[Elecraft] KX3 2-meter module progress report

[Eric Swartz - WA6HHQ, Elecraft]

-------- Original Message --------
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