[RFI] DSP for a noisy environment

[CR]

One reason the Elecraft IF DSP (or any other IF DSP) works is that it's 
applied before the AGC detector, keeping the noise from reducing 
receiver gain. Quite a few audio DSP boxes are available, though and one 
might work well, depending on the type of noise.  The disadvantage to 
conventional audio DSP is that noise that drives the AGC reduces 
receiver gain.

You might consider an analog RF noise cancelling accessory; ask around 
locally and see if anyone has one you could try.

Below are links to some eham reviews. You can be sure of hearing 
everything bad about a product at that site as well as the good, and 
some of it will be worthwhile heads-up's. Some reviews, however, will 
also mention how to avoid what the bad reviews don't like, usually but 
not always RTFM.

MFJ-1026 and 1025 http://www.eham.net/reviews/detail/1205
http://www.eham.net/reviews/review/105339 (the 1025 model has no preamp)

DX Solutions NCC-1
http://www.eham.net/reviews/detail/7361

Timewave ANC-4 (formerly sold as the JPS ANC-4)
http://www.eham.net/reviews/detail/1138

Odds are that your noise is radiated from the building wiring and you 
may find success by coupling the "noise antenna" input on any of these 
to that wiring with a current probe made from a split RFI ferrite; see
http://www.interferencetechnology.com/the-hf-current-probe-theory-and-application/

If you coupled to a power wire near the antenna that might work, but you 
run the risk of also cancelling any of thw desired signal the wiring 
picks up, and also overloading or damaging the noise canceller with the 
high RF level when you (or any other rooftop antenna user) transmit.

A disadvantage to RF noise cancelling is that -- assuming it works in 
your situation - it will probably need to be readjusted for each 
frequency your net uses.  That might be easier once you mark the control 
positions where a null is found. And because it is in line with the  
transmitted RF when you key up, you may want to key the cancellers' 
RX/TX relay with a PTT signal instead of using built-in RF sampling. 
Keeping the noise-sampling antenna/probe away from the transmitter 
antenna is a good idea because of that problem, too, and the fact that 
if outside, it can pick up the desired signal as well and reduce THAT.


Cortland
KA5S

http://www.interferencetechnology.com/the-hf-current-probe-theory-and-application/#sthash.MQFkIEKB.dpuf
On 2/21/2014 8:30 PM, wa3afs at nycap.rr.com wrote:
> We did try a KX3 and its DSP was quite an improvement.  That is why I am looking to see
> what rigs may work well in this environment and the budget of the NWS who have agreed to
> 'look into' andd possibly fund this effort.