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 ProWhip Delta Loops 
Silent Key

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Post Re: ProWhip Delta Loops
That's a very strange loop if it's designed to be a half-wave of wire at its design frequency! The impedance of a half-wave loop is extreme - very difficult to match and will cause high losses in any feedline.

Steve G3TXQ


Sun Apr 05, 2015 4:27 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G7CBR wrote:
The wires should be equal lengths on all 3 legs and measure a half wavelength at the frequency of use. So the 8 metre version should have 24 metres of wire +/- for 40 metres. The angle at the bottom of the V should be as close to 90 degrees as possible. Dont do what I did and mount it in the clear as 25 foot and then ignore the weather, the poles will snap. Luckily I have a selection of glass fibre whips that I broke on fish and could splint the broken ends. The wire will also flex at the point it enters the pole and eventually break. Birds will see it as a good place to roost and become tangled in the wire, being right on the coast this usually means seagulls.
All in all a good antenna if you only have a small garden, nosy neighbours and have worked into Canada and US on 10 watts on HF. Will also tune up on 6 metres and have had some good contacts into Europe. Very directional and could do with a rotator, but will work close to ground so makes it easy to turn using the Armstrong method


Thanks for the info. Am thinking of making one for 15 meters but maybe use 300 ohm twin feeder with 4:1 balun to make it tunable with the ATU but I want to aim it stateside as struggle to get there with my 40 meter doublet. The doublet has to run over my house and down to an 18 foot high post as only have a 30 foot garden and no front garden. The delta loop using the fibreglass poles is probably my best chance of doing this and I would mount it at around 15 feet high.

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Dennis


Sun Apr 05, 2015 6:29 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G3TXQ wrote:
That's a very strange loop if it's designed to be a half-wave of wire at its design frequency! The impedance of a half-wave loop is extreme - very difficult to match and will cause high losses in any feedline.

Steve G3TXQ




That is why it is fed through a 9:1 balun. Mine was checked with an antenna analyser and was resonant just below 7 MHz, so needed at atu to work correctly. Good antenna spoilt by being not as strong as the east coast gales off the sea.


Fri Apr 10, 2015 9:12 am
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 ProWhip Delta Loops 
Silent Key

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Post Re: ProWhip Delta Loops
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ


Fri Apr 10, 2015 4:12 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G3TXQ wrote:
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ


I was playing with them on NEC this morning, and I think about 21m was resonant on 14MHz. It gave a good SWR on 28 as well, with good side nulls.

But everywhere else it would have been out of range of an internal tuner

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Fri Apr 10, 2015 4:52 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G3TXQ wrote:
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ


Is it a dipole that looks like a loop rather like a single cobweb element might?

Cheers, Dave.


Fri Apr 10, 2015 5:32 pm
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 ProWhip Delta Loops 
Silent Key

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Post Re: ProWhip Delta Loops
G7VQE wrote:
Is it a dipole that looks like a loop rather like a single cobweb element might?


Could be - but everything on the web page refers to it as a "Delta Loop".

Steve G3TXQ


Fri Apr 10, 2015 10:18 pm
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 ProWhip Delta Loops 
Silent Key

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Post Re: ProWhip Delta Loops
If a 24m loop shows a resonance around 40m, you're almost certainly measuring a resonance of the coax braid - not the loop. The impedance of the loop is so high - tens of thousands of Ohms - that it's almost impossible to stop the braid radiating.

Steve G3TXQ


Sun Apr 12, 2015 8:11 am
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G3TXQ wrote:
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ





That was the length of wire in use and it showed the best SWR on an antenna analyser at the lower end of 40 metres. could tune it for any band but top band up to 6 metres. but as I said very directional and needed to be turned towards the area you want to work. The impedance depends on where you feed the antenna, and the pro whip is fed at the upside down apex so is near to 50 ohms at any length close to resonance. Can only go by what I measured the antenna at when tuning.


Sun Apr 12, 2015 12:28 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G3TXQ wrote:
If a 24m loop shows a resonance around 40m, you're almost certainly measuring a resonance of the coax braid - not the loop. The impedance of the loop is so high - tens of thousands of Ohms - that it's almost impossible to stop the braid radiating.

Steve G3TXQ





As the RSGB books say it depends on where it is fed. And this might be true if fed in the centre of a leg, but the closer you come to a corner the impedance drops. You can also decrease the angle at the bottom of the V and feed in the middle of the apex by bringing the elements down to your preferred connector to bring to resonance. It is just a opened out folded dipole at the end of the day.


Sun Apr 12, 2015 12:34 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
Sangoma wrote:
G3TXQ wrote:
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ


I was playing with them on NEC this morning, and I think about 21m was resonant on 14MHz. It gave a good SWR on 28 as well, with good side nulls.

But everywhere else it would have been out of range of an internal tuner






Don't use the internal tuner as it will not work on anything worse than 2:1, always use the manual one and can tune up on any HF band.


Sun Apr 12, 2015 12:36 pm
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 ProWhip Delta Loops 
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Post Re: ProWhip Delta Loops
G7CBR wrote:
Sangoma wrote:
G3TXQ wrote:
A balun wont change the resonant frequency - it changes the impedance. Have I understood correctly that you've measured a loop with a total wire length of 24m to be resonant just below 40m?

Steve G3TXQ


I was playing with them on NEC this morning, and I think about 21m was resonant on 14MHz. It gave a good SWR on 28 as well, with good side nulls.

But everywhere else it would have been out of range of an internal tuner






Don't use the internal tuner as it will not work on anything worse than 2:1, always use the manual one and can tune up on any HF band.



I get a loop of that dimension to be resonant nearer to 12MHZ, and an impedance at 7MHz to be about 3000ohms, and the radiation pattern at 7MHz to be nearly circular, and a "gain" of around 2.5dBi, which means a loss compared to a dipole.

Something is very strange.

When I said out of range of an internal tuner, the SWR was 10:1 or worse.

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Sun Apr 12, 2015 12:52 pm
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 ProWhip Delta Loops 
Silent Key

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Post Re: ProWhip Delta Loops
G7CBR wrote:
G3TXQ wrote:
As the RSGB books say it depends on where it is fed. And this might be true if fed in the centre of a leg, but the closer you come to a corner the impedance drops. You can also decrease the angle at the bottom of the V and feed in the middle of the apex by bringing the elements down to your preferred connector to bring to resonance. It is just a opened out folded dipole at the end of the day.

All those things are true for a loop that has a perimeter of about one wavelength, including the comment about a "folded dipole opened out"!

But a 24m perimeter loop is way too short for 7MHz - it should be more like 45m. When you see a resonance close to 40m the coax is almost certainly the more significant radiator than the loop.

Steve G3TXQ


Sun Apr 12, 2015 1:08 pm
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