[Elecraft] [KX3] Re: KX3 2-meter module progress report

[Edward R Cole]

Wayne/Eric:

I'm not trying to reply for David, but we have similar objectives for our KX3.

Using 50-54 MHz as IF for the 2M module is genius in my 
thinking.  28-30 MHz too often used as IF for higher bands limits use 
to few frequencies.  Having the full 2m band is very nice for 
multiple uses on this band.

I am not subjected to strong out of band signals as many are so this 
is not as important to me.  In many of my applications I will have a 
preamp ahead of the radio so use of a band-pass filter could be 
used.  Of course one must provide protection of a preamp when 
transmitting since the KX3 does not provide separated Rx antenna.  RF 
switched preamps are available.  I have on in use on a 2m yagi 
dedicated to FM use.

I think if overall frequency stability is 10-Hz is will suffice for 
use with JT65 sw.  The lowest decode window I use is 20-Hz and that 
will work on 2m-eme.

For use with mw transverters one must remember that the frequency 
error of the IF radio is additive to the overall frequency 
error.  This is not as bad as freq. stability issues for LO's driving 
mw multiplier chains.  PLL synthesizers are gaining acceptance with 
mw'ers as super stable LO's.  Since historically freq drift on mw 
frequencies was measured in terms of KHz's, an overall error of 10-20 
Hz is a huge improvement.  Knowing your mw frequency accurately 
improves chances of detecting mw signals since one is not tuning over 
half the band for below noise signals while pointing antennas with 3 
degree beamwidths.

JT65 and its variants are what I have in mind for weak-signal use on 
mw's up to 10-GHz.  Again the 144-MHz IF error is added/subtracted to 
the LO+multiplier chains freq. error.  I am using phase-locked LO's 
above 1296 MHz so essentially all error is that of the KX3-2M, alone.

73, Ed - KL7UW, 600m to 3cm
----------------------
Subject:        [KX3] Re: KX3 2-meter module progress report
Date:   Wed, 16 Oct 2013 11:20:44 -0700
From:   Wayne Burdick <n6kr at elecraft.com>


David Anderson <gm4jjj at yahoo.co.uk> wrote:

  > What is the planned receive frequency coverage of the 2m module?

144-148 MHz, minimum, for full sensitivity. However, we allow tuning 
well above
and below this range (at least 20 MHz), even though sensitivity 
gradually falls
off. For example, this allows copy of weather-band stations at 162 
MHz which are
generally very strong, at least at my QTH near San Francisco.

  > Is there any 144-146 band pass filter to limit strong out of band signals
from pagers and other fixed services outside the band?
  > I have in the past studied our RF environment on the band.
http://www.gm4jjj.co.uk/preamp/index.html

Filtering is included at all stages of the receive path, including a 
10-element
band-pass filter ahead of the mixer. But because the module is so 
small, there's
no room for a high-Q, tuned band-pass filter at the input; instead, we use
low-loss low- and high-pass filters to preserve sensitivity. To 
reduce the need
for narrow input filtering, we used a high-intercept LNA that is 
likely to do OK
in all but the very worst RF environments. This increases current drain of the
radio on 2 meters somewhat compared to other bands, but we felt it was an
acceptable tradeoff.

Since the KX3-2M module has its own antenna jack, you could use an external
high-performance 144-148 BPF if required. It isn't clear from your sweeps (the
URL above) whether this would be necessary for your use of the 
module, though it
certainly wouldn't hurt.

  > Is the frequency stability basically the same as that of the KX3?

HF/6-m and 2-m stability are correlated since they're referenced to 
the same LO.
For CW/SSB, we strongly recommend performing the KX3's extended VFO 
temperature
compensation procedure, providing typical stability of +/- 2 to 3 Hz 
on 6 meters
and +/- 5 to 10 Hz on 2 meters. The standard compensation (done at 
the factory)
yields greater variance, but is entirely sufficient for FM or AM operation. We
hope to simplify the extended compensation procedure in conjunction with the
KX2-2M product release.

In both transmit and receive mode, the operating frequency is subject to small
asynchronous corrections arising from temperature changes. On 6 
meters and lower
these corrections have a granularity of 1 Hz. On 2 meters they're 
about 3 Hz due
to the conversion scheme used. We're looking into improving the 
granularity on 2
meters, but the overall range of corrections--about +/- 5 to 10 
Hz--is about as
good as it gets on this band with a conventional temperature-sense IC.)

  > You will have gathered that my interest is weak signal work on 
144 and as an
IF for microwave transporters.

What modes do you plan to use?

73,
Wayne
N6KR


73, Ed - KL7UW
http://www.kl7uw.com
dubususa at gmail.com
"Kits made by KL7UW"