In order to connect a 2m/70cm radio and a 1.25m radio to a triband
antenna (2m/1.25m/70cm), one requires a triplexer and diplexer. I'd
like to cut down on the number and size of equipment to do this.

I asked Comet about making a single compact unit that takes 2m/70cm on
one port and 1.25m on the other. Mick Stwertnik told me that they
designed and specced it out, but the cost would be a prohibitive
$200-ish.

So I investigated making my own and found Jim Tonne's Diplexer program.
I asked him if he could extend the program to allow for designing
triplexers. He had some hackish solution that sort of worked, but he
doesn't know the math to do it correctly in the first place.

Where should I go from here?

--
David Griffith
--- Put my last name where it belongs

In article ,
(David Griffith) wrote:

In order to connect a 2m/70cm radio and a 1.25m radio to a triband
antenna (2m/1.25m/70cm), one requires a triplexer and diplexer. I'd
like to cut down on the number and size of equipment to do this.

I asked Comet about making a single compact unit that takes 2m/70cm on
one port and 1.25m on the other. Mick Stwertnik told me that they
designed and specced it out, but the cost would be a prohibitive
$200-ish.

So I investigated making my own and found Jim Tonne's Diplexer program.
I asked him if he could extend the program to allow for designing
triplexers. He had some hackish solution that sort of worked, but he
doesn't know the math to do it correctly in the first place.

Where should I go from here?

David-

I take it your 2m/70cm radio has a single input with an internal
diplexer. I use a Comet CFX-324 triplexer, but my Kenwood TM-742 has
three separate inputs.

It seems to me that your radio's input might satisfy the need for a
2m/70cm diplexer. What would happen if you connected your triplexer's
2m and 70cm ports together with a co-ax T?

You might check SWR looking into the T, to see if it was close to 1 to 1
on both bands with the antenna and 1.25m ports terminated.

Rather than using the triplexer/diplexer combination, there might be
less loss if you use a separate antenna for 1.25m, with just a diplexer
for 2m/70cm.

Fred
K4DII

In article ,
Fred McKenzie wrote:

Rather than using the triplexer/diplexer combination, there might be
less loss if you use a separate antenna for 1.25m, with just a diplexer
for 2m/70cm.

David-

I was not thinking. With a separate 1.25m antenna, no duplexer would be
needed with your radio for the 2m/70cm antenna! That might be the
simplest arrangement.

Fred
K4DII

Fred McKenzie wrote:
In article ,
Fred McKenzie wrote:

Rather than using the triplexer/diplexer combination, there might be
less loss if you use a separate antenna for 1.25m, with just a diplexer
for 2m/70cm.

I was not thinking. With a separate 1.25m antenna, no duplexer would be
needed with your radio for the 2m/70cm antenna! That might be the
simplest arrangement.

I've reached the same conclusion. Thanks everybody.

--
David Griffith
--- Put my last name where it belongs

Hey OM:

Here I thought this was the homebrew forum. The separate antenna is the easy way out,

I'd go with sum pin diode switching and a frequency sense circuit to switch the pin diodes. Or there are some good mercury wetted relays out there that can handle 100 watts.


On Thursday, December 6, 2012 4:15:39 AM UTC-5, David Griffith wrote:
In order to connect a 2m/70cm radio and a 1.25m radio to a triband

antenna (2m/1.25m/70cm), one requires a triplexer and diplexer. I'd

like to cut down on the number and size of equipment to do this.



I asked Comet about making a single compact unit that takes 2m/70cm on

one port and 1.25m on the other. Mick Stwertnik told me that they

designed and specced it out, but the cost would be a prohibitive

$200-ish.



So I investigated making my own and found Jim Tonne's Diplexer program.

I asked him if he could extend the program to allow for designing

triplexers. He had some hackish solution that sort of worked, but he

doesn't know the math to do it correctly in the first place.



Where should I go from here?



--

David Griffith

--- Put my last name where it belongs

Maybe I am out of line here, but what you are asking is dumb.

Diplexers / Duplexers - what ever you want to call them are by nature only about 50% efficient.
This means that you are throwing away half of your transmitted power and half of your capiable receive in the diplexer.. DUMB!

Antenna manufacturers makes multiple tri band antenna's.
But in order to do it efficiently - you have to start with a resonant antenna.

Because 70 cm and 1.25 CM are not multiples of wavelengths of 2 meters - the best you can come up with is a compromise antenna...

The Diamond V2000 is a good example of this.
It does 2 meters, 70 cm and also 6 meters...

They do this by making the antenna into segments and placing capacitors between the sections. The capacitors divides the antenna into segments.

The RF looks down the array, till it finds the length it is looking for and then it uses it, much like a Yagi Uda antenna for television...

