RF gain sweet spot
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I found something interesting when I was working the CQ VHF contest this last weekend.
I live in the city in which my noise level stays around S3. while searching for weak signals, I started to reduce the rf gain. as I reduced the gain I watched the S meter go down and as I contuned to reduce it more the S meter would start to climb back up. I found if I set the RF gain to where I got the lowest S meter reading ( S1 ) and then Increase the gain ever so slightly just to the point to where I would get the 2nd bar on the S meter to flicker was the sweet spot. as the RF gain is reduced my noise floor dropped, but it had no effect on the signals, so it seems to improve the Sig to noise ratio. so I now I reduce the gain to the lowest S meter bar ( S1 ) and then add gain just untill the 2nd bar just wants to flicker.........so I guess this is called Dip the S meter I don't know how well this works on hf as I work mostly 6 meters. I thought I would pass this tip along. it might now work for everyone but it sure helped me dig out the weak ones..... maybe someone in the know can explain what is going on....... Ed K7WIA |
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Dave,
By setting the RF Gain as you did, you have maximized the dynamic range of your receiver. The lowest level signals that you will be able to hear (and understand) will be at your local noise level - there is no sense (to me at least) to use more than the amount of gain that will give you a small bit of atmospheric noise in the audio. By reducing the RF Gain, you have set that point where signals stronger than your local noise will be heard - they just seem to "jump out of the noise". Add to that the fact that your ear gets accustomed to hearing a constant noise level, and will ignore signals that have less intensity than that level - so reducing the noise into the ears is good. The K3 has ample gain, and without human intervention, the band noise is just like another signal - if it is present, the K3 will amplify it. Note that this is a different concept than "riding the RF Gain" - it is a simple, listen for the band noise, and reduce the RF Gain until it is at a tolerable level - then do not change the RF Gain for that band/antenna combination. Use the AF gain to further vary the audio level - the AGC will take care of the rest. 73, Don W3FPR On 7/20/2011 6:55 PM, K7WIA wrote: > I found something interesting when I was working the CQ VHF contest this last > weekend. > I live in the city in which my noise level stays around S3. > while searching for weak signals, I started to reduce the rf gain. as I > reduced the gain I watched the S meter go down and as I contuned to reduce > it more the S meter would start to climb back up. > I found if I set the RF gain to where I got the lowest S meter reading ( S1 > ) and then Increase the gain ever so slightly just to the point to where I > would get the 2nd bar on the S meter to flicker was the sweet spot. as the > RF gain is reduced my noise floor dropped, but it had no effect on the > signals, so it seems to improve the Sig to noise ratio. > so I now I reduce the gain to the lowest S meter bar ( S1 ) and then add > gain just untill the 2nd bar just wants to flicker.........so I guess this > is called Dip the S meter > I don't know how well this works on hf as I work mostly 6 meters. > I thought I would pass this tip along. it might now work for everyone but it > sure helped me dig out the weak ones..... maybe someone in the know can > explain what is going on....... > > 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 |
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In reply to this post by KD7PY
K7WIA's experience with his 6m receiver got me to try this with my
K3. I have an ARR P50VDG preamp installed and see typically S4 flickering up to S5 for noise connected either 6m yagi. Reducing RFGain immediately increases s-meter reading with the ARR preamp so I switched it off. Noise is almost not readable on the s-meter and reducing RFGain does not result in increase in s-meter reading until I rotate the RFGain less than 3-oclock postion. There is not enough s-meter resolution to tell if there is any reduction in noise (none detectable by ear until s-meter begins to rise). Finally, I tried this with the internal K3 preamp turned on. Normal noise reading is S3. Reducing RFGain exhibited the same as not using any preamp except s-meter stays at S-3 until I rotate below 3-oclock position whereby the reading climbs above S3. Considering that I am in rural Alaska I should have less ambient noise floor than K7WIA but do not see the behavior he is seeing. Comments? I would be interested to know if he is using a K3 (radio was not specified) and whether that was running with a preamp and what kind? My take on my readings is that the ARR has more than enough gain (maybe too much) and I am seeing amplified noise. But I do not get the s-meter behavior seen by K7WIA when reducing RFGain? 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-? 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 |
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Ed,
