Peter penned: "What would you use for this measurement ?

Upon further reflection (no pun intended) -
   - an HP Vector Impedance Meter.

HP made a very nice one with a top end of 108 MHz.

The circuit I 'dreamed up' over a ten years ago
while moonlighting as a broadcast engineer in the
form of that resistive bridge was a product of
inspiration at the eleventh hour -

- as I was afraid a certain GR Z bridge I had planned
on borrowing might be not be available after all.

The GR Z bridge (or some suitable substitute) was
needed for the measurement of a most critical
parameter: the Z (impedance) as seen at the base
of 240 plus foot 1/4 wave guyed vertical for 1.06 MHz.

I had been contracted at the time to install and
tune a new ATU - Antenna Tuning Unit - at a 10 KW
AM broadcast station.

As it was - I did get to borrow the GR bridge, but
the inspired circuit *still* played a critical
part - I had to re-tune the ATU and part of the
process calls for finding the parallel resonant
point ... my "R" bridge works optimally for this
purpose - as one can easily see the phase change
most radically with frequency as one tunes with a
signal generator through the resonance point on a
tuned circuit (the ATU in this case) - at this point
the composite Z (R+jx) remains fairly constant and
causes little change in the amplitude of a signal, but
the phase stands out and identifies the resonant
point like a sore thumb.

Whilst your suggestion is most likely valid - I doubt
you can assure accurate numerical results without
some difficulty (calibration charts etc) over several
octaves (unto a decade) of bandwidth ...

Jim

----- Original Message -----
From: "Peter L. Peres" <plp@ACTCOM.CO.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, July 09, 2002 2:11 PM
Subject: Re: [EE]: Directional couplers & T/R test sets


> On Tue, 9 Jul 2002, Jim wrote:
>
> >   "Try to make a "
> >
> >'cause this technique works, is perfectly
> >valid AND works from DC to as high as your
> >construction techniques will allow (making
> >it largely 'frequency independent') ...
>
> Hey, you're the guy who advocates buying suitable equipment from Ebay.
> What would you use for this measurement ?
>
> Peter
>
> PS: BTW, I did 'try' and make what I proposed, for 27MHz.
>
>

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