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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 01-04-2009, 7:06 PM
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Default 1:1 or 1:4 for inverted L HF antenna ?

It was nice out this weekend so I started a project of an HF wire antenna in the back yard. I had a 1:1 balun and a 1:4 balun in the parts box. I made an inverted L for 80 meters. It starts at the center of the yard between two large trees and drapes over one branch about 30 feet up then travels 90 degrees over toward the house. Approximately 20 feet of nylon rope connect the end to a vent pipe on the roof.

The first variant was a 1:4 balun and just two or three 50 or so foot ground radials thrown out on the dirt. I swept it with the MFJ and it was flat on everything above 30 Mhz but I could never get below 3:1 swr below that. It was nice and quiet noise wise and seemed to receive well.

The next day I switched the balun out with a 1:1 type and added 10 or so radials out to 30-60 feet in every direction. The SWR looked nice at 80 meters but the noise is now S9 all the time.

I know verticals are known for noise but is there some sort of compromise that can be made here to reduce it?

Also, which balun type should be used? I'm pretty sure it's the 1:1
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Old 01-04-2009, 8:55 PM
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Most terrestrial noise is vertically polarized. Not much way around it either with an L.

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The SWR looked nice at 80 meters but the noise is now S9 all the time.
This is about accurate. My 75m dipole comes in with a consistent S9-S9+20dB noise level with no signal, and it's a junky setup - about 20 feet off the ground. At 60 feet I would imagine 20+ consistently.

That's an indication that your antenna is working

1:1 balun would be the best. The L will have between 36 and 50 ohms radiation resistance depending on quality of your ground field.

You don't even really need a real balun, just a coax choke. Maybe 10-15 turns on a 4" form - don't scatter the windings, make it a nice coil and secure it.

Most people are amazed to realize the noise levels on 75m and 40 to a lesser extent. The best thing to do is to learn to work your radio's gain and AGC curve.

Try an experiment - tune in a moderate signal, then turn your RF gain ALL the way down, and engage "fast AGC". Then turn your AF gain (volume) ALL the way up. Pin it. Now bring your RF gain back in to where the conversation is easily audible. You will generally get much better signal quality this way.

Just beware that this setup does negate most of the "gain control" aspect of your AGC, so if a louder station than the first one comes in, it will blow your ears off. Listen for a minute to make sure there isn't a powerhouse in the round table.
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Last edited by jonny290; 01-04-2009 at 8:57 PM..
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Old 01-04-2009, 9:23 PM
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Thanks for the tips.

The only real HF station I've used was at house in the middle of nowhere so the noise was nice and low. I was just surprised at the consistent high levels and wondered if that was just unique to my area.

Another thing that confounded me is that if these noise levels are normal then how are consistent conversations conducted? I hear guys just casually chatting away all over the bands. Am I correct in assuming that they are running beams in much more ideal RF environments? I can't imagine they are dealing with this all the time. It's like trying to hold a conversation with your head out the window of an airplane.
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Old 01-04-2009, 9:36 PM
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If I had S9 noise I'd take up cake decorating or embroidery or something.......!

Try a Faraday shield around a tuned loop - should cut down the noise considerably.
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Old 01-04-2009, 9:52 PM
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I believe that upwards of 90% of 75m operators use amplifiers to at least get them to the 500w level. There isn't much 'barefooting' going on down there, simply due to the noise.

And it's winter, even, when noise levels are lower. Summer brings thunderstorms, and more static/noise.

