antenna comparisons/tests

[bob85]

Bandwidth always has a 'cost' in efficiency.
- 'Doc

not true imho with a gamma match setup,
from what i have read and experienced with the avanti/hybrid 7/8,

maybe there is a flaw in my testing and just maybe i cant read

 

[W5LZ]

bob85,
Or, maybe I just didn't say it correctly. The typical expectation for an antenna's bandwidth is usually far more than is 'normal'/typical/'standard'/common. That means that increasing that bandwidth by any appreciable amount will change the antenna's characteristics in such a way as to lessen it's efficiency (all 'other' things being 'right', which they never are). The only exceptions to that are antennas that are not 'right' to start with.
This is true when talking about capacitive hats, which deal with antenna's lengths and resonance. It is not -always- true when taking about impedance matching devices, such as a gamma match.
This part is only how I look at 'efficiency', certainly not any kind of 'standard' of definition.
Efficiency defines an area somewhere between 'barely usable' and 'perfect'. Both ends of that range are 'user definable' and subject to the individual doing the defining. The only part that isn't ever going to be reachable is the 'top' end, the 'perfect' thingy. There may be a 'perfect' antenna for my particular situation, but odds are that it'll be far from "perfect" for an antenna! Make sense? Or should that be 'perfect' sense??)
- 'Doc

all puns intended

 

[bob85]

doc i would agree in general high q = lower loss if thats the correct way to say it but the gamma seems to defy this and just any old gamma with the correct capacitance will work but not as good as a correctly proprtioned gamma,
one day i may figure out or learn how to make a near optimal gamma match for my vertical

 

[Master Chief]

one day i may figure out or learn how to make a near optimal gamma match for my vertical

It will probably be a hairpin beta t-match thingy!
:lol :lol :lol :lol :lol :lol :lol :lol :lol :lol :lol :lol :lol

(I crack myself up!)

 

[W5LZ]

...or, a lot like how grounded towers are fed now. With a slightly modified gamma match.
- 'Doc

 

[bob85]

i think MC bought 5000ft of 1/4" aluminum tube by mistake from ebay and hes just looking for things to do with it

 

[villarge]

Starduster Antenna

http://allyoucanupload.webshots.com/v/2004029918301693022



This might clear things up Bob.




Dave....

 

[Marconi]

Hey Villarge, the picture is great, but how about some detail measurements so we can get a better idea of what is going on with the coils?

It looks like this one has three shorter radials in the horizontal plane and three radials with coils or traps that are slanted down. Is that a total of 6 ground plane radials?

Have you ever used an M400 Starduster? How did the M800 work out for you and compared to what?

 

[bob85]

marconi the 3 short legs are the spider that holds the radials just like a regular m400, i can see why you are getting confused its just how he layed it out for the pic,

the lower part of the radials are missing on that pic,
they were there when i gave villarge the antenna but they were battered and one had been replaced with a piece of cheep tubing from a thunderpole or similar copy antenna

his buddy is in the process of rebuilding it with new or replacement parts,

the original radials are about the same length as a regular m400 ( maybe slightly shorter ) only the radiator is shortened with that double loop thingy,
i cannot confirm that the coils have parallel capacitors inside the former because i never stripped it down but thats what old peter said was in there and he aint no mug

as far as i know the guy i bought it from myself and old peter are the only people that ever used that particular antenna, when i bought it it was like new with very little use and it was in the original A/S box,
when i gave it to villarge it was in a sorry state but im happy somebody is taking the time to restore it because they are rarer than rockinghorse shit over here.

 

[W5LZ]

Bob,
If that coil thingy is a loading coil, why would there be a capacitor attached to it anywhere? A 'trap' for multiband use, sure, but not a loading coil. Then again, 'cowpastures' might be a characteristic of that particular antenna, full'a S***. Probably where all that rocking horse crap went to?
- 'Doc

 

[bob85]

doc i always thought they were just a small coil and a slightly short 1/4wave leg, old peter claims they have a small disk ceramic across the coil inside the fiberglass former,

what do you make of the folded loop in the radiator?,
it looks like the folded phasing section in a superjay.

 

[W5LZ]

Yes, that does look like a 'phasing' loop. But if the lengths of radiator above and below that 'phasing' device are not related to a 1/4 wave on 27 Mhz, then that isn't/can't be a 'phasing' device, can it? So it seems to just be another form of loading coil. And as such, no need for a capacitor in it at all I would think. I think that the information you were given about the capacitor isn't exactly correct. Or, if there really is one there, what's it doing? Why bother? Adding a capacitor at that point can affect the 'amount' of loading coil the thing actually represents (makes the coil 'smaller', less inductance). Just seems like a completely unnecessary way of going about it. 'Course, if the idea is to just make something 'different', then it certainly worked - lol. Honestly can't see why though, cuz it certainly wouldn't affect the radiation characteristics of the antenna in a positive way. Won't even consider trying to understand the 'logic' behind the motive, I'm too lazy.
- 'Doc

 

[Marconi]

Hey Bob, is the fiberglass former solid or is it tubular? I would think it would have to be tubular in order to have something inside. If so, then you probably should be able to see how the device is connected to the coil. If the formers are solid pieces of some non-conductive plastic then I doubt there is anything inside.

It looks to me like the tubing passes thru the formers. Or, maybe the tubing is mounted inside the formers and attached somehow at each end. If so, then how are they connected, screws, bolts, or hose clamps?

It all looks like much to do about nothing to me. These coils remind me of those Truck Stop ground plane kits you attach to mobile stingers.

BTW, I seem to remember that there were three prong static arrestor things also attached near the ends of the three ground radials as well. If the ends are missing, then maybe these pieces are too. I have removed these things from my Starduster in the past and it makes no difference that I can tell. I think all this stuff added to the elements is just for show, even in the original M400. I agree with 'Doc, if all this stuff really did what it is supposed to, how would that improve over an element that is of normal length?

Ask Villarge if he would give us the overall top element measurement? If the top is shortened some, then maybe the coil is actually loading the radiator somewhat. If not then this is just for show.

 

[bob85]

doc the caps are supposed to be in the 3 legs not the radiator, as i said i have never looked inside im just retelling what peter told me about one going bad and i could see he had been inside one of the legs,

marconi yes the formers are hollow, the coils from memory are riveted through the formers to the inner tubes, i dont recall any prongs on the legs but i would not bet that there was definately no prongs, the only prongs i remember are the 3 on the radiator,

i will ask villarge if he can get the measurements for the radiator,
maybe old peter will know, he made an aluminum collar in the lathe so he could adjust the radiator length,
i can only ask.

 

[Marconi]

bob, if you ever used the M800, do you recall how it worked out for you?