half wave antennas not needing ground elements?

[BOOTY MONSTER]

i cant use guy wires . they will be spread out across the house and that's the problem now with the ground elements . the height doesnt bother him , its the "stuff sticking way out all around it" LOL .

probally either the steep sloping radials or shortening them by about half will make him happy . yall have got me wanting to make a coil now though LOL .

tinker tinker tinker

 

[Robb]

btw .... any particular reason why you suggest 12 turns instead or 9-10 ?

Yeah, so you could have enough to cut back if it is too much.
9-10 turns is prolly right; I've never done it before. But I've read a bunch and can't recall the particulars. I'll read up on it tonight. Wonder what the 'mystery formula' is for the IMAX myself...

 

[HomerBB]

thanks homer . ive got an idea in mind on making the coil and using PVC pipe for the 1 1/2 inch former . you suggested using 10 or 12 gauge wire for the former and keeping the spacing between the 9-10 wraps the same distance as the wire . im guessing i could use solid 8 or even 4 gauge ground wire from the bulk wire by the foot section at home depot (keeping the spacing the same as the wires diameter) and be just fine ? or even some scrap small diameter copper tubing ?

if i recall correctly copper and aluminum don't like to play nice together and can oxidize/short even when soldered together . i recall bob85's issue with that on his sirio that kept going open circuit at the coil and radiator connection even after he fixed it .... but stainless steel will work fine with either .... correct ?

http://www.worldwidedx.com/cb-antennas/32232-sirio-vs-imax.html

maybe a mod should move this thread to the home brew section , since its basically become about home brewing a base antenna . im fine either way

You've gotten great info since you posted the above, so I think you're equipped to make your decisions now. as for why I used the #10/12 gauge wires - because they were what I had on hand. The former size was arrived at through reading various resources, none of which I can readily point you to now.

Some photos of the 5/8 I built at an alternate sight because my photo server is offline: 5/8^ Redo

Tis is the WWDX link to the thread when i was doing it: My first attempt to build a 5/8 wave homemade

 

[BOOTY MONSTER]

Yeah, so you could have enough to cut back if it is too much.
9-10 turns is prolly right; I've never done it before. But I've read a bunch and can't recall the particulars. I'll read up on it tonight. Wonder what the 'mystery formula' is for the IMAX myself...

The Imax 2000 EXPOSED!
i dont know either , but when they cut the imax open in the exposed article it clearly shows two coils , one inside the other .

You've gotten great info since you posted the above, so I think you're equipped to make your decisions now. as for why I used the #10/12 gauge wires - because they were what I had on hand. The former size was arrived at through reading various resources, none of which I can readily point you to now.

thanks again guys

 

[Robb]

Now - if you could just find a pic of the whole coil - you can blow it up and count the turns and estimate the diameters...

Easier said than done - tho...

I'm guessing that the teflon between the coils is acting like a capacitor. I'd also venture a guess - using the RG-8 coax as a scale - that the outside coil is 1". Guess the rest..

 

[Marconi]

Robb, I think that Tech 833 shows the turns ratios in the circuit diagram at the end of the article and I think it is 7/10 turns on a 11/16" former. I think you will find the same info on the A99 exposed article and the coil is on the same former with 10/19 turns I believe.

 

[jazzsinger]

If you do sloping radials and make them from tiny size wire, maybe stranded 18ga, then use that kite string-size dacron to hold them in place, I bet he would think it an adequate improvement.

I've often heard it said, "It's better to ask forgiveness than permission".

Do it, then show/ask if OK.

Can you fit (even one) 23' wire radial(s)?

surely 23 ft radials would show very high feedpoint impedance just like a .625 or .64 wave radiator does without a coil fitted.thats exactly the reason its shortened fitted with a coil to tune out reactance and the coil tapped at the 50 ohm point to give proper feed impedance.


which in turn would be counterproductive to using it as a counterpoise.

if you really wanted long radials 3/4 wave would be a better bet.

 

[Robb]

I see the link now. Didn't notice on the first read. Says some interesting things

"...That makes the total radiating element length 270.5 inches. Using 27 MHz. (CB) as center frequency (which this antenna was designed for), that makes the Imax 2000 a 0.640 wavelength antenna. (A 5/8 wave antenna is 0.625 of one wavelength). I was very surprised to find that the Imax 2000 is not a 5/8 wave as advertised. The Imax 2000 is actually a .64 wave! The .64 wave is one of the best kept secrets in CB and 10 meter antennas. Not since the Super Penetrator 500 Gold has there been a .64 wave antenna widely available. A .64 wave antenna is the highest gain single element design there is with 0.4 dB more gain on the horizon (free space) than a 5/8 wave element..."
A TRUE .64 wave - nice!

"...The Imax 2000 uses 10 turns of #14 enameled copper wire..."
There it is...

