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Re: LF: VLF in NA, PVC coil bodies/VLF converter

To: [email protected]
Subject: Re: LF: VLF in NA, PVC coil bodies/VLF converter
From: Johan Bodin <[email protected]>
Date: Mon, 13 Mar 2017 11:34:55 +0100
In-reply-to: <[email protected]>
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Hi Joe,

I have almost forgotten that old LF converter. I just rediscovered the web page in an Internet museum! :-)

Regarding T1, inductance depends on the lower frequency limit. I recall that the AL of that 3F3 core (T1) is 0.9uH*n^2 so 25 turns result in about 560uH. A rule of thumb for transformers is to aim for a winding reactance of 5 * system impedance at the lowest frequency of operation which seems to be around 70kHz in this case. The converter will go lower, of course, but the transformer reactance will shunt more of the signal.
The CMOS switch mixer is less sensitive to termination than a diode ring
mixer, I think, so the diplexer is not very critical. You can reduce the
Q to 1 to make tuning less critical and reduce the loss in the diplexer.
Just found this page:
Increasing the impedance around the CMOS switch will redeuce switch
losses and perhaps also improve linearity. You could try to increase the
number of turns on T1 secondaries by 2 or 3 for a 200 or 450 ohm level.
Design the diplexer for this impedance and put a corresponding step-down
transformer at the 10MHz output. Just an idea...
73 de Johan SM6LKM

[email protected] wrote:
 Johan, I'd like to build your FB VLF converter iand use a 10 MHz LO.
L1 C5 and C6 and L2 were scaled for 10 from 4 MHz but a T1 core
is not handy. Is 5 mH per winding satisfactory?

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