SPAM !!!!!!
> From: [email protected] > To: [email protected] > Date: Mon, 19 Oct 2015 10:58:44 -0400 > Subject: Re: Topband: ADC Overload from MW transmitters > > I think the problem here is some people read this as a SDR radios never > overload, or are superior in every case. > > Apparently one person thought they were junk because multiple modest > strength signals would add up to overload them, and that triggered the > response that was misinterpreted to mean they never overload under any > condition or were always superior to roofing filtered systems common in > standard receivers. > > In the case I had here, a *single* transmitter totally wiped the SDR out. > The overload was nothing like the desense or noise in a traditional > receiver. It just was totally useless. It was useless at any signal spacing, > because it had no front end selectivity at all that would reduce levels. > > For my application, it was useless. It was far worse than a K3, which a few > kHz spacing would duplex on most antenna combinations. When the K3 (or > FT1000MP MKV's) did overload, the overload was a desense or composite noise > type sound. It would take out noise floor signals worse, be progressively > less problem for stronger signals, and never be bothered with any antenna > combinations with strong signals. When the SDR overloaded, it was just > totally gone for everything, and wider frequency spacing with the local TX > made absolutely no difference like it does with a normal receiver. I assume > this was from overflowing the ADC, but it was a very dramatic sounding > overload. > > That, coupled with the fact it did not have a traditional knob and panel > system and had some transmitter spurs, made it useless here. But that was > this setup and this application, where a local 1500 watt transmitter within > a few thousand feet of the RX antennas was being used while receiving. This > was a single transmitter multi-op, where one TX signal was allowed on the > air at a time but two or more operators were making contacts. > > I still never find any SDR I listened to, even that one without a > transmitter running, better than analog detection for my ears on > "in-the-noise" signals. > > 73 Tom > > > > > > > > > ----- Original Message ----- > From: "Steve Ireland" <[email protected]> > To: <[email protected]> > Sent: Monday, October 19, 2015 8:07 AM > Subject: Re: Topband: ADC Overload from MW transmitters > > > > Hi Jim > > > > Clearly in a large US city, there is going to be a whole larger degree of > > difficulty than here. > > > > Perth is still pretty much a small city in world terms, with a population > > of about 2 million. In addition to the ABC transmitters, we have about > > half a dozen other transmitters, but only two of these have signals of any > > size – 6PR (10kW) and 6IX (2kW), with the former of these putting in the > > largest signal to me, with its transmitter/antenna on the banks of the > > Swan River estuary about 15km away. > > > > When I used my HPSDR, originally I had no filtering in front of the ADC > > and had some overload problems on 160m from the local BC stations. > > However, a simple Chebyshev HPF got rid of this. Later when I added the > > Alex bandpass filters, which are part of the HPSDR design, there was no > > longer any need for the HPF. > > > > The main point, as Phil says in his post, is that the amount of protection > > an ADC is going to need will vary widely, depending on factors such as > > local AM BC transmitters and how strong they are. In my case, all I had to > > do was to use the general coverage facility of the SDR to look at the > > medium wave here, see which of the signals were largest and look for a > > suitable HPF design accordingly . > > > > Vy 73 > > > > Steve, VK6VZ > > > > > > > >> That's typical of medium-size cities in the US for high power > >> broadcasters, but major cities typically have twice as many. Both large > >> and medium-size cities, as well as smaller ones, typically have 6-10 > >> stations in the 5kW range, and more in the 1kW range. Chicago is typical > >> of a large city (like New York, Boston, Los Angeles, San Francisco) -- it > >> has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and 1,000 kHz. There's > >> also a daytime only station with 50kW on 1160 kHz. Cincinnati is typical > >> of smaller cities like Indianapolis, Detroit, Minneapolis, Cleveland, St > >> Louis, and New Orleans, with 2-3 50kW stations and many smaller ones. > >> Cincinnati 50kW stations are on 700 kHz and 1530 kHz. > > > > I grew up in a small town in WV, with three 5 kW stations within two miles > > on 800 kHz, 930 kHz, and 1470 kHz. > > > > Bottom line -- there's a lot more broadcasting in the US than in most > > countries. > > > > --- > > This email has been checked for viruses by Avast antivirus software. > > https://www.avast.com/antivirus > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > > ----- > > No virus found in this message. > > Checked by AVG - www.avg.com > > Version: 2014.0.4830 / Virus Database: 4365/10847 - Release Date: 10/18/15 > > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
