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RE: Computer Woes...

At 08:29 AM 8/9/2005 -0500, Reicher, James wrote:
>Speaking as someone who is NOT a rocket scientist, but as a ham, a
>software designer and developer, and a satellite enthusiast, could
>someone explain what is wrong with the Mode J article?  The authors
>clearly state that their conclusions are by no means scientific and make
>no claims that they've made measurements.  They merely state that this
>seems to work for them.
>Can't some articles be written for laymen?
>BTW, what is MOST embarrassing is mis-spelled words and poor grammar,
>especially in this day of spell-checking!   
>73 de N8AU, Jim in Raymore, MO

Jim and all,

This is in deference to Kevin who brought the fact to the attention of all
on the bb.

Simply put, the article purports to solve 70cm interference from third
harmonic output by a 2m Tx.  But the author inserts the diplexer (it is not
a duplexer) in front of the 70cm preamp to pass 70cm signals.  The
harmonics being on or close to the receiving frequency are passed thru to
the 70cm preamp and receiver with no effect to their strength.

The proper location for the diplexer is on the 2m Tx using the 2m filter
side of the diplexer which WILL reject the passage (transmission) of
harmonics on 70cm.

So the author says his method seems to work.  OK, but what he is filtering
is 2m high-level RF and keeping it from blocking the preamp stage...he is
NOT reducing harmonic energy (RF blocking is a separate problem from
harmonic interference).  Therefore the theory write-up is wrong about what
he is accomplishing.

The greater lesson here: is that there may be more than one reason that you
get interference to your receiver from your transmitter when operating mode
V/U (old term mode-J).  Therefore you need to find out which problem you
have and use the appropriate fix for that problem (the diplexer can be used
for either but is inserted at different locations depending on which
problem you have).

OK that may not be written exactly "simply" but I hope that the reader has
a grasp why the write up is wrong.

Ed - KL7UW 
BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb
Amsat #3212
Modes: V - U - L - S
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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