On 12/1/2013 5:17 PM, John S wrote:
On 12/1/2013 2:42 PM, amdx wrote:
On 12/1/2013 11:48 AM, Irv Finkleman wrote:
Before too much theorizing takes place, why not try just placing it in a
convenient location in the house -- you might be pleasantly surprised.
If that doesn't work, then, and only then, it becomes a technical
problem.

Irv VE6BP


That's good advice, except I have three different audio inputs that all
land where I now have the transmitter.
Besides, we like technical problems! :-)

After my last response to Jeff when I measured the output voltage, I
just realized I can check the loss through the LPF. Hot dog! Can't
wait to get home.
Mikek

Don't fool yourself. A 10x probe has maybe 10pF capacitance. What is
that reactance at 100MHz? About maybe 160 ohms? How will that affect
your measurement?


I don't know.

I put a T on the scope with 50 ohms on one side and the transmitter
driving the other side. The scope is 15pf/1Meg input impedance.


Two of the measurements I made a
50 ohms or antenna and with 110Mhz LPF and without LPF.
Transmitter at 87.5Mhz


50 ohm 7.33Vpp
l
Transmitter---LPF---l
l
scope


50 ohm 7.13Vpp
l
Transmitter---------l
l
scope

I don't know how the 15pf affects this measurement.
But I don't see much loss in my LPF.

Rubber Ducky 8.45Vpp
l
Transmitter---LPF---l
l
scope


Rubber Ducky 8.45Vpp
l
Transmitter---------l
l
scope

I checked this twice, I have digital voltage display on the scope.
So no loss at transmit frequency. I don't know how that works, I'll be
checking for radiation soon!

Is there anyway to compensate for the 15pf, could I put an equivalent
inductance in the scope input circuit? (for this frequency only)

I have two 3db attenuators, when I put those between the transmitter
and the LPF and the LPF and the Load (antenna/50 ohms) I get slightly
less loss with the 50 ohm load and slightly more loss with the antenna.


What say you?
Thanks, Mikek

PS.
I want to check the attenuation of the LPF at 175 Mhz and 262.5. I just
threw away a QST that had an article with a 220Mhz osc. I'll retrieve
that tomorrow.