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Author Topic: How do I feed a Delta Loop using a radials  (Read 3396 times)
WA2TPU
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Posts: 209




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« on: March 28, 2012, 09:44:38 AM »

Hi to all. Over the Winter I lost my 75 meter vertical to the only  ice event we had. I want to put up a 40 meter Delta Loop on a fiberglass pole  where my vertical once stood. The question I pose is how does one feed a Delta Loop using the 68 radials that would be under it? I plan on using a 1to1 balun and feed the Delta Loop vertically polarized in one corner. Where the coax hooks to the balun should I peel back the coax covering so the shield shows and hook a wire via a ss hose clamp to this coax shield then solder this wire to the radial system? Is that the way to feed to Delta Loop with radials?? Also, IF....IF this is the proper way to hook the radials to the loop ....do I need to put heat-shrink/electrical tape over the coax shield  covering it??? or can I leave it open??I'm asking all this because I was told long ago that a Delta Loop will operate even better with a radial system under it.
    Any and ALL thoughts/ideas would be greatly appreciated. Thank you.

Best regards,
    Don sr. - WA2TPU/Qrp
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WB6BYU
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« Reply #1 on: March 28, 2012, 10:07:01 AM »

You don't need to electrically connect to the radial system for it to be effective.

Just feed the delta loop in the normal manner.
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W0BTU
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« Reply #2 on: March 28, 2012, 10:49:27 AM »

Yup. A delta loop doesn't need radials anymore than a center fed dipole does. Radials are for end fed antennas.
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WX7G
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« Reply #3 on: March 28, 2012, 11:05:54 AM »

You were told wrong about a delta loop working better with radials.

So what is a one wavelength loop? It is two half wavelength dipoles in phase. In you case you will (if fed at the correct spot) two half vertical dipoles.
« Last Edit: March 28, 2012, 11:07:41 AM by WX7G » Logged
K3VAT
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Posts: 715




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« Reply #4 on: March 28, 2012, 11:19:15 AM »

Hi to all. ...  I plan on using a 1to1 balun and feed the Delta Loop vertically polarized in one corner. Where the coax hooks to the balun should I peel back the coax covering so the shield shows and hook a wire via a ss hose clamp to this coax shield then solder this wire to the radial system? Best regards, Don sr. - WA2TPU/Qrp

Hi Don,  The other replies have correctly addressed your question on radials and the delta loop (that radials are not needed; the Delta Loop is a closed loop).

If you plan on vertically polarized your delta loop, feeding it at one corner is not correct.  Per ON4UN's classic text on LowBand DXing (p 10.5 in the 4th edition), you need to feed the delta loop down 1/4 wavelength from the apex.  For an equilateral triangle this is easy to calculate.

BTW, since you already have invested lots of time/$ into a very nice radial field, why don't you simply rebuild the vertical (perhaps make it stronger)??  If your vertical was true quarter wave (~65' tall) and the radials were approx the same length (all 68 of them), then modelling would seem to suggest that the delta loop would not be as effective as the vertical for longhaul DX (if you're into that).

GL, 73, Rich, K3VAT
« Last Edit: March 28, 2012, 11:22:07 AM by K3VAT » Logged
K4RVN
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Posts: 778




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« Reply #5 on: March 28, 2012, 01:02:58 PM »

If interested in doing it to get all your QRP signal into the corner fed delta loop, the following info may be of interest to you.
The 1 to 1 balun will not match the impedence of a corner fed delta loop for vertical polarization. The impedence is about 100 ohms so you would need a 75 om matching section of coax to match the impedence, then you could use the 1 to 1 balun to take care of the coax unbalanced feed to the balanced antenna, and help prevent radiation of the coax. The radial system should not be connected, but won't hurt to leave as is and may even help depending on your soil ground properties. Better idea is to throw the 1:1 balun in the desk for future use and buy a new 2:1 balun.
At least that is my view, no expert here but have some years of experience using delta and quad loops.

Frank
« Last Edit: March 28, 2012, 01:43:22 PM by K4RVN » Logged
KI4VEO
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Posts: 166




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« Reply #6 on: March 28, 2012, 01:10:44 PM »

As the others posting have mentioned, the delta loop is a full wavelength antenna and does not require ground radials.

I have 3 Delta loops.  Two are cut for 80M - one is suspended horizontally, the other is an inverted vertical and fed at the bottom.  The BIG one is a 570 foot loop, up at 60 to 80 feet, and fed with homemade 450 ohm open wire line.  All are "matched" using a Tee type, band switched tuner which has a short RG-8X coaxial feed line out to a remote Balun Designs 4:1 balun (Bob makes some really nice balun's).  The 80M inverted delta uses some 300 ohm window line, and the 80M horizontal uses some W7FG 600 ohm open wire line (only because it began life as a W7FG 160M dipole - I just closed it up and kept the feedline in place).  The 2 smaller loops are now used very little since I put up the BIG loop.

