half wave antennas not needing ground elements?

[HomerBB]

I don't know if it will be better than the 17" coil. I was just following through on what I thought Robb was suggesting. As far as on my homebrews, I've always employed a set of GP's with them. What I did read somewhere before is that there was a horizontal V made that one leg was two or more multiples of half wavelengths long and the other was 1.2 wavelength long, and he used a coil to tune it. The point is, the coil may work. I may test it myself . . .

 

[CDX-007]

damn 007 , that's very discouraging !!
the height isnt whats getting his attention the most , its the ground plane elements that'll be stretching across the house . as much as i hate to say this ....... the imax 2000 may be my best option .. or the new sirio gain master . ive really enjoyed the compliments i get on my home brews performance when i had it up .ill just have to take the ground elements off and shorten it to a 1/2wgp and see if itll tune good enough 10 feet off the ground and if it will still be kind of effective......keeping in mind it will do much better at 30 feet . if it doesn't than i guess ill look for a used imax locally . i could still tinker with the real antenna in the back yard .... btw , guy wires would look worse than ground elements since they would be much longer . i guess another option might be to cut my four 1/4 wave elements in half and use eight 1/8 wave ground elements ..... seems to work on the sirio 2008 ..... or just four of them . that would cut its spread in half . ill ask him if that will make him happy .

robb im not very confident in my ability to duplicate the matching network on a imax . it seems to be a coil inside a coil and apparently a lot of engineers arnt really sure whats going on with it . the new sirio antenna is (AFAIK) the first/only 5/8 11 cb antenna to hit the market without ground elements . time will tell if its as good or better or lesser performing than the imax . but yea , the less money i have to spend the better .
thanks guys

Hey Booty, what about using a sleeve radial, a ¼ wave piece of copper or of English alyoominium with the coax running up inside it to the matching network, and isolated by PVC, fiberglass, etc. from the metal mast at it's bottom.

The Imax is a different beast, it's using an inductive match which completely isolates the radiator from coax center & ground, plus makes up for the capacitive reactance of the capacitor which is ½ way up the center of the 3 pieces.

You just need to find your happy place on a coil between radiator & ¼ wave counterpoise, with a vertical counterpoise around the coax... and there's always the idea of simply using the coax shield as the counterpoise, forcing common-mode current down ¼ wave to either a CM choke or a set of ferrite chokes.

...or what about rebuilding it into a SigmaIV type design? Would he hate the ring less than those two 18' radials pairs? You could surely use a Wilson 1000 whip for the top 5.5 feet and form your own Gamma...

 

[BOOTY MONSTER]

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

 

[CDX-007]

Booty, I seriously hope you don't back down to a ½ wave... even coil-loading it to a Sirio 2016 / Spectrum 1600 with shortened radials would be far superior to a ½ wave. I have the base from a Spectrum if you need measurements.

You know, you only need one radial, (could be made of guy wire) for the 5/8 to tune & radiate well. - I have the base from a Spectrum if you want coil measurements.

What if the ends of your current 5/8 were scaled down to wilson whips? They would certainly be less obvious.

Or you could even coil-load shortened radials.

I'm quite interested in the end results of whatever you choose to do.

73

 

[BOOTY MONSTER]

007 i wish i had the knowledge and confidence to build a sigma 4 . i actually started a thread about it .

http://www.worldwidedx.com/cb-antennas/56015-help-me-understand-gama-matches.html

"Hey Booty, what about using a sleeve radial, a ¼ wave piece of copper or of English alyoominium with the coax running up inside it to the matching network, and isolated by PVC, fiberglass, etc. from the metal mast at it's bottom."

in the past i thought of doing that to make a 1/4 wave stick . my idea at the time was to use 1 inch copper pipe and center a mobile stud mount on the copper end cap with a 108/mobile antenna on it . i do understand what you're suggesting would be slightly different since it would be a closed circuit design rather than a resonate/open circuit antenna .

putting a choke 9 feet down the coax from the feed point so that it could be a ground element is something i hadn't thought of though .

yea , i dont wanna drop down to a 1/2 wave either . you guys are giving me some very good ideas and options . thanks

"You know, you only need one radial, (could be made of guy wire) for the 5/8 to tune & radiate well."

hmmmmmmmmmmmm ....... i wonder if he would be happy if i just put a severe downward slope on the ground elements ..... kind of like the basket on a sigma 4 but upside down and without the loop ? ive gotta bounce some of these ideas off him and see what i can do and keep him happy . LOL he knows nothing about antennas though so he will probally look like a deer caught in headlights . hahaha ill make a few drawings since he only cares about what will be seen .

