Matching old equipment to 50 ohms (WS22 SET)

[ChristianFletcher]

I wanted to ask your advice about matching old transceivers to modern 50 ohm antenna systems. I normally use a long wire antenna and this is matched to my 50 ohm modern equipment using automatic ATU installed at the mast head.

My understand of vintage equipment is they would normally be driving end fed antennas long wires and whips high impedance. This is easy for receiving just requiring a resistor and capacitor but not so easy for transmitting.

Can I simply tune the output from the transceiver to 50 using a manual ATU connected in reverse ?

This questing also relates to matching of test equipment to older transmitters as again all my test gear is nominally 50 ohms.

[MichaelR]

I thought the WS22 had its own inbuilt ATU , you should have a Roller coaster built into the unit , is that missing?

Mike

[ChristianFletcher]

Yes the WS22 does have a roller coaster and since posting I have used just that but its on the last turn of the drum. I just use the set 22 as and example. Perhaps my question should be:

I have various portable transciever mostly vintage, that are designed to work with whips or rod antennas. Is it possible to match these to 50 Ohms coax feeds.

Thanks Christian

[jimmc101]

The simple answer is yes, assuming the ATU has a sufficient tuning range.
Remember that in order to match a short antenna of impedance R-jX the ATU has to have an output impedance of R+jX (conjugate match).
To use it in reverse the ATU must 'look like' the R-jX of the original antenna; as long as the output capacitor of the ATU can cover this range (+jX to -jX) then all should be well.

Jim

If you want to start designing matching circuits take a look at RFsim99
http://www.101science.com/RFSim99.exe
and look in the tools section.

[ChristianFletcher]

Thanks for the replies. I guess the best answer is just to give it a try.

Regards Chris

[Skywave]

Originally Posted by ChristianFletcher

I wanted to ask your advice about matching old transceivers to modern 50 ohm antenna systems. I normally use a long wire antenna and this is matched to my 50 ohm modern equipment using automatic ATU installed at the mast head.

Have I read that right? You have a LW aerial and a remotely-controlled ATU (up at the mast head, where the LW aerial is attached) & which then (presumably) feeds down to your transceiver which wants to 'see' a nominal 50-ohms impedance?

I am asking for confirmation of my understanding, please, since this strikes me as an unusual arrangement which, in turn, could - not necessarily - give problems.

Thanks,

Al. / Skywave.

[Herald1360]

Sounds like a neat way to get the signal up to the LW and away from nearby buildings without unwanted radiation or losses......

Isn't it usually the way to operate with a remote whip antenna- like one on top of a building with the TX some floors down?

Chris

[Skywave]

Is it a "neat way" though? What about the earthing arrangements for the LW (read Marconi) aerial?
Let's see what the OP comes back with.

Al.

[Sean Williams]

Er, I would hazard a guess that Christian is using a "Smart Tuner" - these are designed to be Co-ax fed at 50r, and will drive anything over about 9ft of wire.

The "earth" connection can be a spike, or radials, or a counterpoise.

I use one here - with judicious use of switching I can convert from an end fed to a loop antenna.

This used to work perfectly when fed from a TCS12 transmitter - I used to tune the transmitter up into a 50r load, then switch to the antenna - simple!

Cheers
Sean

[Skywave]

Christian Fletcher: "I have various portable transciever mostly vintage, that are designed to work with whips or rod antennas. Is it possible to match these to 50 Ohms coax feeds?"

In concept, yes: the use of a Pi-type AMU (ATU) is the classic approach for feeding end-fed wires such as you describe. In essence, what this device does is to transform the 50-ohms 'wanted load impedance' of the transmitter output into an impedance that matches that presented by the aerial at the end of its feeder where it connects to the AMU. Ideally, the match will be such that any reactance is tuned out (see jimmc101's post above) by the AMU.
However, note:
(a) that the length of the feeder (in this case, a single wire, not 50-ohm co-ax) for a LW and the length of the LW 'proper' will require the settings of the AMU to be adjusted as you change frequency;
(b) that the spacing of the vanes in the variable capacitors in the AMU will often need to be greater than that typically found in a receiving-type matching unit; to some extent this depends on the power you are running;
(c) since this AMU will be at the 'table-top' end - as opposed to 'up in the air', as per your existing arrangements - a good earth connection will be required at the AMU.

HTH

Al. / Skywave.

