In article .com,
wrote:

Hello Group

I have been wondering if it might be an advantage to remotely tune
this active antenna using a varactor? The remote unit uses a 40673
dual gate mosfet followed by a 2N5109 npn vhf/uhf transistor which
feeds a 30 turn bifilar wound 4:1 balun. Then rg58 to the control
unit. The whip is 58"/1473mm in length. Any thoughts on this?

Yes. People have done this to design a tunable antenna so you can do a
Google search on it. The antenna element of the right type is inductive
and the varactor diode capacitance across it can be used to resonate it
at some frequency.

--
Telamon
Ventura, California

David - Huh ?

Hello Group

Thank you for trying but I finally found what I was looking for. I just
needed the right combination of words in my searching.

Richard

David - Now that is a revelation ~ RHF

"Telamon" wrote in message
...
In article .com,
wrote:

Hello Group

I have been wondering if it might be an advantage to remotely tune
this active antenna using a varactor? The remote unit uses a 40673
dual gate mosfet followed by a 2N5109 npn vhf/uhf transistor which
feeds a 30 turn bifilar wound 4:1 balun. Then rg58 to the control
unit. The whip is 58"/1473mm in length. Any thoughts on this?

Yes. People have done this to design a tunable antenna so you can do a
Google search on it. The antenna element of the right type is inductive
and the varactor diode capacitance across it can be used to resonate it
at some frequency.

--
Telamon
Ventura, California

A short whip will not be inductive at frequencies below 150 MHz or so. At HF
they are entirely capacitive probes.

Dale W4OP

In article zUcMe.6912$rR4.2379@trnddc08,
"Dale Parfitt" wrote:

"Telamon" wrote in message
...
In article .com,
wrote:

Hello Group

I have been wondering if it might be an advantage to remotely tune
this active antenna using a varactor? The remote unit uses a 40673
dual gate mosfet followed by a 2N5109 npn vhf/uhf transistor which
feeds a 30 turn bifilar wound 4:1 balun. Then rg58 to the control
unit. The whip is 58"/1473mm in length. Any thoughts on this?

Yes. People have done this to design a tunable antenna so you can do a
Google search on it. The antenna element of the right type is inductive
and the varactor diode capacitance across it can be used to resonate it
at some frequency.

--
Telamon
Ventura, California

A short whip will not be inductive at frequencies below 150 MHz or so. At HF
they are entirely capacitive probes.

He can use an inductor along with the varactor diode for a resonate
circuit, to which the whip can be directly connected.

--
Telamon
Ventura, California

"Telamon" wrote in message
...
In article zUcMe.6912$rR4.2379@trnddc08,
"Dale Parfitt" wrote:

"Telamon" wrote in message

...
In article .com,
wrote:

Hello Group

I have been wondering if it might be an advantage to remotely tune
this active antenna using a varactor? The remote unit uses a 40673
dual gate mosfet followed by a 2N5109 npn vhf/uhf transistor which
feeds a 30 turn bifilar wound 4:1 balun. Then rg58 to the control
unit. The whip is 58"/1473mm in length. Any thoughts on this?

Yes. People have done this to design a tunable antenna so you can do a
Google search on it. The antenna element of the right type is
inductive
and the varactor diode capacitance across it can be used to resonate
it
at some frequency.

--
Telamon
Ventura, California

A short whip will not be inductive at frequencies below 150 MHz or so.
At HF
they are entirely capacitive probes.

He can use an inductor along with the varactor diode for a resonate
circuit, to which the whip can be directly connected.

--
Telamon
Ventura, California

This is true, although perhaps obvious.. Now you have the problem of a
nonlinear device at the antenna input. If he lives in an urban area, it is
an invite to horrible IM and crossmod problems. Usually not considered good
engineeering practice.
A better solution might be to forget tuning the whip input and use a high
IP3 amplifier as in the Amrad project, or use a simple stepper motor to turn
an air variable cap.

Dale W4OP

This is true, although perhaps obvious.. Now you have the problem of a
nonlinear device at the antenna input. If he lives in an urban area, it is
an invite to horrible IM and crossmod problems. Usually not considered good
engineeering practice.
A better solution might be to forget tuning the whip input and use a high
IP3 amplifier as in the Amrad project, or use a simple stepper motor to turn
an air variable cap.

Dale W4OP
-----------------------------------------------------------------------------
Hi Dale
I am presently constructing the Amrad Active Antenna with the specified
parts.
I am kind of in the Burbs but I can see a small mountain about 10 miles
airline that has an FM, 93.1mhz, station, UHF tv, channel 40, station
and who knows what else.
I found plans on building a MW phaser using loop and/or active
antennas. I suspect the Amrad will be the better active antenna. This
will bre a learning process for sure.

Richard