How to build a UHF antenna... - Page 74 - AVS Forum
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Old 03-29-2009, 09:23 PM
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That sounds good. Yeah, petroleum jelly will degrade rubber bands over time, but most good plastics will hold up. Heck, it even comes in a plastic container, heh.
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Old 03-30-2009, 07:43 PM
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Originally Posted by 300ohm View Post

Up to a point, about 1/20 to 1/10 wavelength max IIRC. 4 gauge solid is the biggest Lowes or HomeDepot has, 6 gauge is easier to work with. Use DogTs method of straightening the wire. Clamp strongly one end in vice and the other end in vice grips. Pull straight and hit vice grips with hammer hard multiple times.



Yep, thats the package. Heh, theyre overstating the specs. I knew it. But so far so good, its working well.

Hi to everyone,

I have an improvement on the method for straightening wire (better for soft wire, like copper or aluminum) as recommended by 300 ohm.

One end in a vice (or another vicegrip, which is what I use), the other in vicegrips. Instead of a hammer, use a come-along. I've used this technique a bunch of times, and it works like a charm. Best not to have any cuts or scrapes on the wire because it might break. I've used this way of straightening copper wire with some serious kinks with very good results, but I did try to straighten the kinks a bit beforehand.

I do this outside, by the way, and low to the ground so it won't get bent again once it's released.

I hope this technique helps someone.

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Old 03-30-2009, 08:23 PM
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Instead of a hammer, use a come-along. I've used this technique a bunch of times, and it works like a charm.

Yep, thats good too. Of course, not everyone has a come-along. Another mod to the technique using equipment that most have, would be one end in a vice the other in vicegrips that is chain wrapped and attached to the frame of a car. Rev up the engine and peal out of the garage. The wire will be straight, heh.
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Old 03-30-2009, 08:45 PM
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LOL! Yes, it will be straight until it skims along the concrete for a bit! The come along is a good tip but not everyone has one...
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Old 03-30-2009, 10:04 PM
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until it skims along the concrete for a bit!

Ahh, thats were the careful art of braking comes in, heh.
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Old 03-31-2009, 06:58 AM
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Originally Posted by jwwm_2 View Post

Hi to everyone,

I have an improvement on the method for straightening wire (better for soft wire, like copper or aluminum) as recommended by 300 ohm.

One end in a vice (or another vicegrip, which is what I use), the other in vicegrips. Instead of a hammer, use a come-along. I've used this technique a bunch of times, and it works like a charm. Best not to have any cuts or scrapes on the wire because it might break. I've used this way of straightening copper wire with some serious kinks with very good results, but I did try to straighten the kinks a bit beforehand.

I do this outside, by the way, and low to the ground so it won't get bent again once it's released.

I hope this technique helps someone.

whatever method of straightening, tensioning with or without mechanical shocking or with twists, the wire will bend and unstraighten under its own weight and you have to support it afterwards.

with tensioning other than hand pulling you need to be cautious about the wire breaking and whipping through the air.

any method would be good to have eye protection.
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Old 03-31-2009, 08:31 AM
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Originally Posted by NightHawk View Post

I have't seen a commerical pre-amp with only a 300 Ohm input.

Channel Master makes them (Winegard did too):

Channel Master Spartan 3 Model 3041DSB

They have them at my local Fry's here in Plano, TX. $50

Hope this helps.

Mike
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Old 03-31-2009, 11:38 AM
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Do directors work as well for bow-tie type antennas as they do for the LPs? Or at all?
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Old 03-31-2009, 02:49 PM
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Do directors work as well for bow-tie type antennas as they do for the LPs? Or at all?

You need a lot of them for a little bit more gain. Think of the practical build problems, heh.
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Old 03-31-2009, 03:12 PM
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Chuck one end of wire(s) in a drill motor and secure the other end to any type anchor --car bumper, tree, or antenae mast, and ETC, and turn the drill motor slowly while pulling at the same time. It not only straightens but stiffens the wire (copper, steel, stainless, or other).
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Old 03-31-2009, 04:22 PM
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Yep, but that also puts little twists in the wire. At microwave frequencies, such twists are significant. Not sure of the effect at uhf frequencies, so I like my wire bare, untwisted.
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Old 04-01-2009, 01:13 AM
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Quote:
Originally Posted by 300ohm View Post

Yep, thats good too. Of course, not everyone has a come-along. Another mod to the technique using equipment that most have, would be one end in a vice the other in vicegrips that is chain wrapped and attached to the frame of a car. Rev up the engine and peal out of the garage. The wire will be straight, heh.

