K3S DSP Filter Plots
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Hi Bill,
Thanks so much for the data for the two filter configurations. This will give me a pretty good idea of the shape factor of the 200hz DSP filter. I just ordered a K3S, and the technician that helped me with some of my questions said that no one has ever asked him about the shape factor of the DSP filters. So I guess we are breaking new ground with this thread. The definition of a filter's shape factor is the width of the filter between its -6 dB points and it's -60 dB points. Since we are using an S-meter to determine signal strength as we move away from the signal's center frequency, it is a rough approximation of true signal strength. We are also going to assume that the K3 S-meter is 6 dB per S-unit all the way from S5 to S9+40dB. I am also assuming that these reading would be symmetrical if you had measured the lower side of the filter skirts. Given those assumptions and their limitations, let's see if we can determine the shape factor of the two filter scenario's you measured. Data Set 1. Cascading the DSP 400hz filter with the 400hz roofing filter gave a -6 dB point approximately 140hz higher than the center frequency (extrapolating 1 dB down from the -5 dB frequency of +134hz). That would make the width of the filter at the -6 dB points approx 280 hz. The S6 level would represent a drop of 58 dB from the center of the filter (+40 dB + 18dB), so the -60 dB frequency would occur at approx +216hz from the center frequency. That would make the -60 dB width of the filter (216hz + 216hz) = 432hz. So the shape factor of this cascaded 400hz roofing filter and 400 hz DSP filter would be 432hz/280hz = 1.52. Notice that this is a better shape factor than the roofing filter alone which has a Elecraft documented shape factor of 2.1. Data Set 2. The DSP filter has been narrowed to 200 hz in this scenario and still cascaded with the 400hz roofing filter. This should give the opportunity to dtermine the shape factor of the DSP filter itself since it is entirely contained within the passband of the wider 400hz roofing filter. The -6 dB point of the DSP filter is approx +70 from the center frequency ( extrapolating again 1 dB down from the -5 dB frequency of +68hz). That would make the filter width at the -6 dB points (70hz + 70hz) = 140hz. As in the first scenario, the S6 level would represent a drop of 58 dB from the center of the filter (+40 dB + 18dB), so the -60 dB frequency would occur at approx +146hz from the center frequency. That would make the -60 dB width of the filter (146hz + 146hz) = 292hz. So the shape factor of the 200hz DSP filter is 292hz/140hz = 2.08. Based upon the data provided, the shape factor of the DSP filter is virtually identical to the shape factor of the roofing filter. I'm not surprised that cascading two 400hz filters with identical shape factors create a resultant filter with a better shape factor than either filter alone. I ordered the XG3 with my K3S, so I will obtain data for the 50, 100, and 150 hz DSP filters inside of the 400hz roofing filters. I will also obtain data for the 200hz DSP filter inside of the 2800hz SSB filter. The data should be identical to the 200hz filter inside of the 400hz roofing filter. Thanks to all that replied to my inquiry. Charles K5UA ______________________________________________________________ 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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I believe 5 dB is the correct number. But Lyle's suggestion to use the dBV function is a good one.
Vic 4X6GP/K2VCO > On 17 Nov 2015, at 1:04 AM, [hidden email] wrote: > > We are also going to assume that the K3 S-meter is 6 dB per S-unit all the way from S5 to S9+40dB. ______________________________________________________________ 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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I believe there's more than one correct answer. In earlier times, the
"Collins Standard" was 6 dB/S-unit and 50 uv = S9. My 75S3 came in at 53 uv for S9, and pretty much held to the 6 dB/S-unit below that. Not so much above S9 With my service monitor feeding my K3, it is exactly 50 uv = S9 because I set it for that. It's a little hard to tell on the bar graph S-meter, but it seems to be about 5 dB/S-unit below S9. It also seems to be about 5 dB/S-unit above S9 [i.e. quite linear, in the logarithmic sense :-)]. I've often wondered why S-meters go above S9 which should be about the strongest signal you ever receive and thus would be full scale. 73, Fred K6DGW - Northern California Contest Club - CU in the Cal QSO Party 1-2 Oct 2016 - www.cqp.org On 11/16/2015 10:09 PM, Vic Rosenthal wrote: > I believe 5 dB is the correct number. But Lyle's suggestion to use > the dBV function is a good one. > > Vic 4X6GP/K2VCO > >> On 17 Nov 2015, at 1:04 AM, [hidden email] wrote: >> >> We are also going to assume that the K3 S-meter is 6 dB per S-unit >> all the way from S5 to S9+40dB. ______________________________________________________________ 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 fact I've always calibrated my K3 S-meter to be 5 dB per division both above and below S9. This seems to me to be a consistent way to do it that's easy to read and easy to mentally convert to dBm. And the K3 amazingly consistently sticks to this 5 dB calibration from S1 to 50 dB over.
