Author Topic: Wire antennas anyone?  (Read 1421 times)

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Offline K4TQF

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Wire antennas anyone?
« on: April 08, 2014, 03:25:02 PM »
Anybody on this forum using wire antennas ?  Rhombics, OCF dipoles, Beverage & the like? Seems like every antenna book I pick up is  concerned with getting the Balun right to match 50 ohm coax.  Well... what if you don't own coax? It looks like I'll need to go back to pre WW2 info. I guess the gov't dumping surplus coax on the market after WW2 changed everybody's thinking about feed lines. That and the fact that factory made transmitters  use a convenient SO-239. :confused:

I live in a hysterical district, and am not allowed any metal towers, verticals etc... But, I'm lucky to have 3.5 acres of wooded land that the shack sits on.

I ask because I ran across this paper on the internet. "Hams and the Conjugate Match" July 16, 2001, by R. Dean Straw, and a rebuttal paper "Response to Dean Straw’s “Hams and the Conjugate Match” January 24, 2005, by Walter Maxwell, W2DU (Revised April 16, 2011)

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #1 on: April 08, 2014, 03:25:32 PM »
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I ask because I ran across this paper on the internet. "Hams and the Conjugate Match" July 16, 2001, by R. Dean Straw, and a rebuttal paper "Response to Dean Straw’s “Hams and the Conjugate Match” January 24, 2005, by Walter Maxwell, W2DU (Revised April 16, 2011)

Oh God… don't get that subject started again :icon_shh: There are people who disagree with Walt and every time that subject starts up posts get deleted because feathers get ruffled.

Word of advice, ignore that article and also forget using coax. Use open-wire line and a good link-coupled tuner. In your case it should be even easier if you are going to have a push-pull amp that's link coupled to the feedline anyway.

P.S. Remember the topic on the old board about using a curtain antenna in an historic district?

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #2 on: April 08, 2014, 03:25:57 PM »
Brian:
I guess I wasn't around for that one... Oh, no, I'm not about to go out and spend money on coax... If the "big boys" can do it with open wire...
Go ahead an delete this if it's gonna cause trouble.

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #3 on: April 08, 2014, 03:26:10 PM »
No, wire antennas fed with balanced line compared to coax feed antennas is a good topic :icon_thumbup:

Offline KL7OF

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Re: Wire antennas anyone?
« Reply #4 on: April 08, 2014, 03:26:28 PM »
Now this is my own experience.......I have always had an abundance of coax....I was in the metal salvage business and bought a lot of surplus gov't wire and metals at military base auctions....There was always some coax in the mix and I would save out the good stuff..I started making resonant wire antennas fed with coax...Never used a Balun...Never used a tuner....I found that if the antenna was cut for the operating freq and fed with coax, and the antenna was operated in a frequency range that kept the SWR below 2 to 1  there were no problems with feedline radiation and no transmitter problems.....This has worked well for me because I have the room and supports to put up antennas for every freq that I wanted to operate on and I have plenty of coax to feed these antennas with...The freq range of such antennas is limited ....but as an AMer  I operate only a narrow range within each band so this is not a problem..I have ham buddys that use OWL  and they have good results as well....The OWL does seem to have more weather related problems, especially in Alaska and Washington State winters....Owl is effected more by wind, snow , rain, and especially ice....

If the situation had been different and I had not the supply of coax that I have,  and the space for multiple antennas, I would probably have used OWL and a tuner....So, Don't take this as a statement that coax is the only way to go and that baluns are unnecessary, because that is NOT what I am saying....I just wanted to relate my experience with wire antennas fed with coax....This method has worked for me for many years and is still working.....

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #5 on: April 08, 2014, 03:26:51 PM »
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Now this is my own experience.......I have always had an abundance of coax....I was in the metal salvage business and bought a lot of surplus gov't wire and metals at military base auctions....There was always some coax in the mix and I would save out the good stuff..I started making resonant wire antennas fed with coax...Never used a Balun...Never used a tuner....I found that if the antenna was cut for the operating freq and fed with coax, and the antenna was operated in a frequency range that kept the SWR below 2 to 1  there were no problems with feedline radiation and no transmitter problems.....This has worked well for me because I have the room and supports to put up antennas for every freq that I wanted to operate on and I have plenty of coax to feed these antennas with...The freq range of such antennas is limited ....but as an AMer  I operate only a narrow range within each band so this is not a problem..I have ham buddys that use OWL  and they have good results as well....The OWL does seem to have more weather related problems, especially in Alaska and Washington State winters....Owl is effected more by wind, snow , rain, and especially ice....

