[TenTec] THANK YOU AND APOLOGY - for Billy

[Rick - DJ0IP / NJ0IP]

Sweet.  I like that program.  Thanks Gary.

I think most people know this goes on.  It's just difficult to calculate
this stuff yourself.
What is still little known is how bad broadband noise can be at multi-tx
stations if someone brings along a low cost radio..
And it is very unpleasant when you tell someone his brand new radio is
dirty.
They just don't want to believe it.

I ran a lot of multi-single contests in the 1990s using a pair of Omni VI's
(one for RUN, one for searching for multis).
I did not have band filters initially.  Later I bought two complete sets of
Dunestar BPFs.

We still could operate in the same room (without filters) with antennas
located on the same roof of the same large building (4U1VIC), but we did
have certain frequencies we had to avoid.  We only had trouble with
harmonics.  Of course at the larger events with 6 stations transmitting at
the same time, intermodulation would be a major factor.

On one of the 3 expeditions I did to 4U1VIC, one of the guys brought his
Japanese radio with him and insisted we use it for the multi station.  We
quickly swapped it out for the second OMNI VI because it was overloading.
We were running about 700w.

We (BCC) began using band filters in 1988.
One year earlier on our first team expedition, we had none and it was pretty
much a disaster - also because we had tri-band beams.  After that we only
took monobanders on our big expeditions.  Of course the little expeditions
with just a couple of guys take tri-banders from 'you know who'.

Our larger multi-multi stations now use filters and stubs when needed.

I have never personally used stubs.
I have never owned a multi-multi station either.
Kind of tough to do when you can only put up one single antenna.  ;-)

Tnx agn for the link.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Gary - AB9M
Sent: Monday, July 28, 2014 8:39 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy

Rick,

go to http://www.arcticpeak.com/radiopages/intermodulationproducts.htm and
plug in 14020, 21020, and 28020 in as the frequencies of the three radios in
your example. Look at the odd order results of the PA mixing products which
WILL occur in close proximity when there is NO bandpass filtering to
attenuate out of band ingress and egress of unwanted products.

Yes, we need to be selective in using the best radios for a multi TX
operation.  We also need to provide adequate bandpass filtering so that no
IMD products are produced  in the PA and first IF of other on site radios.

73 & DX,

Gary - AB9M
-----Original Message-----