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Message |
    
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1035
Registered: 9-2004
| | Posted on Sunday, January 15, 2006 - 11:43 pm: | 
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833, im hoping you have the time to answer a question or two about feeding a .64 wave antenna.
i am interested in building my own .64 wave, aluminum groundplane antenna, and it seems that the major difference in the current designs is in the feedpoints.
one guy uses a coil.
one guy uses a "trombone" tuning mechanism.
i have read your past reviews, and i recall you having some opinions about the way these antennas are fed.
can you tell me what your favorite method would be?
have you ever built one?
i am a good metal fabricator, and i have access to aluminum and a TIG welder if need be.
what do you think?
thanks for the help in advance,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 521
Registered: 11-2001
| | Posted on Monday, January 16, 2006 - 10:44 am: |
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Hey Kid, Jay says the trombone has significantly less losses. I'm no expert, but I don't believe that is necessarily ture or that it really makes a big difference. The gamma would appear, just from a physical standpoint, to be able to force the current higher up the radiator and thus may be of some advantage if the idea of current distribution higher up on the radiotor has any merit. The .64 ground plane that Wolf Radio makes also has two inductive coils higher up on his radiator and the way I understand their function this might also induce currents higher up the antenna as well. The designer even touts that as and advantage. |
Tech833
Moderator
Username: Tech833
Post Number: 1153
Registered: 8-2002
| | Posted on Monday, January 16, 2006 - 12:29 pm: |
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My favorite method of feeding these antennas is a tapped coil. The trombone tuning method does offer a power capability improvement, but at the cost of giving the major gain lobe some 'up-tilt'. That reduces gain on the horizon. My field plots of the I-10K proves this.
The tapped coil is what the famous Radio Shack .64 antenna used, and almost every other 5/8 wave antenna that was successful.
A good compromise: The Maco V-5/8 uses a ring which is schematically the same as the tapped coil, but also offers increased power handling capability.
With any .64 wave, there will be a very slight capacitive inductance component at the tap point which can be cancelled by a turn or two of coil between the tap and the vertical radiator. Therefore, a tapped coil feed will also have a slightly wider bandwidth than a trombone tuned .64 wave antenna.
A gamma feed will work too, but the added series capacitance of the gamma will reduce the bandwidth further.
The Avanti Super Penetrator used a folded vertical trombone method that seemed to work very well with very high gain on the horizon (almost no lobe distortion) at the cost of greatly reduced bandwidth. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1038
Registered: 9-2004
| | Posted on Tuesday, January 17, 2006 - 12:14 am: |
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i hoped you two would take an interest!
my antenna will be centered on 27.2mhz
a 2 mhz bandwidth would be nice, but i can deal with 1.5 for a 2 to 1 SWR curve.
as for power handling, mine will never see more than 1.5K. i doubt it will ever see that much, but it seems like a good design criteria.
i am leaning toward the coil so far.
it also seems the easiest to fabricate.
any certain alloy to use for the coil?
for the radiator?
what would the coil specs be?
EX: length, turns, spacing, diameter, tap location?
as for the Maco 5/8 wave:
i calculate .64 of the wavelength to be 23 feet, 1 11/16".
can the maco be adjusted for this length?
sure would be nice to just buy this antenna and make it longer.
if lengthened; would it be a true .64 wave antenna?
what is the bandwidth of the Super Penetrator?
i would like to research this antenna design.
thanks for the help guys,
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1157
Registered: 8-2002
| | Posted on Tuesday, January 17, 2006 - 9:12 am: |
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My dad was really into CB and ham radio at the time I remember playing with his antennas (he was unable to assemble or install them himself). I am not positive, but I seem to remember the SWR being flat near the middle of the band (channel 20?) and close to 1.5 at 1 and 40. Don't hold me to it though.
If course, you can artificially broaden the bandwidth by using lossy coax cable. I always used Heliax, so the loss was nearly zero. If I had used cheap RG-8 cable, I'll bet it would have been nearly flat across the whole band. Artificially, of course.
