It was hard to tell what the original hardware stack looked like as a
previous owner had apparently tried some misguided fixes. Ameritron
supplied me with the Teflon center insulator, an insulated washer and a
brass or copper shield (?) that must have not been the right one as it would
have been a tight fit over the RF carrying conductor, with no insulation
between the two. Perhaps the toroid lead dress is involved as well, as the
toroid they supplied was wound in the wrong direction when mounted for
minimum lead length. In other words, when mounting it as the original was,
the forward and reflected power meters were reversed in function. Do you
happen to know what core material was used in the toroid? I have a couple
cores of 43 and 61 mix and could rewind the unit and achieve proper lead
dress.
Can you clarify your last statement that reads: "and the especially includes
using a Teflon center insulator and
> a insulated washer to hold the board up." I'm not sure which "board" you
mean here. I used the insulated washer between the toroid and the board -
maybe that wasn't right?
K8AC
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Floyd Sense" <sentek@sprintmail.com>; <amps@contesting.com>
Sent: Sunday, March 16, 2003 11:29 AM
Subject: Re: [Amps] Accuracy of Ameritron forward power meter?
> > I suspect the problem might be the lack of a copper or brass shield
> between
> > the toroid and the conductor carrying the RF.
>
> Directional couplers always require care to make flat, but the problem is
> almost never a "shield" between the current transformer secondary and
> primary.
>
> The largest problems are almost always improper layout, connections, or
lead
> dress that cause ground loops around the sensing diodes.
>
> As I recall the couplers in those amps are reasonably flat when everything
> is built correctly. You calibrate around 7 or 14MHz, never at one end. In
> particular you have to watch PC board grounding to the RF connector and
the
> shield grounding of the lead from the RF deck up to the grounding point
near
> the directional coupler. Be sure you did the hardware stack correctly in
the
> transformer, and the especially includes using a Teflon center insulator
and
> a insulated washer to hold the board up.
>
>
>
>
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