Forgot this. The meter is a 200 uA movement. The cal resistors are two 25K
pots. The filters off the RF chokes are .01 uF. The caps off the diodes
cathodes to ground are 330 pF silver mica. The two 10 ohm resistors go to
ground too. After the .01 uF caps, each side goes through a .001 uF feedthrough
cap to the 25K pots. Everything is shielded together excepth the meter and two
pots and their selector switch for Fwd and Rev.
Best,
Will
*********** REPLY SEPARATOR ***********
On 2/3/06 at 3:59 PM Will Matney wrote:
>All,
>
>I found this while researching toroids. If your building a RF power meter
>(wattmeter or SWR meter), Collins design, and want to use a transformer in
>it here's the following.
>
>For use from 1.5 to 30 MHz, the transformer can be an Amidon Associates
>T68-2 toroid. That's an iron powder type 2 (red) material. It uses 36
>turns of 26 gage magnet wire for the secondary. The toroid size has an OD
>of 0.690 and an ID of 0.370. The primary is one pass of the incoming RF
>which can be any wire just going through the center of the toroid carrying
>the power to the load. One turn means to pass through it, not one wrap
>around it. For lower frequencies, they specify a ferrite with a
>permeability of 125 which would be 61 mix. The two chokes, after the
>signal from the transformer is rectified, should have an XL of 100,000
>ohms. The two rectifiers are matched hot-carrier diodes #HP2800. The two
>10 ohm resistors off the diodes anode should be carbon and closely
>matched. This also uses two 5 pF piston trimmers off each side to null it
>out. If it's hard to null, a Faraday shield was recommended.
>
>Best,
>
>Will
>
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