Randall J wrote:
I operate a Part 15 station for my neighborhood (FM) and have
acquired
an AM transmitter. I've seen plans for vertical antennas but would
rather make my own from the few parts I have. I have 8ft of aluminum
tubing and would like to make a loading coil using 3 inch diameter
PVC
pipe. Given the frequency I operate on (1610khz), 8 ft of tubing, and
a
3.5 inch coil form, how many turns of 22AWG insulated wire would I
need
to wrap? (Oh the tubing is in two pieces and I can slide the top
piece
up and down).

Is there a program I can download to find this out?

Randall

Hi Randall, I did this for a friend of mine a few years back.
Download the demo version of EZNEC and model an 8' vertical on 1.610
MHZ. You will find quite a bit of capacitive reactance. Your loading
coil should cancel the reactance. Determine the required inductance by
L=Xl/(2*pi*Fmhz). Xl is reactance you need to cancel.
The coil will be in the millihenries. Consult the ARRL Handbook for
a estimate on the # of turns on a 3.5" form for a given Inductance.

73 Gary N4AST

wrote:
Randall J wrote:

I operate a Part 15 station for my neighborhood (FM) and have

acquired

an AM transmitter. I've seen plans for vertical antennas but would
rather make my own from the few parts I have. I have 8ft of aluminum
tubing and would like to make a loading coil using 3 inch diameter

PVC

pipe. Given the frequency I operate on (1610khz), 8 ft of tubing, and

a

3.5 inch coil form, how many turns of 22AWG insulated wire would I

need

to wrap? (Oh the tubing is in two pieces and I can slide the top

piece

up and down).

Is there a program I can download to find this out?

Randall


Hi Randall, I did this for a friend of mine a few years back.
Download the demo version of EZNEC and model an 8' vertical on 1.610
MHZ. You will find quite a bit of capacitive reactance. Your loading
coil should cancel the reactance. Determine the required inductance by
L=Xl/(2*pi*Fmhz). Xl is reactance you need to cancel.
The coil will be in the millihenries. Consult the ARRL Handbook for
a estimate on the # of turns on a 3.5" form for a given Inductance.

73 Gary N4AST


OK Gary, guess I'm a little dense on the subject but the EZNEC software
is a bit complex for me. Can't seem to figure out the Reactance of my
8ft x 1/2inch aluminum antenna. I did find that the "SRC Dat" gave an
impedance of 0.2714 - J 9981 ohms. How do I find the reactance?

I do have the 1988 version of the ARRL handbook and have found the
formula for finding the inductance which in turn can be solved for "n",
the number of turns.

Randall

Randall J wrote:

OK Gary, guess I'm a little dense on the subject but the EZNEC software
is a bit complex for me. Can't seem to figure out the Reactance of my
8ft x 1/2inch aluminum antenna. I did find that the "SRC Dat" gave an
impedance of 0.2714 - J 9981 ohms. How do I find the reactance?

I do have the 1988 version of the ARRL handbook and have found the
formula for finding the inductance which in turn can be solved for "n",
the number of turns.

Randall

The reactance is the "J" part, and negative means capacitive. So at the
source, the impedance is 0.2714 ohms of resistance in series with 9981
ohms of capacitive reactance. You'll need 9981 ohms of inductive
reactance to cancel it out. That would mean an inductance of
9981/(2*pi*f), which would be 1.59 mH at 1 MHz for example.

If your inductor has a Q of 200 (which might be hard to do for that
large an inductance), its loss resistance will be 9981/200 = 50 ohms. My
guess is that your ground system will also have a resistance of about
that, unless you put in quite a few fairly lengthy radials, giving you
an overall feedpoint resistance of about 100 ohms. The efficiency would
then be 0.2714/100 = 0.27%.

Roy Lewallen, W7EL