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&S 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 < [email protected]> 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
