2 choices for NVIS antenna -- Need advice

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Rastaman147

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New HAM here... My transceiver and materials for an HF (RX) antenna should be arriving tomorrow. FT-897 with max TX of 100w.

Thinking ahead to when I upgrade my license to general and begin my journey into HF -- At this point, my interests are leaning toward NVIS, and I'm trying to get a plan together for a usable NVIS antenna.

From what I can gather so far, the obvious choice of antennas would be a homebrew version of the AS-2259, and there are some really good plans for this, so I will be building one, but It will take up most of my back yard, and will need to be removed regularly for lawn maintenance, so I am considering this one to be secondary, backup antenna.

My yard is ideal for a windom antenna, so I've decided to build one for my primary HF antenna. Good-neighbor policy, stealth, and not damaging my transceiver are my primary objectives, antenna performance would come in at 4th place after these.

Here's my dilemma:

I can put up a 132 foot long windom on one side of my yard, but the trees I would be using are my neighbor's trees, and I would be using the branches that extend into my yard. According to the manufacturer and several other antenna plan articles I've read, this will allow me to use the 80m and 40m bands without a tuner and several other HF bands with a tuner.

W8AMZ OCF / WINDOM

I would also need (feel compelled to) ask my neighbor's permission. From what I've read, this is something a HAM should try to avoid at all cost (for the purpose of not being blamed for interference issues).

If I use the other side of my yard, I could put up a 66 foot long windom, that will work for 40m. This would be using my trees, would be very stealthy, and I wouldn't need to say a word to anyone.

So, I guess my question boils down to: Is it likely that a commercial antenna for 80m or 40m erected by a novice, following the instructions (but with no real-life experience regarding what does and what doesn't cause RF interference to TV's, telephones, etc) will result in interference issues with my neighbor's stuff?

My neighbor's house is about 30 feet from where the antenna would be.

A second question is: If I go with the 40m antenna, will it be usable at all on 80m (RX and TX)?

I understand that this antenna design is not optimal, and there are better options performance-wise, but based on other HAM's accounts, it is definitely an option worth exploring. If it does work, it will solve all my problems easily.
 

prcguy

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The Windoms you mentioned would work ok for the advertised bands but a 40m version will not work on 80m very well, even if you could tune it. A good friend recently got a Buxcom (I believe) 40m Carolina Windom due to space restrictions and it working very well for him. One thing to consider is feedline loss can go way beyond advertised specs when the mismatch gets real bad, so if you’re going to run a lot of coax it pays to use an antenna with a reasonable match to the coax and many of the Carolina Windom types have an ok match on several bands.

I have several AS-2259s and stock they resonate at 5MHz and 10MHz and were designed to be used with a tuner. The element lengths were chosen for reasonable performance across a wide range of frequencies while keeping the size manageable and to avoid a very high impedance and possible arcing at the feedpoint. A stock AS-2259 is not a very good antenna for amateur use but it’s a good starting point to build on.

I changed the wire out on one of my 2259s to resonate on 40m and 80m, which makes the antenna larger, and mine with about 30ft of guy string on each leg needs a space of 188ft X 128ft. You can improve the 2259 by raising the feedpoint higher like 25 to 30ft and not running the elements down close to the ground, which eats up some efficiency.

Many people have a good NVIS antenna and don’t even realize it. Any dipole that is around 35ft or lower favors NVIS and the best height would be about 1/4 wavelength above ground at the highest band for NVIS, which is typically 40m, so 30-33ft is ideal. Lower will start to degrade distant low angle reception and will also reduce efficiency in NVIS mode. An AS-2259 clone can be useful for fixed portable use since its wire elements become the guy wires to hold it up, but I think you can do much better with another type antenna.

Another thing to consider is a dipole that is shortened up to about 70% of full size (compared to half wave) will only be down a dB or so from the full size version, assuming there are no feedline losses incurred from the mismatch or you use balanced feedline all the way to a tuner. With that said, my favorite antenna these days for 80 through 10m is the 94ft long ZS6BKW dipole which is simply a center fed dipole with critical length of balanced line (about 40ft) then a 1:1 choke balun and whatever length of coax you need to reach your radio. Except for 80m on a ZS6BKW where the match will be maybe 7:1 or 10:1, it has a very reasonable match on all bands 40-6m except for 15m and avoids a high loss condition on these bands using long runs of coax.

So if you put up a horizontal dipole of some kind and keep it below about 35ft you will have your NVIS antenna but it will also work fine for DX unless you get it too low like under 10ft. Even with horizontal antennas only a few feet off the ground and QRP power I can still make good coast to coast and DX contacts, so a so called NVIS antenna can do more than heat the clouds.

