RadioBanter - View Single Post

February 11th 05, 02:45 AM

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