K2 receive sensitivity
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Hi to all on the reflector. I'd like to put something out here and see
if others experience the same thing or if I possibly have a problem with my K2 sn5834. Someone (I don't remember who) mentioned that a great way to test receive sensitivity is to simply check for an increase in noise level when switching from a dummy load to a resonant antenna on a dead band (like 10m is lately), and I am a great believer in that method. I have used it for years with various commercial and homebrew rigs. So here's the deal. K2 set for 10 meters, preamp off, antenna is resonant wire (and also used a beam). When switching between dummy load and antenna, there is no (or barely perceptible) change in receiver noise output. With the preamp on, the change is noticeable, as the noise increases both with dummy load and antenna connected. What I'm concerned about is the preamp off situation, as all other receivers I have tested do show a marked change in receiver noise when doing this test. I have already set the agc threshold so that there is no reduction in band noise when turning agc on and off. Band pass filter alignment was done with a minimum signal from a signal generator and IF and filter alignments were done with Spectrogram and everything seemed to check out OK. BTW, the I used two antennas for this test, a 3 el tribander at 40 ft and a OCF dipole cut for 160 and tuned with ATU. Do others have the same or similar results with this test? I'd really like to know if my K2 is behaving normally or I have a problem. BTW, the results improve as you lower the frequency, but the first band that shows a really marked increase in noise level with this test is 17m. Any and all comments are appreciated. 73, Paul, N2PD _______________________________________________ Elecraft mailing list Post to: [hidden email] 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
Paul, N2PD
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Paul,
I am not certain your test is entirely valid. If there is no atmospheric noise on the band you are using, you should notice no difference in level switching from a dummy load to an antenna. The bandwidth of the receiver will make a great difference as well, and that is both the IF bandwidth and the front end bandwidth. The K2 does have the low pass filters at the receiver front end - some other receivers run with a wide open 'DC to Daylight' front end which will pick up more wideband noise. You are not necessarily comparing apples to apples with such a simplified subjective measurement. It would be much more informative to actually measure the MDS at a given receiver bandwidth and at the frequency of interest. Measurements of that nature should be controlled and can be used for valid comparisons. 73, Don W3FPR > -----Original Message----- > > Hi to all on the reflector. I'd like to put something out here and see > if others experience the same thing or if I possibly have a problem with > my K2 sn5834. Someone (I don't remember who) mentioned that a great way > to test receive sensitivity is to simply check for an increase in noise > level when switching from a dummy load to a resonant antenna on a dead > band (like 10m is lately), and I am a great believer in that method. I > have used it for years with various commercial and homebrew rigs. > So here's the deal. K2 set for 10 meters, preamp off, antenna is > resonant wire (and also used a beam). When switching between dummy load > and antenna, there is no (or barely perceptible) change in receiver > noise output. With the preamp on, the change is noticeable, as the > noise increases both with dummy load and antenna connected. What I'm > concerned about is the preamp off situation, as all other receivers I > have tested do show a marked change in receiver noise when doing > this test. -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Don Wilhelm wrote:
>Paul, > >I am not certain your test is entirely valid. If there is no atmospheric >noise on the band you are using, you should notice no difference in level >switching from a dummy load to an antenna. > >The bandwidth of the receiver will make a great difference as well, and that >is both the IF bandwidth and the front end bandwidth. The K2 does have the >low pass filters at the receiver front end - some other receivers run with a >wide open 'DC to Daylight' front end which will pick up more wideband noise. >You are not necessarily comparing apples to apples with such a simplified >subjective measurement. > >It would be much more informative to actually measure the MDS at a given >receiver bandwidth and at the frequency of interest. Measurements of that >nature should be controlled and can be used for valid comparisons. > >73, >Don W3FPR > > > >>-----Original Message----- >> >>Hi to all on the reflector. I'd like to put something out here and see >>if others experience the same thing or if I possibly have a problem with >>my K2 sn5834. Someone (I don't remember who) mentioned that a great way >>to test receive sensitivity is to simply check for an increase in noise >>level when switching from a dummy load to a resonant antenna on a dead >>band (like 10m is lately), and I am a great believer in that method. I >>have used it for years with various commercial and homebrew rigs. >>So here's the deal. K2 set for 10 meters, preamp off, antenna is >>resonant wire (and also used a beam). When switching between dummy load >>and antenna, there is no (or barely perceptible) change in receiver >>noise output. With the preamp on, the change is noticeable, as the >>noise increases both with dummy load and antenna connected. What I'm >>concerned about is the preamp off situation, as all other receivers I >>have tested do show a marked change in receiver noise when doing >>this test. >> >> > >-- >No virus found in this outgoing message. >Checked by AVG Free Edition. >Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 >11:04 AM > > > > > always some level of atmospheric noise on 10 meters, even when the band is not open. The method of sensitivity quick-test I described was endorsed by many notable amateurs, including the late Doug DeMaw, W1FB, who I'm sure you have heard of. That's where I got the method from. But I guess what I'm asking of the guys on the reflector is whether or not they are experiencing the same result using this quick-test with the K2. 