Yes, you could lengthen a V-5/8, but why? The difference between a 5/8 wave and a .64 wave is almost nothing at all. Maybe 0.2 db gain or so? You could do the same thing by eliminating an additional connector in your system. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1042
Registered: 9-2004
| | Posted on Tuesday, January 17, 2006 - 5:13 pm: |
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so the consensus is that the Maco is the best bet for the money.
i guess i was operating under the assumption that the take off angle was different enough between these two antenna designs to warrant going with a .64 wave.
for all the trouble it would be to build the antenna; if the performance is going to be nearly equal, i'll just buy the maco.
would there be any advantages as far as take off angle is concerned, to using the Maco as a .64 wave, or would you just use it as its intended?
thanks for all your help paul, and marconi,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 530
Registered: 11-2001
| | Posted on Tuesday, January 17, 2006 - 5:38 pm: |
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Kid, you talk about the difference between .64 and .625 as though it is a choice. Personally, I believe all these longer that 1/2 wave antennas derive the lenght from the manner by which they are fed or matched. Any length over the 1/2 wave is not resonant. Something has to bring these longer elements into resonance at whatever lenght they end up being, so it is not a choice whether the V58 can be 20' or 22' or 23.676544'.
Just go check out the difference in feeder designs between the Imax and the A99 that Tech 833 has provided us. You will see the matchers are similar, but are actually different all at the same time. But you would not be able to see that unless 833 had exposed it for us. None-the-less it is true. So trying to make an A99 24' long without doing something different concerning the matcher is pure folly. And that also applies to the V58 or any other antenna that is designed as a total package.
Just my opinion. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1051
Registered: 9-2004
| | Posted on Tuesday, January 17, 2006 - 9:28 pm: |
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i guess i should have worded my question better.
i am referring to electrical length; not just extending the vertical sections up a bit.
i may be wrong here, but isnt electrical length the only inherit difference between a .625 and a .64 antenna?
i understand that the change needs to be made at the feedpoint.
i am operating under the assumption that the maco derives its full .625 length from the tuning ring.
the vertical section is only about 20' right?
so would you make the tuning ring a larger diameter?
or could you extend the vertical sections by .015 wavelength (.640-.625) and then retune the ring for lowest SWR?
i am trying to learn here. sorry if you thought i knew more than i do.LOL
i know lotsa stuff, but there are huge holes in my knowledge.
so, am i mistaken in my contention that all the different feeding methods described so far, are different methods of acheiving the same goal; a .64 electrical length?
thanks again for the lesson guys,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 535
Registered: 11-2001
| | Posted on Wednesday, January 18, 2006 - 1:34 am: |
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833, do I read some assumptions in the words you post above concerning bandwidth and gain? I do not mean to suggest that the assumptions are significant, but that they are measurable and have scientific meaning or significance? The following are your words;
With any .64 wave, there will be a very slight capacitive inductance component at the tap point which can be cancelled by a turn or two of coil between the tap and the vertical radiator. Therefore, a tapped coil feed will also have a slightly wider bandwidth than a trombone tuned .64 wave antenna.
A gamma feed will work too, but the added series capacitance of the gamma will reduce the bandwidth further.
The Avanti Super Penetrator used a folded vertical trombone method that seemed to work very well with very high gain on the horizon (almost no lobe distortion) at the cost of greatly reduced bandwidth.
Couldn't this all mean that those feeders that add bandwidth show less gain than those feeders that show a more narrow bandwidth? Is this not the answer to the question of the author of this thread? And would that thus mean that the Avanti, showing the least bandwidth of all, would naturally show the most gain? And that antennas that show increased bandwidth probably have more losses in the feeder in order to show the add bandwidth?
Just some thoughts I had about your words. |
Al_lafon
Intermediate Member
Username: Al_lafon
Post Number: 168
Registered: 3-2005
| | Posted on Wednesday, January 18, 2006 - 11:46 am: |
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Hello take a look at J pole antenna can be made from copper or aluminum see this you'll need to
resize for 11 meters |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1100
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 4:34 pm: |
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just saw a .64 wave antenna from ARCHER for sale on the auction site. it went for 155.00 plus the 55.00 shipping fee.
it was brand new in the box and was called the archer .64 wave gain antenna
cat. # 21-964
anyone know anything about this antenna.
if there is a coil used at the feedpoint, it must be inside the vertical radiator because i couldnt see anything.
seems this might be something i could build if i had the manual.
matt |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2320
Registered: 7-2004
| | Posted on Saturday, January 28, 2006 - 6:01 pm: |
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that's the famous radio shack 'super antenna' of the late 70's that 833 mentioned in the 3rd post from the top, kid! |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1104
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 7:58 pm: |
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thanks pat! i scrolled up, and there it was!
glad to hear that 833 likes it too.
i want one!
i'll probably have to build it judging from the price the last one drew.
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1177
Registered: 8-2002
| | Posted on Saturday, January 28, 2006 - 8:05 pm: |
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Kid, there is a coil in the small plastic base at the bottom of the aluminum vertical element.
