sirio changed the top one . no longer an astroplane clone

[Marconi]

Did the mate say why he was selling his GM?

BTW, I have experienced problems with the N and O Top ones when the bottom of the antenna was set too close to something below it, maybe even at 20' feet can have some affect. That is where I first noticed the affect with my OTO mounted 20' feet above my I-10K laying on the ground underneath.

I also was in a hurry to get my NTO up the other day and I wanted to mount it straight inline with the supporting mast, either inside or outside. I had some 1.75" heavy wall aluminum so I used 12' feet as the mast and placed the antenna mast down inside and it was not a good fit.

I was in a hurry and didn't want to drill and bolt them to secure the antenna. The antenna will actually turn inside the supporting mast. I was only planning for it to be mounted for a few days, so.....

Not very good construction I admit. Almost immediately I noticed that the antenna made TVI, so I'm thinking this was why and it was a bad move. Earlier I mounted the antenna side by side with the hardware supplied and I never saw any TVI on either mount at my location. So I would caution that all parts of the antenna system really needs to be secured well.

 

[bob85]

eddie,
i don't know the guy who sold the gainmaster, he was local but unknown, a buddy that lived local but moved to the coast a few years ago bought it in the hope he will be able to talk to us,

the arrl open sleeve article explains transmissionline mode and antenna mode currents,
with the original astroplane i would isolate the mast and feedline about 1/4wave below the hoop to minimise antenna mode currents in the mast/feedline, don't know if that will help performance or not

 

[Marconi]

eddie, i don't know the guy who sold the gainmaster, he was local but unknown, a buddy that lived local but moved to the coast a few years ago bought it in the hope he will be able to talk to us,

the arrl open sleeve article explains transmissionline mode and antenna mode currents, with the original astroplane i would isolate the mast and feedline about 1/4wave below the hoop to minimise antenna mode currents in the mast/feedline, don't know if that will help performance or not

Bob, have you tried you insulating ideas since Multimode did his a while back. You remember I tried it, albeit, I insulated the antenna side by side on the mast instead of raising it up, and I recall I may have seen some difference, but it was not remarkable as I recall. Have you been able to successfully duplicate the idea with the remarkable results that MM200 posted?

I can insulate my OTO using two 1" x 30" Delrin type plastic rods set on either side of the antenna and the mast with my sturdy fence brackets I use, but 9' below the bottom hoop will be pretty iffy construction. I can guy it well above the connection point and cut down on the stress if you tell me that you have been able to duplicate your earlier success with that idea.

However, when I isolate the mast in modeling, I always see a drop in gain. I can't say I understand why or if that is what happens in real life or not, but that is what Eznec shows me. In fact when I add a mast and/or the feed line to the mix, whether it is physical or hypothetical (virtual) like Eznec does it...I always see a nice increase in gain.

That said, and in reference to your discussions with Cebik or your understanding from other sources concerning modeling, you claim is that their contention is that modeling is not a reliable source of good info unless it includes a mast and feed line in the model, and that may be true. So my question for you is, what did the source(s) say was the expected results in such case either way? Was the model going to be better or worse? Do you know and/or did you ask that defining question to an open ended statement? What was the affect we might expect?

Until I started modeling, I presumed this caution meant the models would be deficient, bad, negative, not show us the results it should, but in modeling it shows me the opposite. How did you interpret those particular words when you read from others or heard it from Cebik? Can you help me understand this dilemma?

I'll try and read that stuff about transmission/antenna line mode again, but thus far it has been like reading Greek so far. Can you help me there too, and maybe explain in a few words how you see that issue in more practical and simple words and descriptions?