72 Paul N2PD _______________________________________________ Elecraft mailing list Post to: [hidden email] 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
Paul, N2PD
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In reply to this post by N2PD
I've never been floored by the K2's sensitivity. I've done the test you
mention, though probably not as thoroughly. When plugging in an antenna, I do hear the noise floor come up. Sometimes I have to crank the AF gain to hear it but it happens. I figure above 20 meters, that's what the preamp is for so I've never really troubled myself with it. Also, given the current state of the sunspot cycle, I've been on 80, 40, 30 and some 20 meters and that's about it. Even on 20, I find the rig acts deaf although I know it does hear fine. That AGC action is different than other rigs I've had so the K2 acts differently. - Keith N1AS - - K2 5411.ssb.100 - -----Original Message----- From: Paul Del Negro I'd like to put something out here and see if others experience the same thing or if I possibly have a problem with my K2 sn5834. ... check for an increase in noise level when switching from a dummy load to a resonant antenna on a dead band (like 10m is lately) _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
RE: K2 receive sensitivity
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In reply to this post by N2PD
Hi Paul:
The test on one band isn't valid on other bands because the band QRN changes a great deal with frequency. The fact that you hear little or not change in background QRN when you remove the antenna on 10 meters with the preamplifier off is because the K2 is optimized for maximum sensitivity and greatest dynamic range across the HF spectrum. The sensitivity of a receiver - its ability to hear weak signals - is a function of the bandwidth of the receiver, the overall gain of the receiver and the amount of internal noise generated in the receiver. Most receivers, including the K2, have more than enough overall gain, so the things to look at are the bandwidth and internal noise generated in the receiver. Narrower bandwidths make a band sound "quieter" because they filter out noise as well as signals on adjacent frequencies. The most rigorous test is to check the receiver at the narrowest bandwidth you'll use. (That's why a weak CW signal is easier to copy than an equally weak SSB signal. The SSB signal requires a wider bandwidth at the receiver, so more noise comes through that reduces the signal-to-noise ratio.) The internal noise in a receiver is a concern only when it competes with a weak signal being received. Of course, in order to hear the weak signal on any receiver the signal must be strong enough to be heard over the band noise - the background QRN - being received along with the signal. If, when you connect the antenna, you hear the background noise increase you can be sure your ability to hear signals is limited by the unavoidable background QRN and not the receiver. On the higher-frequency bands, typically 14 MHz and up, the background QRN may be low enough that the internal noise in the receiver might mask weaker signals. You sense when that's happening when you disconnect the antenna while listening to the background noise and the noise level does not change! The K2's preamplifier is a low-noise amplifier that boosts incoming signals so they easily over-ride the internal noise. In order to do this, the preamplifier must be placed at the input to the receiver, ahead of the I.F. filters, so it amplifies not only the desired signal but signals over a wide range of frequencies around it as well. On the lower frequencies, too much "front end" gain (ahead of the I.F. filters) such as provided by the preamplifier can lead to overloading of the receiver by extremely strong signals outside of the passband. So the K2's preamplifier can be turned off when it's not needed. That results in a receiver that has the low noise figure needed for the higher frequencies and optimum strong signal handling capability on the lower frequencies. While your test is a good quick check to see if the receiver is limiting your ability to hear weak signals, a more meaningful test for comparing receivers is to measure their signal-to-noise plus noise and minimum discernable signal (MDS) levels. Normally such measurements require some rather costly test equipment. However, Elecraft created a simple test oscillator that you can use to measure the signal-to-noise plus noise ratio at 1 uV and, based on that, you can estimate the MDS with good accuracy. It works with any receiver covering 80, 40 or 20 meters. The oscillator produces accurate crystal-controlled outputs on the three bands. It can also be used to calibrate your K2's S-meter and do other tests. Check out the XG2 Three Band Receiver Test Oscillator/S-Meter Calibrator on the Elecraft web site at: http://www.elecraft.com/mini_module_kits/mini_modules.htm It's the second-to-last item on the