 

[CDX-007]

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)?

 

[Robb]

Then...
Make the coil out of aluminum wire instead of copper.

 

[BOOTY MONSTER]

well , i guess i could use the entire 30 feet of 1 1/2 inch mast as a element

 

[CDX-007]

well , i guess i could use the entire 30 feet of 1 1/2 inch mast as a element

Could you try maybe 27' of supporting mast as a 3/4 wave counterpoise?

 

[BOOTY MONSTER]

Then...
Make the coil out of aluminum wire instead of copper.

didnt mean to ignore your suggestion . ive got an idea in mind that i may try just to see if it works and if there's any difference between it and my current loop . i was thinking of using a stainless steel bolt and nuts between the two to keep them separated . i think SS is supposed to play nice with both Al and copper . someone correct me if im wrong on that please .

 

[CDX-007]

didnt mean to ignore your suggestion . ive got an idea in mind that i may try just to see if it works and if there's any difference between it and my current loop . i was thinking of using a stainless steel bolt and nuts between the two to keep them separated . i think SS is supposed to play nice with both Al and copper . someone correct me if im wrong on that please .

I like brass as a coupler material. Works great on my rebuilt Penetrators, some still up and working as well as they always did, after literally decades.

 

[BOOTY MONSTER]

Could you try maybe 27' of supporting mast as a 3/4 wave counterpoise?

yes i could if i didnt have any other ground elements other than the mast . using a steep slope with them at that height would have the bottom of them lower than the shingles . im guessing youre suggesting that length because its a even multiple of a 1/4 wave ? too bad i couldnt go 36 feet for a full wavelength ..... but then id have to have guy wires running across the roof . do you think the 4 ft difference would really make a detectable difference ? or make it tune better ?

ill have to see if i can find a source for brass nuts and bolts . do you think brass is better than SS or are you just saying its another good option compared to SS ?

 

[Robb]

I run my IMAX on 20 ft of steel mast on top of a 10 ft high garage roof. The masting is more than enough to work very well as a counterpoise. I am considering adding another 5 ft - to make it the same length as the radiator - just for giggles. I can spare you the anecdotes of contacts made; sure that you've read them before. It is guyed with dacron as well. Have a GPK for it - but haven't installed it as yet.

Since you are the experimenter here; are you going to use a 1 1/2" form and 12 winds of copper? Are you going to connect an alligator clip to the center of the coax to find the right tap point before making it permanent? Where are you at with this project?
Curious...

 

[BOOTY MONSTER]

im just in the getting ideas point right now .

i was gonna do the 1 1/2 inch former with 9-10 loops that homerbb suggested . i think i can do it cheaply and then compare it to my loop and see if i can tell any difference 10 feet off the ground . which ever works best will go up in the air . as you said ill use a clip to find the best tuning point on the coil then solder it in place and put some non-conductive sealer on it . should the entire coil be weather proofed ?

an imax would be the quick and easy answer and going by comments by the majority of users in this and other forums id probably be happy with the performance of it . but , id really like to stick with modifying my 5/8 (definitely not into a half wave) since i have no other use for it and im really attached to the fat stiff vertical on it . that didn't read quite right ...... but you know what i mean . ive also got half the price of a i10k invested in the parts for it to . im very very confident that there's enough ideas in this thread that i modify it and it still be a decent performing antenna . it'll be after next weekend before i get the parts to start the work on it again though , so ive got plenty of time to read and consider options .

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

 

[CDX-007]

yes i could if i didnt have any other ground elements other than the mast . using a steep slope with them at that height would have the bottom of them lower than the shingles . im guessing youre suggesting that length because its a even multiple of a 1/4 wave ? too bad i couldnt go 36 feet for a full wavelength ..... but then id have to have guy wires running across the roof . do you think the 4 ft difference would really make a detectable difference ? or make it tune better ?

Yes, because a ¾ wave should have a similar impedance & phase angle (+/- 180°) to a ¼ wave, which is what you're currently using for counterpoise.

I'd rather see you use downward sloping 23' guy wire radials, regardless of their height above surrounding elements, but you'd prolly have to reset your coil tap location.

FYI, the Avanti Sigma II 5/8 uses a 15.5" ring, and it is fed at beginning of the bottom of the ring supports making it all active. There's an 8 turn coil shunt to ground ~1" former - air from that bottom feed point to ground.