I'm not sure, but I think Homer might have isolated his A/P too. Where are you going to put the isolator?
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Any Astro Plane Fans ?
- Thread starter tuner
- Start date
I'm not sure, but I think Homer might have isolated his A/P too. Where are you going to put the isolator?
About 1/4wave below the hoop so the mast is an electrical 1/2wave to minimise mast currents Eddie,
1/2wave mast puts the tip at the same height as a 5/8wave on the same pole & gives me about 4ft advantage in height of current maxima vs a 5/8wave,
probably try a coax choke on the isolator then look into making something better.
1/2wave mast puts the tip at the same height as a 5/8wave on the same pole & gives me about 4ft advantage in height of current maxima vs a 5/8wave,
probably try a coax choke on the isolator then look into making something better.
I did isolate the AP sometimes. 1/4 wave below the ring. Put a choke in the coax at that point always. Not sure whether I noticed any difference with isolation or not.
its up but temporary tied to the fence,
isolator & coax choke about 1/4wave below the hoop + 15ft of pole below the isolator,
vswr is very low on mid band, could do with bringing up in frequency for what i want,
The crazy looking astroplane performs better than i expected near the ground which is good news for me.
isolator & coax choke about 1/4wave below the hoop + 15ft of pole below the isolator,
vswr is very low on mid band, could do with bringing up in frequency for what i want,
The crazy looking astroplane performs better than i expected near the ground which is good news for me.
I'm wondering what result you'd get if you were to mount it on a non-metallic support, with appropriate coax choke(s) and a 1/4 wave above any metal tower/mast/guy lines?
Guess I'll have to try it. In my (gu)estimation, it's a folded 3/4 wave and shouldn't need a metal mast for tuning/matching.
I gave my AP away a while back but he has never installed it and I will be getting it back for testing.
I need to know the top hat rod length since he managed to lose them and I will need to fabricate 4 of them to OEM spec, if anyone has that measurement.
Thanks Homer, but I could've sworn they were only 20".
Looks like I'll start with 24".
I thought I'd try a 20' fir 2"x 4" with bolts in place of the U-bolts for mounting, and either pull the coax out @ 90° or wrap an appropriate current or voltage choke every 4' - 6' going down the 2"x 4". Maybe both.
I really want to know what impedance & reactance I'll see w/o any metal mast, and I have a 14' wooden storage shed roof above which to mount it, keeping the base a good 3/4 wave above the ground.
Last edited:
The mast IS part of the antenna as its typically used homer,
for impedance to be near 50ohm with the spacing used the mast should be close to 1-1/2" diameter,
the patent tells us the coax will do the same job,
i can't think of any other cb vertical that won't work correctly if you use a none conductive mast & bring the feedline out at 90 degrees,
or one that changing mast diameter directly effects feedpoint impedance,
for impedance to be near 50ohm with the spacing used the mast should be close to 1-1/2" diameter,
the patent tells us the coax will do the same job,
i can't think of any other cb vertical that won't work correctly if you use a none conductive mast & bring the feedline out at 90 degrees,
or one that changing mast diameter directly effects feedpoint impedance,
That was my understanding, too. Using a nonconducting mast after ~1/4^ below the ring may yield good results, but all the way to the top bracket would be remiss. My metal mast sometimes never reached the earth, but always was at least 9' or longer below the ring.
You wouldn't use a current choke at a voltage maximum.
Example; a 1/4 wave GP.
The current maximum is at the feed point at the base where the coax connector is located. That's the perfect place for a 5T x 4.25" current choke.
The GainMaster uses a 16T x ~3" choke coil.
...which isn't much of a current choke.
The GainMaster, also has the current maximum(s) at the feedpoint but that feed point is in the center of the antenna not at the base. The bottom is at the voltage maximum, 90° from the current maximum, requiring a completely different choke design to choke current from passing the voltage maximum.
I'm referring to where it is being choked not what it is being choked.
Yes it's all current being choked but a standard 5T x 4.25" current choke wouldn't work on the GainMaster or it would've saved them a lot of money in wasted coax, 66" vs 150".
A current choke for the current maximum, a voltage choke for the voltage maximum which should be about center of the ring on an Astroplane.
Last edited:
The gainmaster choke is a current choke NB,
several people have built homebrew versions using 5 turn chokes of rg213,
the choke creates the high impedance voltage node the correct electrical length from the feedpoint,
i predict choking the astroplane up around the ring will spoil the pattern,
imho for best results mount the astroplane on 1/2wave x 1-1/2" mast isolated from the support structure & isolate the feedline at the same point to minimise currents below the hoop.
several people have built homebrew versions using 5 turn chokes of rg213,
the choke creates the high impedance voltage node the correct electrical length from the feedpoint,
i predict choking the astroplane up around the ring will spoil the pattern,
imho for best results mount the astroplane on 1/2wave x 1-1/2" mast isolated from the support structure & isolate the feedline at the same point to minimise currents below the hoop.
Wait, so you're saying Sirio wasted a lot of money wrapping 16T of coax when all they needed was to enlarge the plastic from 3" to 4.25" and wrap 5T x 4.25"?
Those dummies!
"Wind 16 turns of coax..." http://www.transmission1.net/viewtopic.php?f=29&t=33050&sid=7f30548b5c0b08dd76fdbd36c6525435
- No one is chatting at the moment.