Al W6LX >>> It's a little hard to tell on the bar graph S-meter, but it seems to be about 5 dB/S-unit below S9. ______________________________________________________________ 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 k6dgw
The original S meter development for HF radios was done by Art Collins.
At that time the number used was 100 uV for S-9 to coincide with the RST system. Later the value was revised to 50 uV for S-9. Values above S - 9 are stated usually in dB although I've seen some in microvolts. If one ventures into the VHF spectrum then the value changes. {I forget to what value} 73 Bob, K4TAX On 11/18/2015 3:31 PM, Fred Jensen wrote: > I believe there's more than one correct answer. In earlier times, the > "Collins Standard" was 6 dB/S-unit and 50 uv = S9. My 75S3 came in at > 53 uv for S9, and pretty much held to the 6 dB/S-unit below that. Not > so much above S9 ______________________________________________________________ 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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From Wikipedia: https://en.wikipedia.org/wiki/S_meter
"IARU Region 1 Technical Recommendation R.1 defines S9 for the HF bands to be a receiver input power of -73 dBm. This is a level of 50 microvolts at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms. For VHF bands the recommendation defines S9 to be a receiver input power of -93 dBm. This is the equivalent of 5 microvolts in 50 ohms." Alan N1AL On 11/18/2015 03:46 PM, Bob McGraw - K4TAX wrote: > The original S meter development for HF radios was done by Art Collins. > At that time the number used was 100 uV for S-9 to coincide with the RST > system. Later the value was revised to 50 uV for S-9. Values above S - > 9 are stated usually in dB although I've seen some in microvolts. If > one ventures into the VHF spectrum then the value changes. {I forget to > what value} > ______________________________________________________________ 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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Alan <[hidden email]> writes:
> From Wikipedia: https://en.wikipedia.org/wiki/S_meter > > "IARU Region 1 Technical Recommendation R.1 defines S9 for the > HF bands to be a receiver input power of -73 dBm. This is a level > of 50 microvolts at the receiver's antenna input assuming the > input impedance of the receiver is 50 ohms. > > For VHF bands the recommendation defines S9 to be a receiver > input power of -93 dBm. This is the equivalent of 5 microvolts > in 50 ohms." I have always found the VHF definition to be strange, as it seems that a uniform rule is better. My impression is that the K3 and KX3 use the -73 dBm reference even on 6m. Is that right? What about with transverters - does one have gain calibration? Obligatory Elecraft comment: it would be really nice to be able just show signal strength in dBm. ______________________________________________________________ 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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With my Down East Microwave transverters, I am able to adjust the IF
output of each such that the S meter on the K3S corresponds to 50 uV being equal to S-9 on the VHF or UHF bands. The transverters typically have 10 to 15 dB of gain as measured from input to output in receive. It is nice that I can do frequency calibration via the K3S. This corrects minor errors existing in the transverter conversion oscillator. 73 Bob, K4TAX On 11/18/2015 7:18 PM, Greg Troxel wrote: > My impression is that the K3 and KX3 use the -73 dBm reference even on > 6m. Is that right? What about with transverters - does one have gain > calibration ______________________________________________________________ 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 Greg Troxel-2
Both the P3 and the K3 use S9 = -93 dBm on 2 meters. The P3 can read
out in either S units or dBm. And they both treat 6 meters the same as HF: S9 = -73 dBm. Alan N1AL On 11/18/2015 05:18 PM, Greg Troxel wrote: > Alan <[hidden email]> writes: > >> From Wikipedia: https://en.wikipedia.org/wiki/S_meter >> >> "IARU Region 1 Technical Recommendation R.1 defines S9 for the >> HF bands to be a receiver input power of -73 dBm. This is a level >> of 50 microvolts at the receiver's antenna input assuming the >> input impedance of the receiver is 50 ohms. >> >> For VHF bands the recommendation defines S9 to be a receiver >> input power of -93 dBm. This is the equivalent of 5 microvolts >> in 50 ohms." > > I have always found the VHF definition to be strange, as it seems that a > uniform rule is better. > > My impression is that the K3 and KX3 use the -73 dBm reference even on > 6m. Is that right? What about with transverters - does one have gain > calibration? > > Obligatory Elecraft comment: it would be really nice to be able just > show signal strength in dBm. > ______________________________________________________________ > 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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