Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
On 2/26/2021 7:31 AM, John Kaufmann via Topband wrote: > When dealing with narrowband > coherent signals, this can really make very weak signals become > visible on the display That's exactly what I said in my first post. > when they are virtually invisible in a larger measurement > bandwidth. The effect of the bandwidth of bins is to increase the frequency resolution (and decrease the time resolution) of a measurement. It is a fundamental property of spectral measurements that we can not know both frequency and and time with infinite accuracy from the same measurement, because they are the inverse of each other. On 2/26/2021 8:46 AM, Richard (Rick) Karlquist wrote: Averaging is a nice technique that mitigates the poor sensitivity of the mini-flag, but only for "bright lines" due to power supplies, etc. And for signals from ham transmitters. I would be surprised if it would do anything to improve DF'ing power line noise, which is clearly a major application domain. Of course not -- that noise is not coherent. Averaging is useful for chasing noise from electronic sources, not the noise generated by arcing in power systemsn or by lightning, which is impulse noise. Impulse noise will be displayed by horizontal lines on a waterfall if the time scale is fast enough. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
Hi Rick, This next piece of info is not really related, but here is another data point for folks since you mentioned using an AM radio with built in bar antenna tuned to 1710 KHz to track down powerline noise. I just checked the sensitivity of my portable flag versus built in bar antenna on a pretty weak station on 1550 KHz. With the built in bar antenna I can make out (understand) the audio but not well, and with the portable flag and 20 dB of preamp gain the station is loud and clear (using the same receiver which is a DX-440). Actually the portable flag with no preamp receives about the same as the bar end antenna on 1550 KHz on the DX-440. Also checked this station with a Sony Walkman that must have a bar antenna and I can detect the station is there but not readable. Therefore based on my tests the portable flag with just 20 dB of preamp gain will easily outperform an AM radio with built in bar antenna at the top of the AM broadcast band. I did these tests at 1pm and the 1550 KHz station is located 49 miles away and is running 250 watts, and I show up outside their daytime fringe zone by a considerable amount. YMMV. Here is another datapoint from Craig (VK3OD): "I also have access to the R HE200 HF DF antenna that our version of the FCC uses. Even with its preamp it will not detect the majority of noise sources that we encounter. The portable flag can easily hear the Ethernet powerline adaptor buckshot noise from my distant neighbours which this professional DF antenna wont even detect." Note: Craig was using an Advanced Receiver Research preamp which I believe provides 20 dB of gain. I'm not sure what frequency (band) Craig was using, and I'm following up on that. P.S. In my original article submission I mentioned the portable flag may or may not hear weak levels of RFI especially on 160 and 80 meters where the gain is very negative but I also said it's not as bad as it might appear because the normal noise floor often allows us to give away at least 20 or 30 dB of gain (due to ones typical noise floor on those bands). Unfortunately this information did not make the cutting room floor so to speak. Again, this antenna was not intended for anything but direction finding but it certainly will find other uses. Besides its unidirectional properties its broadband capabilities is often very handy. I do appreciate everyone's comments and number crunching (John:). It's a really interesting topic, and the antenna system thermal noise limitation is often a hard topic for folks to understand. The portable flag is definitely not intended to be a receive antenna for weak signal use (DX) on 160 meters to clear the air (so to speak). 73, Don (wd8dsb) On Fri, Feb 26, 2021 at 11:47 AM Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > > On 2/26/2021 7:31 AM, John Kaufmann via Topband wrote: > > I think there may be some semantic confusion over the term "averaging" > and > > how averaging affects noise when making spectral measurements, so let me > > clarify what I mean. My comments are specific to the P3 but are fairly > > Averaging is a nice technique that mitigates the poor sensitivity > of the mini-flag, but only for "bright lines" due to power > supplies, etc. I would be surprised if it would do anything > to improve DF'ing power line noise, which is clearly a major > application domain. > > 73 > Rick N6RK > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
Hi Jim, From the P3 manual:/ / /"The dsPIC further processes the signal for presentation on the 480x272-pixel color TFT LCD display. The "circuitry" shown inside the processor box in the block diagram is actually implemented as software routines. The FFT is the fast Fourier transform, which is a software version of a hardware spectrum analyzer. It reads the incoming signal and calculates the frequency spectrum. Further software routines calculate the power of the spectrum, take the logarithm, and then scale and offset the result so that it reads correctly in dBm on the display." / The raw samples will be in volts, but what gets displayed depends on the processing. The FFT spits out a complex number for each bin. If you take the magnitude of that complex number and square it, you get a number that is proportional to the power in that frequency bin averaged over the length of time that the FFT samples (e.g. 4096 samples @ 60 Megasamples/sec would be a time interval of 4096/60e6 = 68us). The random Johnson