If the situation had been different and I had not the supply of coax that I have,  and the space for multiple antennas, I would probably have used OWL and a tuner....So, Don't take this as a statement that coax is the only way to go and that baluns are unnecessary, because that is NOT what I am saying....I just wanted to relate my experience with wire antennas fed with coax....This method has worked for me for many years and is still working.....

See, you hit the nail on the head. You are talking about mono band antennas designed for narrow resonate bandwidths. Well, most of us want our wire antennas to work on several or on all bands and not just one. That's when open-wire line rules. They way to get around the weather conditions such a rain snow and ice is to use that heavy 450-ohm ladder line or use heavy insulated wire and not bare wire when you make it.

What you want is a really high impedance at the antenna feed point (not the shack end) and then a low impedance (600-ohms or less) at the shack end where it connects to your tuner or equipment.

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #6 on: April 08, 2014, 03:27:48 PM »
There are some who will disagree, but the attachment below is what would be the ideal perfect antenna.

A 1/2 wave 160-meter Zepp fed with balanced line. If the impedance equals the balanced line's impedance at the transmitter end and equals a very high impedance to infinity at the antenna feed point end on 160-meters then it will work on all HF bands and out perform coax fed dipoles in a heartbeat. You will have the maximum voltage possible radiating off of each of the 1/4 wavelength legs of the antenna.

The discrepancy is many have always thought in terms of power and current and not voltage and that's what happens when you live in a low impedance 50-ohm unbalanced world too long :icon_crazy:

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #7 on: April 08, 2014, 03:28:03 PM »
If I was to ever move out into the country somewhere and had a big lot behind my house I would put up two telephone poles or towers spaced far enough apart to either put up a full or half wavelength Zepp for 160-meters and I would build the highest Z balanced line that I could build that would still be practical and hold up in the wind, etc. I'd locate a bunch of big industrial HV porcelain insulators (spacers) that are long enough to make the line around 1200-ohms minimum because the wider the spacing the higher the Z will be at the feed-point to each leg. If anything it would solve possible problems with birds during transmit. I would probably have the most favorite back yard for any cats that lived around the area in less than a week :lol:

What would be really awesome is to have a push-pull RF amp with a 1:1 coupling ratio to the feedline to where it's output Z matched the balanced line :surprised:

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #8 on: April 08, 2014, 03:28:21 PM »
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There are some who will disagree, but the attachment below is what would be the ideal perfect antenna.

A 1/2 wave 160-meter Zepp fed with balanced line. If the impedance equals the balanced line's impedance at the transmitter end and equals a very high impedance to infinity at the antenna feed point end on 160-meters then it will work on all HF bands and out perform coax fed dipoles in a heartbeat. You will have the maximum voltage possible radiating off of each of the 1/4 wavelength legs of the antenna.  :icon_crazy:

Well, I could do the horizontal easily... I may have some 120' tall pines in the back... I'd have to find some tree skinners to climb up and hang it ! I found some of those old brown spacers ( about 10" W) at a couple of different yard sales around here. I have no idea why they would show up in the backwoods of Arkansas... the holes were lined with lead.

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #9 on: April 08, 2014, 03:28:37 PM »
I'm my case its just a fantasy because I doubt I will ever live somewhere where I have land like that and the room. It's fun to think about though and what you could do if it ever happened.

Below is kinda what I meant, but I'm thinking even wider spaced OWL. Like finding some longer 4' to 6' spacers :eek: As long as it was secured at both ends and maybe tied-off with some Dacron rope here and there to keep it from swinging around in the wind it would probably be fine.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #10 on: April 08, 2014, 03:29:46 PM »
OK, let's say I put this antenna up, and I made some wide spacers from CPVC, or the like. What's the reflected wave looking at? In other words... how do I figger the impedance of the output tank? I see all sorts of stuff on the internet about feedlines and antennas, but most are assuming 50ohm "modern" transceivers. :icon_yawn:

Reading from "The Radio Handbook" Editors & Engineers 1946, the tank impedance is stated as Z= 2piFL squared/R where
Z= impedance, L=inductance, f=frequency in cycles, R=resistance in ohms. (Basically, the R in this case would be the inductor.)
In the chart given as an example, the Z is highest at resonance. In this case 18 ohms at f=2150. So, in a sense, the high impedance of the feedline and antenna are "bridging" the very low Z of the output tank.
Is this correct?

