Re: [Elecraft] KXV3: (1) RX ANT signal level during TX; (2) spectra at buffered IF output
Wayne, Thank you for your very comprehensive mail, it certainly has put my mind at rest re potential issues involving separate receive antennas into the K3. 73 Stewart G3RXQ On Sun, 3 Feb 2008 14:42:19 -0800, wayne burdick wrote: Hi all, I'll address both of these issues. 1. RX ANT input signal handling during TX The KXV3's ANT IN jack includes a carrier-operated relay circuit (COR). If the COR kicks in too soon, they relay will switch off/on during keying. So its threshold is set high. It will still serve its primary function, which is to protect the transceiver when unsafe signal levels are present, such as when the RX antenna is in the near field of a KW transmit signal, or when a transmitter is accidentally connected to this port. This leaves a gray zone where the COR doesn't kick in, but the transmit signal may still be very high. High-power contest stations sometimes use additional external T/R switching if they can't avoid the use of closely-coupled receive and transmit antennas. We recently to a close look at this gray zone, and found that we could make an RX ANT jack on steroids by adding two more diode isolation sections. The resulting parts count is considerably higher, but we feel that the added protection during transmit would be worthwhile. So this change will be included in production units (once we use up our present supply of assembled KXV3 modules). Meanwhile, if your antenna configuration and power level warrant this higher degree of isolation, and you already have a KXV3, you can modify it. We're designing a small add-on board to make this easier. It will be supplied free of charge, on request. This unit has not yet been assigned an Elecraft part number, and isn't available yet, so PLEASE don't request it until we announce the details. 2. Buffered I.F. output spectra The pick-off point for the K3's buffered I.F. output -- right at the output of the 1st mixer's post-amp stage -- was selected to give the widest possible bandwidth. Thus there is no filtering of any kind from here to the BNC jack on the KXV3. This creates the opportunity to do *very* wide spectral sweeps, if required -- limited only by the bandwidth of the K3's band-pass filters. As some (armed with spectrum analyzers) have noted, this output signal includes the usual spectra one would expect from a high-level mixer. (And it *is* a very high-level mixer.) A mixer's output includes a broad range of products relating to the sum and difference of its inputs (RF and LO). It also includes products derived from harmonics of the sum and difference, etc. Collectively, these will appear as a comb pattern on an analyzer. This is why the mixer must be followed by band-pass filtering. (In transmit mode this function is performed by the K3's narrow ham-band band-pass filters; in receive mode, by the I.F. crystal filter and DSP filtering.) But the buffered I.F. output is at a different point in the signal chain. So any filtering needed for a panadapter must be included either in the panadapter itself, or in series with it. Some panadapters will require no filtering at all, while some will need various degress of L-C filtering (the L-C filter used on our I.F. noise blanker is a good starting point). If you were only interested in a narrow band sweep, you could use a ceramic or crystal filter. Our FM crystal filter, at about 13 kHz wide, would be a good choice here. Excellent shielding should be used, and possibly additional buffering, to prevent re-radiation of 8.215 MHz back into the K3. A related topic is the exact frequency of the buffered I.F. output. It is nominally 8.215 MHz with our 8-pole filters, and typically 0.8 to 0.9 kHz lower with our 5-pole filters. In addition, the portion of this passband actually present at the audio output is determined by the DSP controls (SHIFT, WIDTH, etc.). We can work with panadapter suppliers to provide this data via the RS232 port, and of course any future Elecraft panadapter would also have this information available. I'll be adding this subject to the Owner's Manual. If you're interfacing a panadapter to the K3 and have any further questions, feel free to e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] KXV3: (1) RX ANT signal level during TX
Date: Mon, 4 Feb 2008 08:31:09 GMT From: Stewart Baker [EMAIL PROTECTED] Subject: Re: [Elecraft] KXV3: (1) RX ANT signal level during TX;(2) spectra at buffered IF output To: wayne burdick [EMAIL PROTECTED], Elecraft Reflector elecraft@mailman.qth.net Message-ID: [EMAIL PROTECTED] Content-Type: text/plain; charset=US-ASCII Wayne, Thank you for your very comprehensive mail, it certainly has put my mind at rest re potential issues involving separate receive antennas into the K3. Ditto to that comment. I was seriously thinking of canceling the KXV3 from my order but all appears well.. Garry/Ve7ajj ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] KXV3: (1) RX ANT signal level during TX; (2) spectra at buffered IF output
Hi all, I'll address both of these issues. 1. RX ANT input signal handling during TX The KXV3's ANT IN jack includes a carrier-operated relay circuit (COR). If the COR kicks in too soon, they relay will switch off/on during keying. So its threshold is set high. It will still serve its primary function, which is to protect the transceiver when unsafe signal levels are present, such as when the RX antenna is in the near field of a KW transmit signal, or when a transmitter is accidentally connected to this port. This leaves a gray zone where the COR doesn't kick in, but the transmit signal may still be very high. High-power contest stations sometimes use additional external T/R switching if they can't avoid the use of closely-coupled receive and transmit antennas. We recently to a close look at this gray zone, and found that we could make an RX ANT jack on steroids by adding two more diode isolation sections. The resulting parts count is considerably higher, but we feel that the added protection during transmit would be worthwhile. So this change will be included in production units (once we use up our present supply of assembled KXV3 modules). Meanwhile, if your antenna configuration and power level warrant this higher degree of isolation, and you already have a KXV3, you can modify it. We're designing a small add-on board to make this easier. It will be supplied free of charge, on request. This unit has not yet been assigned an Elecraft part number, and isn't available yet, so PLEASE don't request it until we announce the details. 2. Buffered I.F. output spectra The pick-off point for the K3's buffered I.F. output -- right at the output of the 1st mixer's post-amp stage -- was selected to give the widest possible bandwidth. Thus there is no filtering of any kind from here to the BNC jack on the KXV3. This creates the opportunity to do *very* wide spectral sweeps, if required -- limited only by the bandwidth of the K3's band-pass filters. As some (armed with spectrum analyzers) have noted, this output signal includes the usual spectra one would expect from a high-level mixer. (And it *is* a very high-level mixer.) A mixer's output includes a broad range of products relating to the sum and difference of its inputs (RF and LO). It also includes products derived from harmonics of the sum and difference, etc. Collectively, these will appear as a comb pattern on an analyzer. This is why the mixer must be followed by band-pass filtering. (In transmit mode this function is performed by the K3's narrow ham-band band-pass filters; in receive mode, by the I.F. crystal filter and DSP filtering.) But the buffered I.F. output is at a different point in the signal chain. So any filtering needed for a panadapter must be included either in the panadapter itself, or in series with it. Some panadapters will require no filtering at all, while some will need various degress of L-C filtering (the L-C filter used on our I.F. noise blanker is a good starting point). If you were only interested in a narrow band sweep, you could use a ceramic or crystal filter. Our FM crystal filter, at about 13 kHz wide, would be a good choice here. Excellent shielding should be used, and possibly additional buffering, to prevent re-radiation of 8.215 MHz back into the K3. A related topic is the exact frequency of the buffered I.F. output. It is nominally 8.215 MHz with our 8-pole filters, and typically 0.8 to 0.9 kHz lower with our 5-pole filters. In addition, the portion of this passband actually present at the audio output is determined by the DSP controls (SHIFT, WIDTH, etc.). We can work with panadapter suppliers to provide this data via the RS232 port, and of course any future Elecraft panadapter would also have this information available. I'll be adding this subject to the Owner's Manual. If you're interfacing a panadapter to the K3 and have any further questions, feel free to e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