Hilarious!

I once spun my car in the rain and hit a curb sideways at 40mph. The suspension was completely trashed. I replaced the suspension parts, hubs and bearings, only to find that the entire body was bent, making alignment impossible. I tried to straighten the body with a come-along, but it just dragged the car around. I eventually used my wife's car and a heavy-duty tow-strap in the manner you described. Worked like a charm... achieved perfect alignment!

Gary
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Old 04-01-2009, 06:50 AM
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I eventually used my wife's car and a heavy-duty tow-strap in the manner you described. Worked like a charm... achieved perfect alignment!

Ooh, good for you. Generally once the cars' frame is bent, its totaled, heh.
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Old 04-02-2009, 08:48 AM
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Hi All,

I was considering re-working my last McLapp based antenna due to less than anticipated performance. It is wood, but I used PVC spacers. It is getting decent signal, but not as many as my first blogspot UHF with 7.5" spacings.

Since it is in my attic, I will try to take the 8 gauge copper elements and tape them to styrofoam.
Does the kind of tape matter? I was thinking that 2 inch wide, clear 3M shipping tape, but I dont know how much of the element to cover with tape (without degrading signal performance).
Also , can you used that "pink" insulating styrofoam from Home Dept that comes in the 4x8 sheets?
How much of the element touches the styrofoam? Do the signal waves pass through the styrofoam, so maybe it does not matter if the foam is as big as the elements?
I was going to space another sheet 4 inches behind the sheet with the elements and cover it with foil for my reflector.

Any suggestions on this method of attic antenna construction would be appreciated. Pictures especially.
Thanks,

George
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Old 04-02-2009, 09:01 AM
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Originally Posted by SonicLogic View Post

You might want to try using Penetrox

Burndy Penetrox is wonderful stuff that I've been recommending for OTA use for a long time. I was originally given some by a friend who had been a career hydro lineman so I've had good experience with using it for years. Glad it has served you so well too. The correct version of the compound is easy to find with some googling. Penetrox is a very fine suspension of zinc in a liquid that holds tenaciously to metal.

Regarding plastics, I've never found it to be adverse on any electrical cable sheathing, although I've never smeared any on PVC pipes. I'll put some on some PVC, ABS, and whatever else I've got today and report back in a few years. Seriously, I don't think it has any bad properties regarding plastic.
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Old 04-02-2009, 09:56 AM
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Originally Posted by 300ohm View Post

Thats my favorite method of constructing an attic antenna. Cheap (recycle packing styrofoam sheets and tape together if necessary), quick, light and styrofoam is the cheap plastic closest to air there is. Then for the reflector, make up another sheet, slap some $1 store aluminum foil on it and use discarded styrofoam blocks cut and glued at the correct distance from the element sheet. As long as the sun doesnt get to it, it will last decades, heh.


Wow, what a perfect Bermuda triangle, heh. I dont know if I would even try for the negative NM figures and your positive NM figures are pretty strong. If you dont have any special local environmental problems, like huge evergreens, I would aim for real channel 26 and hope to get the rest without a reflector.





Heh, yeah it is a nostalgic piece of TV history to many of us. I remember as a kid, the TV repairman had to come once a month (or at least once every two months) to repair our Philco, heh.

I will try to take my 9.5 inch, 8-gauge copper elements and tape them to styrofoam.
Does the kind of tape matter? I was thinking that 2 inch wide, clear 3M shipping tape, but I dont know how much of the element to cover with tape (without degrading signal performance).
Also , can you used that "pink" insulating styrofoam from Home Dept that comes in the 4x8 sheets?
How much of the element touches the styrofoam?
Do the signal waves pass through the styrofoam, so maybe it does not matter if the foam is as big as the elements?
I was going to space another sheet 4 inches behind the sheet with the elements and cover it with foil for my reflector.