page. Ron AC7AC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Paul Del Negro Sent: Monday, January 15, 2007 7:11 AM To: [hidden email] Subject: [Elecraft] K2 receive sensitivity Hi to all on the reflector. I'd like to put something out here and see if others experience the same thing or if I possibly have a problem with my K2 sn5834. Someone (I don't remember who) mentioned that a great way to test receive sensitivity is to simply check for an increase in noise level when switching from a dummy load to a resonant antenna on a dead band (like 10m is lately), and I am a great believer in that method. I have used it for years with various commercial and homebrew rigs. So here's the deal. K2 set for 10 meters, preamp off, antenna is resonant wire (and also used a beam). When switching between dummy load and antenna, there is no (or barely perceptible) change in receiver noise output. With the preamp on, the change is noticeable, as the noise increases both with dummy load and antenna connected. What I'm concerned about is the preamp off situation, as all other receivers I have tested do show a marked change in receiver noise when doing this test. I have already set the agc threshold so that there is no reduction in band noise when turning agc on and off. Band pass filter alignment was done with a minimum signal from a signal generator and IF and filter alignments were done with Spectrogram and everything seemed to check out OK. BTW, the I used two antennas for this test, a 3 el tribander at 40 ft and a OCF dipole cut for 160 and tuned with ATU. Do others have the same or similar results with this test? I'd really like to know if my K2 is behaving normally or I have a problem. BTW, the results improve as you lower the frequency, but the first band that shows a really marked increase in noise level with this test is 17m. Any and all comments are appreciated. 73, Paul, N2PD _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: [hidden email] 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 |
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Sometimes the atmospheric noise on 10 meters can be extremely low. I
recall once working a nearly-antipodal DX station late at night (long after the band had "closed") when there was no indication at all on the S-meter, but perfect copy. It was like VHF weak-signal operation. Bob, N7XY _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by N2PD
Paul,
I am quite familiar with the late Doug DeMaw, and have a lot of respect for his work. That 'test' he described is a quick check to determine if a particular receiver has enough internal gain to hear above the atmospheric noise present on a particular band at any particular time. The receiver bandwidth is an important factor in how much atmospheric noise is heard. It is not a valid 'test' with which to compare one receiver to another - MDS measurement (also at a given bandwidth) does provide a valid comparison. If the 10 meter band is quiet, and you do not hear an increase in noise when the antenna is attached, that says that more internal receiver gain can be used, so you can switch on the preamp. If you can hear an increase in noise without the preamp, you are better off (from a dynamic range standpoint) not turning on the preamp. That is the limit of what can be said about this simple 'test' - it should not be extended to mean anything more that alone. 10 meters is quiet right now - we are in a sunspot low, and many of the characteristics of the low VHF bands (low background and atmospheric noise) is currently present on 10 meters. That will change in a couple years. 73, Don W3FPR > -----Original Message----- > > > Thanks for your reply, Don... it has been my experience that there is > always some level of atmospheric noise on 10 meters, even when the band > is not open. The method of sensitivity quick-test I described was > endorsed by many notable amateurs, including the late Doug DeMaw, W1FB, > who I'm sure you have heard of. That's where I got the method from. > But I guess what I'm asking of the guys on the reflector is whether or > not they are experiencing the same result using this quick-test > with the K2. > 72 Paul N2PD > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Ron D'Eau Claire-2
Ron D'Eau Claire wrote:
>Hi Paul: > >The test on one band isn't valid on other bands because the band QRN changes >a great deal with frequency. The fact that you hear little or not change in >background QRN when you remove the antenna on 10 meters with the >preamplifier off is because the K2 is optimized for maximum sensitivity and >greatest dynamic range across the HF spectrum. > >The sensitivity of a receiver - its ability to hear weak signals - is a >function of the bandwidth of the receiver, the overall gain of the receiver >and the amount of internal noise generated in the receiver. Most receivers, >including the K2, have more than enough overall gain, so the things to look >at are the bandwidth and internal noise generated in the receiver. > >Narrower bandwidths make a band sound "quieter" because they filter out >noise as well as signals on adjacent frequencies. The most rigorous test is >to check the receiver at the narrowest bandwidth you'll use. (That's why a >weak CW signal is easier to copy than an equally weak SSB signal. The SSB >signal requires a wider bandwidth at the receiver, so more noise comes >through that reduces the signal-to-noise ratio.) > >The internal noise in a receiver is a concern only when it competes with a >weak signal being received. Of course, in order to hear the weak signal on >any receiver the signal must be strong enough to be heard over the band >noise - the background QRN - being