[Premium-Rx] WJ DMS105A as an LF receiver.

[GandalfG8 at aol.com]

Hi All

I've been following the comments on the suitability of receivers for MW dxing 
with interest.

Due to severe outside space limitations my main antenna at the moment is 
restricted to a loft mounted broadband active antenna which is hardly ideal at LF 
so, on that, good dx on medium wave is any of the more distant low power 
stations within the UK.
I have got other antennas, including some loops optimised for LF, but that 
tends to be the one that gets used for rough and ready comparisons.

Given the poor signal it's likely to be RX sensitivity that's the limiting 
factor so any comparison isn't going to take much else into consideration but, 
on that basis, I've found that one of the best LF receivers I've owned is a WJ 
DMS105A demodulator that tunes up to 1.6MHz.
I bought this as an add on IF/demodulator for use with other receivers and 
assumed that the input sensitivity would be low because of its intended role but 
that certainly doesn't seem to be the case.
It pulls in signals on virtually all 9Kz segments and far outstrips the 
6790GM, RA1792, and Eddystone 1650, in this respect as well as a variety of other 
receivers and also several WG and HP selective level meters which are often 
favoured by LF beacon watchers here.

Given a tougher test I'm sure it would lose out on other factors, I obviously 
don't have to worry about heterodynes and adjacent strong signals for 
example, but I was still pleasantly surprised.

I still can't understand though why something that's designed as an add on 
demodulator should be so sensitive. By implication it should be able to handle 
quite high voltage levels, so assume it won't be easily overloaded, but would 
appreciate any comments on that and on others' thoughts about the use of these 
things as receivers in their own right.
I'd also be grateful if somebody could tell me what type of filters this uses 
for its six selectable bandwidths on AM/FM and four on SSB.
I know I should just be able to open it up to find out but the internal 
modules still have the original WJ calibration stickers intact so I'm resisting 
pulling those off unless I really need to:-)

Nigel Clarke
G8PZR
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