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Astrobeam

RT2020

RT2020

Active Member
Dec 23, 2011
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Who is the expert around here on theses? I had this one up a few years ago and dropped it adjusting on it and broke a few pieces. I got the bright idea a few weeks ago to resurrect it and I remember why I was glad to take it down before.



Thing is a pain in the butt to tune, can it be tuned on a 15' pole and not change when put up at 40' or will SWR go up or down when at operating height? I know that question prolly cant be answered..lol. I messed with it Fri. till I gave up, there are no tuning instructions in the manual so I messed with the driven stinger and could never get an acceptable for me #, best I got was 1.7 on channel 1 and 2.0 on 40. Seems when I had it up before I had a 1.5 but cant remember.



Anyone have any advice? I have the pigtail and it makes no difference.



Thanks Greg
 

I wonder how you repaired or replaced the broken parts, and how 'close' you got them to the originals?
You're right, if you tune it at 15 feet and then move it to 40 feet, it isn't going to be 'tuned' anymore, that's about as normal as it gets with any antenna. (It works the same way the other way around too.) It may be close, but not as 'right' as it was.

- 'Doc

(And I'm no expert on that antenna!)
 
to tune this antenna you turn it on its back point the front straight up tie it of with cloth or cotton string, make sure no metal is around it, then using the coax that is going to be used on it adjust the swr to lowest. then move to the tower or pole. wished i had some pics but dont have any right now, but that is how we used to do beams back way back when, did a few astroplane beams too, like this. 73s midnight special
 
W5LZ, The tubing I used is a hair smaller on the OD. The top driven element is 2 pieces, I used it for the very top piece. I also spliced a 8" piece in on one of the tubes for the hoop.

Midnight Special, turn it on its back directly on the ground? I have heard this before but was not sure.

Thanks, Greg
 
I have had 3 of them and i never could get them to tune worth a darn.. I gave up on the last one and put up my old Moonraker 4 and never looked back..
 
According to what I understand the AstroBeam (A/B) must be setup properly with the right continuity checks in all of the right places or it will likely give problems with the tune.

In addition I don't think this one came as tunable. I recall that the instructions indicate the construction setup as fixed, and that is probably why there are no tuning instructions.

I do not know the reason for the 75 ohm pig tail sub, or when nor why it is used or not. I have heard tell that some guys use it with good results while other's find the tune is fine without it. That didn't make sense to me, and when I had a chance to ask, I never got a straight answer that made sense.

I have also heard stories that the A/B works well to very well, while other's say it doesn't work well at all.

I know if you don't get all of the parts right on the money and good and tight without overdoing it, you will not be happy. There is also a caution in the original Avanti A/B manual...regarding the connection of the bottom element into the feed point area, and a notation regarding the position of the short stub-fitting for the top radiator on the top bracket plate.

This beam has numerous little parts and little details in the manual that are very important. A casual reading and understanding of the manual might not be good enough to produce a good end-result. This beam construction is not your typical 3 element yagi setup.

I also think the length indicated in the manual for the top radiator maybe short. I read it as somewhere close to 72" as I recall. When I tried to setup my A/P using a full 1/4 wave radiator, I found I had to make this part about 87.5." However, understand that the presence of the other elements on this three element beam may change that some.
 
Last edited:
Staybolt said:
I sold the last one i had to a friend and he has great luck with it....
Click to expand...

Can you get some details? Maybe about the pig tail use, the top 1/4 element length he used.

Staybolt do you have any idea what you did wrong after he got it right?
 
Yes Staybolt would be good to know. Also Marconi I have read the manual numerous times and checked the measurements more times than I can count and also the continuity and it all checks out per the book. Also I just walked out and checked and my pigtail is RG83u and the manual says a dual Rg59u, so whats the deal there?
One other thing Marconi I was pleased with the performance of this beam when I had it up before it just seemed the SWR should be better and thats why I kept monkeying with it and ended up dropping it in the process.
 
RT2020 said:
Yes Staybolt would be good to know. Also Marconi I have read the manual numerous times and checked the measurements more times than I can count and also the continuity and it all checks out per the book. Also I just walked out and checked and my pigtail is RG83u and the manual says a dual Rg59u, so whats the deal there?
One other thing Marconi I was pleased with the performance of this beam when I had it up before it just seemed the SWR should be better and thats why I kept monkeying with it and ended up dropping it in the process.
Click to expand...

2020, that is why I wonder about the length of the 1/4 radiator in the top. As I noted earlier I had to make it longer than I thought the manual indicated to get my A/P Top One to tune into the middle of 11 meters.

If your tune wasn't so good, what frequency were you trying for?

Did you check other frequencies trying to find a better tune?
 
I used my MFJ 259B to tune and as per manual with the stock length on the driven stinger of 77 5/8" it was resonant at 26.025. I am looking for the 11 meter band.
 
RT2020 said:
I used my MFJ 259B to tune and as per manual with the stock length on the driven stinger of 77 5/8" it was resonant at 26.025. I am looking for the 11 meter band.
Click to expand...

Well I guess I was wrong about the length needing to be 87.5" or there abouts.

Thanks for the info.
 
Just wonder why mine has a 6' RG83U pigtail which is 35ohm and it says in the manual a 6' dual 59U? I would like to see a picture of this Dual 59U pigtail.
 
RT2020 said:
Just wonder why mine has a 6' RG83U pigtail which is 35ohm and it says in the manual a 6' dual 59U? I would like to see a picture of this Dual 59U pigtail.
Click to expand...

I think dual RG59U coax at 75 ohms in parallel will get you close to 35 ohms. Does the ends of this pigtail have connectors?

Good report on the mauldropper's thread about another Astro Beam. I don't know how much difference his mistake will make, but the manual sure gives the user a warning. I think he also has the top plate, where the radiator mounts, on backwards too. I didn't post any thing about the plate being backward, so if you agree why don't you go warn him of that too?
 

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