On the interference to the neighbors house, many people have gone to cable TV or satellite and in most areas off air channels 2 through 6 are now gone, so TVI is not as common these days. I can run full legal limit with a dipole over the house and not bother any TV or phone in my house or any neighbors. YMMV.
prcguy
 

Rastaman147

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Thanks, Prcguy - I decided to try putting up some masts using 4x4s. This will get me about 125' of antenna length without asking my neighbor. Still very stealthy, along the treeline. Hopefully this will be enough for a 80m dipole with a reflector. If not, I guess I can bend the antenna a little or go with my original windom choice and bending that.

So far, the new rig works on VHF using my HT antenna in my attic -- On Wednesday, I'll be putting up the Comet GP1 on my 20 foot mast using LMR-400, so hopefully, I'll have great things to report with that. With a luck, weather-wise, I'll have the dipole up this weekend, and hopefully my first attempt at HF will be positive, as well.
 

LtDoc

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Don't get too enthusiastic about NVIS antennas, that designation isn't quite accurate in most cases. If an antenna isn't as high as something on the order of 1/2 to 1 full wave length, then it's more or less a NIVS antenna. I've used the so-called NVIS antennas to do a WAS. I've also used the same antenna to very good effect on higher bands because of the resulting radiation patterns which are not all that 'typical' depending on how/where the thing is mounted.
There are quite a few considerations with the 'style'/type of antenna you decide on. A 'windom' or more correctly, an off center fed antenna (OCF), will certainly work on multiple bands (A 'Windom' is a single wire fed antenna worked against ground). Better have a tuner to make sure though.
I don't know of any ham that hasn't tried more than one type of antenna. If you haven't, you just haven't been around long enough yet. You honestly can't make comparisons until you do that changing of antennas. Each and every installation is different than any other installation. Some times it'll work just fine, others you wonder why anyone would ever use that particular 'style' of antenna. Lot's of variables in all that.
Try one antenna, see how it does. Then, try a different one, see how it does. Then you can make a half-axed guess as to what's the best in your particular situation.
Sounds like a lot of fun, huh? :)
- 'Doc
 

prcguy

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Reflector wire or no reflector wire under your NVIS antenna? I say don't bother and in some cases it will make things worse due to the same kind of ground loss from placing radials for a vertical on the ground instead of elevating them. The only sure way to make it beneficial would be to use a very large screen under the dipole and that's usually not practical.

A Windom that covers 80m would be about 135ft long or the same as a half wave dipole on 80m but a Windom like those sold through Buxcomm will operate on most bands 80m and up with an ok match without a tuner. The 94ft long ZS6BKW I mentioned earlier works very well on 80m with a tuner and works great on 40m through 6m usually without a tuner.
prcguy


Thanks, Prcguy - I decided to try putting up some masts using 4x4s. This will get me about 125' of antenna length without asking my neighbor. Still very stealthy, along the treeline. Hopefully this will be enough for a 80m dipole with a reflector. If not, I guess I can bend the antenna a little or go with my original windom choice and bending that.

So far, the new rig works on VHF using my HT antenna in my attic -- On Wednesday, I'll be putting up the Comet GP1 on my 20 foot mast using LMR-400, so hopefully, I'll have great things to report with that. With a luck, weather-wise, I'll have the dipole up this weekend, and hopefully my first attempt at HF will be positive, as well.
 

PrimeNumber

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Reflector wire or no reflector wire under your NVIS antenna? I say don't bother and in some cases it will make things worse due to the same kind of ground loss from placing radials for a vertical on the ground instead of elevating them. The only sure way to make it beneficial would be to use a very large screen under the dipole and that's usually not practical.
Last summer I put up an MFJ 80/40 trap dipole (~80 feet long). The feed point is 20 feet up on a single piece of PVC pipe, and the ends are about 5 feet off the ground, so it's a very shallow inverted V. Works great for NVIS. Originally I put in a set of reflector wires, but when I took them out the bandwidth increased by about 50%, so they're staying gone. Bandwidth on 40m now covers the entire band, and I can work all the way from the bottom to top without using a tuner. Bandwidth on 80m now just covers the General phone portion, so I just use the internal tuner on my transceiver to tame the band edges down a little bit.

It covers out to 300 miles in any direction fairly reliably on 100 watts, sometimes maybe 500 miles. It was dead easy to put up (or to pull down before a hurricane...). Tuning took a little time, but it was worth the effort.
 

sloop

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I use a BUXComm windom with 4:1 balun made for 80 thru 6. I do have a LDG Z-11Pro tuner but I have never measured an swr greater than 1.8 even with out the tuner. And yes, get your neighbors permission.
 

