Re: [Elecraft] [K2] Sensitivity Spec
Steve, I ran your parameters thru my NF program for three stages using: 1.2 dBNF of 1st stage with 17-dB gain (typical DEMI 10-GHz xvtr spec) followed by 0.1 dB cable loss 1.0 dBNF 2nd stage which nominal for a 144-MHz xvtr and used 10-dB gain followed by0.1 dB cable loss K2 10-dBNF Bw = 500 Hz MDS = -151.2 dBm change gain of 2nd stage to 15-dB results in MDS = -151.4 dBm so 10-dB gain is sufficient The K2 with 10-dBNF has MDS = 137.3 dBm Thus you should see 13.9 dB increase in sensitivity (MDS). But since sky noise temperature at 10-GHz is typ 10K not sure how much noise rise will be seen. At 2m Tsky is about 250K (in a perfectly quiet environ) so same system looking at the 2m sky has MDS = -146.2 dBm At 10m Tsky is about 5,000K (guessing) and MDS = -134.5 dBm Obviously the K2 10-dBNF is sufficient on 10m, assuming adequate system gain to drive the mixers. 73, Ed - KL7UW --- From: Steve Kavanagh <skavanag...@yahoo.ca> To: <elecraft@mailman.qth.net>, <donw...@embarqmail.com> Subject: Re: [Elecraft] [K2] Sensitivity Spec Message-ID: <1122135791.3077810.1502906517...@mail.yahoo.com> Content-Type: text/plain; charset=UTF-8 Thanks for your comments, Don. When you test K2's, can I assume you have the signal generator connected directly to the K2 (or through an attenuator) with no antenna connected? Normally, one might hope that a preamp would provide some improvement in receiver noise figure (and hence MDS, sensitivity, noise floor), or there isn't much point in having it. I've never run into an intermodulation or blocking problem on 10 GHz (sideband noise issues tend to dominate the *rare* strong signal scenario) so I expect to leave the K2 preamp on in an attempt to maximize the sensitivity I agree that most often transverters have lots of gain but I noticed, with the particular combination I have, that the increase in receiver noise output resulting from turning on both the 10 GHz-to-144 MHz and the 144 MHz-to-28 MHz transverters was only about 7 dB (K2 preamp on, AGC off) compared to the K2 alone, rather less than usually seems to be the case, so I was afraid that the front end noise might not dominate the overall receiver noise. The intermediate transverter does have relatively low gain, by design. With a couple of tweaks and a minor repair in the transverters I've now increased this ratio by a couple of dB. Since the 10 GHz transverter noise figure was measured by the manufacturer at 1.2 dB and the K2 is something closer to 10 dB the increase in noise may not have to be all that much for the system to be working right. I haven't felt up to doing all the necessary math this week to make sure, especially without a reliable number for the K2 noise figure. Most likely I'll try it out in the 10 GHz and Up contest this weekend and if it proves to be deaf compared to others' rigs, I'll have to delve deeper. 73, Steve VE3SMA On Tue, 8/15/17, Don Wilhelm <donw...@embarqmail.com> wrote: Subject: Re: [Elecraft] [K2] Sensitivity Spec To: "Steve Kavanagh" <skavanag...@yahoo.ca>, elecraft@mailman.qth.net Received: Tuesday, August 15, 2017, 8:29 PM Steve, Typically, the receiver is limited by the noise floor, so the MDS will not change much whether the preamp is on or off.? While the preamp will increase the strength of the signals, it also adds to the noise floor. Generally a transverter will have a low noise preamp with plenty of gain, so there is usually no advantage in running the transceiver with the preamp on.? Use your ears while listening to a strong signal to see if you can detect overload of the receiver preamp - if so turn it off, but if there is no overload distortion, you can leave it on. Typical MDS measurements are made at 500 Hz. I typically do a quick test of the sensitivity of K2s that I repair.? A -130dBm signal should be detectable above the receiver noise floor.? For that test, I have observed that it makes little difference whether the preamp is on or off.? So I would suggest you test whether strong signal performance is better with the preamp on or off.? My wager is that you will choose to leave it off unless your transverter(s) have negative gain on RX. 73, Don W3FPR 73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: dubus...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] Sensitivity Spec
