A big reduction in receiver noise floor and a huge improvement in
both
transmit and receive phase noise.
That is far too simplistic. Anyone's personal definition of "the
better synthesizer" will depend on what range of frequency offsets
is more important for their particular type of operating.
For HF CW in particular, phase noise at small frequency offsets is
of paramount importance and I wouldn't argue with Don's report of "a
huge improvement in both transmit and receive phase noise" - but
*only* in that specific context. There are also several other
advantages that are relevant to high-performance HF CW that could
also justify upgrading to the KSYN3A.
At close frequency offsets from the carrier, the KSYN3A does indeed
offer a large reduction in phase noise compared with the KSYN3
(which itself was already good). But at wider frequency offsets,
that situation reverses. According to the ARRL review [1], at all
offsets beyond about 6kHz, the older KSYN3 continues to have a lower
noise floor than the newer KSYN3A "upgrade".
Performance at wider frequency offsets, 10-100kHz and beyond, is of
much greater importance in VHF-UHF contesting. This due to a
combination of factors. The strongest signals at VHF-UHF are often
much stronger than on HF, due to the use of high-gain beam antennas;
and also the weakest signals are *always* much, much weaker due to
the lower levels of natural background noise. These two features
stretch the requirement for dynamic range on VHF-UHF far beyond
those for which most HF transceivers are designed.
Anyone transmitting wideband phase noise has a much greater risk of
raising the noise floor of many other stations across the whole
contesting segment of the VHF or UHF band. Running the numbers
reveals that anyone aiming to be a Big Gun in VHF contests has a
responsibility to keep their wideband transmitted noise floor below
about -130dBc/Hz at frequency offsets of 50kHz and more [2]. This
can be a major engineering challenge, and the performance of the
transceiver is almost always the most important building block.
The KSYN3A just about meets the -130dBc/Hz noise floor target at
frequency offsets of 10kHz or more... but according to the ARRL
review [1] the older KSYN3 achieves it much more comfortably, with
10-15dB to spare.
I have both a K3S and a very early-model K3. The K3S (with the
KSYN3A, of course) is used for HF contesting where smaller frequency
offsets are important. Meanwhile the old K3 is now used as a
transverter driver for 144MHz and above - and for that particular
purpose there are very good reasons *not* to replace the original
KSYN3.
73 from Ian GM3SEK
[1]
http://www.arrl.org/files/file/ProductReviewsForDeb/2015/pr112015.pd
f
[2]
https://thersgb.org/members/publications/video_archive.php?id=5703
Sorry, this talk is accessible only to RSGB members, but in a few
words...
G8DOH runs the numbers to demonstrate that the -130dBc/Hz target
for transmitted phase noise is necessary to avoid raising the noise
floor of other stations many kilometres away, and also many tens to
hundreds of kHz away across the band, whenever their high-gain beams
happen to be pointed at each other.
That calculation assumes the UK transmitter power limit of 400W PEP
output. For the US power limit of 1500W output, keeping all other
assumptions the same, the target for transmitted noise floor would
need to be better than -135dBc/Hz. The older KSYN3 can still meet
that more stringent target but the KSYN3A probably cannot.
-----Original Message-----
From: elecraft-boun...@mailman.qth.net [mailto:elecraft-
boun...@mailman.qth.net] On Behalf Of Don Wilhelm
Sent: 27 June 2018 14:23
To: hawley, charles j jr; Charlie T
Cc: elecraft@mailman.qth.net
Subject: Re: [Elecraft] [K3] factory upgrade to K3(s)
Chuck,
A big reduction in receiver noise floor and a huge improvement in
both
transmit and receive phase noise. It is like getting a new
transceiver.
If you are strictly a casual operator, those qualities may not be
important to you, but if you are a DX'er or a contester, or
otherwise
operate in crowded band condition, those things should be important
to you.
73,
Don W3FPR
On 6/27/2018 9:03 AM, hawley, charles j jr wrote:
I decided to bypass the replacement of the synthesizers. Could
you
describe the "huge" difference?
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