[Elecraft] Sherwood on Roofing Filters,Transmitted IMD and Receiver Performance

[K3KO]

One thing stuck out.  "Inserting filters in one direction in his testing for
some rigs resulted in an 8db difference relative to the opposite direction
in a performance parameter."

Are K3 filters properly polarized so this won't happen?  Has the filter
technology improved so this isn't an issue?  Or is it a crap shoot with a
50/50 chance of getting it right even with polarized filters?

One other thing was really interesting.  Manufacturers have forgotten what's
important and has been learned in the past regarding transmitter IMD, keying
waveform, ALC, AGC.  The new generation of designers are all "digital" and
don't have any training on the nits/importance of getting the analog part
right.  Since most of them are not hams.  They don't listen to their product
and have no clue on how it is actually working.  Lab tests only take one so
far.

The fact that anything we hear is analog seems to have been lost.

It was good to see reported in one place that both the transmit and RX
performance of rigs has gotten progressively worse, until recently.   Of
course, the cost in constant dollars has dropped a huge amount.

The TS850 still stacks up quite favorably.  Not a surprise since it was the
rig of choice for contesters for many years.

It would be interesting to have a digital modes evaluated-- especially the
rapid on/off chirp type modes.  My perception is these chirp type modes are
producing really bad "clicks" and wide IMD products.  Also the broader
digital modes which already are 1KHz or more wide need to be looked at.  The
sound card may be putting out tones at all the right amplitudes, but what is
the xmtr doing to them?

K3KO


Bill W4ZV wrote:
> 
> Rob Sherwood's recent Boulder ARC presentation, slides in .ppt or .pdf and
> audio in .mp3, are now available on his website.  This is a very good
> primer for anyone interested in the above issues.  Download both and you
> can view the slides while listening to the audio.
> 
> http://www.sherweng.com/
> 
> 73,  Bill  W4ZV
> 

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