Rastaman147

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Thanks everyone for the replies / advice. I kind of switched gears in the middle of this thread after I found a plan for a regular 80m dipole that can put up entirely on my property without using my neighbor's branches. Since I already have a balun and some 14gauge wire, I decided to try this way first, as it will save me the cost of the windom I was considering.

If I can get decent performance without using the reflector, then I definitely have enough space for this antenna. (reflector is 126', the distance between my masts is 126', so, if inches make a difference with reflectors the way they do with the director, then I would probably not have enough space). But I've got the wire, so I'll give it a try and see what happens.

I realize that NVIS is probably more location/situation dependent on more variables than standard dx, but for me, making a contact with a HAM 2 counties away or on the other side of 2 mountains sounds more practical and more rewarding than talking to someone halfway across the planet, so that is the path I've started on. I understand a lot of trial and error and experimentation is in store for me.

Thanks again for your suggestions -- I'm sure I will be referring back to this thread many times as I experiment with different designs!
 

prcguy

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If you put up an 80m dipole with or without a balun and center feed it with coax its only going to be an 80m antenna, operating other bands will be grim at best. Feed the same 80m dipole with balanced line (450ohm, 300ohm, etc) all the way to a tuner and now you have a good all band HF antenna. Feed the same 80m dipole offset with an appropriate balun and you can get multiband operation with some fudging.
prcguy

Thanks everyone for the replies / advice. I kind of switched gears in the middle of this thread after I found a plan for a regular 80m dipole that can put up entirely on my property without using my neighbor's branches. Since I already have a balun and some 14gauge wire, I decided to try this way first, as it will save me the cost of the windom I was considering.

If I can get decent performance without using the reflector, then I definitely have enough space for this antenna. (reflector is 126', the distance between my masts is 126', so, if inches make a difference with reflectors the way they do with the director, then I would probably not have enough space). But I've got the wire, so I'll give it a try and see what happens.

I realize that NVIS is probably more location/situation dependent on more variables than standard dx, but for me, making a contact with a HAM 2 counties away or on the other side of 2 mountains sounds more practical and more rewarding than talking to someone halfway across the planet, so that is the path I've started on. I understand a lot of trial and error and experimentation is in store for me.

Thanks again for your suggestions -- I'm sure I will be referring back to this thread many times as I experiment with different designs!
 

Rastaman147

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Prcguy - Thanks for that tip. I was planning on setting this up this weekend, but I guess I should probably order some ladder line or twin lead first.

My plans include routing the coax underground from the center mast to my basement, about 25 feet through some pvc conduit, and it would probably be a major PIA to try to route 100 feet of ladder line through the conduit once it's underground, so I'll put it in with the coax now so I can connect it later when I'm ready to experiment.

I guess I can just leave the conduit above ground for now, and bury it after I add the ladder line.

Question, though... I can get the following:

300 Ohm 18g, 0.25 inch separation ladder line,
450 Ohm 18g, 0.75 inch separation ladder line, or
300 ohm 20g twin lead.

If price was not a deciding factor, which would be best of the 3 for 80 meter through 10 meter (with most important bands being 80m and 40m)? Total Length of feedline will be 100 feet. I have an LDG AT-897 PLUS auto tuner.

Also, how should I terminate the ladder line? I wasn't able find much on this. This guy http://www.kg4jjh.com/pdf/Antennas for Autotuners.pdf mentioned terminating the ladder line to a 1:1 balun, then run coax to the tuner. I'm assuming this means use ladder line for the entire run, and terminate to the balun somewhere very close to the tuner with a very short coax patch cable.

I don't think think this article mentions it, but I am assuming the ladder line is attached (and soldered) directly to the antenna wire. Is this right?
 

prcguy

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Here are some things to consider before taking the plunge. Running balanced line all the way from an antenna like a center fed 80m half wave dipole to the tuner can fix all the problems of operating a single antenna over multiple bands, or any frequency from maybe 2 through 30MHz or more. But it can also introduce some problems like accidentally running the perfect length of balanced line to make it impossible to tune on a particular band or frequency. Usually shortening or lengthening the feedline will fix that but you won’t know until it’s all installed and you map it out on all bands.

Then you have to keep the balanced line off the ground and away from metal and running a length of coax from a tuner and transitioning to balanced line can introduce problems. A 1:1 balun would be the first choice for transitioning from coax to balanced line but sometimes a higher ratio is better, there are too many variables with each install. Or learn how to drive EZNEC and spend some time modeling the entire antenna system before you install it.