Any suggestions on this method of attic antenna construction would be appreciated. Pictures especially.
Thanks,

George
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Old 04-02-2009, 10:38 AM
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Does the kind of tape matter? I was thinking that 2 inch wide, clear 3M shipping tape, but I dont know how much of the element to cover with tape (without degrading signal performance).

Since I had a roll of that and a piece of styrofoam handy, a quick test shows it will work just fine.

Quote:


Also , can you used that "pink" insulating styrofoam from Home Dept that comes in the 4x8 sheets?
How much of the element touches the styrofoam?

Sure, if you want to be a spendthrift, heh. Just dont use the priceier foil backed stuff.


Quote:


Do the signal waves pass through the styrofoam,

Yep. Styrofoam is the closest plastic to air, that is readily available to all, there is.
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Old 04-02-2009, 01:15 PM
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Quote:
Originally Posted by Georgio P View Post

I will try to take my 9.5 inch, 8-gauge copper elements and tape them to styrofoam.
Does the kind of tape matter? I was thinking that 2 inch wide, clear 3M shipping tape, but I dont know how much of the element to cover with tape (without degrading signal performance).
Also , can you used that "pink" insulating styrofoam from Home Dept that comes in the 4x8 sheets?
How much of the element touches the styrofoam?
Do the signal waves pass through the styrofoam, so maybe it does not matter if the foam is as big as the elements?
I was going to space another sheet 4 inches behind the sheet with the elements and cover it with foil for my reflector.

Any suggestions on this method of attic antenna construction would be appreciated. Pictures especially.
Thanks,

George

generally the blue is much denser than the pink or white. since this is a nonstandard use how the material takes handling and use is an issue. the white or pink will break easily the blue won't.

never had much luck sticking tape for a long time to polystyrene. though a duct tape with lots of adhesive does best. sticks to blue better because a harder smoother surface.

with the blue being dense you can pierce it with a small diameter nail. you could put holes through adjacent to elements or reflectors and tie down as well.
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Old 04-03-2009, 11:44 PM
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hello 300 Ohm and all again , my sister has a hi-top van with a fiberglass top , the top has a tv antenna laid in it , the lead comes out at the front and goes to a power injector
so I know it is a amped or boosted antenna , of all the antennas we have here in south Mississippi , the van picks up more digital stations with all most no drop outs when travleing , and full scale and no drop outs at all when parked, short of having the top x-rayed how would we find out what the antenna looks like and how it is configured??
we ran a cable in side to her big tv and converter box and it is a better picture than with her cm4228 40 feet tall cm7777 amped
I'm looking in junk yards for one of those fiberglass tops , I will find some where to hide that thing !!
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Old 04-04-2009, 02:12 AM
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up more digital stations with all most no drop outs when travleing , and full scale and no drop outs at all when parked, short of having the top x-rayed how would we find out what the antenna looks like and how it is configured??

Well, youre talking about something that is difficult, if not nearly impossible to computer model, heh. And I dont know where to get an Xray machine that large.

Is it a commercial top ? Maybe the manufacturer has a diagram of how the antenna is laid out ?

If not, maybe you could email them and tell that you plan to mount something on the van roof and would like a diagram so that you could drill without hitting the internal antenna, heh.
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Old 04-05-2009, 01:49 PM
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I am getting a lot of ghosts on a 4221A on one channel. But I happen to have 2 of the old versions of 4221A.

I know Ken on hdtv primer says 4228s work as well or better with 2 baluns one from each side into a combiner. Essentially making them two 4221As side by side.

Well I need on dimension, the distance from the center of one set of bowties to the other, so I know how far apart to space my 4221As apart side by side.

Anyone know that dimension or have one where they can measure it?

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Old 04-05-2009, 03:38 PM
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Let me add another idea. On my 4221A I have very rapid continual moving ghosts on RF 31 about 20 miles away, running 500KW ERP toward me at 300 meters.

I think the only thing saving me where I have a half way watchable picture is the main signal is so strong 95% of the time it over rides the ghosts (they still have a RF51 analog on the same antenna).

I am pretty sure my problem is wind in the trees, but it's a mild wind outside today (4 knots) and it's eating the signal.