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #11 on: April 09, 2014, 10:00:48 PM »
I hear Oklahoma has some wide open spaces !

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #12 on: April 09, 2014, 10:01:08 PM »
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I hear Oklahoma has some wide open spaces !

Know why it's always so windy in Oklahoma?

Because Kansas sucks and Texas blows :lol:

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #13 on: April 09, 2014, 10:01:35 PM »
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Reading from "The Radio Handbook" Editors & Engineers 1946, the tank impedance is stated as Z= 2piFL squared/R where
Z= impedance, L=inductance, f=frequency in cycles, R=resistance in ohms. (Basically, the R in this case would be the inductor.)
In the chart given as an example, the Z is highest at resonance. In this case 18 ohms at f=2150. So, in a sense, the high impedance of the feedline and antenna are "bridging" the very low Z of the output tank.
Is this correct?

Yes, and there are some who will say impedance bridging causes power to be reflected back to the source which creates standing waves, but that's what happens when you use unbalanced coax and not open wire line.

It's called impedance bridging, but with OWL its really voltage bridging. Unfortunately everyone has been brainwashed ever since coax became the norm and that maximum power theorem is for the birds :icon_crazy:

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #14 on: April 09, 2014, 10:01:54 PM »
This happens all the time in the audio world... just yesterday, I had on the bench an old ALtec 352 mixer amp. I grabbed the closest input transformer I had laying around and plugged it in so as to make the XLR jack live. It was a 15K:15K bridging xfmr. I connected a dynamic mic element, which I would bet is below 50 ohms, plugged it in and it worked fine.  :icon_clap:

Seems like I remember the 600 Ohm audio standard coming into use because that was the impedance of #6 open wire on a telegraph pole crossarm.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #15 on: April 13, 2014, 06:35:00 AM »
RE: "perfect antenna.png"

Looking at that drawing, I assumed you meant 130' in height. Is that what you are saying? Or, are you giving that as total feedline length?

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #16 on: April 13, 2014, 08:32:50 AM »
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RE: "perfect antenna.png"

Looking at that drawing, I assumed you meant 130' in height. Is that what you are saying? Or, are you giving that as total feedline length?

To get the best performance with a 1/2 wavelength antenna the feedline length should be a 1/4 wavelength long. That would be for the lowest band you design the antenna to operate. In this case it was for 1.800Mc. Then for a full wavelength antenna the feedline should be a 1/2 wavelength long.



Offline KM1H

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Re: Wire antennas anyone?
« Reply #17 on: April 14, 2014, 03:13:03 PM »
Im another who has no use for a PITA tuner that means retuning for even simple in band QSY's :mad:

OWL is a drag in more ways than one and not everyone lives in the desert with no rain and ice storms. There is really no such thing as a non radiating OWL and local noise pickup can be intense in many areas.

With good quality RG6 almost free for the asking in many places putting up a multiband wire dipole is simple and any half decent vintage rig can tune even all of 80/75M. Ive run 1200W at both ends of the band with it. A good coax balun wound on a couple of 31 mix toroids takes common noise into the noise.

Carl

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #18 on: April 15, 2014, 08:17:20 AM »
Antennas with OWL will not radiate when using them on the frequency they are cut for or if you use a balanced tuner when not on that frequency or band. Say like the one in my pic, on 1.8Mc when it folds back the 130' feedline is pretty much invisible. The only time it will radiate is when changing frequencies or bands and that’s why you need a balanced tuner to eliminate it. It can radiate during tuning as you change bands, but once tuned and equalized (balanced again) it won’t.

