On 3/18/2015 3:28 AM, Jeff wrote:

They do not have to be short - but as long as you have a multiple of 1/2
wavelength between the two diplexer inputs, each input will see the very
high impedance of the other input. Rather easy, since you are operating
on the third harmonic.

Don't forget that it is not a simple as being 1/2 wavelength long, you
have to take into account the input impedance of the filer which may
substantially modify what you are looking at, and may load the other
filter affecting its response. The DCI dual band filters are aligned as
a unit so those sort of effect can be taken into account.

Jeff

The input impedance of the filter active filter would be 50 ohms, so no
loading. And the impedance of the other filter would be very high.

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.

You *might* be able to measure some effect in a lab, but in the real
world it won't make any difference.

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On 3/18/2015 6:49 AM, 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.


True. However - this was specifically made for 144/440 mhz with 50 ohm
impedance. As long as these are the bands he's using and he stays
within a reasonable range of 50 ohms, I don't see what the problem would be.

Again - these units are DESIGNED for this operation. What good would it
be to design and sell such an item if it doesn't work?

DCI has good engineers who know their stuff. Their equipment is top
quality. And while I've never tried this particular unit, I know they
would not let something with your perceived problems out the door.

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On 3/18/2015 1:52 PM, Brian Morrison wrote:
On Wed, 18 Mar 2015 10:55:18 -0400
Jerry Stuckle wrote:

Again - these units are DESIGNED for this operation. What good would
it be to design and sell such an item if it doesn't work?

Well, not much, sometimes you can get caught out by something
unexpected when a change is made to fix a problem and does so but then
you discover some unintended consequences.

That's exactly what I have been dealing with in a system where it's not
easy to measure the frequency response of a combined antenna and filter
in a radiated test. But we managed to do it, just took a while to
create an appropriate test system.


It may not be easy to measure when that isn't your main business. But
for a company which is, I'm sure they have the appropriate equipment and
procedures.

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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?

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On 3/18/2015 1:32 PM, 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

Except he is not paralleling filters. The two diplexers feed different
radios.

And how would YOU suggest he hook them up?

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On 3/19/2015 5:32 AM, Jeff wrote:

Except he is not paralleling filters. The two diplexers feed different
radios.


If you had been keeping up with the thread that was exactly one the
question that the OP was asking: could he parallel filters using coax
and tee pieces.

I have suggested a solution that only uses diplexers; the addition of
filters will probably not make much difference to the resulting
performance unless the radios in use have extremely high harmonic or
spurious outputs or produce very excessive wide band noise or there is
interference from 3rd party out of band transmitters. What will almost
certainly be more of a problem is the de-sense caused by the in-band
transmissions between the voice and data radios. Filtering that out is
not a trivial problem, at least at the spacings available at 2m.

Jeff



I have been keeping up with the thread, Jeff. And he was asking about
using his diplexers. It was others who though adding filters would be
helpful. I have never suggested this setup.

But what is the suggestion you made? And how is it different than the
one I made? And exactly what is wrong with my suggestion?

And he was not asking about desense caused by using different radios and
antennas on the same band. Tom understands this.

But it seems some people keep wanting to to keep going off-topic with
extraneous information not related to the original question.

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On 3/19/2015 12:41 PM, Jeff wrote:

I have been keeping up with the thread, Jeff. And he was asking about
using his diplexers. It was others who though adding filters would be
helpful. I have never suggested this setup.


You obviously have not, because this is what the OP asked:

"Can I anticipate any ill affect from placing a coaxial Tee fitting
across the output of one filter and connecting a jumper to the output of
another filter in order to connect the transceivers to the multiband
antenna? Would there be any additional concerns be raised if one of the
two filters was the dual band model with separate connections for each
of it's two bands on the end being used for input connections? What
about if I make up the assembly using Three separate filters with Two of
them connected to TEE fittings"

That specifically asks about filters not diplexers.

Jeff


In this case the "filter" he is referring to is one section of the
diplexer. Not necessarily the most technical description - but also not
inaccurate.

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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.

--
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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.

On 3/19/2015 11:26 AM, Brian Reay wrote:


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.


I agree. It should work just fine. People do it all the time. This is
really not that much different than what most repeaters use (except, of
course, repeaters use very sharp filters and transmit and receive on the
same band).

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.

snip

You're right, Brian. A lot of flag waving with no basis in fact, by the
usual suspects.

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