I drank the ON4UN coolaid regarding compressed delta loops and built a
batch of 40M loops for field day, 2 tuned to 7.050 MHz and another pair
tuned for 7.175 MHz. They were fed with 1/4 wave sections of RG-11 that
were carefully trimmed to length for velocity factor. I also carefully
trimmed a 1/4 wavelength section of RG-213 so I use two delta loops as a
2 element driven array. I did not use a hybrid power divider at the feed
point - just a coaxial tee connector. My initial thought based upon
successful deployment at field day 2014 (W7PIG 6A WWA) that these arrays
were going to be my new equalizer for a local club (K7LED 6A WWA) that
uses a phased vertical array on a saltwater beach.
I promptly set up a contesting buddy with one of the 2 element delta
arrays for him to do more beta testing during this winters contesting
season. His first observation is that the 2 element delta loop array had
more RX QRN than his dipole that is a flat top at 70ft high. His second
observation was that the 2 el driven array was only slightly better on
transmit.
The difference was significant enough that he routed his dipole to the
2nd receive port of his K-3.
It is a well know fact that a dipole has 8dBi gain when it is 1/2
wavelength high do to the ground reflection. ON4UN is saying in his book
that these compressed delta loops only have 1.6 dBi gain over average
ground.
Based upon real world A - B comparisons of my buddies dipole to the 2 el
driven delta loop array, I am left to wonder if the apexes of the delta
loops need to be raised so the average height is 1/2 wavelength.
At 17M this is not very difficult, at 40M we're looking at 80+ ft high.
Just my 2 bits with real world A - B comparisons to back up my wild claims.
Vy 73, Don KO7i
On 11/23/2014 8:15 AM, Rick - DJ0IP / NJ0IP wrote:
GM George,
The advantage of this type of delta loop is, at low heights, the loop fed
vertically polarized has a lower radiation angle than the dipole. The dipole
will have to be raised a lot higher to match its radiation pattern. The loop
is also more broad banded. Its advantage over a quarter wave vertical is, you
don't need to put lay a bunch of radials, which often can be a nuisance.
As for how to feed it, well I have been feeding loops like this for 35 years
and they have been giving me outstanding results. That does not mean a perfect
match but good enough to use without a matchbox. Of course the impedance
varies with height above ground.
If you have a better idea on how to feed it, please share it with us.
I'm always happy to learn something new.
My source of information on how to feed this type of antenna is from DL1BU (SK,
and ex- chief technical Engineer of the DARC) in his article on loops, printed
in the 1979 issue of CQDL magazine, page 154.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of george fritkin
via TenTec
Sent: Sunday, November 23, 2014 4:40 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] 17 Meter Antenna
Delta loops show marginal gain over a dipole (1.1db), and are much more of a
pain to erect. As far as noise no real proof that is true. And one more
thing, feeding with 1/4 wave of 72ohm is more voodoo engineering you find here
George, W6GF
On Saturday, November 22, 2014 11:18 PM, Rick - DJ0IP / NJ0IP
<Rick@DJ0IP.de> wrote:
Use a telescoping fiberglass pole.
They don't have to be very high.
25 ft. is high enough if you make the horizontal bit a little longer.
That still leaves about 7 or 8' under the antenna so that people can walk under
it.
Scott (W4PA) sells 40' poles. One of those would be perfect.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Reed
Sent: Sunday, November 23, 2014 4:17 AM
To: tentec@contesting.com
Subject: [TenTec] 17 Meter Antenna
I'm sure Gary they are the best antenna for the dollar, but not enough trees here for
support. I was raised on a farm & my late father, W4PFP & elmer, had some
serious wire antennas. I miss the real estate, but not the farming.
Reed W4JZ
Reed,
I had a 80M Delta loop up for quite a few years. It worked extremely well.
Very quiet. It was fed in the corner with 75 ohm coax, then 50 ohm to the
shack. My matching piece of 75 ohm coax was abt
46.5 feet long (1/4 wave x velocity factor of the cable). I'd put another up
but all my trees have grown up.
Gary - KN0V
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