Trevor, long time ago I tore apart a name brand diplexer. It was just
filters as you were thinking about. I believe it was rated about 0.5 dB
loss.

I have a friend who has a truck and runs quarter waves. They work great. A
long time ago I was talking to him as he headed north on I75. We continued
to talk on the 442.3 MHz repeater in Miamisburg until he passed the 110
mile marker, which is about 70 miles. He went over the ridge at that point
and dropped out.

Jim

On Fri, Aug 21, 2020, 11:38 AM Trevor Clarke via mvus-list <
mvus-list@lists.febo.com> wrote:

Trevor, I think you have a good idea regarding using two antennae. I do agree with Tom’s comments but assuming that you are going to mount the antenna at a convenient spot like on the trunk with a trunk lip mount, you will likely appreciate having a little longer antenna. If mounting on the roof, especially a SUV or Van or truck - then I recommend just using the 1/4 wave. On my SUV, I have one 1/4 wave 220 - about 12” long AND another 1/4 wave 146 MHz - about 19” long. Both antennas are on the roof of the SUV.  I have two radios - the 220 goes to 220 of course and the 2M whip goes to the 2M/440 dual bander. This acts as a 3/4 wave on 440 and the SWR is 1:1 so the radio loves it on both bands. But on 440, being 3/4 wave, the radiation angle is pretty high and not as good as a 1/4 wave on 440 but I rarely use 440 so no problem.

I gather that you may have one radio - a triband unit. I have used a Comet triplexer on an Anytone triband radio. I ran a 220 antenna to the 220 port and recombined the 2M and 440 outputs of the triplexer with a 2M/440 diplexer so I could use a second antenna for both 2M/440. This gets a little ’un neat’  but it works. If you have a radio with 3 separate antenna ports, that would be much easier. I was using a Diamond triband whip on the Anytone radio for a while with the antenna mounted on the trunk lip of my car.  It actually worked well on 220 but on 2M, it’s gain is just the same as a 1/4 wave whip. So I went to a 2 antenna setup. Now I use a 5/8 Larson whip for 220 and a 2M/440 Larson for those bands with 3 dB more gain than the triband antenna had.  Works good.

You can definitely make the diplexer (Comet calls it a duplexer) or triplexer with coils and discrete caps.  You should look inside a Comet unit to see an example. The ins loss is very low and usually they can handle 100 to 200 W.

73
Steve
K8DZ

Tom,  are you telling us that your duck does not have sense enough to duck?

Trevor,

I share the other opinions that height is more important than a couple dB
extra
antenna gain.  And it better fits the KISS paradigm, to boot.

All, I've often wondered what the technical distinction is between a
diplexer and a
duplexer.  One rather succinct explanation I read not long ago was that if
it costs
something like $1000 or more, it's a duplexer.  If it only costs around
$100, it's a
diplexer.  The writer went on to say that it was basically a matter of
performance
and how close the two frequencies could be to each other and still achieve
useful
isolation and loss numbers.  For the case of 2m / 70cm, I believe that a
diplexer
should fit the bill.

Dana

On Fri, Aug 21, 2020 at 11:36 AM Tom Holmes via mvus-list <
mvus-list@lists.febo.com> wrote:

Thanks for all the suggestions. I'm looking at 2 antennas for two different
setups. The radio is a tri-band with 1 output and will usually be in my SUV
but will occasionally come into the house. I've got a 2m/70cm antenna in
the house which will likely be fine as I probably won't use 220 much. In
the car I would potentially use 220 more often so I was looking at a couple
of tribanders including the nagoya tb-320a (I've done well with their
portable antennas). It's 2.15/3.8/5.6 dBi with <1.7:1 SWR (per a couple of
user reviews) across all 3 bands. Overall a nicely spec'd antenna for <$60
but the 2m gain isn't fantastic and that's the band I'll use most,
especially simplex (I do a fair amount of DMR on 70cm but have no problems
hitting the repeater in town from quite a ways out).
The options I'm considering are:

1. get the triband and use it as-is for a while. if the 2.15 dBi is not
   enough for good simplex contacts I'll get a dedicated 2m antenna and build
   a </>200MHz or so diplexer.
2. use a decent 2m/70cm antenna and a dedicated 220 with a
   bandpass/bandstop diplexer. more difficult to build but gets the 2 main
   bands going immediately and for a low cost
3. I could go with 3 antennas and a triplexer but I don't think it'll buy
   me too much and the cost if must higher

I lean towards option 1.

On Fri, Aug 21, 2020 at 1:08 PM Steve Koogler via mvus-list <
mvus-list@lists.febo.com> wrote:

--
Trevor R.H. Clarke
Computer Science House
Rochester Institute of Technology
retrev@csh.rit.edu
http://www.csh.rit.edu/~retrev/

My understanding is that yes, it's about the separation of the frequencies.
The rule of thumb I use is, same band=duplexer, different bands=diplexer.

On Fri, Aug 21, 2020 at 1:17 PM Dana Whitlow via mvus-list <
mvus-list@lists.febo.com> wrote:

--
Trevor R.H. Clarke
Computer Science House
Rochester Institute of Technology
retrev@csh.rit.edu
http://www.csh.rit.edu/~retrev/

Yeah, I guess so. He was kind of hardheaded about that.

Tom Holmes, N8ZM

-----Original Message-----
From: mvus-list mvus-list-bounces@lists.febo.com On Behalf Of Dana Whitlow
via mvus-list
Sent: Friday, August 21, 2020 1:17 PM
To: Midwest VHF/UHF Society Mailing List mvus-list@lists.febo.com
Cc: Dana Whitlow k8yumdoober@gmail.com
Subject: Re: [mvus-list] diplexer design

Tom,  are you telling us that your duck does not have sense enough to duck?

Trevor,

I share the other opinions that height is more important than a couple dB
extra
antenna gain.  And it better fits the KISS paradigm, to boot.

All, I've often wondered what the technical distinction is between a
diplexer and a
duplexer.  One rather succinct explanation I read not long ago was that if
it costs
something like $1000 or more, it's a duplexer.  If it only costs around
$100, it's a
diplexer.  The writer went on to say that it was basically a matter of
performance
and how close the two frequencies could be to each other and still achieve
useful
isolation and loss numbers.  For the case of 2m / 70cm, I believe that a
diplexer
should fit the bill.

Dana

On Fri, Aug 21, 2020 at 11:36 AM Tom Holmes via mvus-list <
mvus-list@lists.febo.com> wrote:

could

door

two

loss

electrically

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