On 19/03/15 13:19, Tom W3TDH wrote:
On Wednesday, March 18, 2015 at 1:32:51 PM UTC-4, Jeff wrote:
On 18/03/2015 13:54, Tom W3TDH wrote:
On Wednesday, March 18, 2015 at 8:13:58 AM UTC-4, Jeff wrote:
On 18/03/2015 10:49, Brian Morrison wrote:
On Wed, 18 Mar 2015 06:44:55 -0400
Jerry Stuckle wrote:

I would not expect matching a 50 ohm antenna to a good quality filter
(which these are) would affect their response significantly enough to
cause a problem. After all, this is the exact type of operation they
are designed for.

The stop band performance is dependent on the antenna and filter
impedances out of band, at certain phases this can lead to a
re-entering stop band. I've been dealing with the consequences of this
in my day job very recently, it is a real and significant effect in
some circumstances. It's also not trivial to fix.



Indeed Brian, also if you look at the DCI filters there are quite
large returns in the stop bands.

Jeff

What are the effects of this on my proposed operation?


The effects are that it is not a good idea to parallel filters using
coax and tee pieces.

Jeff

Jeff

Are you deliberately trying to be obscure? "It's a bad idea" is not an effect but rather a rather vaguely stated opinion. Would you please advise what the deleterious effects of connecting the filters in that way would be.



Give that duplexers are just filters connected, in some configurations,
as T, I can't see an issue, provided you avoid introducing 'stubs' due
to lead lengths. If you either keep leads short or go to the trouble of
ensuring all avoiding critical lengths, you should be fine.

To be blunt, I think there has been a lot of 'theoretical flag waving'
in this thread. Having done much the same as what you wish to do and run
the system for years without any noticeable issues, I've tried to give
you the benefit of practical experience. I've three 'white stick'
antennas up, plus a 2m and 4m dipole. I don't run 220MHz as we don't
have an allocation there. Two of the white sticks are more or less
vertically aligned and may be 15 to 20 feet apart. The third is 50 feet
away, at the other end of the house. The 2m and 4m dipole are between
the first two white sticks.

Over the years the White sticks have been used for FM voice on 2m/70cm
and one on 6m. Also things like packet, APRS, etc. Basically, whatever
I'm experimenting / playing with at the time. The 2m dipole is dedicated
to a local repeater, and one or more of the white sticks is usually on
2m and 70cm voice with various duplexers being used. I've even tested a
'crossband talk through' unit (repeater) for a local Raynet team here.
I've only ever used typical amateur duplexers, simply as they were to
hand. It seems you have some better units available.

If you want to use the same antenna for a two radios on the same band,
things do get more complicated, but you've not said you want to do that.

I'd suggest you do some experiments and see how you get on, I'd be most
surprised if you have any real issues. Perhaps mount the antenna on a
ladder leaned against the house, as close as you can to the intended
position.