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Re: Topband: SDR Mythbusters - ADC Overload myths debunked

To: <jim@audiosystemsgroup.com>, <topband@contesting.com>
Subject: Re: Topband: SDR Mythbusters - ADC Overload myths debunked
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Sat, 10 Oct 2015 17:41:25 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
On Sat,10/10/2015 2:15 AM, Steve Ireland wrote:
Of course, I was talking about using a DUC/DDC in a single transmitter/receiver urban/semi-rural station setting on a quarter to half an acre block, which is the setting in which the vast majority of people who subscribe to this reflector would be using a transceiver.

Your use is not nearly so much a majority as you might suspect. A fair percentage of contesters operate SO2R. MANY hams live in proximity to high power broadcast stations. Hams with good antennas in locations exposed to many in-band and out-of-band signals are likely to encounter far higher voltages at the input to the radio than you do.

I thought they were talking about overload from local transmitters.

If you look at Sherwood Engineering's tests, they show the problem we had. The wide spaced dynamic range of SDR's is only 96-99 dB.

The wide spaced dynamic range of the K3 is up around 105 dB. That 5 or 10 dB is helpful with local transmitters, but the real difference we noticed was the SDR just totally goes goofy when it overloads, losing everything, while the regular receivers just "noise up" or de-sense.

Overload characteristics for strong signals have nothing to do with how a receiver works without strong signals to overload it. :)

73 Tom
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