Antenna coupling with antique Transmitter

[Station X]

Reading the first post in this thread I wonder if perhaps we're missing the point? The problem is that the transmitter has far too little RF output when compared with the DC input.

The fact that the transmitter may have been designed to feed a 600 ohm balanced feeder is neither here nor there, as the load seen by the transmitter will depend on feeder length and the nature of the aerial. I assume that with a balanced feeder this will be a dipole cut for the wavelength concerned. I feed my 80 metre dipole with 400 ohm ladder feeder. The fact it's a mismatch doesn't worry me as this is more than compensated for by the loss I'd experience if I used 50 or 75 ohm coaxial feeder.

The transmitter needs to be fed into a dummy load of say 75 ohms and the cause of any low RF output investigated and fixed. Perhaps there is insufficient coupling between the two windings? Once this is done it will be time to worry about feeders, aerials and aerial matching units.

[MichaelR]

Hi ,

Just to make another comment , I have just noticed from the MK3 cct that the Antenna fed is showing going into a DOUBLET antenna.I know the military have used Doublets alot as an antenna and they use open wire feeder to feed the centre section.Theory shows that open line feeders can be used to match the centre section of the Doublet just by cutting the right lengths but that is another issue.

Graham is correct in the logic that it really does not matter if there is a very significant mismatch , the losses in open feeder are very small indeed , normal well matched coax has feeder losses which would far exceed the loss of transfer of energy due to a poor SWR or mismatch with open line feeder.As long as the energy radiates ( the Antenna is an effective radiator) is all that matters. A very good SWR does not mean the Antenna can radiate the energy

Load it up as Graham suggests and do some measurements on Grid drive , Grid Bias etc to the 807

[Buzzkf9cm]

Thanks Graham,

I did as you suggested I wound a 6 turn coil small enough to fit into and underneath the tank coil. I fed the coil into my watt meter, with a 50 ohm dummy load and tuned up the transmitter. What do you know, I got 25 watts on the Bird. I guess I've got a coupling problem. I think I'll use some B&W coil stock and insert them under the tank coils. I'll disconnect the existing coils and leave them installed for a realistic effect.


Thanks to everyone for the help.


de Gary, KF9CM