Radials? and the end fed 1/2 wave (EFHW)

[Marconi]

Marconi wrote

Did he ever have a choice?

Nav, are you answering my question with another question?

I don't know what he's done, that's why I asked. I've done this before, and I was wondering if he could support his claim, without including a 1/4 wave radiator. I know he said "many" antennas, but I'm making a distinction here for Booty Monster to indicate to him again, that there are differences in using radials among different antennas.

If you think an end fed 1/2 wave has a bad match at the feed point, you should see what happens when a 1/4 wave doesn't have radials. Such results will cross your eyes. {Cry_river}

 

[nav2010]

Yes, I've made both a coil shortened quarter wave ground plane from a mobile antenna and i've made a full quarter wave ground plane. In essence its a dipole type of arrangement but if you try and straighten the lower radials that also has a profound effect on SWR. At 90 degrees they have an impedance of about 20ohms, at 45 degrees they are close on a match at 50ohms. Take the radials off and you're in unbalanced cockoo land of nod. Its the same as removing the lower leg of a dipole, you basically have half an antenna with impedance of sillyness proportions.

 

[Marconi]

I just posted my fix for the model I posted last "NB's Claim For Gain". http://www.worldwidedx.com/cb-antennas/133479-radials-end-fed-1-2-wave-efhw-3.html#post347373

Nav, I don't know if this addresses your comments above, but in seeing the error and doing the fix, I think I understand a little better what you were telling me. However, I don't see lowering the radials to the bottom of the Imax as an increase in radial length, I see it as a 1' foot increase in radiator length. Hope I'm close to what your thinking. Thanks for making me look twice, you're right something was happening in that area, even if I don't understand the current flows your image shows us.

I do have a question about the arrows though. Do the down arrows beside the red coax represent coaxial (transmission line) currents or common mode currents on the shield? http://www.worldwidedx.com/attachme...7952548-radials-end-fed-1-2-wave-efhw-a99.jpg

 

[wavrider]

Hey wavrider, have you ever tried using the coax shield as the ground plane or the other half of the antenna on a 1/4 wave radiator?

This is an example for why I suggest to Booty Monster that radials don't always respond the same on all end fed vertical monopole antennas.

Yes, cushcraft multiband verticals use the coax as a counterpoise somewhat as do other verticals.

Some home brew amateur verticals just use a ground rod as counterpoise, so the coax is actually the other half of the antenna.

Not very efficient but the vswr does look good and allows multiband operations.

Not to popular on the bands as the ops usually run the amplifier to make up for the negative gain of the vertical and splatted everywhere due to CMC on the coax.

 

[Marconi]

Yes, cushcraft multiband verticals use the coax as a counterpoise somewhat as do other verticals.

Some home brew amateur verticals just use a ground rod as counterpoise, so the coax is actually the other half of the antenna.

Not very efficient but the vswr does look good and allows multiband operations.

Not to popular on the bands as the ops usually run the amplifier to make up for the negative gain of the vertical and splatted everywhere due to CMC on the coax.

Yep we find all kinds of things available in this World.

My point was that the 1/4 wave radiator will fail dismally at using the feed line or mast. IMO, the 1/4 wave antenna will also not utilize the coax shield as many suggest...is what happens with the Imax/A99 without radials.

 

[nav2010]

I just posted my fix for the model I posted last "NB's Claim For Gain". http://www.worldwidedx.com/cb-antennas/133479-radials-end-fed-1-2-wave-efhw-3.html#post347373

Nav, I don't know if this addresses your comments above, but in seeing the error and doing the fix, I think I understand a little better what you were telling me. However, I don't see lowering the radials to the bottom of the Imax as an increase in radial length, I see it as a 1' foot increase in radiator length. Hope I'm close to what your thinking. Thanks for making me look twice, you're right something was happening in that area, even if I don't understand the current flows your image shows us.

I do have a question about the arrows though. Do the down arrows beside the red coax represent coaxial (transmission line) currents or common mode currents on the shield? http://www.worldwidedx.com/attachme...7952548-radials-end-fed-1-2-wave-efhw-a99.jpg

I never mentioned an Imax's radials?!!
The arrows represent the electrical current flowing on the mounting pole and the coax in both directions and include all currents. I only put the arrows in one direction but they will be reversed depending on RX or TX. Marconi, take a look at a simple half wave GP and you will realise that the SO239 is connected to the base of the antenna, the tuning section is located just above the SO239 and the driven element in its electrical length starts just above the tuning coil. If we attached a ground plane kit to a standard half wave GP, it is advantageous to do it at the bottom of the antenna. This is because we can begin our quarter wave electrical length right at that very point where the coax is terminated.
In an A99 we have a problem, we cannot do that because the coax is grounded at the SO239 but current continues up a short piece of coax in both transmission line and CMC in the centre feed and braid which eventually form into a capacitance tuning network. The mounting pole because it is connected to the outer braid at this point(SO239) is nothing more than a stub. Because the stub is roughly the same length as the coax running inside it then current running to any radial system is subject to travelling from the tuning network back down the coax and up the tube to where ever your radials are located. This screws everything up because you have to add that distance into your radial Length to get a quarter wave.
In essence to make a conventional half wave end fed with quarter wave ground plane out of a A99 we would have to remove the mounting pole from the scenario altogether and make it just like a half wave GP. This would be done by removing the SO239 altogether, having your coax soldered directly to the tuning network then bridging the braid at that point to the top of the mounting pole where your radials are. We still would have the stub in the equation but it would be an inductance issue rather than electrical length issue. But there could still be a problem if we did that modification. If we remove the piece of coax out of the A99, there may be a velocity factor issue to overcome in the tuning network because the current (depending on which coax you use) could be moving either slower or faster inside your mounting pole. This may or may not affect the tuning. Also the losses related to feedpoints and removing them may be a slight issue. One thing is for sure, i'll bet my ass those tuning rings won't be in the same place to get your usual swr reading. Hope that explains.

