Last year I wrote about using the PE1BVQ 3 band endfed in the PACC contest. Because of large winds the antenna kept sliding in. But overall it did actually just as well as the HF5B on the tower except for about 3dB more noise. A vertical antenna in a contest is a good choice if propagation is good around you, but if you need extra gain it can't compete. However, I don't have a large multiband beam at the moment so I have to think about something else to improve my 20m signal. I would prefer to setup a antenna that does equal or better as my endfed and has a lot less noise. I was thinking about a phased vertical system first, but what I want is too complicated to setup at this time. I also thought of my endfed put up higher in the air with radials beneath. But I doubt it is any better as my vertical on top of the tower. So, I came up with the idea to use my GFK mast to make a delta loop for 20m. You can find a lot of drawings and designs on the internet about this antenna but they are all different, I posted a question about these different designs on a dutch hamradio forum and I got even more confused since everyone had other views on it. However, through the forum I found this link to some interesting delta loop designs and a usable formula. It is in dutch, and they use 1:2 balun instead of 1/4 wave 75Ohm coax, but what is left is the same in all languages. My thought is configure my deltaloop with one corner up in the mast. Fed at the corner at the north side to get the best radiation to the south. This way I have minimum interference from my neighbours solarpanels. Most of my QSOs on 20m in a contest are in the southern direction on 20m. A few are to the east and west but almost nothing to the north. The plan is to construct the antenna saturday or sunday depending on the weather. More about it hopefully in the weekend.
Thursday, January 30, 2020
Antenna for PACC 2020
Last year I wrote about using the PE1BVQ 3 band endfed in the PACC contest. Because of large winds the antenna kept sliding in. But overall it did actually just as well as the HF5B on the tower except for about 3dB more noise. A vertical antenna in a contest is a good choice if propagation is good around you, but if you need extra gain it can't compete. However, I don't have a large multiband beam at the moment so I have to think about something else to improve my 20m signal. I would prefer to setup a antenna that does equal or better as my endfed and has a lot less noise. I was thinking about a phased vertical system first, but what I want is too complicated to setup at this time. I also thought of my endfed put up higher in the air with radials beneath. But I doubt it is any better as my vertical on top of the tower. So, I came up with the idea to use my GFK mast to make a delta loop for 20m. You can find a lot of drawings and designs on the internet about this antenna but they are all different, I posted a question about these different designs on a dutch hamradio forum and I got even more confused since everyone had other views on it. However, through the forum I found this link to some interesting delta loop designs and a usable formula. It is in dutch, and they use 1:2 balun instead of 1/4 wave 75Ohm coax, but what is left is the same in all languages. My thought is configure my deltaloop with one corner up in the mast. Fed at the corner at the north side to get the best radiation to the south. This way I have minimum interference from my neighbours solarpanels. Most of my QSOs on 20m in a contest are in the southern direction on 20m. A few are to the east and west but almost nothing to the north. The plan is to construct the antenna saturday or sunday depending on the weather. More about it hopefully in the weekend.
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4 comments:
Hi Bas. Well, how many hours, days and weeks have I spent on delta loops?
The apex-down delta is fine, if you have the supports for it. The apex can go at the top if you only have/want one support. In practice, there won't be much difference.
A 2:1 balun used with a coax feed to the corner will work and give a perfect or near-perfect match if the environment is fairly clear. My 15m delta is still bottom corner fed, and a 2:1 balun gives 1:1 match.
The radiation pattern is the only thing that suffers with a corner feed: it is much less attenuating of high angle signals if you don't want those than if you use the 1/4 wave up from a corner feed point (whichever way up you put the triangle).
And remember, if you initially wanted a phased vertical system, that is essentially what a delta loop is: two closely-spaced verticals, each with one radial.
Apex at the top and feed 1/4 lambda from the top (so a bit up from one of the lower corners). If you make the top angle about 90deg. the feed impedance will be close to 50 ohm => no need for a impedance transformer. Play with the height of the antenna to get best SWR. I used this on 30m while in 9M2 many years ago.
Works like a charm. Vertical polarization, almost perfect 360deg radiation at low take off angle.
Here is the NEC file for 20m, base at 5m AGL, 1mm diam wire. SWR=1.04 (4NEC2)
CM 20m delta loop, rect. top angle, side fed
CE
SY w1seg=31, w1x1=0, w1y1=4.682777, w1z1 = 5, w1rad=5.e-4
SY w2z2=w1y1+w1z1
SY Freq=14.15
GW 1 w1seg w1x1 w1y1 w1z1 w1x1 -w1y1 w1z1 w1rad
GW 2 w1seg w1x1 w1y1 w1z1 w1x1 w1x1 w2z2 w1rad
GW 3 w1seg w1x1 -w1y1 w1z1 w1x1 w1x1 w2z2 w1rad
GE -1
GN 2 0 0 0 13 0.005
EK
EX 0 3 6 0 1 0 0 0
FR 0 0 0 0 Freq 0
EN
The total length of the wire (circumference of the loop) will be:
w1y1*2*(1+sqrt(2))= 22.61m
Height of the loop = w1y1=4.683m, the top is at the height + 5m =9.683 so that will fit a "standard" 10m glasfiber pole. Feedpoint in one of the sides, 1/4 lambda from the top (~ 5.20m)
Thanks for the comments John and Enno. Enno has send me a e-mail with more pictures and explanation. Fed at a quarter wave from the top doesn't need any transformer. I like that most, besides that it gives a nice radiation pattern. So I'll try to make one this weekend. 73, Bas
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