On Tue, 6 Jan 2004 17:26:59 -0600, "Steve Nosko"
wrote:

Motorola's first solid state 450 car phone, the MK, used a 50 W 150 MHz PA
followed by a varactor tripler for 10W at 450. Varactor triplers are tricky
however.

Steve K;9;d/c/i

The worst is suppression of 150MHz, it is almost impossible to
suppress it. Bought some UK commercial integrated modules for 432MHz
which was fed from 144MHz 1W, had a 20W amplifier within a very well
screened and silvered box, but radiation on 144MHz were almost
impossible to suppress, the only way out was to place it deep at the
lowest point of the basement with ferrite chokes on the cables

LA8AK
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Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails
Cannot check every email manually. Please use intelligent title for email.
Mails without titles or using just "hi" is deleted

On Tue, 6 Jan 2004 17:26:59 -0600, "Steve Nosko"
wrote:

Motorola's first solid state 450 car phone, the MK, used a 50 W 150 MHz PA
followed by a varactor tripler for 10W at 450. Varactor triplers are tricky
however.

Steve K;9;d/c/i

The worst is suppression of 150MHz, it is almost impossible to
suppress it. Bought some UK commercial integrated modules for 432MHz
which was fed from 144MHz 1W, had a 20W amplifier within a very well
screened and silvered box, but radiation on 144MHz were almost
impossible to suppress, the only way out was to place it deep at the
lowest point of the basement with ferrite chokes on the cables

LA8AK
--
Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails
Cannot check every email manually. Please use intelligent title for email.
Mails without titles or using just "hi" is deleted

Motorola's first solid state 450 car phone, the MK, used a 50 W 150 MHz PA
followed by a varactor tripler for 10W at 450. Varactor triplers are tricky
however.

Steve K;9;d/c/i

"Paul Burridge" wrote in message
...
On Sun, 4 Jan 2004 16:22:32 -0800, "Tim Wescott"
wrote:

The varactor capacitance change is instantaneous -- think of a capacitor
who's plate spacing is dependent on it's voltage. This is why varactors
are
used for frequency multiplication -- that capacitance change "squeezes"
the
pulse to generate lots of harmonics.

Rubbish. Varactors are not used for freqency mulitplication. They are
freequenty used in VXCOs for modulating (or otherwise varying) the
oscillator output frequency by means of applying a DC bias voltage
which alters the capacitance of the PN junction.
--

"I expect history will be kind to me, since I intend to write it."
-
Winston Churchill

On Sun, 4 Jan 2004 16:22:32 -0800, "Tim Wescott"
wrote:

The varactor capacitance change is instantaneous -- think of a capacitor
who's plate spacing is dependent on it's voltage. This is why varactors are
used for frequency multiplication -- that capacitance change "squeezes" the
pulse to generate lots of harmonics.

Rubbish. Varactors are not used for freqency mulitplication. They are
freequenty used in VXCOs for modulating (or otherwise varying) the
oscillator output frequency by means of applying a DC bias voltage
which alters the capacitance of the PN junction.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

The varactor capacitance change is instantaneous -- think of a capacitor
who's plate spacing is dependent on it's voltage. This is why varactors are
used for frequency multiplication -- that capacitance change "squeezes" the
pulse to generate lots of harmonics.

So your oscillation voltage will certainly affect the tuning, and the
forward bias effects will be most unfortunate.

I have modelled varactor diodes by dinking with the area parameter of the
SPICE diode model, but I'm not a pro in that regard and don't know the
"right" way to do it. SPICE is also not the tool for determining the
behavior of nonlinear high-Q circuits (I believe the best tool still
involves FR-4 and lots of cussing).

"James Fenech" wrote in message
...
Hello,

I have a general question regarding tuning diodes:
Does the oscillation voltage alter their capacitance, or is capacitance a
slow changing value - like resistance and PIN diodes?

The reason I ask is that I am spicing (simulation) a VCO I wish to build
(wide range 140-240MHz) and get an oscillation voltage of 20 volts peak
(maybe the Q is too high). This high oscillation voltage would easily
swamp
the tuning voltage, 3-15 volts, and forward bias the diode itself.

If anyone wishs to reply directly they must remove the "xxx" from the
return
address or write to:
james dot fenech at nec dot com dot au

Thanks,
James.