[Skywave]

Sean,

I am not familiar with the type of AMU that Christian and yourself are familiar with, however there is one thing here that puzzles me. Since the AMU is 'up in the air', how is a low-iimpedance ground connected to it that a LW requires for correct operation? Or is it simply a matter of relying on a 'vertical counterpoise'?

I'm intrigued.

Al. / Skywave.

[ChristianFletcher]

Sorry for late response I been away.

The smart tuner ATU is installed at the top of the roof and is hidden in a bird box. I have a wire running about 50 metres to a tree at the bottom of the garden. The long wire is automatically matched to 50ohm feeder by the smart tuner when I key the transmitter.

I also have an PME earth free installation just to complicate things and have a counterpoise about 150 meters long running at gutter height around the perimeter of the my house. Not perfect regarding RFI, but I run low power and never have a problem. I also have about another 200 metres running 1m above the ground along the garden wall using 10mm SQR insulated cable.

The ATU appears to tune perfectly 1:1 within a second and my maximum power is 150 watts. Most of the time I run about 20 watts, but to be honest I am more interrested in repairing the radios than operating them anyway.

Now I have a few old transmitters and receivers that just have terminal post or a whip antenna these won’t directly match to a 50Ohm feeder in the shack.

This was ok for the WS22 because with the roller coaster wound fully to one end it did match to the feeder. Some of the other sets don’t have anywhere near the tuning range to achieve a match to 50 ohm.

So I just want to operate my old gear from the comfort of the shack without having to setup a cut length wire outside every time I need to operate.

Hope that fills in the blanks for everyone.

Since posting I have started using a manual pie match tuner to match the transmitter to the 50 ohm feeder in the shack and this works ok, but is another link in the lossy chain and adds to the tuning process. I just wondered if there was a simpler solution, that I had not thought of.

I have other test equipment including power meters that I would like to use when restoring these old transmitter, but again all my gear is designed for a 50 ohm termination.

(Off Topic) Regarding the earthing arangement, some day I may install an earth farm and then install the Auto ATU at ground level. I will have to seperate the house wiring and the earth farm probably using a 1:1 Unun in the feeder, but I have not found one off the shelf that offers isolation. The problem is if the neutral to the house ruptures the fault current could flow down the coax to the earth farm hence needing to isolate the feeding arangement.

[Hans_SA7AUY]

I have made a couple of antenna matching units, that you can see here on my web-site. But I am not sure if that design will work for you.

Hans SA7AUY

[ChristianFletcher]

Clever use of a heat sink on your site, I would never have thought that you could make a capacitor. Nice Idea....

[MichaelR]

Originally Posted by ChristianFletcher

Sorry for late response I been away.

(Off Topic) Regarding the earthing arangement, some day I may install an earth farm and then install the Auto ATU at ground level. I will have to seperate the house wiring and the earth farm probably using a 1:1 Unun in the feeder, but I have not found one off the shelf that offers isolation. The problem is if the neutral to the house ruptures the fault current could flow down the coax to the earth farm hence needing to isolate the feeding arangement.

The AMU does not have to be in the sky, you can have it at ground level using your counterpoise.

Before the appearance of these commercial units homebrew arrangements using matching networks for each band and switched using the likes of small vacuum relays were quite successfully used. Each band was setup using an antennalyser or noise bridge and adjusted for lowest swr.

All of the military equipment tends to have differing output stages , the WS22 has an L type ATU whereas the 19set I think used a PI network all of the units have differing output stages .

I must say I do what you do , I love the military stuff and operating it on the bands.

Regards
Mike

[Sean Williams]

Christian,

What sets are you thinking of, and if possible can you post the relevant parts of the PA circuit - you might get away with using a small inductor in series and a cap to ground - thus making the output a Pi match...

Otherwise, try using a 4-1 balun in reverse - it might just give the impedance transformation you need, and sort of force the set in question to work.

As I said, the TCS worked well, but that did have a roller in the tank circuit. Dont think I ever had trouble when using WS12 here either, but cannot remember what that had on the output.

HTH
Sean

[ChristianFletcher]

Thanks Mike

Yes I know the AMU does not have to be in the sky, but by hiding high up in the bird box and using a thin wire my installation is invisible. Because its not grounded I dont get an advantage by installing it at ground level and running the antenna wire up. I actualy run the counterpoise down the back of the gutter down pipe so its all hidden from view.

I think I have enough information now, just wanted to check the the concept of using a manual atu was ok in principle. Yes I will try a 4:1 balun wont cost anything to try.

Regards Chris