Marconi, you are correct. However, there is not much difference in 'gain' with the different feeding methods, but there is a noticeable lobe distortion with the horizontal trombone method.
Reducing the bandwidth (raising the Q) does sometimes increase gain. And, it is also true that reducing the Q (broadening the bandwidth) can sometimes reduce gain (increase feed losses).
In this case, we are comparing a tapped coil vs. trombone. The trombone has a better power handling capability because there is not a big heat buildup and the material in question is larger diameter. A tapped coil has reduced power handling capability due to core saturation and heat buildup. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1105
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 8:50 pm: |
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would there be any benefit to using aluminum strap for the coil such as is used in the "monkey made" and other mobile antennas?
any drawbacks?
in the pic on the auction site,it looks as though the coil would have to be about two inches long.
maybe the pic is skewed.
i really feel that i could build one of these if i knew the length, diameter, no. of turns and tap point of the coil.
im not trying to get you to figure it all out for me 833; its just that i have been searching the net for info on .64 antennas, as well as the Amateurs Handbook, and an old army tech manual i have on antennas, and i cant seem to find ANYTHING on how to build or design one.
if you know of a book that covers this subject in depth (no college textbooks though!)LOL
i would definitely pick it up and read it from cover to cover.
(and then ask you a million MORE questions!)
thanks for the input,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 565
Registered: 11-2001
| | Posted on Saturday, January 28, 2006 - 9:12 pm: |
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Hey kid I have one of those coils around here somewhere. If I can find it, I will email a close up picture of it. It is basically a simple little coil just like 833 notes. It is inside the base of those antennas. It is made up of copper wire wound up on a little piece of PVC and of course it hooks up to the antenna between the SO-239 in the base and the radiator sitting on an insulator that holds the coil. Pretty simple and you should be able to make one from the pictures if they are good enough. I will only email because the pictures on here have to be real small or they will not tranfer. If your email is not available then you will have to email me is guess, if you are interested. I have no idea where it is, but it is here somewhere. It may take a spell for me to locate however. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1106
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 9:54 pm: |
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well, dont ruin the antenna to take a pic for little ol' me. (just send me the darn thing!)J/K!
yes, im very interested! i always check my bulk mail just in case, so go ahead and send the pics.
thanks,
matt |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1107
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 10:00 pm: |
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i also noticed in the pics that the groundplane is on a bracket that puts it about 8-12" above the feedpoint.
again, hard to judge the distance in the pics.
is this measurement critical?
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1178
Registered: 8-2002
| | Posted on Saturday, January 28, 2006 - 11:03 pm: |
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Hi Kid.
Yes, the coil form is probably only about 2 inches high and about 2 inches in diameter. Yes, the ground planes are about 10 inches above the coil. That's the way all the antennas were built back then.
I would gess no more than 4 or 6 turns between tap and ground and probably 1 or 2 turns above the tap. It wouldn't take much.
Yes, you would use some strap for the coil, but would it gain you anything? Maybe some power handling. Probably not much else. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1108
Registered: 9-2004
| | Posted on Saturday, January 28, 2006 - 11:11 pm: |
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thanks so much 833. thats exactly what i needed to know.
i dont ever see myself pushing more power than 1kw PEP.
probably not even that.
i do want to get an ameritron AL-811, so thats what the antenna would have to handle.
do you think 10ga. solid is sufficient for this?
i sure am glad you're in cali. all the east coast guys are sawing logs!
thanks again,
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 566
Registered: 11-2001
| | Posted on Sunday, January 29, 2006 - 12:34 am: |
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I don't have the antenna anymore. The coil was taken out so I just have that part. I won't be tearing the antenna part.
You are right the GP elements are about 12" above the feed point. The radiator set on an insulator at the bottom of this mounting bracket. This coil is inside this bottom insulator and the SO-239 is in the bottom of the insulator. The radiator comes down thru a large washer like insulator at the top part of the bracket where the GP elements are attached. This top circular insulator insulates the radiator from the mounting bracket. I think the wire gauge of the coil was as you say about 10 gauge. The space inside the insulating hub at the bottom is not very big, so the coil is not very big either. At the top of this wire coil is a stud like device that fits up inside the radiator thru the topside of the insulator and this secures the radiator with a small bolt. This establishes the feed to the radiator. The coil is probably 1” long and is about 8-10 loops on maybe ½” PVC. I do not recall how it is tapped into the center of the SO-239 below the coil however. Hopefully I can find it in a box somewhere. I always knew this thing would come in handy one day. BTW all that stuff was braded together on the base hub including the SO-239.