Most of them have good enough antennas and enough power that everybody pegs everybody's meter, or at least tickles 20+ or 40+.
You don't need much signal on SSB to hold an intelligible conversation. I've had many a chat on 20 and 17 where my meter doesn't even move without the preamp on - of course, the noise is much lower there.
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Old 01-04-2009, 11:11 PM
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How long is the wire up in the air? There is a classic NVIS L antenna that is about 25ft of vertical wire and about 75ft horizontal at about 25ft high with several ground radials beneath the wire. This is fed with an antenna tuner at the feed point and works good on 80/40/60m as a cloud burner and usually has low noise pickup. If the vertical wire gets too long it can become a short vertical with a large capacity hat. A quarter wavelength on 80m is about 65ft and if you have 30ft of that vertical it may think its supposed to be a vertical antenna. As others mentioned a balun should not be necessary if you made it a resonant quarter wavelength and a 1:1 would be appropriate if you really had to add one. If I had 60ft or more of unobstructed horizontal space, I would stick up the longest center fed dipole that would fit and use balanced line and a tuner. Noise will be low, signals will be good and you should have happy happy radio time.
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Old 01-05-2009, 1:57 AM
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Two large trees and a vent pipe? Hmm if you have enough separation/real estate, you may have enough room for a nice horizontal delta loop. I too am working on setting one up, but am dependant on fellow firefighters to assist as I am out on post-surgical medical leave. I work 75m almost exclusively due to interference issues with neighbor's computer equipment on 40 and 20. Currently running a dipole at 35' and exploring other options.

Good luck and 73.

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Old 01-05-2009, 2:01 AM
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Lol...yea no sh** That's about how I feel right now.



Quote:
Originally Posted by majoco View Post
If I had S9 noise I'd take up cake decorating or embroidery or something.......!

Try a Faraday shield around a tuned loop - should cut down the noise considerably.
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Old 01-05-2009, 2:06 AM
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Well that's almost exactly what I have going on here. About half the wire is vertical and of course the other half is horizontal.

The whole ladder line thing kind of looked like more work that is practical and that's what always turned me off of it. There's no way to get that ladder line to the shack and tuner in any real practical fashion where it doesn't traverse wires or have to run near a window metal or something.

I guess I need to keep trying different setups.

Quote:
Originally Posted by prcguy View Post
How long is the wire up in the air? There is a classic NVIS L antenna that is about 25ft of vertical wire and about 75ft horizontal at about 25ft high with several ground radials beneath the wire. This is fed with an antenna tuner at the feed point and works good on 80/40/60m as a cloud burner and usually has low noise pickup. If the vertical wire gets too long it can become a short vertical with a large capacity hat. A quarter wavelength on 80m is about 65ft and if you have 30ft of that vertical it may think its supposed to be a vertical antenna. As others mentioned a balun should not be necessary if you made it a resonant quarter wavelength and a 1:1 would be appropriate if you really had to add one. If I had 60ft or more of unobstructed horizontal space, I would stick up the longest center fed dipole that would fit and use balanced line and a tuner. Noise will be low, signals will be good and you should have happy happy radio time.
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Old 01-05-2009, 2:24 AM
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Here's the closes pic of my place. The yellow box is the property line. The box is roughly 100 ft x 50 or 60 ft. There are two large trees in the back side by side and two smaller trees in the front side by side.

I suppose I could try to string something from the front trees to the back which may yield about a 60-70 ft path. I've been avoiding that just for the sake of looks.

The L starts right in the center of that clump of trees in the back and runs over to about the back of the house. The vent is toward the top of the house on the roof line.

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Old 01-05-2009, 6:17 AM
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The inverted L variation on the "long wire" antenna is unbalanced feed so why a balun? With a dipole this I can understand, it's balanced feed so when coax (unbalanced) is used as transmission line a balun at the antenna is used. What you need is a "long wire tuner" or in other words use the "wire" output and ground terminals on the usual ham antenna tuner.
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Old 01-05-2009, 5:43 PM
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Your noise problem is compounded by the vertical element. How about a pushup pole mounted at the peak of your roof eve supporting an inverted-V? Should bring down the noise level, and if you still don't have enough room, how about running a trap dipole inverted?
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Old 01-06-2009, 7:03 AM
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Quote:
Originally Posted by kb2vxa View Post
The inverted L variation on the "long wire" antenna is unbalanced feed so why a balun? With a dipole this I can understand, it's balanced feed so when coax (unbalanced) is used as transmission line a balun at the antenna is used. What you need is a "long wire tuner" or in other words use the "wire" output and ground terminals on the usual ham antenna tuner.
That was going to be my question ... Where's the balanced part of the antenna?



http://patriciaray.net/antennas3.html

(I like how he hooked up a firecracker to the antenna ... I gotta try that sometime!)

