Another Happy Customer
Locked
 
|
I just completed building a K3/100 from a kit. Everything fit perfectly. The
directions were clear. It worked the first time. This is the third K3 in my station. I will get one more this summer and will probably do another kit. It was fun. I also added the GaAsFet 6M preamp to the station and it makes a HUGE difference on Six. Tom, K5RC - Quality Control Engineer by trade. Tom Taormina, K5RC Virginia City NV Home of W7RN and K7RC <http://k5rc.cc> http://k5rc.cc FOC 1760 "Communication is the problem to the answer" - 10cc ______________________________________________________________ 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 |
Re: K3 PR6 preamp [was: Another Happy Customer]
|
|
From: "K5RC" <[hidden email]>
> I also added the GaAsFet 6M preamp to the station and it makes a HUGE > difference on Six. It needs to be pointed out from time to time that whether the PR6 makes "no discernible difference" or "a HUGE difference" depends on one critically important variable: YOUR NOISE LEVEL! Because I live in a large-city metro area complete with big mountain-top RF outlets broadcasting thousands of kilowatts of RF (along with plenty of spurious broadband crud), my noise level on 6 meters is relatively high. Only in my quietest direction (northwest) at the quietest time of day (early morning) does adding the PR6 preamp allow me to hear anything that I can't hear just as well without it. Wouldn't it be nice to really NEED that PR6? Yeah, it sure would... but the realties are what they are. The WSJT software package (for weak-signal digital modes FSK441, JT6M, et al.) includes an easy way to roughly assess your noise level, reading out directly in dB above the receiver's internal noise floor (MDS). If, while using the K3's internal preamp, your antenna noise reads 8-10 dB or more above MDS (typical when using a decent gain antenna in a metro area), the sad fact is that the PR6 probably won't help you. If your antenna noise is only a few dB above MDS, then the PR6 might help, as it is very quiet (i.e., has a low noise figure) and could contribute to a better overall signal-to-noise ratio. On the other hand, if you are lucky enough to not really be able to hear any 6m antenna noise with the K3's internal preamp on... First, double-check to make sure you actually have connected the antenna... And if you have, you should congratulate yourself and get ready to REALLY have some fun on 6 meters once you connect in that PR6 preamp! You might also want to get a good RF power amplifier, as you will want to be able to work all the DX stations you can hear -- some of whom are running REALLY BIG QRO, trust me. You will be in no danger of being an "alligator" station (all mouth and no ears). Bill W5WVO DM65qh -------------------------------------------------- ______________________________________________________________ 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 |
|
|
What is the noise figure of the K3 on six meters?
On SSB bandwidth I barely hear a noise increase when I switch from a dummy load to my antenna. 73 Tom ______________________________________________________________ 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 |
|
|
"The noise figure of the preamp itself is typically 0.5 dB." http://www.elecraft.com/manual/PR6_Owners_Manual_Rev_A.pdf |
|
|
In reply to this post by Bill VanAlstyne W5WVO
Bill,
AS usual you have made an important observation. You made me curious about my 6m environment so: I turned off both my external preamp (RX ANT) and my internal preamp (PRE) and merely looked at s-meter reading (S=1). I removed the antenna with no discernable change in audible noise and s-meter is the same S=1. So with antenna connected I turned on internal preamp (PRE) and S=2. With internal preamp off and my external preamp* on (RX ANT) S=2/3 With both preamps on S=4 Both preamps on with antenna disconnected; S=3 So its a pretty quiet area with only one s-unit rise in noise. For comparison with a 50-ohm termination both preamps see S=4 This indicates the preamps are low-noise below a 290K source. NOW for that QRO and 8-element long-boom yagi - hmm. 73, Ed - KL7UW *Note external preamp is ARR P50VDG Gasfet 0.5 dBNF, 22-dBG ------------------------------ Message: 24 Date: Mon, 21 Jun 2010 20:05:00 -0600 From: "Bill VanAlstyne W5WVO" <[hidden email]> Subject: Re: [Elecraft] K3 PR6 preamp [was: Another Happy Customer] To: <[hidden email]> Message-ID: <E78A2106E87A4F55911F00382D8DD915@BILLHP9250> Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original From: "K5RC" <[hidden email]> > I also added the GaAsFet 6M preamp to the station and it makes a HUGE > difference on Six. It needs to be pointed out from time to time that whether the PR6 makes "no discernible difference" or "a HUGE difference" depends on one critically important variable: YOUR NOISE LEVEL! Because I live in a large-city metro area complete with big mountain-top RF outlets broadcasting thousands of kilowatts of RF (along with plenty of spurious