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1109
Registered: 9-2004
| | Posted on Sunday, January 29, 2006 - 2:13 am: |
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thanks marconi!
i have a pic of the base from the auction site, but a look inside would be great!
i also wonder about the tap point. 833 says to tap the coil about two turns from the top, going to the radiator.
so the aluminum vertical radiator slides over the coil, and is attatched from the inside.
would it make any difference whether the coil was on the outside or the inside of the vertical element?
if the coil is on the outside of the element; is it ok if the element passes through the coil?
or should it sit above it?
do you know what the power rating of this antenna was?
if its high enough, i'll just copy their design.
thanks to both of you for all the help. it means alot to me that you guys who actually understand this stuff will take the time to bring me closer to that understanding. (who knows if i'll ever get there!)LOL
i figure the easiest way for me to construct this antenna is with alum. tubing and PVC for the insulators.
what is the preferred alloy for antennas?
cant wait for those pics marconi!
(you're up late!)
matt |
Marconi
Advanced Member
Username: Marconi
Post Number: 567
Registered: 11-2001
| | Posted on Sunday, January 29, 2006 - 10:00 am: |
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Kid, check your email. The pictures turned out very large and I captured them as small as I could. I will check Image Shack and see if I can get them published smaller. If so then I will resend. I do not have enough light to make them good photos this close up however.
Sorry, |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1111
Registered: 9-2004
| | Posted on Sunday, January 29, 2006 - 11:32 pm: |
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thanks for the pics!
you say thats 1/2" diameter PVC?
it looks bigger. if im looking at them right; there are about 8 turns on the coil, the tap is two turns up from ground, and there are about 6 more turns above the tap.
i wish i had a scanner to show you guys my idea, but i dont.
basically, its a piece of 1/4" alum. plate cut to about 4" by 4" with a large hole in the center.
a piece of alum. tubing about 16" long is welded to the plate centered on the hole. this is the mast attatchment.
drill holes in the plate for the SO-239 and mount it. the ground radials will be attatched with U-bolts, one on top of the plate, and one on the bottom; perpendicular to the first.
aquire a piece of solid fiberglass rod about 14" long with a diameter that just sleeves into the tubing on the base plate.
about 4" up on the fiberglass rod, a piece of UV resistant PVC is sleeved over the rod and epoxied in place.
the fiberglass rod sleeves into the base plate and the alum. tubing below the base plate is drilled through at right angles going through the fiberglass rod.
the PVC sleeve now rests right on top of the base plate.
the coil is wound around the PVC, the bottom is soldered to ground, the center pin of the SO-239 is soldered to the tap point, and the top of the coil is soldered (and bolted) to the vertical radiator which slides over the remaining 7 or so inches of the fiberglass rod, and this gets drilled through and bolted at right angles too.
i figure the bottom section of the vert. radiator should be about 1 1/4", and i think i'll go with 6ga. solid wire. i wonder if i can get stainless steel solid wire?
well whaddaya think?
matt |
Tech291
Moderator
Username: Tech291
Post Number: 351
Registered: 11-2004
| | Posted on Monday, January 30, 2006 - 7:45 pm: |
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KV,
a couple years ago I made a 5/8 wave vertical from a web artical that originated from the U.K.
it worked very well.The coil dimensions were 26mm id,14awg enameled wire,9.5 turns close spaced.tapped at 2 turns from the bottom.there was also a ceramic cap from the tap to the ground side of the so-239.the value of the cap if memory serves was around 35pf.the main radiator was somewhere around 22 feet with 3-9foot ground radials.I did print out the artical and if i can find it will scan you off a copy.Tried to find it on the web last night to no avail.I still have the antenna but have since modified it for 6 meter use including rewinding the coil.