Thanks for your comments, Don. When you test K2's, can I assume you have the signal generator connected directly to the K2 (or through an attenuator) with no antenna connected? Normally, one might hope that a preamp would provide some improvement in receiver noise figure (and hence MDS, sensitivity, noise floor), or there isn't much point in having it. I've never run into an intermodulation or blocking problem on 10 GHz (sideband noise issues tend to dominate the *rare* strong signal scenario) so I expect to leave the K2 preamp on in an attempt to maximize the sensitivity I agree that most often transverters have lots of gain but I noticed, with the particular combination I have, that the increase in receiver noise output resulting from turning on both the 10 GHz-to-144 MHz and the 144 MHz-to-28 MHz transverters was only about 7 dB (K2 preamp on, AGC off) compared to the K2 alone, rather less than usually seems to be the case, so I was afraid that the front end noise might not dominate the overall receiver noise. The intermediate transverter does have relatively low gain, by design. With a couple of tweaks and a minor repair in the transverters I've now increased this ratio by a couple of dB. Since the 10 GHz transverter noise figure was measured by the manufacturer at 1.2 dB and the K2 is something closer to 10 dB the increase in noise may not have to be all that much for the system to be working right. I haven't felt up to doing all the necessary math this week to make sure, especially without a reliable number for the K2 noise figure. Most likely I'll try it out in the 10 GHz and Up contest this weekend and if it proves to be deaf compared to others' rigs, I'll have to delve deeper. 73, Steve VE3SMA On Tue, 8/15/17, Don Wilhelm <donw...@embarqmail.com> wrote: Subject: Re: [Elecraft] [K2] Sensitivity Spec To: "Steve Kavanagh" <skavanag...@yahoo.ca>, elecraft@mailman.qth.net Received: Tuesday, August 15, 2017, 8:29 PM Steve, Typically, the receiver is limited by the noise floor, so the MDS will not change much whether the preamp is on or off. While the preamp will increase the strength of the signals, it also adds to the noise floor. Generally a transverter will have a low noise preamp with plenty of gain, so there is usually no advantage in running the transceiver with the preamp on. Use your ears while listening to a strong signal to see if you can detect overload of the receiver preamp - if so turn it off, but if there is no overload distortion, you can leave it on. Typical MDS measurements are made at 500 Hz. I typically do a quick test of the sensitivity of K2s that I repair. A -130dBm signal should be detectable above the receiver noise floor. For that test, I have observed that it makes little difference whether the preamp is on or off. So I would suggest you test whether strong signal performance is better with the preamp on or off. My wager is that you will choose to leave it off unless your transverter(s) have negative gain on RX. 73, Don W3FPR On 8/15/2017 4:10 PM, Steve Kavanagh via Elecraft wrote: > I'm just trying to evaluate if I have the gain distribution right for a K2 used as an IF for a 10 GHz transverter, through a 2 m transverter mounted inside the QRP top. The K2 manual gives a specification for the MDS but fails to define the bandwidth at which it is measured. Sherwood's receiver table lists some measured values at 500 Hz bandwidth but fails to note whether the preamp is on or off for these measurements. So I am not quite sure what the sensitivity should be. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] Sensitivity Spec
Steve, Typically, the receiver is limited by the noise floor, so the MDS will not change much whether the preamp is on or off. While the preamp will increase the strength of the signals, it also adds to the noise floor. Generally a transverter will have a low noise preamp with plenty of gain, so there is usually no advantage in running the transceiver with the preamp on. Use your ears while listening to a strong signal to see if you can detect overload of the receiver preamp - if so turn it off, but if there is no overload distortion, you can leave it on. Typical MDS measurements are made at 500 Hz. I typically do a quick test of the sensitivity of K2s that I repair. A -130dBm signal should be detectable above the receiver noise floor. For that test, I have observed that it makes little difference whether the preamp is on or off. So I would suggest you test whether strong signal performance is better with the preamp on or off. My wager is that you will choose to leave it off unless your transverter(s) have negative gain on RX. 73, Don W3FPR On 8/15/2017 4:10 PM, Steve Kavanagh via Elecraft wrote: I'm just trying to evaluate if I have the gain distribution right for a K2 used as an IF for a 10 GHz transverter, through a 2 m transverter mounted inside the QRP top. The K2 manual gives a specification for the MDS but fails to define the bandwidth at which it is measured. Sherwood's receiver table lists some measured values at 500 Hz bandwidth but fails to note whether the preamp is on or off for these measurements. So I am not quite sure what the sensitivity should be. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] [K2] Sensitivity Spec
I'm just trying to evaluate if I have the gain distribution right for a K2 used as an IF for a 10 GHz transverter, through a 2 m transverter mounted inside the QRP top. The K2 manual gives a specification for the MDS but fails to define the bandwidth at which it is measured. Sherwood's receiver table lists some measured values at 500 Hz bandwidth but fails to note whether the preamp is on or off for these measurements. So I am not quite sure what the sensitivity should be. Can anyone clarify? 73, Steve VE3SMA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
