequency, even though we used an Acom > 2S1 to ground the antenna line and thus protect the RX front end, the run > station's signal was very loud in the spot radio's RX. > > Is there a way to configure the K3 for variable muting during PTT active times > on the other K3? I'm wondering if the run station's PTT line could be used to > variably mute the spot RX somehow. Full muting is not the goal, but rather a > way to keep the RX "on" but keep the S meter down to S9 or thereabouts, to > allow the RX to recover very quickly. Even with AGC-F, often the first > character of the caller's callsign would be missed due to the recovery time. > Plus it hurt my ears! > > OTs may remember that the Collins 75S3B had a "Mute" jack on the back, to > be used with the 32S3 transmitter. In those days, we could accomplish a > variable mute of the RX by putting a large resistance pot (50K maybe) across > that jack, and switch it in and out with a reed relay following keying. Can this > be done with the K3? > > 73 - Dave N3RD > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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We are all K3 at Multi/Multi NY4A and do not have this problem.
First, your description of loosing the first *character* while waiting for *fast* AGC to recover is certainly not normal, regardless of the input level. The K3's serial number, firmware version and AGC constants would be useful information to begin sorting this out. There was a change to hardware defensive AGC in very early models. The behavior of the AGC is nearly completely configurable, and the constants used in the menu could be responsible for a lot of your perception. * Depending on how much slope you are using in your selected AGC constant, a 60 over 9 signal can be the SAME volume as an S1 signal, OR MUCH louder. Again, that is a chosen setting in the AGC menu entries. Also it would be useful to know whether the level was high enough for the protective relays to kick in. That would have been a clicking in the spotting K3. * At the root of the problem is listening to a 500 volt signal from an adjacent tranceiver/amp and trying to reduce the signal from that to S9, which, frankly, is going to be very difficult. From 500 volts to 50 microvolts is 140 dB. Isolation of switches advertised as "high isolation" are 90 dB, but isolation in switches of 40 to 60 db are far more common if transmitting levels are involved. The common concern with these is not BURNING UP a RX connected to one port on the switch with a QRO signal connected to another port. And to complicate this, there are many possible separate paths. You may improve the isolation in one, only to have another become the new limiting leakage. The sources of these are legion... * Use of "audio" cables for control functions and interconnection, many of which do not even provide 30 dB of isolation at RF frequencies. I have gone to using RG174 and other small coax for such functions to get the better isolation at ALL frequencies. Do not use Radio Shack audio/video cables for your control connections. Also people who design USB RS232 adapters are not thinking about 1500 watt RF amps right next to them. * Unsoldered, or deteriorated crimp connections, or loose connections due to handling. Another reason to use teflon based small coax for control functions. Simply, the isolation between the transmitting and receiving antennas. It is MOST unlikely that you can get 140 db isolation between an HF transmitting antenna and ANY receiving antenna on the same property unless you can get horizontal separation measured in 500's of feet. And even if you do, you can lose most of if even one connector goes bad in the shack. If you get the in-band signal down to 60 over 9, you will have done splendidly. After that, you need to tinker with your AGC constants. This degree of isolation in a K3 pairing will usually allow you hear and work stations up and down 2 or 3 kHz from the QRO running signal, EVEN when the running station is transmitting. Listening ON frequency to the running station will require an AGC setting with very little slope and a decay on the fast side. This is an AGC setting that is usually different than needed by the run transceiver. This presumes that you do NOT have unmitigated high leakage paths in coax, switching, connectors, control lines, etc. Test the leakage with all leads removed (except DC power) and see what all your leads let in just that one lead at a time. What sets up opportunity is the assembly and take down for contests, unless your host has all the stuff already taken care of. Been there, done that, made dozens of stupid mistakes, etc, etc. 73, Guy. On Tue, Aug 17, 2010 at 11:45 PM, Joe Subich, W4TV <[hidden email]> wrote: > > Dave, > > How is the signal reaching the "spotting" K3 during transmit from > the "run" radio? Have you checked the signal level with the antenna > completely disconnected from the run radio? > > If the problem is coupling through the 2S1 and primary antenna > input you could build a pin diode operated attenuator (or even > reed relay switched attenuator), install it in the RF IN/OUT > loop of the spotting radio and control it with PTT from the run > radio. > > 73, > > ... Joe, W4TV > > On 8/17/2010 8:37 PM, Dave Hawes wrote: >> In the recent WAE CW Contest, we had two K3s on the same band, one as >> the live transmitter, and the other either tuning the band or listening on the >> running frequency to assist the run operator. >> >> While listening on the run station's frequency, even though we used an Acom >> 2S1 to ground the antenna line and thus protect the RX front end, the run >> station's signal was very loud in the spot radio's RX. >> >> Is there a way to configure the K3 for variable muting during PTT active times >> on the other K3? I'm wondering if the run station's PTT line could be used to >> variably mute the spot RX somehow. Full muting is not the goal, but rather a >> way to keep the RX "on" but keep the S meter down to S9 or thereabouts, to >> allow the RX to recover very quickly. Even with AGC-F, often the first >> character of the caller's callsign would be missed due to the recovery time. >> Plus it hurt my ears! >> >> OTs may remember that the Collins 75S3B had a "Mute" jack on the back, to >> be used with the 32S3 transmitter. In those days, we could accomplish a >> variable mute of the RX by putting a large resistance pot (50K maybe) across >> that jack, and switch it in and out with a reed relay following keying. Can this >> be done with the K3? >> >> 73 - Dave N3RD >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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