On Sat, 2006-07-15 at 08:14 -0500, James Duffer wrote:
> What is your take on the post which stated the SDR-1000 was to have a MDS of
> "-160?"
It all depends on the bandwidth. Given a 5 Hz bandwidth, -160 dBm MDS
would be gross. In a 20 KHz bandwidth, -160 would be stupendous,
unbelievable, possible only with several minutes of averaging.
>
> My two main HF radios, an Omni VI, and a FT-1000D have, I believe a decent
> MDS, but it still seems that ambient noise is the limiting factor. I don't
> think a MDS of -160 would result in a beneficial improvement.
Most of the time on HF, -135 dBm receiver noise will be completely
masked by antenna noise, unless the antenna has really low efficiency,
like a very short whip or a 160 meter Beverage. There the normal
receiver input noise isn't necessarily masked by antenna noise so a low
noise preamp is needed.
>
> As I recall from the post, the -160 was being predicted with some future
> hard/firm-ware changes.
There is the possibility of noise reduction software reducing random
noise and so enhancing the signal to noise ratio of weak signals. Most
of the time this software depends on the noise being truly thermal
random noise, not atmospheric noise, and in many implementations the
remaining background isn't so random and effectively prevents practiced
ears from copying signals below the noise level.
>
> 73, Jim de wd4air
>
> P.S. That radar site had a microwave system manufactured by Collins radio.
> I also use to work at a microwave repeater site located in Thalman, GA which
> was frequency and space diversity using Collins equipment. I just haven't
> heard many people mention the fact that Collins was big in microwave at one
> time (60s).
I'm not sure but what Collins is till strong in microwaves. When the
high power transmitter department completely moved to Dallas in 1964, we
shared the building with the microwave division. They'd give us a hard
time about using tubes and we'd ask them to show us transistors suitable
for the 1 KW stages, never mind the 250 KW final.
--
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer
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