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

"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

============================

Download program HELICAL3 from website below.
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp

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

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 have some information directly from the FCC concerning antennas for Part
15 (15.219 Operation in the band 510-1705 kHz) which I will share herewith.
My intention is simply informative. I would encourage you to contact the FCC
to clarify your own questions. As you can probably see, you must phrase your
question as if you are a lawyer. My questions were sent to:

I sent the following:

Part 15 regulations says:

[Code of Federal Regulations]
[Title 47, Volume 1]
[Revised as of October 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR15.219]

[Page 732]

TITLE 47--TELECOMMUNICATION

CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION

PART 15--RADIO FREQUENCY DEVICES--Table of Contents

Subpart C--Intentional Radiators

Sec. 15.219 Operation in the band 510-1705 kHz.

(a) The total input power to the final radio frequency stage
(exclusive of filament or heater power) shall not exceed 100 milliwatts.
(b) The total length of the transmission line, antenna and ground
lead (if used) shall not exceed 3 meters.


Concerning the 3 meters maximum length for antenna, transmission, and
ground, would a capacitance hat at the top of a vertical radiator be
included in the 3 meter limit?

For clarification: Suppose I put a 3 meter vertical monopole on top of an
existing structure which has a metal roof. The transmitter would be located
at the base of the monopole, so it would require no transmission line. Would
I be allowed to install a 3 meter diameter (or more) top hat? The top hat
would be shaped like a spoked wheel and would serve the purpose of
increasing the current in the monopole through capacitive coupling to the
metal roof ground.

Thanks for your assistance.

John Smith



The reply to this message from was:

"Answer:

The intent of Section 15.219 is for a maximum 3 meter wire antenna.

The total length of the antenna plus ground lead plus connecting lead
must not exceed 3 meters. The rule doesn't permit a 3 meter diameter
"top hat" but should be applied to the combined length of each radial.
If the combined length of each radial added to the length of the antenna
vertical structure added to the length of the ground wire exceeds 3
meters, it would not be permitted."


I then sent the follow up questions:

"Thank you for answering my question concerning capacitive top hats.

I have two other questions about the 3 meter limit in Section 15.219:

Is a 3 meter diameter circular loop antenna allowed?

Is a square loop antenna of 3 meters per side allowed?

Regards,
John"

The reply from was:

"I have two other questions about the 3 meter limit in Section
15.219:

Question:

Is a 3 meter diameter circular loop antenna allowed?

Answer:

No, the total length of the antenna must not exceed 3 meters.

Question:

Is a square loop antenna of 3 meters per side allowed?

Answer:

No, the total length of the antenna must not exceed 3 meters."


The point here is that you must be very specific. I suspect that, if you ask
"Does a one foot diameter loading coil composed of ten turns constitute part
of the antenna specified in the Part 15 regulations?", they will reply that
the length of the wire in the coil is part of the antenna.

It would probably not be anything you should worry about unless someone
complains, but, if you want to comply with the rules, you should ask them.
Try to think like they do, not as if you want to beat the system. You
already know they don't want your signal to go very far.

My post was designed to be helpful, not argumentative. I hope you will post
your own findings here for everyone's benefit.

John
KD5YI

A hint: Make the loading coil part of the transmitter rather than part
of the antenna.
If every thing is built inside of a single metal box it should be OK.
Put this thing on top of a metal surfaced roof and ground your box to
the surface directly.
The 3 meter pipe should be very close to the box. Like 1 or 2 inches
and you have to subtract any lead length from the antenna size.



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

Found my answers he
http://lpam.info/index.php?page=antennas#loadingcoil



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