I agree that OWL is a PITA when you don’t live in a location where you have the room for it like most of us, but if you do and can put it up without any obstacles then it’s the only real way to go. Even in my limited space location I’m still using OWL and it is a PITA because of it, but it’s still better than using coax if you can make it work.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #19 on: April 15, 2014, 10:34:34 AM »
Well... I have one of those AEA HF antenna analyzers. Unfortunately, it is for coax... the specs say 0-1000 ohms, but the I/O is an N connector with a SO-239 adapter...
I suppose I could experiment with some baluns & known impedances and plot the known to compare with the unknown, homemade OWL.  I think trying to use it thru a tuna
connecting it to the 50 ohm input and the OWL to the balanced output would throw off the readings. Again, I could use a known dummy load and look at how the analyzer would behave.
Just thinking out loud :confused:
MD

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #20 on: April 15, 2014, 11:18:28 AM »
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Well... I have one of those AEA HF antenna analyzers. Unfortunately, it is for coax... the specs say 0-1000 ohms, but the I/O is an N connector with a SO-239 adapter...
I suppose I could experiment with some baluns & known impedances and plot the known to compare with the unknown, homemade OWL.  I think trying to use it thru a tuna
connecting it to the 50 ohm input and the OWL to the balanced output would throw off the readings. Again, I could use a known dummy load and look at how the analyzer would behave.
Just thinking out loud :confused:
MD

Unfortunately those analyzers will not work with OWL fed antennas. As far as the modern tuners go, you would need a 4:1 toroid balun inside for connecting it to OWL. Many of them do have that now, but they leave a lot to be desired. The best way is to just build your own balanced tuner that doesn't need any balun.

Offline KM1H

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Re: Wire antennas anyone?
« Reply #21 on: April 15, 2014, 06:23:38 PM »
Quote
I agree that OWL is a PITA when you don’t live in a location where you have the room for it like most of us, but if you do and can put it up without any obstacles then it’s the only real way to go. Even in my limited space location I’m still using OWL and it is a PITA because of it, but it’s still better than using coax if you can make it work.

A coax fed antenna doesnt require an external tuner in many cases and VSWR loss is low on 160-40M for many ham runs. Use a roof mounted 10-20M ground plane where the vertical polarization can be useful; many AMers get nosebleeds on those bands.  :lol:  I operate 160-6M on CW, SSB, and AM, all coax and not a tuner in sight. CW/SSB only above that.

Quote
Unfortunately those analyzers will not work with OWL feed antennas. As far as the modern tuners go, you would need a 4:1 toroid balun inside for connecting it to OWL

That assumes the load is a perfectly resistive 200 Ohms and if the OWL is 600 Ohms we already have a problem. The tuner doesnt tune the antenna either and once the operating frequency becomes reactive the feedline is no longer a perfect 1/4 wave and the feedline starts to radiate unless you have an automatic tracking tuner. Change bands and the feedline is part of the antenna which is the real reason many think their antenna works so well....it has a horizontal and vertical component and at some point it becomes purely a vertical with T top loading which cancels the horizontal component.

Except on paper an OWL fed antenna is a compromise.

Carl
KM1H

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #22 on: April 15, 2014, 06:40:20 PM »
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A coax fed antenna doesnt require an external tuner in many cases and VSWR loss is low on 160-40M for many ham runs.

B.S. :lol:

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Except on paper an OWL fed antenna is a compromise.

It's only a compromise when using one antenna compared to needing separate antennas for each band or for two bands like 80/10 and 40/15.

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #23 on: April 16, 2014, 06:10:58 AM »
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Use a roof mounted 10-20M ground plane where the vertical polarization can be useful; many AMers get nosebleeds on those bands.

Verticals on the higher HF bands stink unless you are trying to work the occasional stuff overseas. That probably explains why after all these years I've never heard you on the air before. I've used verticals on 20 thru 10-meters before and they were awful for working AM here in the U.S. I've also used 80-meter coax fed dipoles on 10-meters and 40-meter coax fed dipoles on 15-meters, but the bandwidths were so narrow that if the transceiver didn't have a built in auto tuner to keep it's 50-ohm output happy it wasn't happy. And, trying to use them without a tuner on the tube stuff wasn't much better and you had to have one to try and bring the receive level back up when you moved too far away from it's resonate point.

Granted, a center-fed Zepp fed with OWL will leave a lot to be desired on the higher HF bands because of no gain, but at least they will work for someone who only has the room for one antenna and it will still work better than separate coax fed dipoles any day of the week.