received along with the signal. If, when >you connect the antenna, you hear the background noise increase you can be >sure your ability to hear signals is limited by the unavoidable background >QRN and not the receiver. > >On the higher-frequency bands, typically 14 MHz and up, the background QRN >may be low enough that the internal noise in the receiver might mask weaker >signals. You sense when that's happening when you disconnect the antenna >while listening to the background noise and the noise level does not change! >The K2's preamplifier is a low-noise amplifier that boosts incoming signals >so they easily over-ride the internal noise. In order to do this, the >preamplifier must be placed at the input to the receiver, ahead of the I.F. >filters, so it amplifies not only the desired signal but signals over a wide >range of frequencies around it as well. > >On the lower frequencies, too much "front end" gain (ahead of the I.F. >filters) such as provided by the preamplifier can lead to overloading of the >receiver by extremely strong signals outside of the passband. So the K2's >preamplifier can be turned off when it's not needed. That results in a >receiver that has the low noise figure needed for the higher frequencies and >optimum strong signal handling capability on the lower frequencies. > >While your test is a good quick check to see if the receiver is limiting >your ability to hear weak signals, a more meaningful test for comparing >receivers is to measure their signal-to-noise plus noise and minimum >discernable signal (MDS) levels. Normally such measurements require some >rather costly test equipment. However, Elecraft created a simple test >oscillator that you can use to measure the signal-to-noise plus noise ratio >at 1 uV and, based on that, you can estimate the MDS with good accuracy. It >works with any receiver covering 80, 40 or 20 meters. The oscillator >produces accurate crystal-controlled outputs on the three bands. > >It can also be used to calibrate your K2's S-meter and do other tests. Check >out the XG2 Three Band Receiver Test Oscillator/S-Meter Calibrator on the >Elecraft web site at: > >http://www.elecraft.com/mini_module_kits/mini_modules.htm > >It's the second-to-last item on the page. > >Ron AC7AC > > > >-----Original Message----- >From: [hidden email] >[mailto:[hidden email]] On Behalf Of Paul Del Negro >Sent: Monday, January 15, 2007 7:11 AM >To: [hidden email] >Subject: [Elecraft] K2 receive sensitivity > > >Hi to all on the reflector. I'd like to put something out here and see >if others experience the same thing or if I possibly have a problem with >my K2 sn5834. Someone (I don't remember who) mentioned that a great way >to test receive sensitivity is to simply check for an increase in noise >level when switching from a dummy load to a resonant antenna on a dead >band (like 10m is lately), and I am a great believer in that method. I >have used it for years with various commercial and homebrew rigs. So here's >the deal. K2 set for 10 meters, preamp off, antenna is >resonant wire (and also used a beam). When switching between dummy load >and antenna, there is no (or barely perceptible) change in receiver >noise output. With the preamp on, the change is noticeable, as the >noise increases both with dummy load and antenna connected. What I'm >concerned about is the preamp off situation, as all other receivers I >have tested do show a marked change in receiver noise when doing this test. >I have already set the agc threshold so that there is no reduction in >band noise when turning agc on and off. Band pass filter alignment was >done with a minimum signal from a signal generator and IF and filter >alignments were done with Spectrogram and everything seemed to check >out OK. BTW, the I used two antennas for this test, a 3 el tribander at >40 ft and a OCF dipole cut for 160 and tuned with ATU. >Do others have the same or similar results with this test? I'd really >like to know if my K2 is behaving normally or I have a problem. BTW, >the results improve as you lower the frequency, but the first band that >shows a really marked increase in noise level with this test is 17m. >Any and all comments are appreciated. >73, Paul, N2PD >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >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 > > > > > > I am aware that the test I described is only a quick check to see if the ability to hear weak signals is being masked by internal receiver noise. However, the K2 is the only receiver (that I have owned) that has ever "failed" this test on 10 meters (meaning that more gain was needed so the preamp should be turned on) and I am wondering if others experience the same thing or there is something not right with my particular K2. So far, I have not been able to get an answer to that question. I do own the XG2 and have performed MDS measurements on my K2 using the XG2 and also a milspec signal generator I have. The numbers agree very closely with published specs ON 20 METERS. On ten meters I measured an MDS of -124 dbm (preamp off) and -130dbm (preamp on). IMHO, an MDS less than -130 dbm is not acceptable for weak signal reception. Which means to me that on 10 meters the preamp is absolutely required. Knowing that most amateurs do not have the equipment to make MDS measurements on 10 meters, I didn't think I could get my question answered on the reflector (the question being, 'Is my K2 receive sensitivity the same as everyone else's or do I have a problem with mine') by stating my measured MDS on 10 meters. So I opted to put the 'quick-check' method out there instead, hoping that I would get answers like "yep, mine is the same" or " nope, u must have a problem". It appears that the purpose of my original post has been misunderstood by many. I just want to know if my K2 is healthy or not. I think the K2 is a masterpiece of 'elegant simplicity' and my intent is not to knock the rig. I've had more fun since the my kit arrived than I've had since the heathkit days. 73, Paul, N2PD _______________________________________________ Elecraft mailing list Post to: [hidden email] 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