"...Like the Antron 99 coupling capacitor, when measured with a capacitance meter, I measured a value of 4pF for each end. That's measured radiator-to-sleeve and again from ground-to- sleeve. The Imax 2000 radiating element is capacitively coupled rather than connected directly to the coax to isolate the antenna base from high voltages..."

Thing that strikes me about this whole thing is - that it uses a copper wire to get the 22 ft 6 1/2 inches to be a true .64 antenna. Aluminum has a slightly lower velocity factor; so if Booty makes his .625 wave into a true .64; then he will need to make it a bit longer than that. That is; if he is going to go that far with it.

 

[BOOTY MONSTER]

the 6 inch difference between a 5/8 and a .64 has been discussed here before . my understanding is that the difference is detectable by lab grade equipment in a proper controlled setting , but in the real world isn't enough to make any difference that can be detected by human ears over the background noise and certainly not by a radios meter .

also , from what i understand , the diameter of a element also effects the measured wavelength of an antenna . larger diameter elements will be shorter than smaller diameter elements for the same given wavelength . my verticals diameter goes from 1 3/8 -1 1/4 -1 1/8 -1 inch at the top using 6 ft tubing . according to my windows calculator a 36 ft wavelength times .625 is 22 1/2 feet which is 270 inches . a .64 would be 23 ft 1/2 inch . velocity factors come into play here but its a minimal amount . anyhow i run my vertical at 22 1/2 feet . i think when i reconfigure its ground plane ill try maco and master chiefs advice an tune the coil to its lowest vswr on channel 20 with channel 1 and 40 having the same (probably slightly higher) vswr and then adjust the radials length to see if i can get any lower . i got down to 1.3 at 1 and 40 with it at 22 1/2 feet so im guessing maybe just a few inches longer or shorter will make the meter the happiest , but my tx and rx will never know the difference .

if ive misunderstood something somebody correct me

 

[CDX-007]

I see the link now. Didn't notice on the first read. Says some interesting things

"...That makes the total radiating element length 270.5 inches. Using 27 MHz. (CB) as center frequency (which this antenna was designed for), that makes the Imax 2000 a 0.640 wavelength antenna. (A 5/8 wave antenna is 0.625 of one wavelength). I was very surprised to find that the Imax 2000 is not a 5/8 wave as advertised. The Imax 2000 is actually a .64 wave! The .64 wave is one of the best kept secrets in CB and 10 meter antennas. Not since the Super Penetrator 500 Gold has there been a .64 wave antenna widely available. A .64 wave antenna is the highest gain single element design there is with 0.4 dB more gain on the horizon (free space) than a 5/8 wave element..."
A TRUE .64 wave - nice!

"...The Imax 2000 uses 10 turns of #14 enameled copper wire..."
There it is...

"...Like the Antron 99 coupling capacitor, when measured with a capacitance meter, I measured a value of 4pF for each end. That's measured radiator-to-sleeve and again from ground-to- sleeve. The Imax 2000 radiating element is capacitively coupled rather than connected directly to the coax to isolate the antenna base from high voltages..."

Thing that strikes me about this whole thing is - that it uses a copper wire to get the 22 ft 6 1/2 inches to be a true .64 antenna. Aluminum has a slightly lower velocity factor; so if Booty makes his .625 wave into a true .64; then he will need to make it a bit longer than that. That is; if he is going to go that far with it.

the 6 inch difference between a 5/8 and a .64 has been discussed here before . my understanding is that the difference is detectable by lab grade equipment in a proper controlled setting , but in the real world isn't enough to make any difference that can be detected by human ears over the background noise and certainly not by a radios meter .

also , from what i understand , the diameter of a element also effects the measured wavelength of an antenna . larger diameter elements will be shorter than smaller diameter elements for the same given wavelength . my verticals diameter goes from 1 3/8 -1 1/4 -1 1/8 -1 inch at the top using 6 ft tubing . according to my windows calculator a 36 ft wavelength times .625 is 22 1/2 feet which is 270 inches . a .64 would be 23 ft 1/2 inch . velocity factors come into play here but its a minimal amount . anyhow i run my vertical at 22 1/2 feet . i think when i reconfigure its ground plane ill try maco and master chiefs advice an tune the coil to its lowest vswr on channel 20 with channel 1 and 40 having the same (probably slightly higher) vswr and then adjust the radials length to see if i can get any lower . i got down to 1.3 at 1 and 40 with it at 22 1/2 feet so im guessing maybe just a few inches longer or shorter will make the meter the happiest , but my tx and rx will never know the difference .

if ive misunderstood something somebody correct me

Well 1st off, it appears to me that Imax post utilizes bad math. When I do the calcs @ 27.0mHz I see 279.7" not 270.5" and since he didn't mention any corrections for velocity factor, it appears to me to be a 5/8 at 27.2xx...

