[Amps] grid resonance

[R L Measures]

On Aug 5, 2006, at 10:40 AM, Tom W8JI wrote:

>>> Is there a way to measure impedance and Q with it Vic?
>>
>> No, although the sharpness of the dip gives a clue to the
>> Q.
>
> The sharpness of the dip only gives an indication of the
> load impedance seen at the grid or gate. Distance, turns
> ratio between the oscillator coil and the DUT, and many
> other things determine dip depth and shape.
>
> All the dip meter measures is loading on the gate or grid.
> Nothing else.
>
> Where we get in trouble is thinking things tell us more than
> they really do.
>
> By the way, a short mobile antenna is indeed the equivalent
> of a series resonant circuit.

Which is why a 1/4 wave whip has to be shorted to dip it with a  
dipmeter.  However, with a Trio-Kenwood dipmeter, one has the option  
of unshorting the whip, using the C coupling adapter and measuring  
the 1/2 wave dip.

> The parallel resonance of the
> coil is a long way away in a good system.
>
> Parallel resonance only approaches series resonance when the
> L to C ratio is very large.  That can actually mean a sharp
> response without higher Q than something with a wide
> response. If we want to measure something, we should measure
> what we actually want to know whenever possible. Otherwise
> we can build a house of cards.
>
> 73 Tom
>
>
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>

R L MEASURES, AG6K. 805-386-3734
r at somis.org