Anyway, what works the best on the higher HF bands is a horizontal Yagi with at least 3 elements. 8dB to 9dB gain will do more good than anything. I still use my 10-meter mono band Yagi on the tower, but I'd like to have a tri-bander or one that even has 12 and 17-meters then use the my Zepp on 40-meters on down.

P.S. And yes, everyone uses the term "tuner" when the correct term is antenna coupler. It doesn't really tune the antenna, it simply matches and couples your source Z to it. Using the term 'tuner" is just a bad habit we have all falling into.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #24 on: April 16, 2014, 07:13:34 AM »
OK, using the "open wire feeder impedance calculator" ( You are not allowed to view links. Register or Login ) using 14GA wire (1.6MM)      I don't see much change in impedance from 2ft spacing ( 700 ohms) to 5 ft spacing (843 ohms )    600 ohms was achieved @ 9.4 inch spacing. This seems much more manageable.

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #25 on: April 16, 2014, 07:42:08 AM »
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OK, using the "open wire feeder impedance calculator" ( You are not allowed to view links. Register or Login ) using 14GA wire (1.6MM)      I don't see much change in impedance from 2ft spacing ( 700 ohms) to 5 ft spacing (843 ohms )    600 ohms was achieved @ 9.4 inch spacing. This seems much more manageable.

600-ohms is what most hams do and will work fine, its just better to use wider spacing whenever possible. The wider the gap is at the antenna feed-point (not the transmitter end) then the higher Z you will have there. The higher the better. You can use a wider spacer between each leg of the antenna and then "V" the end of the feeder up to it, but having a sharp 90 degree angle straight down always works best.

I'd use at least 1' spacing minimum since you have the room for it. The Z at the transmitter end will change anyway as you change bands. Try and make it work without any external antenna coupler first on the lowest band you will use it on. Just connect it directly to the link coil's output of your push-pull amp. It will be a step down at that point anyway.

If you have room for a full-wave loop you could try that too. Also remember the curtain antenna that guy put up in his historic district after they complained about his modern tower?

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #26 on: April 16, 2014, 10:03:21 AM »
Quote
Also remember the curtain antenna that guy put up in his historic district after they complained about his modern tower?

Yes, I remember that. The only complainers I'll have are the deer. Our house is on a paved city street. The 3.5 wooded acres that the shack sits on is west of  a gravel road behind the house. So, it's well out of view of any tourists and there are no houses on the gravel road. Passers-by would have a hard time seeing #14 black wire back in the woods. Heck, I can't even see the 100' pines out the rear windows of the house. The shack is about 120' from the house. I'll be posting the shack progress pix I had on the old forum. Maybe I can get a Google Earth screen grab to give a better perspective.
TNX, MD 

Offline KM1H

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Re: Wire antennas anyone?
« Reply #27 on: April 17, 2014, 06:48:50 PM »
I only use verticals on 160 and 80 supplemented by 180' high inverted V's. Until I downsized the contest aluminum from 4 high stacks of 4 el on 10, 15, 20; and 4/4 on 40 you would have heard me on any band if you were active during my waking hours. These days it is nothing on 40 as I rebuild the 2/2 into Leeson Moxons and 10/15/20 use HB 4/4/3 el monobanders. Im usually in bed by 10-11 PM Eastern time these days. Lots of the guys from the other place have worked me 160-10M and there were a couple of good nights to the West Coast during the winter when I stayed up to 1AM. Needed a lot of smoke since most of those guys dont hear well, the Beverages here helped to get perfect copy on the 100W stations.

OTOH switching between the main station and the expanding AM side of the basement is a royal PITA so I wont be using the antennas requiring rotators. Currently there is a 75M sloper with 40/15 hanging from it as an inverted V and I run the 180' high 160/80/75 single feedline Vee on a switch.

In the past Ive had excellent results with verticals 20 to 10M US and DX and the current projects are converting a pair of freeby Hi Gain CB 5/8 wave. One for 20/17 will be mounted at one side eave and the other 15/12/10 on a chimney mount about 55' away. With elevated radials they should do well enough.

Still trying to figure out to get a station in the FR, BR, and maybe the attic wired in and easily antenna switched.

Carl

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #28 on: April 25, 2014, 11:14:31 AM »
So, I've ordered this OWL kit:  You are not allowed to view links. Register or Login     Am I allowed to post a commercial link?

