50-70 MHz duplexer design

[PA3CEV]

Hi,


I have a G0KSC 5-4 el Yagi, works fb.

Now I'm looking for a duplexer design to be able to use the aerial for both bands on seperate trx's at the same time.

Any hints?

vy 73 Eric-Jan PA3CEV

[GW8ASD]

Try here.
http://www.crosscountrywireless.net/diplexer.htm
A very helpful company.

Cheers

Tony

[M5TXJ]

Hi Eric-Jan,

There is a design to make a diplexer from RG-213, I'm using one here with good results. It is quite bulky but here that isn't a problem as all coax's are behind a false wall at the back of the shack. If you would like the construction details just let me know.

73 Dave 'TXJ

[G4ASR]

The coaxial design has much better characteristics than the lumped circuitry option. Insertion loss, port isolation and power handling are much superior.
The coaxial version will handle as much power as the feeder can cope with!

I have permission from the RSGB to allow the article (.pdf) to be distributed to anyone who asks me.

73 David G4ASR
VHF Manager, RSGB
VHF columnist, Radcom

[GM4FVM]

G4ASR kindly sent me the article about this diplexer. I built it a couple of months ago and I have finally got around to using it.

It is about 3m by 1m. I have fixed it up in the attic. The insertion loss is 1dB or less, too low for me to measure. It has added to the SWR, but not significantly.

The article dwells quite a bit on the dire consequences of one of the stubs becoming accidentally disconnected. To counter this I built a light timber frame and fixed the co-ax to that. I used T-pieces for the co-ax joints. As was suggested I built it exactly to the stated dimensions using RG-213 co-ax.

I did a lot of testing before I actually put full power into something connected to another rig. My plan was simply to allow cross band working with no risk of transmitting into an open or short circuit due to a misplaced switch. However, it is possible to listen on 6m while transmitting on 4m, and vice versa - though I am not sure why I would want to do that. Being able to listen on both bands at once is certainly handy, with the bonus of just one antenna on my short mast.

Probably, if a lumped component diplexer had been available I would have bought one. However building one which works as well if not better than the commercial one has a very interesting experience.

To make it a perfectly circular process, the first station I worked using it was G4ASR.

Jim
GM4FVM

[GW8ASD]

However, it is possible to listen on 6m while transmitting on 4m, and vice versa - though I am not sure why I would want to do that.
Jim
GM4FVM

I've had lots of cross band QSOs transmitting on 4M and listening on 6M.
Less so since more countries have had 4M but previously -
OH
SP
DL
F
I
OE
etc.

Recently there are reports of stations in the Ukraine asking to be called on 4M.

The Crossband Centre of Activity has recently moved to 50.285 MHz

Cheers

Tony