TECH291
CEF#291
KC8ZPJ |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1116
Registered: 9-2004
| | Posted on Tuesday, January 31, 2006 - 12:26 am: |
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cool! thanks, i can use all the help i can get!
millimeters? where do you think im from? LOL
do you think the coil specs you laid out are close enough for a .64 antenna?
matt |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 59
Registered: 8-2005
| | Posted on Tuesday, January 31, 2006 - 3:48 am: |
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Is it possible one of you still have a picture of the Archer .64 wave antenna. I would very much like to see it if you wouldnt mind sending it to me. |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 60
Registered: 8-2005
| | Posted on Tuesday, January 31, 2006 - 8:17 pm: |
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Thank you very much Kid for sending me the link. Looks like a cool antenna. Did archer also make a 1/2 wave that had the same radials? The radio shack just down the street has an antenna on there roof that looks just like the one in the picture except its not 33 feet tall. Why is it so tall anyways? Imax 2000 is only 24 feet tall. I'm thinking about buying one of the anttron 305's from copper when they get them in. only 18 feet so hopefully no oversized shipping charges. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1122
Registered: 9-2004
| | Posted on Tuesday, January 31, 2006 - 10:44 pm: |
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i think that the 33 foot claim in tha ad came from adding together all the various pieces length.
the guy didnt know what he had.
the correct length should be somewhere around 277"
matt
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Marconi
Advanced Member
Username: Marconi
Post Number: 572
Registered: 11-2001
| | Posted on Wednesday, February 01, 2006 - 2:36 am: |
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Hey kid was the picture you are talking about the ad on ebay that someone posted a link to. Those guys on ebay can say just about anything they want to in their ads, even if it defies all logic or common sense. If it was not the one on ebay then could you send me the picture of the Archer .64 antenna also. I have never seen one. Was it an advertisement or just a photo that some one took a picture of.
BTW I may be wrong but the coil I sent you pictures of went to an antenna that I believe was more like 18' feet. So maybe the Archer .64 antenna that Tech 833 spoke so highly of as the famous (tapped coil) antenna, had an entirely different coil. When I first read his post I was thinking a coil similar to a maco V5/8. But since we have hashed this about for several days and he has not come in an straightened us out, I really cannot speak with any confidence to that issue, 833 will have to address that.
I never knew Radio Shack to ever produce anything that was even close to being considered an industry standard for excellence much less famous, but what do I know. In fact I never knew that RS ever made a .64 antenna, famous or not. Come on 833 clear this up for us and give us a little idea about what this tapped coil thing might look like. The Kid here is wanting to build on that is .64 and he really needs to get it straight. I don't think a feeder for a 1/2 wave will work real good on a radiator that is .64 wavelength long.
I'm from Missouri, some body gotta' show me something here.
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Tech833
Moderator
Username: Tech833
Post Number: 1179
Registered: 8-2002
| | Posted on Wednesday, February 01, 2006 - 10:34 am: |
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Marconi-
I have not seen the picture(s) of your coil assy., so I cannot comment on what it might be used with. By your written description, it does sound more like a 1/2 wave matching network than a .64 network though. However, please do not take my words for gospel since I have not actually seen it. I am only speculating!
As for feedline radiation from an Imax, that is to be expected, and the field plots show this somewhat. What concerns me is you say there was as much RF on the feedline and/or support mast as on the antenna itself. This is unusual. I believe there is something wrong with your antenna if this is the case. My 2 test Imax's showed very little feedline radiation, certainly no more than any other fiberglass stick antenna I have ever tested.
Remember, some (SOME!) feedline radiation is to be expected from ANY anytenna without a counterpoise beneath it. Feedline coupling and magnetic field saturation occur at the feedpoint for many antennas and without something to effectively bleed it or decouple it, this is normal. The Starduster is a good example of decoupling by using the mast as a bazooka isolator. This is also why your SWR changes when you run your coax through your mast rather than outside of it. Besides the obvious feedpoint resistance change, the decoupling becomes a resonance factor as well.
All this does not mean that feedline radiation is some bad thing that everyone suddenly needs to be concerned about. Every antenna suffers from this to some extent or another. This is why you have to model an antenna on a test range before you can accurately implement it. No matter how accurate computer modeling tries to be, there is always the variable of re-radiation and various coupling to distort the most carefully engineered pattern. |
Marconi
Advanced Member
Username: Marconi
Post Number: 575
Registered: 11-2001
| | Posted on Wednesday, February 01, 2006 - 7:32 pm: |
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Thanks for the nice response 833, it all makes a lot of sense.
About the Imax feed line thing. If I used a field strength meter on my transmitter and it goes near full scale when keying up the Imax in AM of FM mode or when talking in SB mode, would you consider that response as RF on the feed line getting back to the rig and showing up on the FS meter?
That is what I am seeing on my Imax installed on a 10' mast with about a 50' run of RG/8U, 95%, foam coax attached. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1128
Registered: 9-2004
| | Posted on Wednesday, February 01, 2006 - 9:30 pm: |
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marconi, my respnse is only a guess, but it could be radiation from the radio causing the field strength meter to deflect.
i know they're supposed to be shielded, but maybe not enough.
just a thought.
i am assuming that you meant that the field strength meter was in the radio room with you.
