[amsat-bb] Re: Success - and thanks!
n5td at vvm.com
Mon Aug 13 14:21:11 PDT 2007
Congratulations to Scott, NW2S, on his recent successes
in working satellites.
In reference to the stated problem:
> The other downside is that even with two transceivers, I'm
> unable to work full-duplex. The two bands on the antenna
> use separate elements and feed points, but share a boom.
> Transmitting on 2m completely overloads the front-end of
> the IC-7000. While full duplex would be useful, it's not
> absolutely necessary.
May I mention some old ideas that could improve the
"Mode-J" desense, which is a very common problem.
There are several ways to improve Mode-J desense.
1.) One is by using a combination of a "Mode-J Filter" on
the 2-meter side, "MMf200-7" which attenuates harmonics
outside the 2m band that can plague the 70cm receiving side,
and a "PSF-432 Bandpass Filter" added on the 70cm UHF
side. (I have several sets of these filters, which are obtainable
from Spectrum International, Inc., Concord, MA, and they
work very well!)
2.) Physical separation of antennas, but I don't recommend
this often because it simply doesn't satisfy the needs of most
3.) By the inverted use of a "2m/70cm Diplexer" (commonly
called duplexers now) connected in the UHF side, which has
the common port connected to the UHF antenna, the 70cm
port connected to the UHF radio input, and the 2-meter port
connected to a small 50-ohm dummy load of some kind.
(There used to be an example of this on the AMSAT site.)
Additional comments: A few other items could have some
affect, such as proper grounding, the amount of uplink power
used, circular polarization, and the use of high-quality coaxial
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