I use a pair of vertically stacked YA-1713's so I am set for VHF.

Makes me wonder if I should rip it all down, put up a 7698P or buy a 91XG and combine them into my stacked VHF yagis?

I just wonder after I go to all the work of mounting my two 4221As side by side, I will still have ghost problems and need to give up and get something very very directional? Which would also mean buying a rotor.

Looking for feed back as this group probably plays with more antennas than any other thread.

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Old 04-05-2009, 06:23 PM
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Well I need on dimension, the distance from the center of one set of bowties to the other, so I know how far apart to space my 4221As apart side by side.

Anyone know that dimension or have one where they can measure it?

Ken Nist on his hdprimer site, under comparing some commercially available antennas, has the NEC .ez files available for download. You can load them into the free 4nec2 program and look at all the dimension details. (actually the free EZNEC 5 demo program can load it too, but its harder to read and is seriously limited in functionality) I would not try making the phasing line between the two antennas without looking at the phasing line design in very great detail.

The horizontal distance center to center between the two CM4221s is exactly 20 inches on the old CM4228.
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Old 04-05-2009, 08:07 PM
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Quote:
Originally Posted by 300ohm View Post

Ken Nist on his hdprimer site, under comparing some commercially available antennas, has the NEC .ez files available for download. You can load them into the free 4nec2 program and look at all the dimension details. (actually the free EZNEC 5 demo program can load it too, but its harder to read and is seriously limited in functionality) I would not try making the phasing line between the two antennas without looking at the phasing line design in very great detail.

The horizontal distance center to center between the two CM4221s is exactly 20 inches on the old CM4228.

300ohm, thank you. It may not be the best thing or way to do it but I was going to just combine the (2) 4221A's into a combiner. I will probably loose most of the gain of the second antenna, but if it narrows my beam width, it should help. I don't lack gain in my situation, but wind caused rapid multi path is killing the signal.

I also wonder if the trouble trying this is worth it. Easier to go to a long boom log/yagi to eliminate ghosts?

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Old 04-05-2009, 09:55 PM
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Originally Posted by Piggie View Post

300ohm, thank you. It may not be the best thing or way to do it but I was going to just combine the (2) 4221A's into a combiner. I will probably loose most of the gain of the second antenna, but if it narrows my beam width, it should help. I don't lack gain in my situation, but wind caused rapid multi path is killing the signal.

I also wonder if the trouble trying this is worth it. Easier to go to a long boom log/yagi to eliminate ghosts?

Yes, it's worth a try. I got 2.5 dB more when I combined two 4221s with a splitter/combiner.

Make sure that the two pieces of coax from the ants to the combiner are exactly the same length, and maybe even from the same batch of coax because the velocity factor can vary. Also, it is very important that the two baluns at the 4221s are connected in phase. If you end up with less signal (or even more confusing, the main lobe divides in two), reverse the 300 ohm connections on ONE of the baluns. This hasn't been mentioned recently, so I thought I better emphasize it.

I ended up with a narrower horiz beamwidth, like you would get with a 4228, which helps with multipath. I also had more gain because the combiner approach is more efficient than the 4228 open wire phasing line system.

I like to use the QUALITY bar on my Apex DT502 to finalize the aim when I have a multipath problem. The angle of acceptance for minimum multpath is much narrower than the beamwidth for max gain when aiming the antenna. This is why aiming an antenna between two azimuths often doesn't work very well, because off-axis aim causes the multipath reflection to be stronger in relation to the direct signal; the reflection can end up at the peak of the main lobe and the direct signal is at a lower gain point on the main lobe. The result is higher BER.

You might still have a problem because optimizing aim for multipath works well for static multipath, but not for wind caused dynamic multipath. But, the additional gain might help with dynamic multipath, as it did for me with dynamic multipath from cars passing in front of my antenna. The reason for that was because less of the limited ability of the error correction system (FEC) was needed for weak signal correction so that more was available for multipath correction.

If you can not measure it, you can not improve it.
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Old 04-05-2009, 11:54 PM
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but wind caused rapid multi path is killing the signal.