The Diamond X 510 is another example - it uses 3 segments and has excellent gain.... Problem is when you make a 2 meter antenna 18' long, you end up with a top heavy vertical that snaps off when it is placed in too much wind or when it gets old and brittle.

The antenna you are looking for was already designed a long time ago.
It is called a Discone antenna...

You make the vertical whip one length, you place at least two ground radials underneath of a resonant length and put the radial system directly under the antenna.

Diamond makes a excellent example.
No need to home brew a antenna in this day and age, except for experimental purposes.

I get disgusted when I listen to the 2 meters and a couple of noob's comes on and starts telling me how they are hams because they build a J Pole antenna and are using walkie talkies and they are able to get into the one local repeater and can talk to people because the repeater is part of a linked repeater system - VOIP.....

If it was not for that repeater being linked, they would have no one to talk to, and when the 10 years comes up for the license, their call sign would be beside all the others from their VE test session that did not advance to General or higher, or did not put their license to good use while they held it.

Channel Jumper wrote:

Maybe I am out of line here, but what you are asking is dumb.

Diplexers / Duplexers - what ever you want to call them are by nature
only about 50% efficient.
This means that you are throwing away half of your transmitted power and
half of your capiable receive in the diplexer.. DUMB!

It is not the diplexer that is dumb, it is your remark that is dumb.

"Rob" wrote in message
...
Channel Jumper wrote:

Maybe I am out of line here, but what you are asking is dumb.

Diplexers / Duplexers - what ever you want to call them are by nature
only about 50% efficient.
This means that you are throwing away half of your transmitted power and
half of your capiable receive in the diplexer.. DUMB!

It is not the diplexer that is dumb, it is your remark that is dumb.

Most of CJ's remarks are that way. I doubt he has ever measured or checked
on the splitters. I have and they are usually less than a half of a DB loss
in them. I am thinking more like a .3 or so of a db loss, but it has been a
while. Anyway from the best I could tell, it met the spec on the case of
the splitter. That was with a HP 8924C test set.

Fine - but if you want to be right - you first have to prove why you think that you are right.
A good example comes to mind.
In the 1970's Avanti came out with a antenna called the Moonraker IV
It was horizontally as well as vertically polarized.
Probably not a new idea, but one thing that you could get with that antenna was a switch which allowed the use of one coax for two antenna's.

Don't you think that it would be easier to use a Diamond X 510 antenna and a 220 MHz and switch them up on the tower then it would be to use a duplexer and try to use both at the same time.

220 is dead except for maybe in the city somewhere where someone has a repeater... No manufacturer makes a 220 transceiver, except as a after thought - the only one I see listed in the AES / HRO catalog has a output of 1 watt.. I guess they use it to control a repeater site or something like that.

200 Mhz offers the benefits of being a little more ground following - like 2 meters, while being a little quieter - like 70 cm.. Rule of thumb - noise is inverse the square of the frequency.. The higher in frequency you go, the less noise you have to overcome. Probably the reason why cell phones are 869 - 913 Mhz and public service is going to 800 Mhz and the T band.

Now I know I am dealing with a CB'r

You cannot use a splitter to connect two antenna's together, and a splitter is not a diplexer.
Even if all you are going to do is use the antenna's for receive only, you will still run into problems..
If it was a television antenna - we use a con - joiner - it basically isolates each antenna from each other, is real good for isolation to prevent multipath, but again, you throw away half of the signal in the Con - Joiner.

A splitter by nature is wasteful, a 2 way splitter should be unilateral, each port receives 50% of the signal.
BUT
When you advance to a 3 way splitter, they are not unilateral.
Unless it is a expensive splitter, you usually end up with one port having about 45% of the signal and the other two sharing the remaining 25% / 30% - between the two remaining ports.
This is the problem I deal with most often with reception issues.

The op buys a splitter, then figures that the television reduces the amount of received antenna power and so they buy a distribution amplifier and they figure that if they amplify the signal it will get better.
The problem being that you not only amplify the signal, you also amplify the noise, plus the amplifier makes some of its own noise.

So we steer them towards a mast head pre amplifier and it solves some problems but not all.
If the antenna is not aimed at the strongest part of the signal - we get little or not reception, or the reception we do get with digital signals is sometimes corrupted by radio waves arriving at the antenna at different times.

I've already explained dipole antenna's - which are a balanced antenna, or a vertical antenna.. So there isn't much of anything else to say except good bye on this one.

A Diplexer filters out the other frequency signal - and con - joins the two antenna's together on one feed line. Or makes believe to the receiver that there is two seperate antenna's, or keeps the rf out of the other side of the transceiver on a dual band transceiver.