SPAM !!!!!!
> From: w8ji@w8ji.com
> To: topband@contesting.com
> 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" <vk6vz@arach.net.au>
> To: <topband@contesting.com>
> 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.
> >
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