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1181
Registered: 8-2002
| | Posted on Thursday, February 02, 2006 - 12:37 am: |
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Could be the radio leaking, and it could be that 95% coax leaking. |
Marconi
Advanced Member
Username: Marconi
Post Number: 576
Registered: 11-2001
| | Posted on Thursday, February 02, 2006 - 3:46 am: |
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Yes Kid good point. This meter is sitting right on top of my radio and when I key up on AM or FM or modulate on SB the meter responds from 0 to 10, up to the full scale of the meter depending on the amount of power the radio is set to produce.
I have thought about this fact you suggest, that it could be just RF coming from the radio. But that is not what is happening, I can assure you. The response has strictly to do with the RF on the feed line coming from these particular antennas. It may be as 833 suggest, it could come from other antennas. I have not checked them all, but the antennas I have here, which are several, do not act this way. If you have such a device at home, try it.
I can even take the meter to the area below the antenna, and as I get near the feed line the FS meter responds similar to that at the radio. Maybe it is a bit more, but not by much more. I have never tried this on an Imax or A99 with a GPK, but I would be interested to know if the results would be the same or maybe even less.
Next question is how do I know that it is not the radio? I have two ways of knowing this.
1. In the test above and for convince sake only, I have the feed line suspended above the earth for some distance from the antenna to the station. This is probably a feature found in many typical installations of these antennas on towers and poles. The line is high enough not to obstruct a human to walk under the feed line. However if I choose and allow the feed line to just lay on the earth from the base of the antenna back to the station, then the FS meter will no longer respond. Thus the affect is not from the radio. I use to think that by placing the feed line on the ground I was eliminating the common mode currents from flowing, but that does not happen either. This current still flows over any part of the feed line prior to reaching the earth. It is as though the earth just absorbs this RF energy. In this case it is for sure to me that this energy is lost. With the line suspended the line is just another part of the antenna radiating RF somewhere and likely it is going right into your stuff at the station and into your neighbors electronics as well.
2. I have other antennas that do not do this at all. Maybe one might cause the meter to wiggle a little, but not like the f-glass jobbers. In these cases it doesn’t matter whether I have the line suspended above earth or laying right on the ground. The RF is just not on the feed line or supporting mast like it is on the f-glass antennas mentioned.
Don't get me wrong guys, these antennas work, and work well. I am just relating an observation that I think is important to maybe consider in some installations.
Some of you guys try this at home if you have the FS meter, and let us know what you find.
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Marconi
Advanced Member
Username: Marconi
Post Number: 578
Registered: 11-2001
| | Posted on Thursday, February 02, 2006 - 9:05 am: |
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Kid Tech 291 gives us yet again other coil configurations. In fact his coil is larger with more coils and he suggest specifically this is for a 5/8 from the UK. He also brings up a cap in there that brings the coil to ground, another angle on design which may be for safety only.
My description suggest a coil a bit smaller and I have the recollection it was for a 1/2 wave antenna.
833 suggest to us a coil that is physically larger but with fewer coils and maybe he was thinking of a 5/8 or .64 radiator and the requirements to match that like 291 mentions.
Point is, you can obviously see that there is a wide range of possibilities with larger, more or less coils, and caps included in the mix.
So a lot depends upon the size of the radiator we are talking about. Right off I would guess that a 5/8 coil may well have fewer coils and possibly may also be physically larger in diameter than one for a 1/2 wave radiator.
Looks like it is testing time, with a lots of trial and error work to be done. Luckely they are all pretty close and the coil design will all depend on the impedance condition we find at the feed point of the radiator we are using. |
Tech833
Moderator
Username: Tech833
Post Number: 1182
Registered: 8-2002
| | Posted on Thursday, February 02, 2006 - 9:51 am: |
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Marconi,
Interesting experiment with your FS meter.
At my station (see picture in the subscribers' photos area), I do not have feedline radiation. Since my wire antenna is fed with a 9:1 balun, and that balun is close to ground level, I can only accurately check the coax from about 5 feet away from the balun back to the radio.
I detect very low levels of RF along the coax before it goes into the pipe underground. On the other aide of the pipe, I detect no RF. Following the coax along the path under the house to the pipe feeding up the interior wall, no RF. Inside at the wall plate, some RF. At the radio, lots of RF. On the radio itself, tons of RF, but still nowhere near as much as on the antenna. I would predict the RF level on the radio could be measured in millivolts.
