I will think about that as a potential kit. If ADC is essential, it
would make the most sense to take an analog IF sample out of the
receiver after the selectivity and have an outboard log amp and ADC
converter.
My Z10000 buffer amplifier should work as an IF sample isolation
amplifier without much change, or an even simpler circuit, such as an
FET follower would be possible since there is no need to make it a
wide-range universal product as with the Z10000 buffer amplifier. The
log amp, ADC and serial output is dead easy. It should have some input
bandpass filtering, however, to keep down the broadband noise.
If you are looking for a visual indication of level, my Z90/91 digital
panadapter provides 60 dB or so of on-screen (and on the data port)
dynamic range and an additional 30 dB of selectable attenuation. The
overall accuracy is within +/- 2 dB and most do better. There is no
provision for absolute calibration as it makes little sense to do this
considering the variable gain in the K2 ahead of the broadband sample,
so the readings are all relative. The Z90 Control software that I've
written includes a provision to log the data to a text file, with values
in dB, again arbitrary reference, so a fixed calibration would be
required should one be interested in specific absolute dBm values.
I have some AD8307 linearity data posted on my web site. It's at Page 29
inside the interim instruction manual that can be found at
http://www.cliftonlaboratories.com/Documents/Quick%20Operating%20Instructions.pdf.
The full range of 80 dB or so will not be achievable if there are strong
nearby signals due to filter skirt issues; hence the 60 dB or so usable
range quoted earlier.
The Z90/91's serial output protocol is open, so anyone that wants to
write their own program is welcome to do so.
Jack
www.cliftonlaboratories.com
[EMAIL PROTECTED] wrote:
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I would be the first to order a unit Jack
Theres some excellent plotting software just waiting for a S meter
interface as you describe.
http://www.g4hfq.co.uk/plphelp/plphelp.htm
Theres little alternative available for those seeking a accurate S
meter on a ham radio transceiver. Besides i see no harm as hams
being professional in our approach to signal measurements. After
all who would buy any test instrument today if it had a 200% error
in accuracy, but thats what we have today in every radio receiver
and transceiver.
Craig
VK3HE
On Tue, 17 Oct 2006 02:30:47 -0700 Jack Smith
<[EMAIL PROTECTED]> wrote:
One possibility for an "add in" S-meter module would be an AD8307
log
amp module paralleling the IF amplifier's input. This will give
you an
honest 80 to 90 dB linear output (db in, linear output), if you
can
manage the shielding, and close to 100 dB if you don't mind a bit
of
non-linearity at the extremes. To avoid loading down the IF amp
input,
you probably need a isolation amplifier.
And, of course, there's always a concern when mucking about inside
the
signal chain. The buffer amplifier I offer with my Z90 digital
panadapter samples the K2's IF at an earlier point, just after the
2N5109 post-mixer amplifier, but the design could easily be used
to
sample after the filters. (The Z90 uses an AD8307 log amp
detector, so I
have some experience with it.)
The log amp's output could then drive an external moving coil
meter, or
it could be digitized via an ADC and brought out on a RS-232
compatible
port for other purposes. Serial output would require an on-board
PIC and
would have to carefully constructed to avoid introducing unwanted
noise
into the K2, but an all-analog solution would be simple enough if
the
output device is to be a D'Arsonval meter movement.
If there's a groundswell of demand for such a beast I will
consider it
as a future kit offering.
Jack K8ZOA
www.cliftonlaboratories.com
[EMAIL PROTECTED] wrote:
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I also looked for a solution to the S meter calibration problem.
I
discussed the problem with Greg Ordy w8wwv Author of the great
program called S meter light. Unfortunately the K2 does not
return
8 data bits via the serial port so the calibration accuracy
would
be close to useless. If the K2 did return 8 data bits you could
obtain 0.1 db accuracy using Gregs program. 8 data bits
returned
via the data port is available on the 756PRO and several other
radios. Elecraft cloned the Kenwood command set which returns 4
or
5 bits or something like that.
Maybe Elecraft would consider this as a future external option
for
the K2 . It certainly would be a first for a ham radio, that is
having a inbuilt calibrated S meter. The crunched up S meter
bargraph is highly annoying and close to useless on the k2.
Craig
VK3HE
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