[Towertalk] 40 meters (Delta Loop)

[n4kg@juno.com]

I hope Tim, K3HX, doesn't mind my public answer 
to his questions which I expect may be of interest
to several readers.    Tom  N4KG

On Fri, 28 Jun 2002 ttt ccccc <k3hx@juno.com> writes:
> OM,
> 
> I'm interested in the delta loop you described for FD.
> 
> I'd be grateful if you could answer the following:
> 
> 1	How did you feed it....middle of a side or at a corner

	To obtain VERTICAL polarization, a Delta Loop
	needs to be fed 1/4 WL down from the APEX (TOP).
	Since each side is ~1/3 WL long, this is 0.08 WL
	above one of the bottom corners.  Feeding at a
	bottom corner is mechanically simpler and results
	in 'mostly vertical' polarization which is what we do
	at our FD site.   N4KG
> 
> 2	How high was the loop off the ground at the lowest point

	Assuming the Loop circumference is 1WL, each side is
	1/3 WL.  IF it is configured as an equilateral triangle,
	each corner is 60 degrees and the height is calculated
	as 1/3 WL X Sin 60 =  0.333 WL X 0.866 = 0.288 WL
	which comes to just over 40 ft for 40M  (80 ft for 80M etc).
	Subtract the loop height from your support height and you
	will know how high the bottom wire is off the ground.	
> 
> 3	Was it with a side parallel to the ground?

	YES.
> 
> 4	What kind of support did you use....conductive or not.

	We used 50 ft high metal lamp posts (between two baseball fields).
 
> 5	What were the dimensons and were these for CW or Phone

	The formula for a Delta Loop is 1005 / F (MHz) in feet.  
	When one side 	is close to the ground, I find that it needs 
	to be shortened	by about 5%.  An antenna analyzer makes 
	trimming to resonance an easy job.   N4KG
> 
> 6	What do you suppose the front - to - side figure was like

	As I recall from modeling, the F/S is pretty low, on the order
	of 3 dB.  Look at the F/S for phased verticals with 1/4 WL
	spacing and 0 degrees phasing for comparison.  You will see 
	an oval pattern with very little F/S.  N4KG
> 
> 7	Any special matching concerns?

	A 1WL Delta Loop looks like 100+ ohms which is easily
	transformed to ~50 ohms by any ODD multiple of 75 Ohm
	coax.  I use 3/4 WL (electrical) of RG59 which comes to 84 ft.
	in the CW Band.  N4KG
> 
> 8	Words of wisdom, counsel or advice....all would be welcome.

	I think we covered all the bases above.   Tom  N4KG
> 
> 73
> 
> Tim  K3HX
> 
> On Fri, 28 Jun 2002 05:00:50 -0600 n4kg@juno.com writes:
> > Hello Kelly,
> > 
> > For Field Day, I used a 50 ft high inverted vee (120 degree apex 
> > angle)
> > aimed at W8 and a vertically polarized Delta Loop aimed at W6.  
> The Delta Loop gives me 6 to 10 dB improvement to the West Coast after
> > 11 pm local time.  The antennas are approximately perpendictular
> > to each other.  IMHO, it is NOT worth making a Horizontally 
> > Polarized
> > Delta Loop unless you can get the apex much higher (80 to 120 ft)
> > since the effective height is so close to the *bottom* wire.  This 
> > is not a problem for VERTICALLY polarized loops.
> > 
> > For the last two years, I've added a 70 ft reflector to the 
> inverted  vee 
> > and it has been a KILLER, allowing us (K4BFT)  to overtake the
> > 20 / 80 CW station for the first time ever.  We use the 40M 
> inverted vee in 15M where it performs quite well.  With the 120 degree 
> apex  angle, the pattern nulls fill in fairly well, giving us an almost

> > omni- directional pattern on 15M.  We use the 40M Delta Loop on 10M
> > to pick up a few extra contacts on that band as well.
> > 
> > Tom  N4KG  in ALA
> > 
> > On Thu, 27 Jun 2002  "Kelly Taylor" <ve4xt@mb.sympatico.ca> 
> writes:
> > > Hi all,
> > > 
> > > Considering options for SS this fall and I'd like some opinions.
> > > 
> > > Options somewhat limited to choice of following:
> > > 
> > > Inverted vee, apex 50 feet versus 1wl loop, hung from same 
> > yardarm.
> > > 
> > > First question: is it even worth doing?
> > > 
> > > If so, diamond shape or delta?
> > > 
> > > Thanks,
> > > 
> > > 73,
> > > kelly
> > > ve4xt