I have a roll of 14ga THHN and a roll of Dacron rope, ( black, so the hysterical district snoops don't see it) I've ordered two center spacers for the antenna, so as to separate the dipole at least double the width of the feed line for a higher impedance feed point. (Y)

I'll mount these to the wall  to bring the feedline into the shack:  You are not allowed to view links. Register or Login
Am I allowed to post a commercial link?

Now, all I need to do is figure 130' from the output of the tuna/transmitter to the antenna... in order to make the feedline reach and allow the antenna to work at optimum height above ground. BTW, I have very poor soil over here in the Ozarks... I may wind up needing  a reflector either parallel with the antenna or on the ground ! :icon_crazy:


Offline W1AC

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Re: Wire antennas anyone?
« Reply #29 on: April 26, 2014, 09:11:24 AM »
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What you want is a really high impedance at the antenna feed point (not the shack end) and then a low impedance (600-ohms or less) at the shack end where it connects to your tuner or equipment.

I'm confused: why is that a "good thing"? Most antennas are well below that value, and even a folded dipole is nominally 300 ohms at the feedpoint. Getting a higher feedpoint impedance would mean introducing reactance or using a transformer, correct?

Bill, W1AC

Offline W1AC

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Re: Wire antennas anyone?
« Reply #30 on: April 26, 2014, 09:21:18 AM »
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Seems like I remember the 600 Ohm audio standard coming into use because that was the impedance of #6 open wire on a telegraph pole crossarm.

Are we going to start writing about the wheelbase on Roman chariots? ;)

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #31 on: April 26, 2014, 10:52:41 AM »
Bill: you said
 "I'm confused: why is that a "good thing"? Most antennas are well below that value, and even a folded dipole is nominally 300 ohms at the feedpoint. Getting a higher feedpoint impedance would mean introducing reactance or using a transformer, correct?

I realize you are quoting Brian here, and this is all way above my pay grade... But, working in the audio field most of my life, I tend to equate RF with AF as they are both waves, albeit at much different frequencies. The analogy here being... transmitter tank>feedline>antenna system as compared to a horn speaker, i.e. driver>throat>horn mouth.  :icon_crazy:

I would refer you to "Radio Antenna Engineering" Edmund Laport, Mcgraw-Hill 1952. In particular, chapter 4, 4.4.2 - 4.10, pages 408-425. In particular, section 4.48 on "Tapered transmission- line section as impedance-matching transformer".
TNX, MD
PS: I think the Laport book can be found as a .pdf on the arpanet.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #32 on: April 26, 2014, 10:58:25 AM »
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Are we going to start writing about the wheelbase on Roman chariots? ;)

Oh, you mean as it relates to the American Railroad standard track guage of 1,435 mm (4 ft 8 1⁄2 in) ? or as it's commonly known as the width of two horses asses side by side ? :icon_wave: OH, wait...

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #33 on: April 26, 2014, 11:49:28 AM »
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So, I've ordered this OWL kit:  You are not allowed to view links. Register or Login     Am I allowed to post a commercial link?

I have a roll of 14ga THHN and a roll of Dacron rope, ( black, so the hysterical district snoops don't see it) I've ordered two center spacers for the antenna, so as to separate the dipole at least double the width of the feed line for a higher impedance feed point. (Y)

I'll mount these to the wall  to bring the feedline into the shack:  You are not allowed to view links. Register or Login
Am I allowed to post a commercial link?

Now, all I need to do is figure 130' from the output of the tuna/transmitter to the antenna... in order to make the feedline reach and allow the antenna to work at optimum height above ground. BTW, I have very poor soil over here in the Ozarks... I may wind up needing  a reflector either parallel with the antenna or on the ground ! :icon_crazy:

14 gage wire is ok, 12 gage would be better and stronger though.

Attached below is some info from 1937 for the feeder length. There's a lot of mis-information on the other boards and on the web in general saying that the feeder should always be an odd multiple of a 1/4 wavelength, but that applies to end-fed Zepps only. I highlighted the parts about the lengths. The first part deals with center-fed Zepps and the second part deals with end-fed Zepps. For a center-fed Zepp the length needs to be an even 1/4 wave so when it folds back it will be balanced and won't radiate. So, for a 1/2 wave antenna with 130' on each side the optimum feeder length is 130'. It can be a shorter even multiple length, but it will still work better if it's 130'.