I suspect he was not using a K3 because he said the S-meter did reduce when the RF Gain was reduced. You could turn off the K3 preamp and turn on the attenuator and see if that drops the ambient noise level. With your external preamp, I suspect you can reduce the K3 gain substantially. 73, Don W3FPR On 7/21/2011 1:13 PM, Edward R. Cole wrote: > K7WIA's experience with his 6m receiver got me to try this with my > K3. I have an ARR P50VDG preamp installed and see typically S4 > flickering up to S5 for noise connected either 6m yagi. Reducing > RFGain immediately increases s-meter reading with the ARR preamp so I > switched it off. Noise is almost not readable on the s-meter and > reducing RFGain does not result in increase in s-meter reading until > I rotate the RFGain less than 3-oclock postion. There is not enough > s-meter resolution to tell if there is any reduction in noise (none > detectable by ear until s-meter begins to rise). Finally, I tried > this with the internal K3 preamp turned on. Normal noise reading is > S3. Reducing RFGain exhibited the same as not using any preamp > except s-meter stays at S-3 until I rotate below 3-oclock position > whereby the reading climbs above S3. > > Considering that I am in rural Alaska I should have less ambient > noise floor than K7WIA but do not see the behavior he is > seeing. Comments? I would be interested to know if he is using a K3 > (radio was not specified) and whether that was running with a preamp > and what kind? > > My take on my readings is that the ARR has more than enough gain > (maybe too much) and I am seeing amplified noise. But I do not get > the s-meter behavior seen by K7WIA when reducing RFGain? > > > 73, Ed - KL7UW, WD2XSH/45 > 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 |
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In reply to this post by Edward R Cole
I believe that all this does is prove what I have said many times for over two years---every K3 is different with respect to its RFG/AGC characteristics.
The RF Gain "calibration" is an attempt to fix this variability. --- On Thu, 7/21/11, Edward R. Cole <[hidden email]> wrote: From: Edward R. Cole <[hidden email]> Subject: Re: [Elecraft] RF gain sweet spot To: [hidden email] Date: Thursday, July 21, 2011, 11:13 AM K7WIA's experience with his 6m receiver got me to try this with my K3. I have an ARR P50VDG preamp installed and see typically S4 flickering up to S5 for noise connected either 6m yagi. Reducing RFGain immediately increases s-meter reading with the ARR preamp so I switched it off. Noise is almost not readable on the s-meter and reducing RFGain does not result in increase in s-meter reading until I rotate the RFGain less than 3-oclock postion. There is not enough s-meter resolution to tell if there is any reduction in noise (none detectable by ear until s-meter begins to rise). Finally, I tried this with the internal K3 preamp turned on. Normal noise reading is S3. Reducing RFGain exhibited the same as not using any preamp except s-meter stays at S-3 until I rotate below 3-oclock position whereby the reading climbs above S3. Considering that I am in rural Alaska I should have less ambient noise floor than K7WIA but do not see the behavior he is seeing. Comments? I would be interested to know if he is using a K3 (radio was not specified) and whether that was running with a preamp and what kind? My take on my readings is that the ARR has more than enough gain (maybe too much) and I am seeing amplified noise. But I do not get the s-meter behavior seen by K7WIA when reducing RFGain? 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ   500 KHz - 10-GHz   www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-? 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 ______________________________________________________________ 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 |
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In reply to this post by KD7PY
Yes I am using the K3
I was using the preamp that is in the K3, I also have the ARR P50VD preamp on the back of the K3 but using it just raises the background noise to S7. Remember I live in the city. I can turn off the preamp that is in the K3, disconnect the antenna listen to the hiss of the K3, and then hook the antenna back and hear the noise increase.. i am going to try it with out using any preamp at all...I can still detect the weak beacon that are in my area. and still hear a increase in noise when the antenna is connected. but just to reduce the background noise has helped my 73 yo ears make the weak ones stand out better. even without the preamp on I still get the 2nd bar on the S meter to flicker, and i can reduce the Rf gain just slightly ( not much) to dip the S meter. just the joys of living in a big city, powerline, and wireless headphones on 6 meters Ed K7WIA |
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Ed,
When one reduces the RF Gain on the K3, the S-meter indication increases. So how are you accomplishing this "S-meter dip"? I do not doubt your results, but perhaps your description of the S-meter deflection has been misunderstood. 73, Don W3FPR On 7/21/2011 4:00 PM, K7WIA wrote: > Yes I am using the K3 > I was using the preamp that is in the K3, I also have the ARR P50VD > preamp on the back of the K3 but using it just raises the background noise > to S7. > Remember I live in the city. I can turn off the preamp that is in the K3, > disconnect the antenna listen to the hiss of the K3, and then hook the > antenna back and hear the noise increase.. i am going to try it with out > using any preamp at all...I can still detect the weak beacon that are in my > area. and still hear a increase in noise when the antenna is connected. but > just to reduce the background noise has helped my 73 yo ears make the weak > ones stand out better. > even without the preamp on I still get the 2nd bar on the S meter to > flicker, and i can reduce the Rf gain just slightly ( not much) to dip the > S meter. > just the joys of living in a big city, powerline, and wireless headphones > on 6 meters > > Ed K7WIA > 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 |
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In reply to this post by KD7PY
Ok we did the RF calibration per the K3 utility program using the XG3 for the signal source and I see no change with the way the S meter responds, being I use the K3 for 6 meters only I set the S meter calibration for that band using the XG3 this is how my S meter is set up in the Confg. menu.
