Jim, from what you have told us, I cannot see any reason for having all
three signals in time phase, i.e., simultaneously keyed.
so, why not think about sequential keying? Key Rig A. At the conclusion of
that code character, key Rig B. At the conclusion of its code character,
key Rig C. And so on.
That time diversity should greatly minimize the possibility of
cross-products, etc. and the other problems that you have noted since only
one transmitter is actually emitting at a time. Also, it seems to me that
time diversity in keying would be far simpler to implement than space
diversity in your antenna system.
Perhaps I am missing a point in your system here, but seems like sequential
keying would be much more appropriate even though it will require the
development of the necessary keying logic.
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
Bill Miner wrote:
>
> Jim,
>
> I have been watching your posts regarding this project and I do have one
> caution for you! If you do not have enough isolation between
> transmitting antennas it is possible to get external RF back into the PA
> of any of your transmitters and that PA will act as a high level mixer.
> One symptom of this could be an increase in SWR. At VHF/UHF and
> microwave frequencies the fix for this is the use a circulator or
> directional coupler on the output of the transmitter. In your case I
> believe the easiest method would be to make sure you have plenty of
> distance between transmit antennas. This would mean
> no antennas on the SAME boom! The most common of the mixing products is
> 2A+B or 2A-B. As I am sure you will see.... some products will be
> outside of the ham bands and may get you into possible trouble with
> some government agency!
>
> I believe a good source for additional information on this subject would
> be someone at W1AW since they have lots of experience with multi
> transmitters. Talking to W1RFI might be a good place to start.
>
> I hope this is helpful and I hope you are successful with your project.
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