The stuff you bought will work and will make 600-ohm OWL. It's a shame they don't make wider stuff because using 1200-ohm OWL would be better.

P.S. On most bands the typical center-fed Zepp will be around 1200-ohms at the transmitter end of the feeder, but on some bands it will be a lot lower. That's why its better to use a higher Z feeder if possible.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #34 on: April 28, 2014, 11:47:46 AM »
Brian:
I think you posted that diagram somewhere else, as I have it printed out laying on my desk.

The 1952 "Radio Antenna Engineering" Edmund Laport book can be had here:
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or as a printed bound paperback for $15.98 + shipping, here :
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TNX, MD

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #35 on: April 28, 2014, 05:35:55 PM »
I love it when those old antenna books talk about calculating the VOLTAGE and making it double for 100% MODULATION. They knew how to do it back then and it kinda throws everything being taught today out the window when compared to lossy current fed antennas :icon_wave:

An example lesson would be the war between Edison and Tesla, DC vs AC. Well, which one proved to better in the end?

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #36 on: May 09, 2014, 10:15:20 AM »
Speculation called for:

OK, so I've gathered most of the parts for the "perfect antenna", still waiting on the expensive pulleys. I've been reading about antenna impedance as it relates to height above ground.

 I rented an excavator several years ago to dig out a place on the hillside for the shack. ( my 3.5 acres lies at  a 20 degree, or more, slope from top to bottom.) Here in the Ozarks, I found out pretty fast that we have only about 18 inches of topsoil. That topsoil consists mostly of rotted leaves, etc... not what I would call real "dirt".
Below that it is solid rock. So, I have what would be considered a poor ground for RF. What effect will that have on the dipole ? Am I going to wind up with a "cloud burner"?

Anybody care to speculate on this?
TNX, MD

PS: I have a couple of trees picked out, but I won't know the true height of the antenna until I pull it up with a marker string attached. ( I would estimate 60-80 feet H )

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #37 on: May 09, 2014, 02:56:06 PM »
I might add to the post above that the 1952 FCC ground map shows me to be in "zone" 8. That includes the Mississippi river delta. So that is BS. I have lived in the Mississippi river delta and that "dirt" goes down forever... hard to find bedrock down there. The Memphis, TN artesian water supply comes from a depth of  1500ft.  Black gumbo, a couple of clay & sand layers, then water. The crust up here in NW Arkansas is what they call "Karst"... It's like swiss cheese thru limestone with springs everywhere and the "Fayetteville shale" formation below the limestone. 

Offline KM1H

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Re: Wire antennas anyone?
« Reply #38 on: May 09, 2014, 05:41:02 PM »
Sounds a lot like here, topsoil varies from zero to about 12" on average with a couple of small holes down to 4'. The 180' tower sits on a concrete pad that varies 7-14" below grade to NH granite.
The steel wire mesh reinforced concrete is epoxied to the granite and the tower base plate sits on a 3/4" steel pin that goes thru the center. I had to rent a big trailer mounted air drill to bore a 2" hole 8' for the expandable utility grade guy anchors...4 towers was a lot of work!

A horizontal antenna isnt at all fussy about a poor RF ground, its the opposite of a vertical. What counts is the reflection zone XX wavelengths away based upon height. Since Im on the top of a hill that is only flat for about 20-30 acres before gradually falling off in all directions about 500' in 1/2 mile or so my reflection zones are well down in elevation.

The HFTA program on the ARRL Antenna Manual CD is good for pattern plotting.

Carl

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #39 on: May 10, 2014, 07:59:38 AM »
Generally a half wave Zepp like that works best when it's 1/4 wavelength off of the ground, but its not mandatory. If you can get it up at least 60' then it will work great from 80-meters on up. It will still work ok on 160-meters with a little less range, but its no real biggie.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #40 on: May 10, 2014, 11:23:21 AM »
Here's a "ground test" I found online from the ARRL handbook. But, I guess the real test is to put the thing on the air !

"The "Ground Conductivity Test" is from the ARRL Antenna Handbook...
The book I have is from 1994....and it is on page 27-35 that's chapter 27 page 35........
Conductivity Soil, Measurement of....

It takes 4 rods.......9/16" diameter and 14 inches long these 4 rods are driven into the ground 18 inches apart in a straight line......drive them in 12 inches...