SMTR OF: 027 SMTR SC: 012 SMTR PK: OFF SMTR MD: NOR this is set with the preamp on in the K3 -107 dbm = S3 -73 dbm = S9 -33 dbm = 40/9 Ed K7WIA |
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In reply to this post by Don Wilhelm-4
Don, when the RF gain is fully cw ( max ) I have 3 bars on the S Meter, when I slowly reduce the RF gain control I watch the S Meter and when I get it just past the 9 o'clock position the S Meter will reduce to only 1 bar showing. you can hear the background noise drop as you do this, then I just add a bit more gain back just enough to hear the noise increase back up. the lowest I can reduce the S meter is to 1 bar showing, I add just enough gain back to get the 2nd bar to flicker.. if i reduce the gain to much the S meter will start to climb back up in the normal maner....
Ed K7WIA |
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In reply to this post by KD7PY
oops this should be reduce to the 3 o'clock posistion,,,sorry
Ed K7WIA |
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In reply to this post by KD7PY
> Don, when the RF gain is fully cw ( max ) I have 3 bars > on the S Meter, > when I slowly reduce the RF gain control I watch the S Meter > and when I get > it just past the 9 o'clock position the S Meter will reduce > to only 1 bar > showing. ??? As I gradually reduce the RF gain on my K3, the S meter reading climbs gradually towards full scale. I guess there is something different with your settings Ed? 73 Gary ZL2iFB ______________________________________________________________ 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 |
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In reply to this post by KD7PY
Ed,
Something is strange. It may be your ambient noise level, so try it with the K3 connected to a dummy load (or just no antenna). Normally, as the RF gain is reduced, the S-meter indication will increase. Apparently your K3 is doing something different. At a 9 o'clock position, my K3 indicates S-7 when the K3 is connected to a dummy load. 73, Don W3FPR On 7/21/2011 5:04 PM, K7WIA wrote: > Don, when the RF gain is fully cw ( max ) I have 3 bars on the S Meter, > when I slowly reduce the RF gain control I watch the S Meter and when I get > it just past the 9 o'clock position the S Meter will reduce to only 1 bar > showing. you can hear the background noise drop as you do this, then I just > add a bit more gain back just enough to hear the noise increase back up. > the lowest I can reduce the S meter is to 1 bar showing, I add just enough > gain back to get the 2nd bar to flicker.. if i reduce the gain to much the > S meter will start to climb back up in the normal maner.... > > Ed K7WIA > 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 |
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In reply to this post by KD7PY
I don't know but I like it this way, as my noise floor changes through the day I do have to readjust the sweet spot, but it is just a very small turn of the RF knob....
I checked this with the noise blanker on and off and I see the same effect, it's just with the blanker off I can only reduce it to 2 bars on the meter. could be I got a special K3.. Ed K7WIA |
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In reply to this post by KD7PY
Well when i disconect the antenna I have no bars on the S meter, a 2 inch piece of wire at the ant port gave me 1 bar on the S meter and I can still dip the meter,,
THIS ALL HAPPENS AT THE 3 O'CLOCK POSITION>>>>NOT AT 9'CLOCK MY ERROR Ed K7WIA |
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In reply to this post by KD7PY
OK I just did a test using the XG3 set at the 1uv & 50uv level and I can dip the S meter. it dips the signal level of the XG3 shown on the S meter...
