The Sherwood Engineering data says that for the 2 kHz spacing dynamic
range test, the K2's performance was limited not by nonlinearity
(intermodulation distortion) but by the K2's oscillator phase noise
sidebands. The same table says the same thing about the Ten Tec Orion's
performance in the 10 kHz spacing dynamic range test, and it is listed
as the top performer in their table. I think this data speaks more to
the excellent wide dynamic range performance of these radios more than
to the inferiority of their phase noise performance.
The Sherwood "Receiver Test Data Table" has a column labeled "LO Noise
Spacing" and another column labeled "kHz" immediately to the right. For
the K2 data near the top of the spreadsheet, I interpret the entries in
these columns as meaning that the single sideband phase noise power (in
a 1 Hz bandwidth) for the K2's oscillator spectrum is -123 dB relative
to the oscillator carrier power at 10 kHz away from the carrier
frequency (someone please tell me if I'm wrong). This is not too shabby
considering the price of the K2.
Cost is an important consideration. Poseidon Scientific Instruments of
Perth, Austrailia builds sapphire loaded cavity resonator microwave
oscillators which are quite popular with high resolution, high dynamic
range radar system designers. These sport SSB phase noise performance
of better than -145 dBc/Hz at only 1 kHz from the carrier at 10 GHz
carrier frequency! These can be used with regenerative frequency
dividers to produce even more phenomenal performance at lower (read HF)
frequencies, since the phase noise sideband spectrum extent also gets
divided by the same ratio as the carrier frequency. If you plan to get
one to replace your K2's oscillator, you might wish to know that they
cost more than $100k each. You might also wish to know that if you
actually want to measure the phase noise of one of these, you'll need
another oscillator phse locked to the first one, with as good or better
phase noise performance, not to mention a pretty fancy low frequency
spectrum analyzer and a few other peripherals, which means you'll need
to spend more than $200k.
Given that I'm only looking for weak CW signals on 40 Meters in the
presence of QRM from another ham a mile away from me, and not trying to
extract the doppler shifted radar pulse echo of a gnat at 200 miles
range from that of the mountain behind him, I'll stick with my original
K2 oscillator at about 0.5% of the cost.....
Bob
WB4TGG
[EMAIL PROTECTED] wrote:
In a message dated 16/03/05 22:48:02 GMT Standard Time, [EMAIL PROTECTED]
writes:
The K2's I've tested fall down on LO
phase noise performance. Also note that the K2 measurements on the Sherwood
web site state that the receiver performance is limited by phase noise. I
agree the RX works very well, but I've attracted comments on the air (when
running QRO) re transmitted phase noise.
------------------------------------------------
I wonder if there is an obsession with numbers. To place the matter in
perspective, the Sherwood Engineering web site does list the K2 which is serial
#3170 or about 2 years old? as being the 7th from the top of all the ham radio
receivers tested. The aspect of the effects of phase noise being only one of
many parameters that determine the final result.
I would presume that to measure phase noise needs the resources of a well
equipped professional lab. Whilst personally I am well equipped to carry out
servicing of radios from HF through to UHF, cannot even really scratch the
surface in terms of measuring phase noise. The professional communications
systems servicing organisation I worked for despite being well equipped for testing
from HF though to microwave in the field had little that could be used
seriously for testing phase noise except for probably some rather expensive HP
spectrum analysers that were issued only recently to maintain a new 8GHz digital
microwave system.
Before slagging the K2 one should take more seriously what it represents in
terms of outlay, costing only a fraction of cheapest HF transceivers available
on the market. Admittedly you have to build it yourself, but still the
performance of the K2 as what it was primarily designed for, a QRP CW transceiver
takes a heck of a lot of beating. There are shortcoming that occur with the
additional added components, though even these have been mitigated by later
modifications.
Do the persons reporting phase noise on K2 TX really know what they are
talking about or just pushing out some mumbo jumbo that just happens to be the
popular quotation of the day? To be frank most hams including myself would
probably not be be aware what phase noise is even if it jumped out and bit them.
Bob, G3VVT
K2 #4168
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