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Antenna Question

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So, for the short term, I've opted to go with a variant of a buddipole. Two 20m vertical ham sticks tied together with a MFJ-347. This basically turns it into a 1/4 wave dipole....not ideal compared to a 1/2 wave, but I have been picking up stations from as far away as Hungary, the Slovak Republic and even Brazil. So, it does work.

The real question I have is transmitting.

I got a LDG antenna tuner and it does seem to be adjusting the SWR down to anywhere from 1.2-1.5:1. I can see the watt meter indicating transmission to full power set on the radio.

However, I am unsure as to whether I'm really getting out. I have the radio sitting on the railing of my back deck which is about 12 feet off the ground. Again, I know it isn't ideal. I'm thinking that I've got myself a nice NVIS setup right now with out intending to. The railing is made from the PVC type stuff...think TimberTech or Trex...same stuff. Would that inhibit transmission in any way? I can't see how since it isn't metal.

I'll be putting it onto a tripod with a mast of about 6 feet and leaving it on the back deck...so this would give me about 18 feet above ground. I'll try that tonight, time permitting.

Anyone see any logic with my thinking or deductions here? Am I missing anything?

Thanks
 
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Tuners only make the radio happy by presenting a good SWR to the radio. If the SWR is screwy on the antenna side of the tuner, much of the transmit power is lost as heat. Take a real SWR bridge and check the SWR of the feedline and antenna. Alternatively, run balanced feedlines, a balun and a tuner that supports balanced feedlines.
 

cockpitbob

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I've used that same set-up. The higher off the ground the better, of course. Being low raises the SWR as well as making it an NVIS pattern. I've taken the clipper/saw off an extendable pruning pole to use as a mast.

Have you set the lengths of the 2 stainless whips for lowest SWR? Even 1" can make a difference. Use a tape measure to ensure they are the same length. Without a tuner my SWR was around 1.7:1 with it 18' above the ground.

But don't sweat the SWR too much. The important thing is to keep it below 2:1 to keep the radio happy (and safe). This link shows that even with a 2:1 SWR you are only loosing 11% of your power. That's nothing. Remember that one S-unit is a 4:1 change. So even if you are loosing half your power (6:1 SWR) it's like going from S-9 to S-8.5. No big deal.

Your main losses will be in the feed line. If the feed line is short (< 40' ish) your losses will be small, even if the tuner is correcting a big mismatch.

So, make sure the whips are the correct length. Get it as high as you can. Keep the radio safe with the tuner (SWR < 2:1) and have fun.
 
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I've used that same set-up. The higher off the ground the better, of course. Being low raises the SWR as well as making it an NVIS pattern. I've taken the clipper/saw off an extendable pruning pole to use as a mast.

Have you set the lengths of the 2 stainless whips for lowest SWR? Even 1" can make a difference. Use a tape measure to ensure they are the same length. Without a tuner my SWR was around 1.7:1 with it 18' above the ground.

But don't sweat the SWR too much. The important thing is to keep it below 2:1 to keep the radio happy (and safe). This link shows that even with a 2:1 SWR you are only loosing 11% of your power. That's nothing. Remember that one S-unit is a 4:1 change. So even if you are loosing half your power (6:1 SWR) it's like going from S-9 to S-8.5. No big deal.

Your main losses will be in the feed line. If the feed line is short (< 40' ish) your losses will be small, even if the tuner is correcting a big mismatch.

So, make sure the whips are the correct length. Get it as high as you can. Keep the radio safe with the tuner (SWR < 2:1) and have fun.

You must spread some Reputation around before giving it to cockpitbob again

Thanks, sir! I need an SWR meter in the worst way! I'd prefer a digital one. Looking at MFJ, they seem on the pricey side.

Any other manufacturers you can suggest?
 

cockpitbob

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I know there's a bunch of antenna analyzers out there, several with graphing displays. Unfortunately I've never used any of them. I have an old mfj one.