noise voltage you get from a resistor has a two-sided Gaussian distribution with zero mean and standard deviation sigma, so the random noise voltage does average to 0 volts. The noise power on the other hand has a one-sided Gaussian distribution with a variance of sigma^2. If you average after conversion to power (this is what is typically done in a spectrum analyzer), the random noise won't average to 0.0 watts, instead it will converge toward the average noise power (i.e. number proportional to sigma^2). This is why the thermal noise displayed on a spectrum analyzer doesn't tend toward minus infinity dBm when you average it, instead it tends toward sigma^2 as you apply more averaging. When you calculate KTB and convert that to dBm (e.g. -174 dBm for room temperature in a 1 Hz bandwidth), you are getting the sigma^2 value. But the Gaussian distribution has tails that extend beyond 1 sigma, that is why the displayed noise has jagged peaks before it is averaged. Some of the noise power samples taken in the time interval of the FFT are going to be less than sigma^2 and some are going to be significantly greater than sigma^2, but if you average enough of them (from any given frequency bin), you get a number that converges toward sigma^2. 73, Mike W4EF On 2/25/2021 7:39 PM, Jim Brown wrote: On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote: The P3 averages power, not amplitude, so using longer averaging times just smooths the display and doesn't reduce random noise. It has nothing to do with power. Last I looked, the P3 is reading and displaying the instantaneous voltage in the IF, and can be calibrated to voltage at the input. I've been doing swept measurements of complex quantities for nearly 40 years, first at audio frequencies and now at RF. Averaging DOES cause random contents of a bin to approach zero (or the noise floor), making correlated signals stand out. This has long been well understood. I the principle to measure the dynamic response of broadcast signal processing in a peer-reviewed paper to the Audio Engineering Society in 1986. The test signal was a swept sine embedded deep in musical program material to the point that it was barely audible to a trained listener, and detected by a synchronized swept narrowband detector. Because the swept excitation and swept detector are synchronized, the measurement produces the complex response of the system, and program material, being non-coherent, averages out. http://k9yc.com/AESPaper-TDS.pdf 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
On 2/26/2021 7:31 AM, John Kaufmann via Topband wrote: I think there may be some semantic confusion over the term "averaging" and how averaging affects noise when making spectral measurements, so let me clarify what I mean. My comments are specific to the P3 but are fairly Averaging is a nice technique that mitigates the poor sensitivity of the mini-flag, but only for "bright lines" due to power supplies, etc. I would be surprised if it would do anything to improve DF'ing power line noise, which is clearly a major application domain. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
I think there may be some semantic confusion over the term "averaging" and how averaging affects noise when making spectral measurements, so let me clarify what I mean. My comments are specific to the P3 but are fairly general. The P3 has an AVERAGE function. It allows you to perform averaging of video traces over time intervals between about 50 milliseconds and 1 second. If I am trying to measure the dBm value of random noise, the trace looks somewhat ragged at the lowest averaging times. The trace on the display will bounce up and down several dB. I want the average value of the trace because that's what gives me the noise spectral level. I can do some visual averaging of the ragged trace to obtain the average. However, enabling longer averaging times in the P3 makes this easier because it reduces the jaggedness and the trace converges to a pretty smooth one. However, the smooth trace has exactly the same *average* value as the jagged trace. Anyone who has a P3 can demonstrate this to themselves. So, when I say the averaging hasn't reduced the noise level, it's the average level of the noise that hasn't changed. On the other hand, if I really want to make a weak narrowband signal stick out of the noise, then I will reduce the noise bandwidth of the spectrum measurement. The narrower bandwidth will filter out more noise in the RF (not video) domain. In the P3 you do this by reducing the frequency span. With the P3 you can vary the frequency span between 200 kHz and 2 kHz. Because the noise bandwidth is approximately span/450 in the P3, a 2 kHz span, for example, should give a factor of 10 (or 10 dB) reduction in average noise compared to a span of 20 kHz. When dealing with narrowband coherent signals, this can really make very weak signals become visible on the display when they are virtually invisible in a larger measurement bandwidth. I hope this clears up any confusion. 73, John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Jim Brown Sent: Thursday, February 25, 2021 10:39 PM To: topband@contesting.com Subject: Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!) On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote: > The P3 averages power, not amplitude, so using longer averaging times just > smooths the display and doesn't reduce random noise. It has nothing to do with power. Last I looked, the P3 is reading and displaying the instantaneous voltage in the IF, and can be calibrated to voltage at the input. I've been doing swept measurements of complex quantities for nearly 40 years, first at audio frequencies and now at RF. Averaging DOES cause random contents of a bin to approach zero (or the noise floor), making correlated signals stand out. This has long been well understood. I the principle to measure the dynamic response of broadcast signal processing in a peer-reviewed paper to the Audio Engineering Society in 1986. The test signal was a swept sine embedded deep in musical program material to the point that it was barely audible to a trained listener, and detected by a synchronized swept narrowband detector. Because the swept excitation and swept detector are synchronized, the measurement produces the complex response of the system, and program material, being non-coherent, averages out. http://k9yc.com/AESPaper-TDS.pdf 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