I find that a 4:1 balun is necessary, using my Tee type tuner, if I make large excursions from the native resonance point of the loop - my BIG loop is easy to load on 160 thru 10M - just a bit "iffy" on a portion of 15M.  

I suspect that one day it will even work better, once I get my Heathkit SA-2060A on-line.  I had Bob construct a current balun for the Heathkit, to replace the voltage balun.
« Last Edit: March 28, 2012, 01:12:20 PM by KI4VEO » Logged
K3VAT
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Posts: 715




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« Reply #7 on: March 28, 2012, 01:34:47 PM »

I have 3 Delta loops.  Two are cut for 80M - one is suspended horizontally, the other is an inverted vertical and fed at the bottom.  The BIG one is a 570 foot loop, up at 60 to 80 feet, and fed with homemade 450 ohm open wire line. 

Hi Howard, did you compute the wire length of you "BIG" 80M loop before you strung it or was that just a convenient length that you had laying around?  Reason I ask is because yours is about 2 and 1/4 wavelengths for 80M rather than the traditional 1 wavelength long loop (actually 1.06 lambda is commonly used).  May be this explains why you need a 4:1 balun, as traditionally a 1 wavelength delta loop has a feedpoint impedance of around 100 ohms (Hence, the BalunDesigns #2112 a 2:1 balun Bob makes for loops and quads).

So have you checked that baby out for 160M yet?

73, Rich, K3VAT
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WA2TPU
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Posts: 209




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« Reply #8 on: March 28, 2012, 02:00:39 PM »

Thanks so much to all that replied to my query on the radials being connected to the Delta Loop feed line. I see there's no need to physically connect the radials to the feed-line. Also, I will re-consider making a stronger 1/4 wave vertical on 75/80 meters and installing it again above the existing radial system. As a vertical it worked very well but when I lost it I really considered the Delta Loop for that band as a better option since the fiberglass pole would be guyed using the outer legs of the Delta Loop wires. And since what I've gathered from the replies is that the existing radial system would not make a huge difference under the Delta Loop as I once was told long ago. So, why put up a Delta Loop on 75/80  when another stronger built vertical for this band would utilize the radials all ready there.
Again, thanks to all for your kind  replies and input. I really appreciate it.
Best regards,
   Don sr. - WA2TPU/Qrp
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WB6BYU
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« Reply #9 on: March 28, 2012, 02:45:25 PM »

Quote from: K3VAT

...did you compute the wire length of you "BIG" 80M loop before you strung it or was that just a convenient length that you had laying around?  Reason I ask is because yours is about 2 and 1/4 wavelengths for 80M rather than the traditional 1 wavelength long loop (actually 1.06 lambda is commonly used).  


Probably tuned for CW in the low end of the band.

Using a two-wavelength loop reduces the high angle radiation and focuses more at lower
angles.  W4RNL has an article on it here:  http://www.cebik.com/content/a10/wire/horloop.html
This is better for DX, but not as good for local NVIS operation.


Quote


May be this explains why you need a 4:1 balun, as traditionally a 1 wavelength delta loop has a feedpoint impedance of around 100 ohms.



The impedance of a loop varies depending on whether it is vertically or horizontally
polarized, among other factors.  It usually is in the 100 - 140 ohm range.   The
feedpoint impedance increases as the wire is made longer, so while a 4 : 1 balun
gives around a 2 : 1 SWR on the fundamental, the match gets better as the loop is
used on higher multiples.  As shown in the article I linked to previously, a horizontal
square loop is around 180 ohms on the second harmonic.  A loop for 80m or 160m
fed with a 4 : 1 balun gives an SWR of 2 : 1 or better on all harmonic resonances
through 10m.
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K3VAT
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Posts: 715




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« Reply #10 on: March 28, 2012, 03:08:31 PM »

Probably tuned for CW in the low end of the band.  Using a two-wavelength loop reduces the high angle radiation and focuses more at lower angles.  W4RNL has an article on it here:  http://www.cebik.com/content/a10/wire/horloop.html This is better for DX, but not as good for local NVIS operation.

Thanks Dale, yes the Cebik article is very interesting; and good point on the impedance.  Wish I had sufficient room for one wavelength 80M horizontal loop.  73, Rich, K3VAT
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N4JTE
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Posts: 1156




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« Reply #11 on: March 28, 2012, 03:19:53 PM »

 As already, said no conection should be made between the loop and the radials, however all vertically polarized antennas will benefit from an improved with good near ground conditions. Your existing radial system can only help with the overall performance if situated under the antenna in a usefull pattern.
Bob
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