Paul, N2PD
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Paul,
I do not have 10 meter specific MDS measurements handy. I can measure 2 K2s sometime in th efuture if it is necessary, but it will be after I get the workbench cleared. If you have the equipment, measure the RX VFO injection level to the mixer (TP1) - it should be +7 dBm for good mixer performance. Assuming the mixer presents a 50 ohm load to the VFO signal and your measurement does not interfere with the loading, you should see a 500 mVrms voltage at the mixer port or 1.416 volts peak to peak on a 'scope. In-situ measurement is not the best for this, substitution would be better, but you can draw some conclusions based on the in-situ measurement if the input impedance to the measuring device is high enough (you will be measuring in the 23 to 24 MHz range, so be certain the instrument is capable of accurate readings at that frequency (a 150 MHz 'scope with 150 MHz 10X probe should give good measurements). If the 10 meter VFO input is sufficient, you should be getting full benefit from the mixer, and there is nothing short of reducing the losses in the bandpass filters, T-R switch, and Low Pass Filter that will improve the MDS on 10 meters. If you find the mixer input level low, it can be adjusted by changing the resistors on the U2 buffer, but check all bands so you don't overdrive the mixer if you change the level. If the VFO level changes between bands, look for some frequency dependency in the VFO ALC circuit. My reasoning: - beyond the mixer, the K2 response should be the same from band to band, the only thing that will make changes on one band and not others is between the antenna jack and the mixer. 73, Don W3FPR > -----Original Message----- > I do own the XG2 and have performed MDS measurements on my K2 using the > XG2 and also a milspec signal generator I have. The numbers agree very > closely with published specs ON 20 METERS. On ten meters I measured an > MDS of -124 dbm (preamp off) and -130dbm (preamp on). IMHO, an MDS less > than -130 dbm is not acceptable for weak signal reception. Which means > to me that on 10 meters the preamp is absolutely required. snip... > I just want to know if my K2 is healthy > or not. > I think the K2 is a masterpiece of 'elegant simplicity' and my intent is > not to knock the rig. I've had more fun since the my kit arrived than > I've had since the heathkit days. > 73, Paul, N2PD > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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I measured my K2 on 28 MHz 200 Hz bandwidth, CW mode as follows:
MDS: 28 MHz Pre-amp off: -125 dBm Pre-amp on: -133 dBm I have a page at http://www.cliftonlaboratories.com/k2_rx_sensitivity.htm discussing K2 sensitivity measurements and presenting the results for my K2 and also results supplied by Stan, W5EWA, for his K2. Since we used different signal generators, there's a calibration issue of course, but our results were generally similar, except at 28 MHz where his receiver measures hotter than mine. Jack www.cliftonlaboratories.com _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by N2PD
I too have noticed my K2 (5411) seems to be a bit deaf, getting worse as
you go up the bands. When I compared it side by side with the 830s, the 830s detected and decoded a lot more atmospheric noise than the K2 did. After some pondering I've come to believe what I'm hearing is not necessarily a lack of sensitivity, but a difference in AGC action. My 830s had and aggressive AGC. So did the Drake 2B. Each of them aggressively reduces gain for even the smallest signals which means the signal will always be turned down to a level that approaches that of the noise. Big signal get squashed in a big way. Even the background noise on the higher bands was amplified enough to get into the AGC. With such aggressive AGC action, the rig is run with AF gain a bit higher making the presence of static very obvious. The K2 seems to be different. The AGC isn't as aggressive so a weak signal actually *sounds* weaker and a strong one is stronger. I run the AF gain lower since average to strong signals are strong and you want to turn them down. This keeps the noise level quieter than the Kenwood / Icom / Drake / TenTec stuff I've owned which is exactly why the K2 is so nice to use. There may be a lack of sensitivity on 10 meters, but there's a preamp built right into the rig. That way when you don't need the extra sensitivity, you can turn it off and enjoy the quiet performance and better dynamic range of a rig with a tad less overall (excess?) gain. Just some random ramblings, I guess... 73! - Keith N1AS - - K2 5411.ssb.100 - -----Original Message----- From: Paul, N2PD ... However, the K2 is the only receiver (that I have owned) that has ever "failed" this test on 10 meters (meaning that more gain was needed so the preamp should be turned on) and I am wondering if others experience the same thing or there is something not right with my particular K2. _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Don Wilhelm-3
Paul,