broadband crud), my noise level on 6 meters is relatively high. Only in my quietest direction (northwest) at the quietest time of day (early morning) does adding the PR6 preamp allow me to hear anything that I can't hear just as well without it. Wouldn't it be nice to really NEED that PR6? Yeah, it sure would... but the realties are what they are. The WSJT software package (for weak-signal digital modes FSK441, JT6M, et al.) includes an easy way to roughly assess your noise level, reading out directly in dB above the receiver's internal noise floor (MDS). If, while using the K3's internal preamp, your antenna noise reads 8-10 dB or more above MDS (typical when using a decent gain antenna in a metro area), the sad fact is that the PR6 probably won't help you. If your antenna noise is only a few dB above MDS, then the PR6 might help, as it is very quiet (i.e., has a low noise figure) and could contribute to a better overall signal-to-noise ratio. On the other hand, if you are lucky enough to not really be able to hear any 6m antenna noise with the K3's internal preamp on... First, double-check to make sure you actually have connected the antenna... And if you have, you should congratulate yourself and get ready to REALLY have some fun on 6 meters once you connect in that PR6 preamp! You might also want to get a good RF power amplifier, as you will want to be able to work all the DX stations you can hear -- some of whom are running REALLY BIG QRO, trust me. You will be in no danger of being an "alligator" station (all mouth and no ears). Bill W5WVO DM65qh 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep [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 |
|
|
Ed
There's a more reliable way of doing this. Turn on the dBV measurement facility on the K3 and turn off the agc, reduce rf gain a bit. Arrange for 50ohm resistor noise to indicate 0dB and then substitute the 6m antenna and see the difference. BTW the preamps won't be "below a 290K source" - they're already at 290K or more! 73 Graham > With both preamps on S=4 > Both preamps on with antenna disconnected; S=3 > So its a pretty quiet area with only one s-unit rise in noise. > For comparison with a 50-ohm termination both preamps see S=4 > This indicates the preamps are low-noise below a 290K source. > ______________________________________________________________ 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 |
|
|
In reply to this post by Bill VanAlstyne W5WVO
OK, I did as you suggested and turned off AGC and set RF gain = 50%
and here is the result: Meter IntPre ExtPre Ant Load -20dbV N N N N K3 disconnected -19.7 N N N Y K3 connected to load -18.2 Y N N Y -15.5 N Y N Y -3.3 Y Y N Y -19.5 N N Y N K3 connected to 3-elem yagi at 55-feet -15.4 Y N Y N -1.1 N Y Y N +8.4 Y Y Y N N=off, Y=on There is slightly more noise on the antenna than with the 50-ohm load, only 3.2 dbV difference using only the Internal Preamp. The External Preamp shows a 14.4 dbV increase over the 50-ohm load. Running both preamps probably only raises the noise level and does not improve receiver sensitivity in any significant manner. Note that the gain difference between preamps influences the meter reading as well as noise figure. Running the ExtPreamp by itself is likely the best configuration for best sensitivity. Using Y-factor between the load and the antenna one could determine the G/T ratio and maybe overall noise temperature (and noise figure). Theoretically, T = Tsky + Tant + Trx Tsky at 6m is high, perhaps 2000K (but this was the question that started this thread) Tant is unknown, but probably a significant portion of the 290K ground noise, assume 150K (a factor of F/B ratio and sidelobe levels) Trx should be determined primarily by the preamp: Tpre = 290*10^(NF/10)-1 = 290*10^(0.5/10)-1 = 290*(10^.05 - 1) = 290*0.122 = 35K The K3 noise figure will add a little but is reduced by a factor of the preamp gain (if NF(K3) = 5 dB then Tk3 = 290*2.16 = 676K The cascaded noise temp, Trx = Tpre + Tk3/158 = 35 + 676/158 = 40K Sensitivity looking at the load is -139 dBm using the 2.8 KHz SSB bandwidth* Looking at a 2000K sky the noise floor is -130 dBm*, assuming antenna noise to add 150K One would need to calculate P = KTB from the noise voltage readings where P = E^2/R to arrive at actual noise power. I wonder how linear the dbV meter readings are with this approach? 73, Ed *Note calculations using my eme pathlink sw: http://www.kl7uw.com/emelink.xls Ext Preamp P50VDG: 0.5 dBNF, 22-dBG - I would expect similar results from the PR6 ------------------------------ Message: 36 Date: Thu, 24 Jun 2010 11:38:45 +0100 From: "Graham Kimbell \(G3TCT\)" <[hidden email]> Subject: Re: [Elecraft] K3 PR6 preamp To: "Edward R Cole" <[hidden email]>, <[hidden email]> Message-ID: <004901cb1389$6e506180$0602a8c0@a> Content-Type: text/plain; charset="iso-8859-1" >Ed >There's a more reliable way of doing this. Turn on the dBV measurement >facility on the K3 and turn off the agc, reduce rf gain a bit. Arrange for >50ohm resistor noise to indicate 0dB and then substitute the 6m antenna and >see the difference. > >BTW the preamps won't be "below a 290K source" - they're already at 290K or >more! > >73 >Graham 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep [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 |
