[Lowfer] Analog VS SDR LF comparison

[Douglas D. Williams]

Well, as I mentioned to this group a few weeks ago, I planned to do a
series of comparisons between an analog receiver and an SDR at VLF/LF
frequencies, using the same antenna.

In order to receive the same signal simultaneously on both receivers with
the same antenna, I would need some sort of "splitter". KIWA Electronics
manufactures two models:

http://www.kiwa.com/LFCombiner

Neither one completely covered the frequency range I am interested in,
which is 5kHz to 500+kHz, so I commissioned a "special order" model, which
I received today. BTW, I would like to take this opportunity to thank Craig
Seigenthaler at KIWA for his help in this. In addition to the custom
splitter/combiner, I own one of their 500kHz low pass filters, and can
recommend their products without reservation. They are built like a Sherman
tank.

The antenna that will be used in this comparison is a custom Clifton
Laboratories Z1501D active whip, located about 50' from my house with the
base up 20' from ground. The "custom" part is I asked Jack at Clifton Labs
to lower the bottom range of the active antenna from 20kHz to below 8kHz,
which he did with flying colors (all the way to about 3kHz).

The setup is as follows:

Output from the Clifton Labs indoor DC coupler goes first to the KIWA
500kHz low pass filter, then to the KIWA splitter. Output "A" goes to an
AMRAD LF converter custom built by Todd Roberts with an OCXO for stability,
then to an Icom R75 with the OCXO option, as well as a 500Hz and a 250Hz
crystal filter. Output "B" goes directly into a Winradio Excalibur Pro
G33DDC receiver.

At first, I was going to run two instances of Argo on the same PC, one for
each receiver, but I ultimately decided to connect the two receivers into
two separate PCs.


Got it all hooked up today, and here are my initial results, after briefly
calibrating both receivers with WWVB.


This is afternoon copy of beacon MP, both receivers tuned to 137.780 kHz,
and the same version of ARGO running on each computer, with the settings as
close as I could get them.

Beacon MP is approximately 464 miles from my QTH. Nice daytime signal.

First, the R75+AMRAD converter:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/R75MP1.jpg

Second, the Winradio G33DDC:

https://dl.dropbox.com/u/33457409/R75%26Winradio%20Comparison/WINRADMP1.jpg


In my opinion, there is essentially no difference in the two screen
captures.

I will continue to do direct comparisons throughout the listening season,
at different frequencies (all 500 kHz or below).

In a week or so, I am having the wooded portion of my land cleared out,
which will put my receive antenna much more in the clear and away from
trees.

Once that happens, and the LF season really gets underway, I should be able
to do some really "weak signal" comparisons in the Part 15 Lowfer band.

-Doug KB4OER