Hi Jim and gang, I would like to make one minor correction and then add some more info. On my SDR receiver I should have said I increased averaging from 1 to 10 in my previous post (not 2 to 10) and this really made the noise floor drop and smooth out and this really helped expose the signal of interest on what I call the RF Spectrum Display. I just ran another simple test to understand how my SDR receiver responds to changes in the averaging value. Averaging does indeed improve the signal to noise ratio when looking at what I call the RF Spectrum Display, but it does not change what I see in the waterfall display. What's amazing with averaging is a signal that I can't see in the RF spectrum Display when average is set at 1 suddenly is 5 dB over the noise floor when I set averaging to 10. The peaks of the noise floor drops by at least 5 dB (and really smooths out) which exposes the CW signal I am generating locally for this test of the averaging function. Sorry to take up so much bandwidth on the topband reflector, but it really is an interesting discussion. Just FYI, Don (wd8dsb) On Thu, Feb 25, 2021 at 11:24 PM Don Kirk wrote: > Hi Jim, > > It’s funny that you brought up this topic as yesterday when I was doing > comparisons of the signal I could hear on my 160 meter vertical TX antenna > versus my portable flag, I increased the averaging value on my portable SDR > receiver connected to my portable flag and the signal that was barely > visible on the RF spectrum display when using my portable flag suddenly > stuck out like a sore thumb when I increased the averaging value from 2 to > 10 (the peaks of the noise floor dropped way down and smoothed right out). > This was a signal that was only 0.6 S units above my noise floor on my > TS-180s using my TX vertical and 1.0 S units above my noise floor when > using my half size pennant. I’m indeed able to see signals using my > portable flag with the DX engineering preamp that are not much above my > main stations noise floor (but I don’t know what my main stations noise > floor really measures, nevertheless I don’t consider it abnormally high). > I will try and determine my main stations noise floor as time permits. > > Just FYI, and 73. > > Don (wd8dsb) > > On Thu, Feb 25, 2021 at 10:40 PM Jim Brown > wrote: > >> On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote: >> > The P3 averages power, not amplitude, so using longer averaging times >> just >> > smooths the display and doesn't reduce random noise. >> >> It has nothing to do with power. Last I looked, the P3 is reading and >> displaying the instantaneous voltage in the IF, and can be calibrated to >> voltage at the input. >> >> I've been doing swept measurements of complex quantities for nearly 40 >> years, first at audio frequencies and now at RF. Averaging DOES cause >> random contents of a bin to approach zero (or the noise floor), making >> correlated signals stand out. This has long been well understood. >> >> I the principle to measure the dynamic response of broadcast signal >> processing in a peer-reviewed paper to the Audio Engineering Society in >> 1986. The test signal was a swept sine embedded deep in musical program >> material to the point that it was barely audible to a trained listener, >> and detected by a synchronized swept narrowband detector. Because the >> swept excitation and swept detector are synchronized, the measurement >> produces the complex response of the system, and program material, being >> non-coherent, averages out. >> >> http://k9yc.com/AESPaper-TDS.pdf >> >> 73, Jim K9YC >> _ >> Searchable Archives: http://www.contesting.com/_topband - Topband >> Reflector >> > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
Hi Jim, It’s funny that you brought up this topic as yesterday when I was doing comparisons of the signal I could hear on my 160 meter vertical TX antenna versus my portable flag, I increased the averaging value on my portable SDR receiver connected to my portable flag and the signal that was barely visible on the RF spectrum display when using my portable flag suddenly stuck out like a sore thumb when I increased the averaging value from 2 to 10 (the peaks of the noise floor dropped way down and smoothed right out). This was a signal that was only 0.6 S units above my noise floor on my TS-180s using my TX vertical and 1.0 S units above my noise floor when using my half size pennant. I’m indeed able to see signals using my portable flag with the DX engineering preamp that are not much above my main stations noise floor (but I don’t know what my main stations noise floor really measures, nevertheless I don’t consider it abnormally high). I will try and determine my main stations noise floor as time permits. Just FYI, and 73. Don (wd8dsb) On Thu, Feb 25, 2021 at 10:40 PM Jim Brown wrote: > On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote: > > The P3 averages power, not amplitude, so using longer averaging times > just > > smooths the display and doesn't reduce random noise. > > It has nothing to do with power. Last I looked, the P3 is reading and > displaying the instantaneous voltage in the