It sounds like you need to stabilize your mast. Guy wiring is an easy technique to do so.
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Old 04-06-2009, 01:13 PM
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Quote:
Originally Posted by Piggie View Post

I am pretty sure my problem is wind in the trees, but it's a mild wind outside today (4 knots) and it's eating the signal.

Makes me wonder if I should rip it all down, put up a 7698P or buy a 91XG and combine them into my stacked VHF yagis?

I just wonder after I go to all the work of mounting my two 4221As side by side, I will still have ghost problems and need to give up and get something very very directional? Which would also mean buying a rotor.

A different tree solution from north-of-the-border:
http://www.digitalhome.ca/forum/show...7&postcount=25

If you can not measure it, you can not improve it.
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Old 04-06-2009, 02:36 PM
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Hmm, thats odd. Ive always found the bow-ties and GHs to be better for getting a signal thru oak, maple, basswood type trees. More front metal spread over a wider area towards the transmitter is why I think its so. But the corner reflector yagi could possibly have the edge on swaying trees in front, who knows and whos tested ? Ill have to test that one of these days, since I have a couple of those types.

But one thing I dont have, is a full time laboratory staff, heh.
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Old 04-06-2009, 03:43 PM
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I would think so too, but I wanted to present another viewpoint for consideration because Piggie said:
Quote:
Looking for feed back as this group probably plays with more antennas than any other thread.


If you can not measure it, you can not improve it.
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Old 04-06-2009, 03:54 PM
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Quote:
Originally Posted by rabbit73 View Post

Yes, it's worth a try. I got 2.5 dB more when I combined two 4221s with a splitter/combiner.

Make sure that the two pieces of coax from the ants to the combiner are exactly the same length, and maybe even from the same batch of coax because the velocity factor can vary. Also, it is very important that the two baluns at the 4221s are connected in phase. If you end up with less signal (or even more confusing, the main lobe divides in two), reverse the 300 ohm connections on ONE of the baluns. This hasn't been mentioned recently, so I thought I better emphasize it.

I ended up with a narrower horiz beamwidth, like you would get with a 4228, which helps with multipath. I also had more gain because the combiner approach is more efficient than the 4228 open wire phasing line system.

I like to use the QUALITY bar on my Apex DT502 to finalize the aim when I have a multipath problem. The angle of acceptance for minimum multpath is much narrower than the beamwidth for max gain when aiming the antenna. This is why aiming an antenna between two azimuths often doesn't work very well, because off-axis aim causes the multipath reflection to be stronger in relation to the direct signal; the reflection can end up at the peak of the main lobe and the direct signal is at a lower gain point on the main lobe. The result is higher BER.

You might still have a problem because optimizing aim for multipath works well for static multipath, but not for wind caused dynamic multipath. But, the additional gain might help with dynamic multipath, as it did for me with dynamic multipath from cars passing in front of my antenna. The reason for that was because less of the limited ability of the error correction system (FEC) was needed for weak signal correction so that more was available for multipath correction.

I have read Ken's notes (about the best site I found for the old 4228 for information all in one place) extensively. Also the part about combining two 4221As for double lobes. Given my radar plot actually I am going to try out of phase on purpose and in phase.

I added my radar plot if you are curious. Note I only care about UHF 16, 28, 31, 36. All others are too far away to be considered consistently watchable or are not really on the air, etc.

I have a 54 degree spread. The station with the worst wind fade is 31, with 36 being second behind it but not nearly as bad. 16, 28 despite 28 being the weakest most distance only wind fades in extreme conditions and 16 almost never breaks up. The two worse, 31 and 36 are also the ones on farthest apart at 54 degrees.

I am not sure how precise the pattern ends up. But it looks like if I went 23 inches out of phase I would target my two weakest stations. I guess the question and proably only known by experimenting is will the middle ones 16, and particular 28 have enough signal to come in. Any thoughts besides just try it?

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I have also over the last couple years reading have learned that the point of least mulitpath is much tighter than than most lobes that have gain. Thanks for bringing it back up, nothing is ever too trivial to mention. And I do have a roll of good RG6 where I make identical jumpers, another good point being from the same piece.

I know it's 99% experimenting and 1% theory a lot of the time!

- Please don't PM with any thing that could be useful to the general group.
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