[Lowfer] Isotron type MEDfer or LOWfer antenna??? And....

[Lyle Koehler]

Possibly the strange tuning behavior of your MedFER antenna is caused by
self-resonances in the large loading coil. Things should settle down when
you get rid of all that excess inductance beyond the tap.

Although a number of hams have used the Bilal Isotron successfully, most of
the favorable reports have come from people operating on 40 meters and
higher frequencies. I expect that the Isotron will work as well (or as
poorly) as any other electrically small antenna. Best results on 80 and 160
meters require such antennas to be mounted as high as possible, basically
because most of the radiation is from the feedline and/or support structure.
(It's not because of any magic plates that enhance the "capture area", as
the BS on the Bilal web page would lead you to believe.) A 160 meter
Isotron, properly tuned and matched, when mounted on top of a 50 foot pole,
should theoretically be able to work just about as well as a 60-foot
vertical. So would a 10-foot mobile whip!

Unfortunately the FCC rules for MedFER operation include the transmission
line in the 3-meter length limit. OK, so you get rid of the feedline and
mount the MedFER antenna AND transmitter on a tall pole or building. Then
the conducting support structure and/or the wires that carry the power and
keying signals provide the "feedline radiation". Is this legal? Technically,
no. In fact there was a specific written FCC response a couple of years ago,
concerning Part 15 operation in the AM broadcast band. At the time, it was
brought to the attention of the Lowfer reflector by John Andrews. I've
attached the text of that FCC letter for the benefit of those who missed it
(or wish they had)...

Lyle, K0LR

___________________________________

In the August 2, 2000 edition of Radio World magazine, there was an
interesting response from the FCC to a letter questioning the legality of
some equipment being sold that supposedly conforms to the 100 mw/3 meter
requirements of Part 15 for unlicensed operation in the AM broadcast band.
It may be of interest to the LF community.  The original letter was from
Robert Ladd, of WNRR(FM) in Bellevue, Ohio.  Here is the response:
------------------------------------------------------------
Mr. Ladd:

Your inquiry was referred to me for reply. Before responding, I ran your
question by our lab people who are responsible for issuing the required
grant of certification on the AM transmitters before they can be marketed or
used.

Under Section 15.219 of our rules, the maximum power is limited to 100 mW
input to the final RF stage and the total length of the antenna plus the
connecting lead plus the ground lead may not exceed three meters.

The antenna is part of the package that is certified. If a loading coil is
used in the antenna design, we count the electrical length of the coil
toward the three meters. In other words, this rule is designed to keep the
practical transmission range no greater than about 250 feet.

If the installer/user places the transmitter atop a metal pole or other
conducting structure and grounds the transmitter to that structure, the
height of that structure also is counted toward the three meters maximum
length.

You did not mention the FCC ID number on the transmitter, so I am not able
to identify the responsible party. If you can supply that number to us, I
would be happy to provide it to our laboratory staff. If no FCC ID number
exists, the equipment may not be legally imported, sold or used.

Let me know if you need additional information on this issue.

John A. Reed, Senior Engineer, Technical Rules Branch
FCC Office of Engineering and Technology, Washington.