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Re: LF: RX Sensitivity on 500 kHz

To: [email protected]
Subject: Re: LF: RX Sensitivity on 500 kHz
From: "Dave Sergeant" <[email protected]>
Date: Thu, 19 Apr 2007 21:38:49 +0100
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Interesting analysis Chris! Not really got round to tabulating actual 
figures, and one significant factor which makes it difficult is the 
slow QSB on all signals, do these relate to peaks of QSB perhaps?

You are the strongest signal I receive here with G3KEV and SM6BHZ 
closely behind, all around 589 on peaks.  G3AQC slightly down on 
them. G3UNT varies from just above noise to around 579, as are 
GI4PDE, GI3PDN. Not heard Derek G3GRO yet. There seems quite a lot of 
activity on the band tonight including a new GW3 stations! These are 
using my Datong UC/1 feeding  K2 on 28MHz, 400Hz cw filter. Antenna 
Butternut vertical base resonated, noise level varies and is normally 
fairly low but does get up to s6 at times.

Making excellent progress with the TX here, I now have built twin 
VXOs at 5.9 and 6.4MHz and mixed them to produce a nice 500kHz sine 
wave. VXO range checked and adjusted (pulling one crystal low with a 
10uH choke and the other one high with the tuning cap) and now nicely 
covers the whole 3kHz. On with the keyed driver tomorrow.

Looking for a tuned circuit for the mixer output I realised I could 
scrounge one from an old MW radio IF -  worked like a dream with only 
a small tweak needed to peak the output. Which brings the next 
question, have people had problems with IF breakthough on MW?

73 Dave G3YMC

On 19 Apr 2007 at 20:38, CHRISTOPHER OSBORN wrote:

> Dear LF,
> I have just calibrated my 500 kHz DC RX using an AF-derived agc and
> s-meter. The agc / s-meter are driven after a narrow audio filter. I
> used a signal generator and a switched attenuator.
> Attaching my receive loop aerial rotated for minimum local QRM I have
> a usual noise level of about 7 dB (uV) - S 4 - 5  (assuming S9 = 50
> uV) The main station end fed wire aerial gives a noise level of 16 dB
> (uV) - S6  !! At times the local noise level is significantly worse.
> My apologies to those who have called me and have not been heard.
> The RX internal noise with aerials disconnected is well below 0 dB
> (uV).
> Assuming there's no flaw in my calibration method I have registered
> the following stations' readings, using the loop rotated for optimum
> signal:
> G3KEV     32  dB (uV)
> G3ROO    25    "
> G3GRO    19    "
> G3UNT     18    "
> Any comments or suggestions are welcome.
> Is there a list of 500 kHz operators ?
> To date I have registered 19 of whom I have worked 14.
> 73 Chris G3XIZ

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