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1-7 of 7 messages
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2 element phased receiving antenna system ncc1
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by VK1KHV on November 3, 2009
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i have a NCC-1 phasing two active whips
its been sitting in a spacing of 20 meters for around 12 months.
ive been useing it on 160,80,40
40 the spacing is too wide its not good.
my question is.
i want it to work better on 80.
it seems to work best on 160. but thats 1/8 spacing and i read 1/4 is best.
should i pull them closer together?
maybe w8ji will give me an answer as he designed the system.
73
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RE: 2 element phased receiving antenna system ncc1
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by N3OX on November 3, 2009
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Which way are you firing with it? If you're doing end-fire unidirectional (in line with the two elements), you can space them really close, but it should work fine with 1/4 wave spacing.
How are you determining it's not working? Have you measured the pattern or are you just going on what you're hearing on the bands?
I've got a flag here, which up to some high angle extra pattern from the top and bottom feed wires is basically two close spaced end fire verticals with a cardioid pattern.
And if I listen *VERY* critically and I'm careful with matching signal levels using attenuators, I *can* tell that it's better than my transmitting vertical but it's actually really hard to tell, because the overall receiving improvement is VERY subtle.
The exception to that is when I have some loud interfering thing that I can drop into the null. A two element array is only going to give you a few dB improvement in a few directions and will only have substantial F/B in the end fire (though you can use bidirectional end fire and have side nulls if you have arbitrary phasing) .
I can rotate my flag 360 degrees continuously so if I've got a loud noise locally I can null it off the back. It also does a great job in the spring when thunderstorms start up across the USA... I can listen to EU well, especially on 80m, but again, this is an anisotropic noise issue.
Other times, when the noise is coming from all around, I have to really think and listen and switch back and forth and really **try hard** to hear any difference between my flag and my transmitting vertical, and I can "aim" it right at my desired destination!
On 160m system should be a couple dB better by comparison according to
http://www.w8ji.com/receiving.htm
and
http://www.k7tjr.com/rx1comparison.htm
Two verticals should be about 4dB better than one in terms of receiving directivity. My situation is more subtle; my flag is 2dB better than one vertical.
I'm not saying these improvements aren't improvements, I'm just saying that if you're in a quiet location with noise coming from all around it might actually be hard to tell.
A lot of people report wonderful results with simple receiving arrays that suggest that something else is at work besides the basic directional characteristics. I think that "something" is probably common mode noise issues or local noise concentrated in azimuth coming from the neighborhood.
On the rare occasions I'm up at sunrise, having 20dB F/B is a wonderful, wonderful thing on 80m. Off to my East there's a building whose elevators have noisy variable frequency drives. On my transmitting vertical, the noise from them is about S9+20dB when someone's riding. Pointing the flag out West makes them almost disappear, and even pointing to JA (330 degrees) is pretty good. I've made several contacts that would have been very hard or impossible without the flag.
On a quiet winter night on 160m when all I have is a little power line buzz that mostly gets covered by propagated noise from around the compass, there's often zero practical difference between my flag and vertical. If I weren't careful I'd still notice a "big difference" for various reasons, but if I'm careful to minimize those, I can barely tell the difference.
73
Dan
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RE: 2 element phased receiving antenna system ncc1
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by W8JI on November 3, 2009
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The optimum spacing depends on what direction you are trying to receive, what directions you can place the antennas, and what direction the problem is from.
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RE: 2 element phased receiving antenna system ncc1
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by VK1KHV on November 3, 2009
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im in the middle of nowhere so there is no problem
noise is small and in all directions. but i do use it to get rid of chinese radar for example. even bad qrn
the antennas are setup so that there halfway between endfire and broadside for USA and europe.
basically the signals hit on a 45degree halfway between broadside and endfire.
looking to get more out of it on 80meters.
dxeng suggested adding another element and switching to it for tighter spacing which made sense.
ive also seen that you suggest 1/8 spacing for receive four squares.
thanks tom (w8ji)
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RE: 2 element phased receiving antenna system ncc1
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by VK1KHV on November 4, 2009
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and what i mean by that is they run true north south so in endfire they would goto the poles
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RE: 2 element phased receiving antenna system ncc1
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by W8JI on November 4, 2009
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You won't get much broadside directivity at spacings less than 1/2 wave. You sure will get deep nulls though at any spacing. The spacing mainly controls the null width, and the null gets wider as the antennas get closer except you lose sensitivity in all directions as they are closer.
Did you ever look at patterns in textbooks? What textbooks do you have? I'm thinking the ARRL Antenna Handbooks might have some patterns for verticals at various spacings and phasing. I looked but cannot find where that was at.
I just don't know what directions things are for you. I would plan it for widest null in the directions of problems. Getting the null placed on the dominant problem is much more important than a few dB gain when receiving.
Tom
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RE: 2 element phased receiving antenna system ncc1
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by VK1KHV on November 4, 2009
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ive seen patterns yes.
i have low band dx'ing on4un
arrl textbook. and many others.
youve also published some stuff.
so your saying closer spacing creates a very DEEP null (in DB)
but also starts to make it touchy. which is what i see in the AM broadcast band where there spaced close
you can get 40+db null but its real touchy. you have to be right on the money.. feed current's and also phase.
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