 

[nav2010]

Yep we find all kinds of things available in this World.

My point was that the 1/4 wave radiator will fail dismally at using the feed line or mast. IMO, the 1/4 wave antenna will also not utilize the coax shield as many suggest...is what happens with the Imax/A99 without radials.

Read this simple dipole explanation Marconi.
Dipole antenna :: Radio-Electronics.Com
Then explore what happens to the voltage and the current on an end fed half wave antenna.

 

[nav2010]

Wavrider wrote

Not very efficient but the vswr does look good and allows multiband operations.

Wav, you could solder a 50ohm resister at the end of your 50ohm coax and the swr looks sensational but it won't bloody resonate. Were taking about phase relationships between half and quarter waves here not what looks nice on a swr meter. Giz a clue we folk.

 

[Needle Bender]

I just posted my fix for the model I posted last "NB's Claim For Gain". http://www.worldwidedx.com/cb-antennas/133479-radials-end-fed-1-2-wave-efhw-3.html#post347373

Nav, I don't know if this addresses your comments above, but in seeing the error and doing the fix, I think I understand a little better what you were telling me. However, I don't see lowering the radials to the bottom of the Imax as an increase in radial length, I see it as a 1' foot increase in radiator length. Hope I'm close to what your thinking. Thanks for making me look twice, you're right something was happening in that area, even if I don't understand the current flows your image shows us.

I do have a question about the arrows though. Do the down arrows beside the red coax represent coaxial (transmission line) currents or common mode currents on the shield? http://www.worldwidedx.com/attachme...7952548-radials-end-fed-1-2-wave-efhw-a99.jpg

I'm a little lost regarding my "claim for gain" but I remember when I had the 3/4 wave radials on the Imax it seemed more broad banded.

What Nav2010 is saying about the base of the A99 is, if you could drill a hole through the radial mounting hub and continued into the antenna until you just met the coax shield inside the top of the A99 mounting tube and just below the matching network, then screwed a brass bolt through that hole all the way to contacting the coax shield inside - you would have eliminated about 24" of travel for the radial current which otherwise has to go back down from the match, inside the tube along the shield of the 12" piece of coax, to the bottom where the SO-239 is, then back up the outside 12" of the A99 mounting tube before it gets to the radials hub.

 

[BOOTY MONSTER]

is there a different signal inside the tube vs. the outside like coax has 3 signals on its 3 surfaces ?
i know i'm using wrong terminology , but i'm sure someone will correct it for me

 

[Needle Bender]

is there a different signal inside the tube vs. the outside like coax has 3 signals on its 3 surfaces ?
i know i'm using wrong terminology , but i'm sure someone will correct it for me

Hey Booty, I don't know if that's how the RF sees it, but if I'm ever stuck using an A99 I'm going to just use a 5' fiberglass isolation pole and a choke about 26" down the coax from the A99 SO-239 connector.
Hopefully I'll have it high enough so the ground conductivity won't matter.
I'm still not convinced that a 1/2 wave needs or will even TOA benefit from the addition of 1/8-1/4 wave radials as long as it's isolated and given the minimum of .06wl counterpoise.

 

[Marconi]

Hey Booty, I don't know if that's how the RF sees it, but if I'm ever stuck using an A99 I'm going to just use a 5' fiberglass isolation pole and a choke about 26" down the coax from the A99 SO-239 connector.
Hopefully I'll have it high enough so the ground conductivity won't matter.
I'm still not convinced that a 1/2 wave needs or will even TOA benefit from the addition of 1/8-1/4 wave radials as long as it's isolated and given the minimum of .06wl counterpoise.

I don't know either NB, I can't see the current flow either. I'm not sure what the significance of 26" is either, or did I ask that already?

Not that it makes a hootin' lot of difference, but if you read the article again I think you'll see he said .05 wl was the minimum necessary counterpoise in his testing, but I could be wrong too.

Good discussion, I just wish I understood current flow.

O yeah, did y'all know the matching coil in the A99 was a single wire and the shield is probably tapped at the resonance point, with one end attached to the outside of the capacitor and the other end attached to the center conductor of the coax, and a the short tail, maybe 3" floating up inside the insulator inside the capacitor? If I could do the drawing like Nav did, I would draw it for you guys that are curious. That is the way it looks to me

 

[BOOTY MONSTER]

The Antron 99 exposed! by dxzone.com

can any of the pics in the antron 99 exposed article help any OGP ?

 

[Marconi]

The Antron 99 exposed! by dxzone.com

can any of the pics in the antron 99 exposed article help any OGP ?

I have the real thing. I don't need a picture, but thanks anyway.

 

[Robb]

Looks just like the Imax.
Two coils (inner and outer) and all . . .