Re: [Elmer 101] Part 5 - Done - Check this out


Date: Thu Jul 11 2002 - 13:56:51 CDT

No tuning pot...just a shorting wire.

I kind of thought I'd have to do something with C7 I just don't want to have
to remove L1 and take a winding off.

I'll pop a tuning pot in there to see what happens.

> Usually, a RF probe connected to a multimeter will display
>rms volts, which is 0.7071 times as large as peak volts. This is
>for a sinusoidal waveform. What you'd usually measure on
>the scope is peak-to-peak volts. Note that you'd HAVE TO
>use a 10X attenuator probe connected to the scope, else
>the coax capacitance will completely de-tune the 14 MHz
>resonant circuits you're probing. Even with the 10X probe,
>there's some de-tuning due to probe capacitance.
> In any case, 1.4v at the base of Q4 is looking good.
>Your 14.107 does seem a bit high. Do you have the tuning pot
>hooked up? If not, then wiring it in will help decrease this
> If you've got the tuning pot wired in, then you may have to
>tweak the VFO frequency by adding a small-value capacitor
>at the C7 position.
>----- Original Message -----
>From: "Brian" <>
>To: <>
>Sent: Wednesday, July 10, 2002 7:10 PM
>Subject: [Elmer 101] Part 5 - Done - Check this out
>> 6 parts, looks like a breeze...but wait...I'm a scope rookie and
>> couldn't get my scope to do what I wanted it to do, only what I was
>> telling it to do...which are two different things most of the time.
>> So I built my first RF probe out of my junk box according to the
>> diagram Dave put in the SWL+20 docs.
>> On the base of Q4 I was able to peak up to 1.41 volts with the RF
>> probe. Is this good? Bad? Other? How should this look on my scope?
>> 1.4v peak to peak?
>> My FC shows 14.107 Mhz at the base of Q4. Hmmmm...I hope somewhere in
>> there we'll be bringing that down. I want this set up for the
>> bottom/middle of 20m.

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