Unless you need to go stealthy or portable I would use the 450 ohm window line over 300 ohm due to lower loss. With a balanced line fed 135ft dipole I would also use a tuner specifically designed for balanced line and not adapt a coax output tuner to balanced line unless I could run the balanced line very close to the tuner and use a very short run of low loss coax like LMR400.

A 135ft center fed dipole with ladder line all the way to a tuner is a classic and great all band antenna. I have just enough room for one at my house and have a Palstar and Johnson Matchbox tuner with balanced outputs but instead I chose the ZS6BKW 94ft dipole because it has a good match on most bands and its only down a tiny bit from a 135ft dipole on 80m. It’s also designed to be fed with any length of coax coax and a 1:1 choke balun at the transition to ladder line with very predictable performance and no problems with landing on the magic length of balanced feedline to ruin your day.

If you can’t run your balanced line right to the tuner or real close and use a very minimal length of coax, I would suggest looking at other antennas that don’t have as much baggage to deal with.
prcguy

Prcguy - Thanks for that tip. I was planning on setting this up this weekend, but I guess I should probably order some ladder line or twin lead first.

My plans include routing the coax underground from the center mast to my basement, about 25 feet through some pvc conduit, and it would probably be a major PIA to try to route 100 feet of ladder line through the conduit once it's underground, so I'll put it in with the coax now so I can connect it later when I'm ready to experiment.

I guess I can just leave the conduit above ground for now, and bury it after I add the ladder line.

Question, though... I can get the following:

300 Ohm 18g, 0.25 inch separation ladder line,
450 Ohm 18g, 0.75 inch separation ladder line, or
300 ohm 20g twin lead.

If price was not a deciding factor, which would be best of the 3 for 80 meter through 10 meter (with most important bands being 80m and 40m)? Total Length of feedline will be 100 feet. I have an LDG AT-897 PLUS auto tuner.

Also, how should I terminate the ladder line? I wasn't able find much on this. This guy http://www.kg4jjh.com/pdf/Antennas for Autotuners.pdf mentioned terminating the ladder line to a 1:1 balun, then run coax to the tuner. I'm assuming this means use ladder line for the entire run, and terminate to the balun somewhere very close to the tuner with a very short coax patch cable.

I don't think think this article mentions it, but I am assuming the ladder line is attached (and soldered) directly to the antenna wire. Is this right?
 

AC8PT

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I ham a new ham; yet, I have had good coverage of N. A. from Or. To Fla. & Ca. to Ont. & N. Mex. to New England and throughout the Midwest using either a Chameleon Zepp (50 ' radiator, 25' matching @ 25' horizontal) or a Chameleon Hybrid (60' EFW, 9:1 impedance transformer @ 20' horizontal). My station is pretty simple with an IC-7000 and a Tentec Eagle for transceivers.
 

Rastaman147

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Prcguy - Just an update - I am still waiting for my ladder line (back -ordered until 4/30), but i have my 80m dipole up, the pvc conduit has been buried, and I put in a length of twine to thread it through, once it arrives. Right now, I'm using the rg-8x and a 1:1 balun and I am really impressed with the Rx. It will be another 3 weeks or so before I take my test to upgrade to General, then I will get to try out the Tx. I've been working with the demo of ez-nec, and it will take a while until it's actually a useful tool, but it's really cool software. Anyways, I'll keep you posted. Thanks again!
 

prcguy

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You can bury coax but not ladderline, not even in PVC. Hopefully that's what you have in mind.
prcguy


Prcguy - Just an update - I am still waiting for my ladder line (back -ordered until 4/30), but i have my 80m dipole up, the pvc conduit has been buried, and I put in a length of twine to thread it through, once it arrives. Right now, I'm using the rg-8x and a 1:1 balun and I am really impressed with the Rx. It will be another 3 weeks or so before I take my test to upgrade to General, then I will get to try out the Tx. I've been working with the demo of ez-nec, and it will take a while until it's actually a useful tool, but it's really cool software. Anyways, I'll keep you posted. Thanks again!
 

Rastaman147

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I was planning to bury the ladderline along with the coax. I was not aware this would be an issue, but the overwhelming consensus from what I see on the web is 'definitely not!'. I suppose I could run the ladderline from the feedpoint to an attic vent, but it will be nowhere near as clean of an installation, and it will be a major PIA.

FWIW, on receive, anyway, the RG-8x sounds really, really good. Thanks for the heads-up -- I guess I'll just keep the ladderline and save it for some future project.
 

Rastaman147

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Actually, I could get a few more feet of ladderline, then I would have enough to run it to my VHF mast and route it into my house where the VHF coax goes in. Shouldn't be a big deal. Or would it be a problem to connect the ladderline to my transceiver with a 10 - 15 foot length of coax?
 
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