Check out Jack Smith's website for a fairly simple method of determining the sensitivity of your K2. There are some readings that Jack took of his K2, and also readings that I took on my K2. I've provided a link to the page so you should be able to go right to it. http://www.cliftonlaboratories.com/k2_rx_sensitivity.htm You can also check out the rest of his website while you are there. He has some interesting information on the K2, as well as a nice Panadapter that you might want to take a look at. Stan Rife W5EWA Houston, TX K2 S/N 4216 -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Don Wilhelm Sent: Tuesday, January 16, 2007 10:07 AM To: Paul Del Negro; [hidden email] Subject: RE: [Elecraft] K2 receive sensitivity Paul, I do not have 10 meter specific MDS measurements handy. I can measure 2 K2s sometime in th efuture if it is necessary, but it will be after I get the workbench cleared. If you have the equipment, measure the RX VFO injection level to the mixer (TP1) - it should be +7 dBm for good mixer performance. Assuming the mixer presents a 50 ohm load to the VFO signal and your measurement does not interfere with the loading, you should see a 500 mVrms voltage at the mixer port or 1.416 volts peak to peak on a 'scope. In-situ measurement is not the best for this, substitution would be better, but you can draw some conclusions based on the in-situ measurement if the input impedance to the measuring device is high enough (you will be measuring in the 23 to 24 MHz range, so be certain the instrument is capable of accurate readings at that frequency (a 150 MHz 'scope with 150 MHz 10X probe should give good measurements). If the 10 meter VFO input is sufficient, you should be getting full benefit from the mixer, and there is nothing short of reducing the losses in the bandpass filters, T-R switch, and Low Pass Filter that will improve the MDS on 10 meters. If you find the mixer input level low, it can be adjusted by changing the resistors on the U2 buffer, but check all bands so you don't overdrive the mixer if you change the level. If the VFO level changes between bands, look for some frequency dependency in the VFO ALC circuit. My reasoning: - beyond the mixer, the K2 response should be the same from band to band, the only thing that will make changes on one band and not others is between the antenna jack and the mixer. 73, Don W3FPR > -----Original Message----- > I do own the XG2 and have performed MDS measurements on my K2 using the > XG2 and also a milspec signal generator I have. The numbers agree very > closely with published specs ON 20 METERS. On ten meters I measured an > MDS of -124 dbm (preamp off) and -130dbm (preamp on). IMHO, an MDS less > than -130 dbm is not acceptable for weak signal reception. Which means > to me that on 10 meters the preamp is absolutely required. snip... > I just want to know if my K2 is healthy > or not. > I think the K2 is a masterpiece of 'elegant simplicity' and my intent is > not to knock the rig. I've had more fun since the my kit arrived than > I've had since the heathkit days. > 73, Paul, N2PD > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: [hidden email] 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 |
RE: K2 receive sensitivity
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In reply to this post by N2PD
Paul wrote:
hank you for your response, Ron. (and also Don). I am aware that the test I described is only a quick check to see if the ability to hear weak signals is being masked by internal receiver noise. However, the K2 is the only receiver (that I have owned) that has ever "failed" this test on 10 meters (meaning that more gain was needed so the preamp should be turned on) and I am wondering if others experience the same thing or there is something not right with my particular K2. So far, I have not been able to get an answer to that question. I do own the XG2 and have performed MDS measurements on my K2 using the XG2 and also a milspec signal generator I have. The numbers agree very closely with published specs ON 20 METERS. On ten meters I measured an MDS of -124 dbm (preamp off) and -130dbm (preamp on). IMHO, an MDS less than -130 dbm is not acceptable for weak signal reception. Which means to me that on 10 meters the preamp is absolutely required. ---------------------------------- I think "failed" is a misnomer. It sounds as if the only receiver in your comparative tests that is behaving ideally is your K2. The last thing you want is excess "front end" gain. All you want is just enough to bring signal levels up above the internal receiver noise and then have the bulk of the gain *after* the i.f. filters where only the signal of interest is being amplified. The K2 exhibits that characteristic, as you observed. On the lower frequencies no pre-amp is needed. The band noise easily over-rides any internal receiver noise. But on 10 meters it does not until you turn on the preamp. That means the K2 does not have excess front end gain on the lower bands that will limit its dynamic range. It sounds like the receivers you're using to compare the K2 with have a less-than-ideal gain distribution. To the "heart" of your question, yes, on my K2 at least, the preamp is needed on 10 meters. I've not tested the MDS on that band, but at the narrowest bandwidth my receiver's ability to "hear" is limited by the external noise under the quietest band conditions, as indicated by the "DeMaw test": removing the external antenna and noting a significant drop on QRN. That means that seeking a better MDS is a waste of effort for me with my antenna system. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Ron, you are completely correct - if you can hear the atmospheric noise at