One side of the 120 AC line to a 100 watt light bulb...the other side of the bulb to a 14.6 ohm resistor.........they say to make up the resistor by paralleling 5 of them...3 of which are 68 ohm 1 watt....the other 2 are 82 ohm 1 watt......then the other end of the resistor goes to rod #1 .......the other side of the AC line goes to the farthest rod.....
You now have two AC voltage test points......V1 is across the resistor. V2 is voltage measured between rods #2 and #3.....
In general these two voltages they say should be from 2 to 10 volts......
Formula for calculation is......

C = 21 x V1/V2
 
This gives you the Millisiemens per meter.They do say that the measurements can vary considerably depending on moisture content of the ground..... example given is a chart was someplace in New Jersey back in 1976.........the guy took measurements daily for 90 days......measurements varied from 15 to 30 Millisiemens per meter over that period of time..."

I would assume the "neutral" side of the AC line to gnd. YMMV

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #41 on: May 11, 2014, 09:30:39 AM »
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Sounds a lot like here, topsoil varies from zero to about 12" on average with a couple of small holes down to 4'. The 180' tower sits on a concrete pad that varies 7-14" below grade to NH granite.
The steel wire mesh reinforced concrete is epoxied to the granite and the tower base plate sits on a 3/4" steel pin that goes thru the center. I had to rent a big trailer mounted air drill to bore a 2" hole 8' for the expandable utility grade guy anchors...4 towers was a lot of work!

A horizontal antenna isn't at all fussy about a poor RF ground, its the opposite of a vertical. What counts is the reflection zone XX wavelengths away based upon height. Since I'm on the top of a hill that is only flat for about 20-30 acres before gradually falling off in all directions about 500' in 1/2 mile or so my reflection zones are well down in elevation.

The HFTA program on the ARRL Antenna Manual CD is good for pattern plotting.

Carl

Carl:
 My daughter lives about 7 miles west of Portland, ME. While digging a footing for her front porch several years ago... all I ran into was "coastal plain". Basically, very sandy dirt.  Looks like you are about 30 air miles inland. Like you said, verticals are a whole different ballgame.
MD

Offline KM1H

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Re: Wire antennas anyone?
« Reply #42 on: May 11, 2014, 06:02:05 PM »
That coastal plain was all below water when Greenland was correctly named by the Vikings; it will be below water again some day as a natural planetary event not controlled by Al Gore or his lunatic followers.

Carl

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #43 on: May 16, 2014, 06:45:22 AM »
Well, I may be over thinking this whole thing. I have been reading up on the "delta match" method of connecting an OWL to a dipole. But, it's not actually a dipole... it's a longwire... no center insulator. Using  1.8MHZ as the lowest operating frequency, the feeders would connect 30 meters on either side of center. They would then taper down to the 600 ohm portion of the feedline at a distance of 82 feet from the antenna. This whole thing is basically a delta loop suspended in the air by the horizontal  longwire portion of the antenna. I feel like I'm painting myself into a mono-band corner here.  :confused:

These calculations are from the "Radio Handbook" 10th ed, 1946, by Engineers & Editors

Offline W5HRO

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Re: Wire antennas anyone?
« Reply #44 on: May 17, 2014, 07:29:07 AM »
I would just string up the 1/2 wave Zepp up 60' minimum and be done with it.

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #45 on: May 17, 2014, 07:42:32 AM »
Yup... that's the plan for now... :icon_thumbup:

Offline K4TQF

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Re: Wire antennas anyone?
« Reply #46 on: May 26, 2014, 05:47:17 PM »
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I'm confused: why is that a "good thing"? Most antennas are well below that value, and even a folded dipole is nominally 300 ohms at the feedpoint. Getting a higher feedpoint impedance would mean introducing reactance or using a transformer, correct?

Bill, W1AC

Bill: Here's another article you may find useful:    The Exponential Transmission Line, Charles R. Burrows, Bell System Technical Journal Vol 17, P555, October 1938

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Offline K4TQF

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Re: Wire antennas anyone?
« Reply #47 on: July 14, 2014, 08:50:04 AM »
I think I can do this pretty easily. Have most parts on hand... Need to revive balanced tuna... :icon_thumbup:

Report at 11... not say'in what day.
TNX