[AMPS] A tuned line problem

[Radio WC6W]

On Fri, 15 Dec 2000 09:35:13 -0500 "Tom Rauch" <w8ji@contesting.com>
writes:
Hi Tom,

>I use conventional relays in my "line stretchers". They are perfectly 
>fine up to 30 MHz, if you select relays with short internal leads. 
>You can use an open-frame relay and cut the armature wires off the 
>normal tabs. Just mount the relays on a PC board or copper sheet 
>and bring the leads out back, with the relays all next to each other. 
>The flying lead from one armature connects to the adjacent relay.

  I actually had all the relays lined up to do it that way but, I need to
keep this thing good up at the harmonics and looking at 30MHz, which
means 90 MHz for the 3rd harmonic, the 10 (10 amp rated) relays, plus
their interconnects, become a considerable portion (about 3 feet) of the
line.

  This is for transmitting and I'm trying to impedance invert the ends of
the line at the harmonics.

>You might have to capacitor-compensate the relays at the 30 MHz 
>end of things to keep the "bump" down, depending on the relay, or 
>use a "sandwich" of another board on top as a groundplane to 
>establish an impedance of 50 ohms in the system.
>
>I'm building a system now for receiving antennas, and will use 
>"BCD" line sections to get every couple degrees from 0 to 358 
>degrees. 0-178 is taken care of with delay lines, while the 
>remainder is accomplished with a 180 degree inversion of the 
>output.
>

  If you want to get real fine resolution, you might consider using a
trombone line, for the last few inches, such as might find in a junked
HP8741 or similar.  

73,
  Marv  WC6W









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