all, the receiver will hear signals right down to the noise level. Once that amount of distributed gain is achieved, the next most important characteristic of a receiver is the dynamic range which is an indicator of how strong a signal can be received before the receiver blocks and distorts (reducing the ability to hear weak signals in th evicinity of strong ones). When I was a young ham (that was back in the youth of SSB), I did get the impression that there was a relationship between how loud the receiver was and how sensitive it was. After some study and some receiver design, and more years of experience, I discovered that those old thoughts relating sensitivity and 'loud' were indeed quite different. One can always add more amplification and make it louder, but making the noise louder is not necessarily a good thing - one must make the signal louder and not the noise to improve the reception of weak signals. If you want an extreme descrition of how a really quiet receiver can sound, Rick Campbell KK7B often has an apt description in his writings about his phasing receivers. 73, Don W3FPR > -----Original Message----- > > I think "failed" is a misnomer. It sounds as if the only receiver in your > comparative tests that is behaving ideally is your K2. > > The last thing you want is excess "front end" gain. All you want is just > enough to bring signal levels up above the internal receiver > noise and then > have the bulk of the gain *after* the i.f. filters where only the > signal of > interest is being amplified. > > The K2 exhibits that characteristic, as you observed. On the lower > frequencies no pre-amp is needed. The band noise easily over-rides any > internal receiver noise. But on 10 meters it does not until you > turn on the > preamp. That means the K2 does not have excess front end gain on the lower > bands that will limit its dynamic range. > > It sounds like the receivers you're using to compare the K2 with have a > less-than-ideal gain distribution. > > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.16.12/628 - Release Date: 1/15/2007 11:04 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
RE: K2 receive sensitivity
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You and I are of the same "Ham generation" Don. In the 1950's I acquired a
"dream receiver": a National HRO-5. It featured two tuned RF amplifier stages ahead of the mixer, two I.F. amplifiers after the filter and two stages of audio delivering several watts of power to an 8-inch speaker! I, too, equated "sensitivity" with the HRO's ability to fill the room with noise. After learning a little bit about proper gain distribution in a receiver I fashioned a step attenuator that I put between the antenna and the antenna jack to cut down on the overall signal strength reaching the first stage. It was amazing how much the attenuator reduced the background QRN without cutting the signals down nearly as much, especially on 80 and 40 meters. What was happening was that very strong signals well off of my desired frequency (e.g. shortwave broadcasters around 40) were overloading either the RF amplifiers or the mixer. The result sounded exactly like normal background QRN, but it wasn't. Adding attenuation made weak signals jump up out of the noise level. The loss of overall gain was easily made up for by simply turning up the volume. That led to an ongoing interest in receivers. My old correspondence includes many schematics and notes exchanged with Doug DeMaw and Wes Hayward, much of it about direct-conversion and phasing receivers. I've also followed the impressive work by Rick Campbell, but I've never had the pleasure of working him or corresponding with him. Of course, modern receivers like the K2 has are, by and large, much more tolerant of strong signals than receivers of only a few years ago, thanks to improved mixers and amplifiers. I think that's given a lot of operators a false sense of security. They don't think to try turning the preamp off (or turning the attenuator on) and turning up the AF gain when digging for a weak signal, but when a strong out-of-band signal is managing to cause overload somewhere in the front end, that can make the weak signal much easier to copy. Ron AC7AC -----Original Message----- Ron, you are completely correct - if you can hear the atmospheric noise at all, the receiver will hear signals right down to the noise level. Once that amount of distributed gain is achieved, the next most important characteristic of a receiver is the dynamic range which is an indicator of how strong a signal can be received before the receiver blocks and distorts (reducing the ability to hear weak signals in th evicinity of strong ones). When I was a young ham (that was back in the youth of SSB), I did get the impression that there was a relationship between how loud the receiver was and how sensitive it was. After some study and some receiver design, and more years of experience, I discovered that those old thoughts relating sensitivity and 'loud' were indeed quite different. One can always add more amplification and make it louder, but making the noise louder is not necessarily a good thing - one must make the signal louder and not the noise to improve the reception of weak signals. If you want an extreme descrition of how a really quiet receiver can sound, Rick Campbell KK7B often has an apt description in his writings about his phasing receivers. 73, Don W3FPR _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by N2PD
The G2DAF receiver did it for me when he demonstrated gain and s/noise ratios. A friend built that rx and it was completely different to others I had listened to. If I remember rightly he had no gain in the front end, only matching to the antenna and input filters; all the gain was in the IF.
