[Lowfer] Loop Coupling Xfmr

[Jay Rusgrove]

Bill/Mike

I'd keep an eye open for distortion products caused by those non biased
junctions. A double pole transfer relay at the antenna would completely remove
the final during transmit. A single pole double throw relay with the arm to the
transformer, one connection to the transmitter output and the other connection
to the separate receive feedline back to the shack. Separate feedlines for
transmit and receive offers the advantage of leaving the tranmitter/feedline
chain intact while being able to do whatever you want to the receive line - like
adding filters, step attenuators, splitters and the like. That has been the
optimum way to do it for years on vhf, uhf and the microwave bands. May just be
the hot ticket on LF as well!

Jay Rusgrove, W1VD

Bill Ashlock wrote:

> Mike,
>
> Since you are running with a Vcc of only 14.5v the primarary inductance can
> be lower than 400uh. At 1w RL = (Voutp-p)^2/8 = 24.5 ohms for the effective
> load on the transmitter. You want to have the transformer's primary XL at
> least 5 times this or 122 ohms, right? At 185k that would be 105uh. So if
> the primary measures more than 105uh with 7 turns you are OK.
>
> I think I may have come up with a way to receive and transmit on the same
> loop but still have the final at the base of the loop. If you turn off the
> Vcc supply the signal may just pass through the final transistors in reverse
> with some attenuation. Have some more tricks in mind using a negative bias
> on the coax if this doesn't work. According to Jay he has to attenuate the
> signal off his transformer by ~20db to prevent receiver overload, so there
> is plenty of signal to give up. I'll try this at home and let you know how
> it works.
>
> Bill
>
> >From: "WE0H" <we0h@core.com>
> >Yea, I was playing around with the turn's ratio and removed one to try it
> >and later realized that the inductance would be way under 400uh now.
> >Whoops.
> >I'll fix it tomorrow and will try for 9 turns. It is at 7 turns now. If 9
> >is
> >worse, I'll have to do a double pass with the loop wire and double the
> >other
> >side as well.
>
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--
Jay Rusgrove
Advanced Receiver Research
Tel: (860)485-0310
FAX: (860)485-0311
www.advancedreceiver.com
E mail: advancedreceiver@snet.net