[Lowfer] WWVB clock on 60 kHz

[Michael Sapp]

Garry: I thought you might see an improvement in your receiver performance 
with a good brick wall LPF to lower the AM BC overload effects at LF/MF.  I 
use an e-probe for my boat anchor receivers on the other side of my basement 
and they all respond well to having a well matched LPF for the LF range and 
a 10.5:1 transformer at the balanced antenna input terminals.  I see a 
similar improvement with a high order Butterworth  HPF to limit AM BC energy 
for 1.8 to 30 MHz reception.     Of course, their is some IMD in the e-probe 
fet itself, but scrubbing the unneeded RF energy for a  given analog or 
digital receiver  is usually  a big help.

If you can measure microvolts or dBm it can be interesting to measure total 
RF from an antenna with and without a filter in line.  I did that with my NE 
EWE and it had something like 138,000uv with no LPF and 20,000 uV or so with 
a 500kHz LPF in line. The other directions were lower values but a similar 
proportional change.


 I have one of those $20 RTL dongles and a basic DBM upconverter for it to 
cover MF/HF and it is pretty much useless without the HPF with the 8 bit 
sampling dynamic range limitation... but it works fairly well with the HPF 
in line.   Perhaps I'll take the plunge on one of those new SDRPlay modules 
as they as 12 bit sampling with an extra 2^4 dynamic range improvement over 
the 8 bit receiver dongles.

SIW is coming in well again this AM on wspr-15. When I switched to a single 
IF receiver (SIW only vs 2nd IF for XND) the SNR on SIWcame up about 4dB.  I 
ran QRSS 60 overnight at 185.3 but TAG was the only solid signal received. 
There were a few traces of WM at times but not enough to make a positive ID.

73, Mike wa3tts




----- Original Message ----- 
From: "Garry" <k3siw at sbcglobal.net>
To: <lowfer at mailman.qth.net>
Sent: Monday, February 06, 2017 12:41 AM
Subject: Re: [Lowfer] WWVB clock on 60 kHz


> Hi Mike,
>
> Glad the wspr-15 came through for you from lowfer SIW.
>
> Interesting idea to try a LPF to block broadcast signals. I've had a 
> high-order band-reject filter collecting dust because I figured the eprobe 
> itself was generating the interference, not my sdr-iq receiver. But it was 
> easy to check what happens when the filter is placed in-line between the 
> eprobe and sdr-iq. As for decoding the clock information from WWVB on 60 
> kHz, no go. But France-inter on 162 kHz still works fine and DCF77 on 77.5 
> kHz looks much better, though too weak to decode (JJY on 40 kHz was also 
> too weak; it should improve as local sunrise nears). I liked the cleaner 
> look on the waterfall and at 15-30 kHz the 60-Hz harmonic comb level is 
> reduced, allowing, for example, JXN on 16.4 kHz to be evident on the 
> waterfall. Bottom line - I think I'll keep the filter in-line except when 
> tuned for Navtex on 518 kHz, which is slightly above the filter cut-in 
> frequency. Thanks for the suggestion.
> -- 
> Garry, K3SIW, EN52ta, Elgin, IL
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