Last edited by k9rzz; 01-06-2009 at 7:08 AM..
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Old 01-06-2009, 3:54 PM
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If the vertical portion is 1/4 wavelength what is the wavelength of the antenna, HUH? (;->) Seriously, once upon a time I had an inverted L (sort of with the vertical as a lazy V) 125' total length with the far end about 40' up fed by a "half pi" network in a weather tight metal box. The feed point was 10' off the ground for safety so what do you make of that?

Just to goof on your graphic a little more, if the vertical part is 1/4 wave the rest is superfluous unless the horizontal is 1/2 wave making it 3/4 wave overall. Those are your 90 degree (current) points where you get a 50 ohm match, otherwise you need a matching network. Nice illustration of an inverted L, too bad the text is all wrong except for the radials part.

Last edited by kb2vxa; 01-06-2009 at 4:01 PM.. Reason: goofing
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Old 01-06-2009, 4:12 PM
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That illustration is almost a photograph of what I have setup here. The only difference is that I put a 1Meg Ohm resistor across the balun because some have said that it could reduce static charges.
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Old 01-06-2009, 7:19 PM
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Well,it's not 'my' graphic ... see the link below it, and I thought that it was understood that the total length of the wire was 1/4 wave. If you had a tree branch that's 1/4 wave high, then that's it ... you're done! (and it's a pretty big tree for 80 or 160m for which most inverted L's are made for ). If the total length is more than 1/4 wave then I would just call it a random wire and then it would indeed need an antenna tuner or 'something'.

FYI: if you follow that link, it shows this antenna:



I made one of these for 40 meters, except I fed it on the side so it was vertically polarized (and no radials needed). The bottom wire was just 7 or 8 feet off the ground it was *KILLER* for 40 meter DX !! I would simply call CQ late at night on 40 cw and get VK's, ZL's, and PY's all the time.

I *HIGHLY* recommend this antenna.

Last edited by k9rzz; 01-06-2009 at 7:23 PM..
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Old 01-06-2009, 7:39 PM
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Thats a very specific antenna for 40m in two directions, not a good general purpose antenna.
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I made one of these for 40 meters, except I fed it on the side so it was vertically polarized (and no radials needed). The bottom wire was just 7 or 8 feet off the ground it was *KILLER* for 40 meter DX !! I would simply call CQ late at night on 40 cw and get VK's, ZL's, and PY's all the time.

I *HIGHLY* recommend this antenna.
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Old 01-06-2009, 8:39 PM
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What would happen if you put another loop going the other direction that intersects it but doesn't electrically touch it? Like an egg beater that can be switched. I wonder what that would do?
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Old 01-06-2009, 8:45 PM
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Quote:
Originally Posted by mancow View Post
What would happen if you put another loop going the other direction that intersects it but doesn't electrically touch it? Like an egg beater that can be switched. I wonder what that would do?
Sounds pretty ugly. You can get a free copy of EZNEC and model it to see what the numbers and graphs look like.
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Old 01-07-2009, 12:54 AM
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Quote:
Originally Posted by prcguy View Post
Thats a very specific antenna for 40m in two directions, not a good general purpose antenna.
prcguy
NOT

I had one, I used one, it was not that directional, and it was an AWESOME DX antenna!

Have you ever built a rotatable loop, perhaps for the AM BC band? Nulls are sharp, not broad.

(but hey, if you don't want to believe me ...)
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