2nd, is that in my own testing, (and for only my own peace of mind and expectations) I have come to experience about an S-unit improvement at about 50-100 miles when comparing a .64 to a .625, or perhaps it's those dang P500 elevated radials lowering the TOA, either way, I'm a .64 believer due to my own testing - but that's just me.

Booty, if you made a single 23' radial from diminutive wire would that perhaps pass?

[Off topic?] I decided to play here and added one (23') to my Imax which I have mounted where I had the I-10K.

- Something magical is happening;

I have less than a 2:1 SWR from 22mHz to well over 30mHz.

I'm using about 86' of 213 and about 34' of mast beneath it from the 11' high roof beneath the mast.

There three 9' @ 50° down angle wire radials to insulators, beginning 8' below the Imax mounting plate, and no other guy wires.

I don't yet understand how this can work so well, and it does, but I have a mind to leave it alone since it's a useful vertical for multi-band local rag-chew.

I've never before seen an antenna system with such wide bandwidth without using a tuner or oddball matching network. Perhaps the Imax 'oddball' matching network is seeing and matching the different guy wire length and/or mast length...? []

 

[BOOTY MONSTER]

6 inches made a s-unit of difference ? 6 db ? that pretty amazing considering that a 5/8 has 1.5 db of gain over a dipole . does that mean a .64 has 7.5 db of gain over a dipole ?

i would have thought the only way 6 more inches would make such a dramatic difference would be if it were 6 more inches behind the fly of my pants

the problem isnt with the height or diameter of the vertical element , its the big azz ground plane spreading across the house . i think it looks rather nice myself

 

[Moleculo]

inches made a s-unit of difference ? 6 db ? that pretty amazing considering that a 5/8 has 1.5 db of gain over a dipole . does that mean a .64 has 7.5 db of gain over a dipole ?

No, it has more to do with the differences between the major lobe radiation angles than anything else.

 

[CDX-007]

No, it has more to do with the differences between the major lobe radiation angles than anything else.

Yepperz, thats my best guess, too.

I was rather surprised when I discovered the I-10K was designed to be a 5/8 wave instead of a .64 wave.

I can't recall where or which, but I do remember reading something about a null-zone out maybe 30 miles experienced by either a .625 or a .64.

Refresh my memory if you know.

Maybe that's why Jay designed it to be a .625 ...?

 

[jazzsinger]

i would have thought the only way 6 more inches would make such a dramatic difference would be if it were 6 more inches behind the fly of my pants

that would turn you from female to male Booty,lol.which is indeed a dramatic difference.

as for .64 waves,do you not think its a bit suspect the only place you ever see .64 waves mentioned is cb forums? a bit like magic swr grease.

no doubt descending from a certain manufacturers over hyped claims to outdo competition when cb was at its peak of popularity.

why is it you never see this magical antenna mentioned in any antenna books,in any professional antenna context or why is it you don't see manufacturers discontinuing 5/8 waves in favour of .64 waves as the gains claimed seem incredible for the price of an extra 6 inch of aluminium.

i'll tell you why,because they know its bullshit,like just about every other magical claim you read on cb forums,not to mention the boxes of some well known brands of antennas like the A99,because those companies realised most cb'ers were gullible!!!

the simple fact of the matter is the only thing that will improve one 5/8 wave over another is using less lossy coil materials or better coil design or a more efficient matching system and using full size radials instead of shortened ones which all cost premiums,outwith that a 5/8 wave is a 5/8 wave.if they were all built using equal quality materials they would all perform the exact same.

heres another point you might want to consider,both your 5/8 wave or .64 wave can only be that on ONE single frequency,how many people only use one frequency?

above and below that frequency they will either be more or less of those fractions,infact you go much above that frequency your .64 will soon be in the region of increasingly high radiation angle as it passes the optimum radiator length in relation to fraction of a wavelength.you go in the opposite direction it won't be far till that .64 becomes a 5/8 wave.

same is true of a 5/8 wave.

6 inch of aluminium giving 6db gain, if that was the case linears would have parallel 6 inch pieces of aluminium instead of transistors.

 

[Marconi]

Jazzsinger, I agree with you for the most part.

Many years ago I read an old recap of a report about two Japanese RF engineers that duplicated the early 19th century development work done that produced the 5/8 wave radiator idea for the broadcast industry. These two engineers claimed that the 5/8 wave idea could be improved by making the radiator .64 wavelength.

I don't remember any more details and I have not been able to locate that report since my initial reading. I think it has to be in some old material I have around here, but I'm not sure. Back in those days we had no INTERNET and the article had to be in some publication.

If anyone has read something similar let me know, I would like to read it again. I think maybe that information could be the Genesis of the CB BS story about the .64 wavelength antenna back in the 70's or early 80's.