Ed K7WIA |
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I think the RF pot has a weak spot near the CW end. I don't know how it's made, but if the resistance is decreasing as it goes toward CW then it is minimum at three o'clock and increases slightly to full CW. Just my 2 cents. Kurt, W7QHD > Date: Thu, 21 Jul 2011 15:17:19 -0700 > From: [hidden email] > To: [hidden email] > Subject: Re: [Elecraft] RF gain sweet spot > > OK I just did a test using the XG3 set at the 1uv & 50uv level and I can dip > the S meter. it dips the signal level of the XG3 shown on the S meter... > > Ed K7WIA > > -- > View this message in context: http://elecraft.365791.n2.nabble.com/RF-gain-sweet-spot-tp6604787p6608708.html > Sent from the Elecraft mailing list archive at 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 ______________________________________________________________ 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 |
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In reply to this post by Don Wilhelm-4
I seem to recall that somebody demonstrate a similar artifact in the RF
gain control to Elecraft at Dayton. Anybody recall just what that demo was? 73 de Brian/K3KO On 7/21/2011 21:37, Don Wilhelm wrote: > Ed, > > Something is strange. It may be your ambient noise level, so try it > with the K3 connected to a dummy load (or just no antenna). > Normally, as the RF gain is reduced, the S-meter indication will > increase. Apparently your K3 is doing something different. > At a 9 o'clock position, my K3 indicates S-7 when the K3 is connected to > a dummy load. > > 73, > Don W3FPR > > > On 7/21/2011 5:04 PM, K7WIA wrote: >> Don, when the RF gain is fully cw ( max ) I have 3 bars on the S Meter, >> when I slowly reduce the RF gain control I watch the S Meter and when I get >> it just past the 9 o'clock position the S Meter will reduce to only 1 bar >> showing. you can hear the background noise drop as you do this, then I just >> add a bit more gain back just enough to hear the noise increase back up. >> the lowest I can reduce the S meter is to 1 bar showing, I add just enough >> gain back to get the 2nd bar to flicker.. if i reduce the gain to much the >> S meter will start to climb back up in the normal maner.... >> >> Ed K7WIA >> > ______________________________________________________________ > 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 > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1390 / Virus Database: 1518/3778 - Release Date: 07/21/11 > > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1390 / Virus Database: 1518/3778 - Release Date: 07/21/11 ______________________________________________________________ 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 |
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In reply to this post by Kurt Cramer-2
The RF pot in the K3 is a encoder, not a carbon pot found in old tube radios used as a volume control.
Ed K7WIA |
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In reply to this post by KD7PY
Ed,
Ok, I have just confirmed your experience (but I cannot explain it). If I tune to a band where the noise level is S-3 and I reduce the RF Gain a bit (to the 2:30 or 3 o'clock position), the S-meter reading will reduce, but if I reduce the RF Gain more CCW, the S-meter reading will increase as expected. The schematics tell me that the reduced RF Gain is the same as increased AGC - so there is something strange going on between the full CW position of the RF Gain control and the 3 o'clock position. It does not respond as I would expect. Maybe Lyle can chime in with some "words of wisdom" to explain this "happening" - Wayne is on vacation, so I don't think he can be of much help right now. Ed, I no longer doubt your report - but I do find it a bit strange. 73, Don W3FPR On 7/21/2011 4:52 PM, K7WIA wrote: > Ok we did the RF calibration per the K3 utility program using the XG3 for the > signal source and I see no change with the way the S meter responds, being > I use the K3 for 6 meters only I set the S meter calibration for that band > using the XG3 this is how my S meter is set up in the Confg. menu. > > SMTR OF: 027 > SMTR SC: 012 > SMTR PK: OFF > SMTR MD: NOR > this is set with the preamp on in the K3 > > -107 dbm = S3 > -73 dbm = S9 > -33 dbm = 40/9 > > Ed K7WIA > 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 |
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In reply to this post by KD7PY
OH! Well, my non tube type K2 has a carbon pot. > Date: Thu, 21 Jul 2011 15:34:01 -0700 > From: [hidden email] > To: [hidden email] > Subject: Re: [Elecraft] RF gain sweet spot > > The RF pot in the K3 is a encoder, not a carbon pot found in old tube radios > used as a volume control. > > Ed K7WIA > > -- > View this message in context: http://elecraft.365791.n2.nabble.com/RF-gain-sweet-spot-tp6604787p6608745.html > Sent from the Elecraft mailing list archive at 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 ______________________________________________________________ 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 |
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