The radio case is bonded to the station ground.
Coax is 1/2 inch foam Heliax.
Jumpers are Times LMR-400.
Coax run total length is around 100 feet. |
Marconi
Advanced Member
Username: Marconi
Post Number: 580
Registered: 11-2001
| | Posted on Thursday, February 02, 2006 - 11:25 am: |
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Paul, if it was the radio making the RF then why does it completely stop when I put the coax down on the earth up to the house. My antenna is just up on a temporary mast at 10' with about 50' of RG\8u 95% shield.
That is all I have to do to stop the effect into the station. Strange! As soon as I get to feeling better and can do some checking I will be doing just that. This Imax is new and I am totally surprised. I have some still snap shots of my FS meter on my radio with the key down and the face plate of my TS 570 in the scene showing out put on the rig and the meter. I did it with the line up and with it on the ground. I sent photos to another friend so he could see and he too was amazed. I have a problem getting pictures on the forum or I would post them there.
Maybe I will email them to Lon and he can get it to you and I think you can see the affect I am seeing. I have not tried it, but I think I will see the same thing if I take the FS meter off of the radio as long as it is close to the line it will do the same. I may even try that with some photos.
I never knew that I had this going on until some time back I left my FS meter on my radio rack and I saw it responding to my transmission and that was using my A99 in a pine tree about 90 feet up with a 120' of pretty new bury flex RG 213.
Regarding the amount of current. I did say it was about as much on the line as it is on the antenna, but truthfully I do not know that for a fact. I have access to a amp meter that will read amperage in a line and if that will work in this situation then I will do that test soon also and report what the meter uses. This meter is used in many settings by repairs people. My brother-in-law does A/C work and he uses it to read amperage going into the feed lines of a compressor to check the amperage draw for normal or excess. This device may work on this line if it is sensetive enough to read this low of amperage. I assume the aperage in this case to be at or less than maybe 2-3 amps in the antenna and something less in the line depending on the watts imput from my rig. I will keep you posted.
Thanks,
Eddie |
Tech808
Moderator
Username: Tech808
Post Number: 9166
Registered: 8-2002
| | Posted on Thursday, February 02, 2006 - 11:41 am: |
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Marconi,
I would be happy to forward Paul the information for you or you can send it to him direct.
Below is how to contact all of the Copper Forum Moderators direct.
Moderator Name
Admin Admin
Forummaster Forummaster / forummaster@copperelectronics.com
Moderator136 Hal / Moderator136@copperelectronics.com
Moderator1516 Gayle / Moderator1516@copperelectronics.com
Tech237 Simon / Tech237@copperelectronics.com
Tech291 Dennis / Tech291@copperelectronics.com
Tech548 Jeff / Tech237@copperelectronics.com
Tech808 Lon / Tech808@copperelectronics.com
Tech833 Paul / Tech833@copperelectronics.com
Tech8541 Richard / Tech8541@copperelectronics.com
Hope this helps,
Lon
Tech808
CEF808
N9OSN
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Tech833
Moderator
Username: Tech833
Post Number: 1186
Registered: 8-2002
| | Posted on Thursday, February 02, 2006 - 9:43 pm: |
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Hope the spam spiders don't find that info...
Well, Marconi, if laying your coax on the ground 'fixes' it, then you are effectively detuning something, therefore 'fixing' the problem. Tell you what I would do- Just lay the coax on the ground and get some sleep. |
Marconi
Advanced Member
Username: Marconi
Post Number: 581
Registered: 11-2001
| | Posted on Thursday, February 02, 2006 - 10:50 pm: |
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Well 833, I know that nothing is fixed by laying the coax on the ground even though the responses to the station that I noted did go away. In fact I said that in my prior post. So, I will do as you suggest and try and take a nap.
I think your inference is pretty well taken, that no one really cares about the issues anyway. So I will just take my nap now.
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Tech833
Moderator
Username: Tech833
Post Number: 1188
Registered: 8-2002
| | Posted on Friday, February 03, 2006 - 10:47 am: |
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No need to nap on my account. That is just what I would do!
RF flowing away from the antenna over the skin of coax is so common, nobody even thinks about it anymore. Unless it becomes excessive.
