[Lowfer] Medfer Antenna.

Tue Oct 27 12:27:11 EDT 2009

Lee:

Greetings to you. First, what I have tried, and second, what
I have read.  I once built a Vectronics Part-15 A.M. BCB xmtr
for a church that was wanting to broadcast to the local
community around it. I built the kit as stock, and used the
recommended Stainless steel 102" CB whip as an antenna.
My test setup was::: The whip mounted to a 6 foot wooden step
ladder, the xmtr was connected directly to the whip. NO Ground
lead, or radials. The area was totally surrounded by forrest,
but was high up on a hill. Definitely the worst possible
setup to test. I used 1610 KHz as the test frequency, and
peaked the xmtr using a scope with pickup near the whip. I fed
audio from a mixing board in the shack, got in my car and drove 
around the neighborhood. Maximum distance was 1/2 mile in all
directions. Most auto radios have better A.M. sensitivity than 
table top, and cheap portable radios, So I guesstimated that
reliable coverage with that type of setup would be around
1/4 mile in all directions.
The Vectronics kit made note NOT to use any type of loading
coil, or serious signal loss would occur. The components in the
kit were specifically chosen, and designed to operate into the 
impedance that would be presented to the xmtr by the whip, or
a similar small wire antenna. To use coils, and top-hats, etc.
just bypass the built in matching circuit. Read your kits info.
to see what it recommends on optional antennas.
Some of your questions; YES, the top-hat is considered in the
total length of the antenna. Ground radials are not considered
to be part of the antenna length. The wire going from the xntr
ground to the radial / ground rod is part of the total length.
Mounting the set on a rooftop ::::  there have been those who 
have done this, on top of metal roofs, or put a radial set on
the roof and connected the xmtr by a very short piece of wire
to the radials. Most have considered this the same as radials
on the ground. 
What I have read :::::: The serious Part-15 Micro-Broadcasters
use telescopic TV masts ( 40 foot ) or a section of tower.
They mount a box on the mast / tower to house the xmtr, and 
any tuning unit, to get the actual antenna as high in the air
as possible. They run a short ground wire to the mast / tower
to ground the xmtr. The mast / tower is not considered to be
part of the antenna length. Some have driven ground rods at 
the base and connected radials to the base also.
>From all information available, Height above ground will be
your best friend for the antenna.

I hope you find this information useful.  73 to you ::: 

Andy - KU4XR - EM75xr - Friendsville, TN.
LOWfer Beacon " XR " @ 185.29893 KHz ( QRSS-60 )
Coordinates:  N:  35* 43' 54" - W:  84* 3' 16"
http://www.myspace.com/beaconxr

--- On Mon, 10/26/09, LEE BAHR <pulsarxp at embarqmail.com> wrote:

> From: LEE BAHR <pulsarxp at embarqmail.com>
> Subject: Re: [Lowfer] Medfer Antenna.
> To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" <lowfer at mailman.qth.net>
> Date: Monday, October 26, 2009, 9:59 PM
> 
>  I need input.  I have a small legal AM transmitter
> kit I want to put on the
>  hi end of the AM BC band.  I have a lake house in a
> small subdivision in
>  the country.  the subdivision is a circle you can
> walk around in a matter
>  of a few minutes.  My house is near the middle of all
> this.  I want to
>  legally send out AM on the transmitter with subdivision
> news.  I would
>  suspect the diameter of the circle is around 1200 to 1500
> feet.
> 
> I have not built up the transmitter as yet but have built a
> loading coil
>  on a 4 inch PVC pipe and made an antenna that looks like a
> HF ham mobile
>  antenna.  (Base loaded).  It is just a little
> taller then 9 feet and has a
>  top hat made up of 2 foot long welding rod on the
> top.   Rules say:
>  antenna/ground wire/ and feedline less then 10 feet
> approx.  (Does the top
>  hat count in the length)?
> 
>  I can mount the antenna with transmitter at it's base on
> the ground and
>  put radials in the ground.  Would the radials count
> in the length
>  calculated by the FCC?  I can also mount the antenna
> along my house ridge
>  near aluminum gutters.  This would put the base up at
> around 18 foot.  I
>  know hooking a ground up at this point would make the
> thing illegal.  I
>  think hooking a ground  to the gutters would also
> make it illegal.
> 
> So it comes down to, do I put it up in the air with no
> ground radials or
>  do I put it on the ground and can I have ground radials or
> just a ground
>  stake and which system would cover the most territiry?
> 
>  I really want to be legal with this thing since it will be
> running all the
>  time and the goal is to just cover the small 50 home
> subdivision.   (The
>  area has very few AM stations which can be heard at this
> location).>
> 
> I could also build an antenna on a 10 or 11 inch diameter
> PVC pipe around 10
> foot long and mount it on the ground with or without
> radials or ground stake
> with xmtr at the antenna base based on what the FCC
> considers legal.  I
> guess this would work better then my 4 inch loading coil
> with magnet wire.
> The 10 inch diameter pipe could be wound with silver plated
> teflon covered
> wire or plain covered stranded nbr 14 or 12  house
> wire.  Maybe my initial 4
> inch dia coil is good enough to work no matter at what
> position I place it.
> 
> I'm just wanting to put up the best legal antenna for local
> coverage.
> 
> Lee, w0vt
> 
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