[Elecraft] Noise blanker [was: K2 battleplan?]

[G3VVT at aol.com]

In a message dated 30/04/05 16:12:07 GMT Daylight Time, mm at UDel.Edu  writes:

I've  noticed the majority of K2s seem to be built with the NB.  I  don't
have it, and since I don't seem to be having any man-made noise  problems
I've been wondering when & where the NB is useful.  Is it  mainly for
presumably noisier urban and suburban areas?  Without it  would something
like Spectrogram show continual spikes at certain  frequencies?  And
finally, would the DSP board have any substantial  effect on the sort of
man-made noise the NB  addresses?


Reply: --------------------------------------------------
 
At first I thought the KNB2 noise blanker in my K2 was not working as it  had 
no effect on the normal type of noise received at my QTH. Then  after quite a 
few months found that the NB did indeed work and very well, but  only on 
impulsive noise with sharp rise times like automobile ignition  interference. 
Seems that the KNB2 is a lot more selective in what it will  suppress. My old 
faithful Yaesu FT-480R 2m multimode on the other hand is not as  choosy and will 
work over a wider range of noise types. The FT-480R if anything  is rather 
simpler in the NB circuit design than the KNB2. The FT-480R picks up  the RX wide 
band input half way through the two roofing filters that provide  initial 
bandwidth control after the first mixer. It uses a relatively high  gain IF 
section controlled with AGC to feed a detector circuit that gates G2 in  the 2nd 
mixer MOSFET. It does work exceptionally well though, removing a variety  of 
noise types. If the KNB2 worked to the same degree I would be very  happy.
 
The incidence of the type of interference that the KNB2 will gate out  is 
seldom experienced at my QTH, so it gets very little use. In  retrospect could 
have saved a some money by leaving the KNB2 out in my  K2, though as has been 
pointed out in other postings there are some QTH  where this noise blanker is 
really useful.
 
Only hope that eventually some future mod or redesign of this module  may be 
of benefit with the type of noise I suffer from.
 
As regards use of the DSP2, I do not have one in my K2, but do have an  
external Timewave DSP-9+ available. The DSP-9 works I would guess in a  similar way 
to the DSP2 in that it is in the audio chain. Impulsive noise is not  removed 
by this device in noise reduction mode (NRr), though longer term noise  that 
the normal noise blanker will not touch is suppressed in amplitude during  
it's duration. I would guess the audible effect is in a way similar to what used  
to happen with ANL circuits in the AM days. The DSP-9 and would presume other 
 audio DSP devices have a longer delay in response time and so prevent  any 
chance of removing sharp rise time noise.
 
Though it may be looked on as heresy by the K2 CW fraternity, in the  
Timewave DSP-9+ SSB mode, morse can be almost completely eradicated by the  action of 
noise reduction on tone (NRt). When going over to CW with an external  DSP 
device, the user has to be careful that this NRt facility is switched off,  
otherwise little morse is heard.
 
Bob, G3VVT
K2 #4168