Topband: Square "loop" antenna for 160

[Richard (Rick) Karlquist]

On 1/31/2022 6:22 PM, Radio KH6O wrote>
> I have to live with CC&R homeowner restrictions. I plan to erect a disguise
> wire antenna around the perimeter of my roof; total length will be about
> 190 feet. Elevation will be about 20 feet above ground and will be fed with
> 150 ohm twin lead.*
> 
> My question is: Should this be a continuous loop or should the point
> opposed the feedline be terminated with an insulator, thus giving two
> 
> Jeff KH6O
> Naval Air Staiton Point Mugu, CA

Warning, long posting.  Sorry for the BW.

It just so happens that I have a horizontal square loop antenna made of 
#18 insulated wire, that has a perimeter (AKA length) of 200 feet, and 
an adjustable height of zero to 30 feet, and is in the clear, away from 
buildings, etc.  It has a drive impedance of about 5 ohms + j600, IOW a 
Q of about 100, and therefore a bandwidth of a dozen or two kHz.  At 30 
feet, it consistently has a gain of -30 dB vs my 90 foot top loaded 
vertical over a massive ground screen on high conductivity ground. 
Except for certain stations within a few hundred miles where the loop 
might be "only" 20 dB down from the vertical, due to NVIS or short skip, 
or something.  Reducing the height to 20 feet only affects the gain by a 
few dB.

IMPORTANT!  The size of this loop is too large for it to be "magnetic" 
with constant current.  However, I use a trick to make the current 
constant.  Without that, the loop would be even worse.

Now to your questions:

Not closing the loop creates a bent dipole.  It is approaching a half 
wave, but will still need loading coils.  I don't know how loading coils 
are going to qualify as "stealth".  I live on 20 acres so I don't think 
about stealth.  I will say that I have also erected full size 160 meter 
dipoles at a height of 30 feet.  Your bent dipole at 20 feet would be 
worse than this of course.  My dipoles had a fairly narrow bandwidth, 
maybe a few dozen kHz.  I don't remember for sure, but the gain was 
perhaps 6 dB higher than the loop, but don't quite me.  Running the 
legal limit power, you will be lucky to get a watt or two EIRP.  The 
digital modes like FT8 will be your only viable option.

If you don't have an amplifier, you need to get a cheap used tube type 
one.  They don't command much money these days.

Puh-leeze! don't feed it with twin lead.  You need a remote matching 
network at the feed point.  Hopefully with some frequency switching so 
you can cover more than a sliver of the band.  The question about 
stealth is again raised.

BTW, I only use my loop for receiving.  I worked a JA while using it for 
receive when it was lowered to 10 feet.  It generally receives as well 
as the vertical in terms of signal to noise ratio, with the loop at its 
usual 30 foot height.

73
Rick N6RK