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BRIAN,

Low Noise Receive "Only" Coax Cable Loop Antennas for
160 Meter to 10 Meter HF Shortwave Bands -by GreerTech


I built one of these Coax Cable [Shielded] Loop Antennas for
the 60 Meter Shortwave Band; my intended Lowest Frequency:

- 4.75 MHz to 5.06 MHz with a MidPoint of 4.905 MHz
- Cut to 13.5 Feet [1/10WL] VF=0.66 using RG8 Coax Cable.
- Square shape 3.4 Feet per Side with 4.8 Cross-Arms.
- Round shape 4.3 Diameter Circle.
- Coax Cable Lead-in-Line 5 Feet.

This Coax Cable [Shielded] Loop Antenna is very 'quiet' and
work very well if you are limited to an InDoor Antenna ONLY.

I tried using a Tuner {Pre-Selector} with it; but with my
Icom IC-R75 and Kenwood R-5000 Receivers the Tuner proved
to be un-necessary.

* The Coax Cable [Shielded] Loop Antenna can be used to
NULL-OUT 'local' RFI/EMF man made Noise within the house.

* For the Shortwave Band Frequencies above 5 MHz to 25 MHz
the Coax Cable [Shielded] Loop is an NON Directional Antenna.

* For the AM/MW Broadcast Band (530 kHz to 1700 kHz) it becomes
a Directional Antenna and the use of a Tuner {Pre-Selector} helps.

TIP: I used some 5/8" or 3/4" (White) Low Pressure Water Line
Polyethylene Tubing as a "Form" to hold the Loop in a Circle Shape.
Sort of like a Big Hula Hoop. Build your Loop and just before
you are ready to assemble at the bottom; slide the Coax through
the Polyethylene Tubing. Cut the Polyethylene Tubing so that it
is about 2" shorter than the Circumference of the Coax: This is
to leave 'room' to make the Bottom "Joint" to Complete the Loop.
Shape-Out the Polyethylene Tubing so that it is a Circular Loop.
Finally make the Bottom Coax Shield {Connection} Joint.

FWIW: Sometimes when using this Loop with the Icom IC-R75,
I will have a clear and listenable Signal with NO 'apparent'
S-Meter Reading. The Signal is so quiet that I can use the
#2 Pre Amp and still have a Cleaner and More Listenable Signal
then by using my 75 Foot Low Noise Inverted "L" Antenna. The
Inverted "L" will have an S-7 to S-9+10dB S-Meter Reading, but
the background noise level will be S-2 to S-4 and a small
amount of noise can be heard with the program audio.

SUMMARY: An "Easy-to-Make" Coax [Shielded] Loop Antenna.
A very good Antenna for SWLs with Noise Problems and who
are 'limited' to InDoor Antennas ONLY. Makes a nice Second
Antenna for dealing with some types of Reception Problems.
NOTE: I would make my next one with RG58 or Mini RG8.

RECOMMENDATION: If you are going to use one of these Coax
[Shielded] Loop Antennas InDoors with an OutSide Antenna with
a single Radio/Receiver. Buy a 'quality' Antenna Switch like
the MFJ-1702C; Alpha Delta 2; Daiwa CS-201 and others.




These will allow you to 'switch' between Antennas; and they
automatically "Ground-Out" the Un-Used Antenna. Also these
Antenna Switches have a "Center" position that "Disconnects
and Grounds both the Antennas when the Radio/Receiver is
not-in-use. {A Nice Safety Feature.}


iane ~ RHF
.
.
= = = "Brian" <imaginaryfriend@wh*tth*f*ck.c*m> wrote in message
= = = news:<U0Ged.6046$5i5.5787@...>...

Anyone familiar with this particular antenna ?
Have you had success ?
Is it necessary to use an antenna tuner ?
Just curious.

-Brian

.

I read with great interest your email describing your antennas, also read GreerTech
Articles.

I think you have made a nice job, also by the detailed description on how to build it.

Three questions:

1. You took the Velocity Factor into account while WN6F states in his update (March 2004): ".... I incorrectly assumed that since we are using coax as antenna elements, that they would be subject to a cable's velocity factor. Since the loop element is really the outer braid skin, it is not subject to velocity factor. Only the inner differential-mode of coax is subject to velocity factor, and NOT the common-mode outer surface conductor of the braid, which is what we are using as the antenna!
My standard formula for calculating the loop circumference for the frequency of interest at 1/10th wavelength without any VF, is:

(1005 / freq mHz) * 0.10 "


Did you find that it is better to take it(VF) into account after all? There is quite a difference in element length between VF=1 and VF=0.66.

2. After preparing the antenna "elements" according to the different Shortwave Bands, did you check if they are actually optimized for those bands?

3. If they are really optimized, does it mean that they resonate at that frequency?

Or did I something along the way?

Sorry if it is too long :( .

Niki