IF, and can be calibrated to > voltage at the input. > > I've been doing swept measurements of complex quantities for nearly 40 > years, first at audio frequencies and now at RF. Averaging DOES cause > random contents of a bin to approach zero (or the noise floor), making > correlated signals stand out. This has long been well understood. > > I the principle to measure the dynamic response of broadcast signal > processing in a peer-reviewed paper to the Audio Engineering Society in > 1986. The test signal was a swept sine embedded deep in musical program > material to the point that it was barely audible to a trained listener, > and detected by a synchronized swept narrowband detector. Because the > swept excitation and swept detector are synchronized, the measurement > produces the complex response of the system, and program material, being > non-coherent, averages out. > > http://k9yc.com/AESPaper-TDS.pdf > > 73, Jim K9YC > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote: The P3 averages power, not amplitude, so using longer averaging times just smooths the display and doesn't reduce random noise. It has nothing to do with power. Last I looked, the P3 is reading and displaying the instantaneous voltage in the IF, and can be calibrated to voltage at the input. I've been doing swept measurements of complex quantities for nearly 40 years, first at audio frequencies and now at RF. Averaging DOES cause random contents of a bin to approach zero (or the noise floor), making correlated signals stand out. This has long been well understood. I the principle to measure the dynamic response of broadcast signal processing in a peer-reviewed paper to the Audio Engineering Society in 1986. The test signal was a swept sine embedded deep in musical program material to the point that it was barely audible to a trained listener, and detected by a synchronized swept narrowband detector. Because the swept excitation and swept detector are synchronized, the measurement produces the complex response of the system, and program material, being non-coherent, averages out. http://k9yc.com/AESPaper-TDS.pdf 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
The P3 averages power, not amplitude, so using longer averaging times just smooths the display and doesn't reduce random noise. John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Jim Brown Sent: Thursday, February 25, 2021 8:03 PM To: topband@contesting.com Subject: Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!) On 2/25/2021 2:29 PM, John Kaufmann via Topband wrote: > The P3 noise measurement bandwidth was about 100 Hz in my measurements. I hope that everyone realizes that setting a high value for averaging cancels non-correlated noise in spectrum displays, including the waterfall, greatly increasing the visibility of correlated signals and noise. Correlated can be understood as non-random, and includes nearly all ham transmission modes and most electronically generated noise like computer clocks, trash from electronic power handling and switch-mode power supplies. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
On 2/25/2021 2:29 PM, John Kaufmann via Topband wrote: The P3 noise measurement bandwidth was about 100 Hz in my measurements. I hope that everyone realizes that setting a high value for averaging cancels non-correlated noise in spectrum displays, including the waterfall, greatly increasing the visibility of correlated signals and noise. Correlated can be understood as non-random, and includes nearly all ham transmission modes and most electronically generated noise like computer clocks, trash from electronic power handling and switch-mode power supplies. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: The WD8DSB mini-flag antenna (LONG!)
The P3 noise measurement bandwidth was about 100 Hz in my measurements. Quoting from the P3 user's manual, "the effective bandwidth of the P3 is generally one display pixel, which is approximately span / 450. I used a span of 50 kHz, so it comes out to 111 Hz. Because the relationship is only approximate, I round it to 100 Hz in my calculations, which is good enough for my purposes. To obtain the noise density in a 1 Hz bandwidth, you just subtract 20 dB (a factor of 100 for the difference in bandwidth) from the measured noise level in the P3. 73, John W1FV -Original Message- From: Topband [mailto:topband-bounces+john.kaufmann=verizon@contesting.com] On Behalf Of Lee STRAHAN Sent: Thursday, February 25, 2021 4:46 PM To: topband@contesting.com Subject: Topband: FW: The WD8DSB mini-flag antenna (LONG!) Hi John, What did you use as the P3 bandwidth for your noise measurement? And conversion to 1Hz equivalent. The P3 has its own bandwidth and is not affected by setting the receiver bandwidth. Lee K7TJR OR (Note: what follows is a long, technical discussion about noise and “small” antennas. I invoke some math and physics here, so if you are not comfortable with it, feel free to disregard or delete this e-mail. I went through this exercise to help teach myself the limits here and maybe others might find it helpful or educational as well.) _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: FW: The WD8DSB mini-flag antenna (LONG!)
Hi John, What did you use as the P3 bandwidth for your noise measurement? And conversion to 1Hz equivalent. The P3 has its own bandwidth and is not affected by setting the receiver bandwidth. Lee K7TJR OR (Note: what follows is a long, technical discussion about noise and “small” antennas. I invoke some math and physics here, so if you are not comfortable with it, feel free to disregard or delete this e-mail. I went through this exercise to help teach myself the limits here and maybe others might find it helpful or educational as well.) _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