David G3UNA ----------------------------------------- Email sent from www.ntlworld.com Virus-checked using McAfee(R) Software Visit www.ntlworld.com/security for more information _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: RE: K2 receive sensitivity
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David,
If you ever get the opportunity try out a receiver which uses G3SBI's H-mode mixer up front followed by a > +40dbm IIP3 IF / filter strip, same principle but improved 'numbers' with the linearity of tuned circuits and IF filters now becoming the limiting factors in receiver IMD performance. 73, Geoff GM4ESD David G3UNA wrote: > The G2DAF receiver did it for me when he demonstrated gain and s/noise > ratios. A friend built that rx and it was completely different to others > I had listened to. If I remember rightly he had no gain in the front end, > only matching to the antenna and input filters; all the gain was in the > IF. > > David > G3UNA > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by N2PD
In a message dated 1/17/07 6:37:02 AM Eastern Standard Time,
[hidden email] writes: > The G2DAF receiver did it for me when he demonstrated gain and s/noise > ratios. If I remember rightly he had no gain in the front end, only matching > to the antenna and input filters; all the gain was in the IF. Depends on what version he built. The last version used a push-pull RF amplifier and mixers, all low-noise triodes. There *was* some gain in that front end. The RF amplifier had just enough to make up for the losses in the tuned circuits, and the two mixers had some gain, but not a lot. They were primarily designed for dynamic range and low noise, not gain. The result was that there wasn't much gain ahead of the selectivity. Another example is the fabled Squires Sanders SS-1R receiver, which used balanced 7360 mixers and no RF stage. But it cost $700 back in the early 1960s! IMHO, the trend started with a 1957 QST article by W1DX called "What's Wrong With Our Present Receivers?". There was also QST articles called "The Miser's Dream" in 1965, and "An Experimental Receiver of 75 Meter DX Work", in 1971, which showed receivers using those basic principles. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Modular construction (was RE: K2 receive sensitivity)
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In reply to this post by Geoffrey Mackenzie-Kennedy-2
Space is certainly a factor unless the designer is prepared to employ
shielding, filtering and ground fencing. I believe that construction using shielded modules has a great deal to offer, and I am not convinced at all that in the long run the method is 'too' expensive *if* equipment performance is used as the yardstick. Certainly easier to add options provided that some system design thinking had been done at the outset. Small high performance filters in my experience require some form of shielding between resonators and great attention to leakage past the filter, but it can be done e.g. 14 pole HF crystal ladder filters with the crystals side by side in a straight line. 73, Geoff GM4ESD ----- Original Message ----- From: "David Cutter" <[hidden email]> To: "Geoffrey Mackenzie-Kennedy" <[hidden email]> Sent: Friday, January 19, 2007 6:47 AM Subject: Re: RE: [Elecraft] K2 receive sensitivity >I read about that some while ago but have not come across such receivers. >My guess is that the limiting factor is also governed by space, ie how do >you make a high performance filter fit a small space, vis leakages. > > David > G3UNA > > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
Re: Modular construction (was RE: K2 receive sensitivity)
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Yes, all in a staight line should be *easy* it's when a square format is required that things get interesting.
David G3UNA > > From: "Geoffrey Mackenzie-Kennedy" <[hidden email]> > Date: 2007/01/19 Fri AM 11:52:40 GMT > To: "David Cutter" <[hidden email]> > CC: "Elecraft Discussion List" <[hidden email]> > Subject: Modular construction (was RE: [Elecraft] K2 receive sensitivity) > > Space is certainly a factor unless the designer is prepared to employ > shielding, filtering and ground fencing. I believe that construction using > shielded modules has a great deal to offer, and I am not convinced at all > that in the long run the method is 'too' expensive *if* equipment > performance is used as the yardstick. Certainly easier to add options > provided that some system design thinking had been done at the outset. > Small high performance filters in my experience require some form of > shielding between resonators and great attention to leakage past the filter, > but it can be done e.g. 14 pole HF crystal ladder filters with the crystals > side by side in a straight line. > > 73, > Geoff > GM4ESD > > ----------------------------------------- Email sent from www.ntlworld.com Virus-checked using McAfee(R) Software Visit www.ntlworld.com/security for more information _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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