|
|
On Thu, 24 Jun 2010 11:52:46 -0800, Edward R Cole wrote:
>Running both preamps probably only raises the noise level and >does not improve receiver sensitivity in any significant >manner. I suggest that you defer judgment on this until you're trying to copy very weak signals during a band opening. The additional preamp at the patch point (in my case an ARR) definitely DOES improve RX sensitivity at times when the external noise level is low. I'm not suggesting that the ARR is better -- indeed, I doubt that it is. But it was bought and paid for when the K3 showed up, and it works fine. :) 73, Jim K9YC ______________________________________________________________ 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 |
|
|
In reply to this post by Bill VanAlstyne W5WVO
Jim,
Your comment is a little confusing. First you state that you believe the External preamp definitely improves sensitivity (when external noise level is low). I agree. I said the same in my original e-mail. Then you state that you are not suggesting the ARR is better. Not better than what? It is definitely better than the internal preamp, but it is probably close to the same performance as the PR6 (regarding sensitivity). Elecraft claims exceptional dynamic range for the PR6 which the ARR probably does not have (which is important in urban high noise environs or in high density QRM that happen in openings/contests). I did some checking of the K3 specs: Sensitivity with (internal) preamp turned-on is spec at -136 to -138 dBm at 500-Hz bw. -138 dBm is equivalent to noise figure of 9.5 dB. With the PR6, the K3 is spec at -143 to -144 dBm at 500-Hz bw. That is equivalent to a noise figure of 5-dB. Since the PR6 spec is 0.5 DBNF with 18 dBG this implies that the K3 receiver has a NF of 20-dB (all preamps off). The ARR preamp is spec at 0.5 dBNF with 22-dBG so the resulting sensitivity should be -148 dBm. So doing a little more reverse analysis, this implies the internal preamp NF is something like 5-dB if you assume the gain is 10-dB (I could not find what the gain of the internal preamp is). How does this translate for the 6m operator? In high noise environs the internal preamp is probably adequate since external noise predominates. In low noise areas the PR6 or ARR definitely will improve sensitivity by 7 to 10 dB. If you are considering doing eme or meteor scatter on 6m the low-noise external preamp is going to help quite a bit. Antennas elevated above the horizon do not see the thermal noise of the ground or as much man-made noise. Sky noise at 6m is still quite high compared to higher VHF and UHF frequencies so placing the preamp at the K3 is acceptable if your coax is not lossy. Remember my statement that I though running both internal and external preamps might not result in better sensitivity? I took the numbers I developed for both the PR6 and internal preamp and input to my spreadsheet. The result is total sensitivity of -152 dBm. So maybe running both internal and external preamps is better. (As jim point out) you have to evaluate this in real conditions as results will differ depending on your local noise environment. One caveat is turning on both preamps may lead to overdriving the receiver resulting in reduced dynamic range or even distortion. 73, Ed - KL7UW Final note: SSB sensitivity numbers at bw of 2.8 KHz are 7.5 dB lower than at bw of 500-Hz. ------------------------------ Message: 31 Date: Thu, 24 Jun 2010 13:15:30 -0700 From: "Jim Brown" <[hidden email]> Subject: Re: [Elecraft] K3 PR6 preamp To: "[hidden email]" <[hidden email]> Message-ID: <[hidden email]> Content-Type: text/plain; charset="us-ascii" On Thu, 24 Jun 2010 11:52:46 -0800, Edward R Cole wrote: >Running both preamps probably only raises the noise level and >does not improve receiver sensitivity in any significant >manner. I suggest that you defer judgment on this until you're trying to copy very weak signals during a band opening. The additional preamp at the patch point (in my case an ARR) definitely DOES improve RX sensitivity at times when the external noise level is low. I'm not suggesting that the ARR is better -- indeed, I doubt that it is. But it was bought and paid for when the K3 showed up, and it works fine. :) 73, Jim K9YC 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep [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 |
|
|
On Thu, 24 Jun 2010 23:15:52 -0800, Edward R Cole wrote:
>Then you state that you are not suggesting the ARR is better. Not >better than what? The Elecraft 6M preamp 73, Jim K9YC ______________________________________________________________ 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 |
«
Return to [K3]
|
1 view|%1 views
| Free forum by Nabble | Edit this page |