If you get a chance to browse the Tessco or Talley Comm websites, you will find grounding kits for Heliax cables. The grounding kits are used for lightning drains (of course) and also to give the RF one last chance to escape the cable shield before entering the building. |
Rick330man
Junior Member
Username: Rick330man
Post Number: 21
Registered: 9-2005
| | Posted on Saturday, February 04, 2006 - 6:33 pm: |
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I had one of those Archer .64 omni-directional ground planes. It was an exceptional antenna. The base of the antenna was barely above my roofline - just 12' off of the ground. Even at that low height, it easily outperformed everything in the neighborhood - including my Archer 1/2 that it replaced, a Starduster, an Astroplane, an Archer 5/8, Wilson Sigma 5/8, etc. Unfortunately, it got hit by lightning and fried the coil. |
Marconi
Advanced Member
Username: Marconi
Post Number: 585
Registered: 11-2001
| | Posted on Saturday, February 04, 2006 - 7:57 pm: |
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Hey 330, the one that the Kid referred us to in this thread indicates that the .64 Archer was about 32' - 33' long. Kid suggested that this might mean all the metal pieces added together.
Do you recall how long it was? |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 62
Registered: 8-2005
| | Posted on Saturday, February 04, 2006 - 10:17 pm: |
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I think I found a house here local that has one of these Archer .64 wave antennas. I thinking of going up there and asking if I could take it down for them. There's no coax connected to it and there's plants growing all over it from there chimmney, LOL! |
Twowatt
Member
Username: Twowatt
Post Number: 73
Registered: 7-2005
| | Posted on Friday, April 14, 2006 - 12:02 am: |
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hey Marconi,
have you thought of putting toroids on each end of your coax, and seeing if there is any difference with the coax on the gound vs over 6' in the air?
AND how about placing the coax at 3' above the ground; 6' above and 9' above to see if the FS meter reading changes?
regards |
Marconi
Advanced Member
Username: Marconi
Post Number: 645
Registered: 11-2001
| | Posted on Friday, April 14, 2006 - 3:04 pm: |
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I will try that when I get through with my nap, but I believe as long as the coax is far enough above the earth so as to not transfer the Common Mode currents into the Earth, the coax will radiate like a too short or too long non-resonant antenna and it can be detected all the way back to the rig.
I will get back. |
Tech833
Moderator
Username: Tech833
Post Number: 1309
Registered: 8-2002
| | Posted on Saturday, April 15, 2006 - 10:28 am: |
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Unless your coax is well grounded, that is correct. |
Haansgruber
New member
Username: Haansgruber
Post Number: 1
Registered: 8-2009
| | Posted on Friday, February 24, 2017 - 12:07 pm: |
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There is a .64 wave antenna Radio Shack made called a Crossbow .64 wave Ground Plane Antenna, Started out at 44.95 then raised 10.oo to 54,95 in the 1981 Radio Shack catalogue. The difference between the two antenna patterns is actually quite significant as well and the lower angle of radiation.
"The .64 wave has been one of the best kept secrets in CB and 10 meter antennas for decades. There has not been a .64 wave antenna widely available since the 70's and early 80's. There were just 2 of them on the market back then, and they were both designed for CB only. The "Super Penetrator 500 Gold" made by Hy-Gain, and a ground plane from Radio Shack called the "Crossbow .64". I personally owned the Crossbow .64 from Radio Shack. I bought it back in 1978 when they first introduced it. In 1978, it sold for $44.95. I had it until 1988. It was an all aluminum, 22 feet total length antenna, with four 9 foot radials. I never had an antenna that performed like that one did. I talked a lot of DX with that antenna without really trying.
Most people do not realize the importance of the number ".64" (or 64% of a full wavelength). A .64 wave antenna is the highest gain single element design available anywhere with at least a 0.8 dB/d (or higher) of gain towards the horizon, than any 5/8 wave element. But most importantly, a .64 is the longest radiating element you can use before the transmit radiating pattern begins to collapse on itself. It is a slightly longer element than a 5/8 wave element. The number "5/8" converts to a .62 wave length. The .64 may only be a .02 wave length bigger, but on 10 meters, that equals 4 inches of added efficient element."
The .64 wave is the longest and most efficient single radiator antenna
I hope this helps
73' n CUL
haans gruber |
Thehobo
Intermediate Member
Username: Thehobo
Post Number: 146
Registered: 2-2004
| | Posted on Sunday, February 26, 2017 - 10:54 am: |
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if one wood like to see a .64 lay out, go to mr coilys site and look at the pictures he has posted on his site.. just mite help someone in there effert to build there own.. just a thought
thehobo
thehobo
269150 monitor ch.
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