Ian White GM3SEK wrote:
cliff wright wrote:
Hi! I've been wanting to upgrade my old Zmatch ATU which is 30 years
old for a while but although I've come across several designs, both
one and 2 coils I cannot find the actual inductance values required.
I seem to remember an article in a magazine some years ago that had them
but I haven't been able to locate it so far.
I have some very nice Silver plated coil stock that I would like to
use but as I have determined for myself the value of the coil is
critical as the network doesn't like the tuning position for any 2
bands to coincide.
Failing the use of an air cored coil I might try a Toroid, but The
coil stock is in my hands right now. Any help greatly appreciated!
Regards Cliff Wright ZL1BDA ex G3NIA
See VK5BR's website:
http://users.tpg.com.au/ldbutler/SingleCoilZMatch.htm
Hi Ian. Yes I've seen that page. However I'm constrained not so much by
capacitor values and ratings as by the size of an existing box it goes
into. Now I'm retired I don't have access any more to "metal bashing"
facilities as I did and it would be much easier to use an existing box
which is 115mm high, 200mm f/b and 300mm wide.
I sold my original Z match some years ago which tuned very well and
built this one with some very nice silverplated copper tube coil stock
which I had around at the time. Unfortunately I'm not very confident
that the coils which are nearly 90 mm diam overall aren't being
excessively affected by the closeness of the metal chassis.
Fortunately I have an LCR bridge which measures down to uHenries
so I will measure up the coils again and check for resonance.
The tuning is done with a twin gang 210 pF max Tx cap from a pre WW2
TX with some of the lossy dielectric replaced and the coupling cap to
the TX is a 1950's beefy 500pF TX type well insulated from earth.
With my current G5RV I find that the tuning is VERY critical and the
matchng on 80M is with rather too low a tuning cap value.
So as you see it would be reassuring to have actual indiuctor values in
u Henries to work with so as to determine which size and type of coil
will best suit my purpose.
BTW I run about 200W max with an old Kenwood 820s at the moment.
73's Cliff Wright.