K3 Preamp 2
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I often see posts from US stations questioning the need for any preamp below 20m and just now challenging the need for preamp 2 on 10m.
That may be all well and good in the land of the huge antennas and the thousands of big signals from the US and Europe but let me tell you that down here, when you are scratching around for weak signals on 10m and 12m, preamp 2 makes a world of difference. Barry Simpson VK2BJ. Sent from my iPad ______________________________________________________________ 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 Message delivered to [hidden email] |
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Hi, Barry,
It's not the signals that determine whether you need a preamp, it's the noise level. A receiver should have enough gain to put its internal noise floor below the external, atmospheric noise floor, so that it doesn't become the limiting factor in hearing weak signals close to the noise. That's what makes a preamp necessary. Certainly, if your noise floor is lower than here in urban North America, there may be cases where a preamp does us no good, but is necessary for you. I think I once posted a case study here a while ago... but I would have to go searching for it. The numbers I used were definitely US-biased. Life for a ham here has become a really discouraging exercise in trying to copy signals below your neighbors' app-enabled pet massagers and internet-controlled wine coolers, all fed by those infernal switch-mode power supplies. My two neighbors' homes are really just enormous square wave-producing things. This is also why everybody you hear is running 1,000 watts or more. It's power inflation. The military spends millions on radar jamming equipment... when all they'd have to do is do whatever my neighbor Johnny is doing. He must have a phased array radar, arc-welding, barrage jamming plant next door. If you ever bring your rig over here on vacation, be sure to pack a 60 dB attenuator with it. R, Al W6LX From: Barry Simpson <[hidden email]> To: [hidden email] Sent: Saturday, April 7, 2018 2:25 PM Subject: [Elecraft] K3 Preamp 2 I often see posts from US stations questioning the need for any preamp below 20m and just now challenging the need for preamp 2 on 10m. That may be all well and good in the land of the huge antennas and the thousands of big signals from the US and Europe but let me tell you that down here, when you are scratching around for weak signals on 10m and 12m, preamp 2 makes a world of difference. Barry Simpson VK2BJ. Sent from my iPad ______________________________________________________________ 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 Message delivered to [hidden email] ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by Barry Simpson-2
Barry,
Not disagreeing. I bought my K3, SN4043, in 2010. It has an internal preamp (push PRE) which gives about 10-dB gain (I think). A few years went by and Elecraft announced the PR6 external "add-on" preamp to improve 10m and 6m receiver performance. They kind of admitted the bare K3 was lacking gain at those frequencies. That "system" gain minimum is needed to overcome following stage NF for best sensitivity (MDS). I've measured -145dBm MDS on 6m with my PR6. K3 was about -133 dBm without the PR6 on 6m (-73 dBm is S9; 9 s-units should be 6x9 = 54 dB; -73dBm-54dB = -129 dBm). Of course ambient noise will rule how weak a signal can be copied. On lower freq. HF bands thermal sky noise has long been that limitation; at 25-MHz Tsky starts to drop as one transitions into VHF. Recent (?) rise in residential/industrial RF noise has affected pretty much everyone (I live in a widely dispersed community of 4,000 in Alaska and noise at 2m has become terrible (S7 over a S3 noise floor). Use of a preamp may become unproductive at some level of noise (maybe). I do 6m eme and use a GasFet preamp at the antenna for minimizing NF and it helps enough over just using the PR6 (with internal preamp off). I use DIGOUT1 to turn on/off the PR6. Since it has a nice bypass, I use that to connect to my tower-top 6m preamp. BTW I have copied 6m-eme signals just using the PR6. I don't have a K3s so assuming preamp-2 is equivalent to the PR6-10 (expanded to 24-MHz). I actually wonder if there are some arc-welder rock bands? Or dueling Plasma TV's? I'm heading up north (frequency-wise) to 1296 for a little quiet-time <snicker> 73, Ed - KL7UW Hi, Barry, It's not the signals that determine whether you need a preamp, it's the noise level. A receiver should have enough gain to put its internal noise floor below the external, atmospheric noise floor, so that it doesn't become the limiting factor in hearing weak signals close to the noise. That's what makes a preamp necessary. Certainly, if your noise floor is lower than here in urban North America, there may be cases where a preamp does us no good, but is necessary for you. I think I once posted a case study here a while ago... but I would have to go searching for it. The numbers I used were definitely US-biased. Life for a ham here has become a really discouraging exercise in trying to copy signals below your neighbors' app-enabled pet massagers and internet-controlled wine coolers, all fed by those infernal switch-mode power supplies. My two neighbors' homes are really just enormous square wave-producing things. This is also why everybody you hear is running 1,000 watts or more. It's power inflation. The military spends millions on radar jamming equipment... when all they'd have to do is do whatever my neighbor Johnny is doing. He must have a phased array radar, arc-welding, barrage jamming plant next door. If you ever bring your rig over here on vacation, be sure to pack a 60 dB attenuator with it. R, Al W6LX 73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: [hidden email] ______________________________________________________________ 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 Message delivered to [hidden email] |
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Barry is in VK. If he operates from the middle of nowhere, local noise is
nonexistent and local activity is extremely sparse. It means you hear lots of weak stations, most of which you have little chance of working unless you have good antennas and run power. So preamp is a plus in receive but it causes frustration when trying to call. I remember frustration as VK2/NO9E hearing many US on 10m, with little success except contesting. Also the band full of US station during the ARRL 160m contest. Ignacy, NO9E -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ 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 Message delivered to [hidden email] |
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