Is it possible to make a 5/8 wave antenna from the 23' flag pole in my yard?

[Captain Kilowatt]

Just to clarify, Captain Kilowatt is correct about not being able to use a gamma to match a 5/8 wave groundplane and his reason is correct also. The antennas impedance is too high and the gamma can only match antennas that are below the line impedance.

That means in order for Wolf to have added the gamma into the mix and still provide a good VSWR, the matching loop near the base already had to drop the input impedance from several hundred ohms to below 50 ohms so the gamma could bring it back up to 50.

That is what I was talking about before even seeing the Wolf antenna and how it is made. The use of his loading coil alters the base feedpoint impedance. It is not possible to simply use only a gamma match at the base of a conventional 5/8 wave.A 5/8 needs a coil somewhere to basically extend it to an electrical 3/4 wave which is much easier to tune. Also the Wolf gamma match is not what I was picturing as I was thinking a match similar to that used on a yagi element.

 

[Captain Kilowatt]

The Captain and Shockwave are correct, however, is there any reason he couldn't put a small gamma on the flag pole and use an antenna tuner with it? It wouldn't be the most efficient way of doing things but it should still work. It would also likely be the least noticeable of his options for the flag pole.


The DB

If he was to use an antenna tuner then he may as well eliminate the gamma at the antenna element since it will do no good whatsoever for reasons stated above unless a coil (more losses) is added. Best bet is an automatic tuner located right at the base feedpoint and then length of the element will not matter as far as impedance is concerned but take off angle will change with length.

 

[Shockwave]

The Captain and Shockwave are correct, however, is there any reason he couldn't put a small gamma on the flag pole and use an antenna tuner with it? It wouldn't be the most efficient way of doing things but it should still work. It would also likely be the least noticeable of his options for the flag pole.


The DB

The gamma can only cause the high impedance of the end fed 5/8 wave to rise even higher. Since it's taking us further in the wrong direction to form the desired match, why use one at all? If an antenna tuner is an option and it can be placed right at the base of the flagpole, that would probably work best given the physical aspects of this disguise antenna.

You'll need to get some ground radials in the dirt using something like a garden edger to cut a slot in the ground. I'd put at least 16 radials in the ground at 9 feet long. Connect them to the ground of the antenna tuner, not to the flagpole. If the tuner has a longwire terminal, connect it to the flagpole. If not, connect the center pin of the SO-239 on the tuner to the flagpole.

Even though the flagpole may not be insulated from the ground, you can be sure it also is not at RF ground. Between the cement and relatively low coupling to ground a single short conductor in the dirt will give, this won't be a big issue once you match the antenna to the 50 ohm cable.

 

[freezy]

how about a full wave dipole and call it a dog-run or clothes line?

 

[nav2010]

Just to clarify, Captain Kilowatt is correct about not being able to use a gamma to match a 5/8 wave groundplane and his reason is correct also. The antennas impedance is too high and the gamma can only match antennas that are below the line impedance.

That means in order for Wolf to have added the gamma into the mix and still provide a good VSWR, the matching loop near the base already had to drop the input impedance from several hundred ohms to below 50 ohms so the gamma could bring it back up to 50.

Too lossy a system.
Simple solution is to get some fibreglass the same as the inside diameter near the base of the flagpole, cut the flagpole at 5/8ths or maybe about 6 inches shorter than 5/8ths then insert the fibreglass or delrin so as to isolate it. Leave a good four inch gap. Then just use either a loop or coil matched to 50ohm and forget the gamma. He could then just use a thin aluminum rod at the top on a hose clamp and slide it up and down to fine tune it.

 

[jazzsinger]

would probably be easier and more efficient using the flagpole to mount an inverted v dipole that doubles as guy wires. not many people will complain about guy wires holding a flagpole up.

i wouldn't imagine a ground mounted 5/8 wave would have a great radiation pattern anyway, unless your planning on becoming a subdivision of haarp.

 

[cjruger]

I have abandoned the flag pole idea. I have however strong up a 5/8 wire verticle. I made a 2.75 diameter alumine coil, of about 3-4 turns. The aluminum rod is 1/4". It wont get swr better than 2.6:1. Do i need a coil with more lenght, like say copper wire and 15-20 turns?

 

[Needle Bender]

You'll need to add at least one 1/4 wave counterpoise in the horizontal plane.

You'll then need to find the tap point on your coil where it's closest to a 50 ohm impedance.
I'd use 12-14ga copperwire and make it 10 turns at your 2.75" diameter, then locate the 50 ohm tap point, the horizontal radial(s?) connect to the bottom of the coil where your coax shield & ground is also connected.

Years ago I recall hearing of a 5/8 10m flagpole antenna with 1/8 wave of straight wire feeding it at the base - which was grounded.

I remember he said he put the shield right to ground with a ground rod at the connection to the 1/8 wave long wire which went straight to the pole just above ground level. It worked great on 10m for both local & dx. I suppose the 4.5' of wire made it appear to be a 50ohm 3/4 wave.

Also, I was wondering if a gamma might actually work if the base of the pole was at ground potential so the apparent impedance would be near zero through the pole right to ground like a dead short (0 ohms) to ground.

I wonder...

 

[BOOTY MONSTER]

home brew copper tubing antenna coil - YouTube

i used 10 turns on mine . you will need ground elements , i'll suggest four 9 footers .