If you're not tinkering with antennas a lot you can get by with a simple cross needle SWR meter. Just turn the power way down, give your call sign and don't qrm anyone. But a real analyzer really makes fussing with an antenna easier.
 

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I use same set up except with mini sticks. I have them configured as a vertical dipole using some PVC pipe for support mounted to a music stand. They are on my balcony 7 stories up. Here's what I do: set the antenna in spot you selected, connect analyzer to coax with ant and check the resonance with whips at equal length, write down resonant frequency and measure length of each whip. Pick your favorite operating frequency(mine is 14.076 for JT operations). If ant resonance is lower than what your favorite op freq is, make each whip 1 inch shorter. Recheck resonance with analyzer. From there you can calculate KHz per inch. Calculate how many inches you need to move the whips to get to your op freq. Measure the Swr with analyzer. Should be very close to where you need to be. Now all you need to do is connect to your tuner and rig. Should be able to get very close to 1.0:1. Keep in mind that bandwidth will be narrow. Using the analyzer, you can now measure the bandwidth +/- 2:1 SWR from your optimum point. I've worked Japan, Australia, deep EU on 30 watts or less. Hope this helps. de WA1TSL.


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quincy

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Also, keep in mind that these compromise antennas will produce some common mode current on outside of coax shield, which may or may not help your signal. If this becomes a problem with RF getting back to the shack, you can use a 1:1 isolation transformer at antenna feed. I've used it with and without the xformer. At 30w doesn't make a big difference. If you decide to use the 1:1, you will need to re tweak the whip lengths slightly.


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quincy

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Also, use pskreporter.com and see if you can track your signal. The JT and PSK modes make it easy to find out where your signal is going. I believe CW will work as well but haven't tried it yet, not sure about SSB.


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Well, mystery solved. Buddy brought over his AA-600 rig tester. Popped that puppy on to the feed line....and BOOM...say hello to a 10+ SWR!!!

So, my buddy shows me how to run the thing and it is wicked easy.

Had the wife in the house running it while I started dicking around with the whips to get a better SWR. Got it down to something around 2. Best I could get.

So I take the feedline back from her and take it downstairs and I hook the analyzer back up...and the bastard had shot back up to 10. Then I realized...my friend admonished me to not stand too close to the antenna during tuning. Well...who knew 8 feet was too close.

Gotta love learning things the hard way. So, tonight, I'll put out further away from the house and will stand inside the house when she runs the test. HOPEFULLY, I'll get a better SWR out of it.

But, this has basically forced me to go with a more reasonable antenna. One of the Elmers in town is going to help me build a full wave 40m off center fed dipole. I've ordered the 4:1 current ballun (sp?) and coax from HRO and will be headed to Home Depot to pick up the wire.

Anyone suggest a good rope/string to use to hold up the antenna? The Elmer says not to waste money on Para Cord. Nylon rope/string? What do you use?
 

cockpitbob

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You want black cord, just so it blends in.
Black dacron cord, about the same size or slightly thicker than 550 paracord is the best. The dacron isn't rotted by the sun the way nylon is.
That said, I have a wire antenna that has been held up by black 550 paracord for 3+ years now. I suppose someday the sun will rot it enough for me to replace it, but it's doing fine so far. It's just getting a little hard.

Any of these in 1/4" or 3/16" should be fine. Also check the usual ham radio distributors. BTW, Polyester is the same as Dacron. Trade names.
 
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quincy

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Well, mystery solved. Buddy brought over his AA-600 rig tester. Popped that puppy on to the feed line....and BOOM...say hello to a 10+ SWR!!!

So, my buddy shows me how to run the thing and it is wicked easy.

Had the wife in the house running it while I started dicking around with the whips to get a better SWR. Got it down to something around 2. Best I could get.

use?[/
ce3ad0a635e1d31bd4b4d4041e381e5f.jpg
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QUOTE]

The 40m sticks have narrow bandwidth as shown. However, the higher frequency sticks have a flatter/wider bandwidth.
 
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