[Amps] working backwards to setup tank

[Gary Schafer]

I have found that the mfj works best while using the lowest frequency that
will give you a reading. Most capacitors are measured / speced at 1000 Hz.
Going higher in frequency you start to measure stray capacitance, and
inductance has more of an effect to skew the reading.

With the MFJ you will find that with small values of capacitance it will not
read at low frequencies. The MFJ reads capacitance by measuring the
impedance that the capacitor presents at the frequency selected. The MFJ has
a limited range of impedance that it will measure so you have to select a
frequency that falls into its impedance range.

What I do when building tank circuits is calculate the input and output
capacitance, set the capacitors to that value using the MFJ or other
capacitance bridge, and then prune the coil for resonance in circuit.

73
Gary  K4FMX

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Partain, Chuck
> Sent: Wednesday, April 19, 2006 10:20 AM
> To: garyschafer at comcast.net; Phil Clements; PA3DUV; amps at contesting.com
> Subject: Re: [Amps] working backwards to setup tank
> 
> I have another question on the MFJ analizer.
> 
> If I set it to capacitance, and I want to see what those caps are set at
> when I find
> the sweet spot on a peticular band..what frequency should I set the MFJ
> at? same frequency I would guess
> but it gives me "interesting " results..
> 
> 
> 
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
> Behalf Of Gary Schafer
> Sent: Tuesday, April 18, 2006 8:54 PM
> To: Partain, Chuck; 'Phil Clements'; 'PA3DUV'; amps at contesting.com
> Subject: Re: [Amps] working backwards to setup tank
> 
> 
> If you want to test it at lower power, figure what plate voltage and plate
> current will give the same load impedance as the high power load you are
> designing for.
> Example: 3000 volts at 1 amp (using 1.8 factor) gives 1666 ohms. If you
> decrease the plate voltage to 1/2 and the plate current to 1/2 you will
> have
> the same load impedance.
> 1500 volts at .5 amp (still using 1.8 factor) gives 1666 ohms.
> 
> 73
> Gary  K4FMX
> 
> 
> > -----Original Message-----
> > From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On
> > Behalf Of Partain, Chuck
> > Sent: Tuesday, April 18, 2006 6:49 PM
> > To: Phil Clements; PA3DUV; amps at contesting.com
> > Subject: Re: [Amps] working backwards to setup tank
> >
> > :) yea, its all out of the circuit, at this point i'm not even going
> thru
> > it.
> > right from the plate thru the resistor to gnd as you do when you setup
> > initially.
> > No power ever applied, the analyzer is AOK
> >
> > If I use a 2k ohm load I can set it up for a good match, but when the
> amp
> > is running
> > the setups are off by a bit, this was my sanity check, now i'm nutso ;)
> >
> >
> >
> > ________________________________
> >
> > From: amps-bounces at contesting.com on behalf of Phil Clements
> > Sent: Tue 4/18/2006 6:29 PM
> > To: 'PA3DUV'; amps at contesting.com
> > Subject: Re: [Amps] working backwards to setup tank
> >
> >
> >
> > > > I set this tank circuit up and tuned at 7.250mhz, came up with a
> > > beautiful
> > > > output
> > > > then tried to do the reverse check. I put a 2k resistor from the
> plate
> > > to
> > > > ground, hooked
> > > > the MFJ analizer up using the settings previously obtained and for
> th
> > e
> > > > life of me cannot find
> > > > a good resistive value to make the swr analizer 1:1 swr or close. I
> > used
> >
> > Is your antenna relay keyed up or jumpered?
> >
> > (((73)))
> > Phil, K5PC
> >
> >
> >
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> 
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