[TowerTalk] Telrex 40 M Beam restoration

Tue, 9 Jan 2001 09:08:57 -0800

Hi Chris,

Don't lose heart over my comments. Even if the 40M329 has some weakpoints, 
I suspect that between some computer optimization work with the dimensions
and some mechanical modifications to the element design, you'll be able to 
come up with a real nice antenna. This antenna is pretty old, so it was probably
designed before people were using NEC and knew about element taper corrections.
In fact, I remember Doc Sheller, KN8Z saying that after Jim Lawson, W2PV came
out with his papers on the effects of element taper, he ended up changing the 
dimensions on his Wilson 3 element 40 meter yagi elements by something like 12"
each to make it really play. 

If you haven't done so already, pick up a copy of Dave Leeson's book "Physical
Design of Yagi Antennas". This book is a treatise on how to calculate and improve
wind survival ratings of yagi antenna elements, booms, and masts. With an 
Excel spreadsheet, and the taper schedule from the 40M329, you can probably
figure out where it will fail, at what wind speed it will fail,  and how to improve it. 

Have fun!

Mike, W4EF.....................

----- Original Message ----- 
From: "Chris Kepus" <ckepus@calweb.com>
To: "Michael Tope" <W4EF@dellroy.com>
Sent: Monday, January 08, 2001 10:02 PM
Subject: Re: [TowerTalk] Telrex 40 M Beam restoration

> Hi Mike,
> Thank you for your response to my message on the Telrex 40M329 beam.  The
> overall response was quite surprising (pleasantly).  I am a bit
> disappointed that many of the responses suggested that the mighty T-Rex
> might be more bark than bite.  As soon as I digest all the responses, I
> will get back to you with an answer to your question about the tips.
> Once again, thank you very much.
> 73,
> Chris
> W7JPG
> 
> 
> ----------
> > From: Michael Tope <W4EF@dellroy.com>
> > To: W8JI@contesting.com; towertalk@contesting.com; Chris Kepus
> <ckepus@calweb.com>
> > Subject: Re: [TowerTalk] Telrex 40 M Beam restoration
> > Date: Monday, January 08, 2001 11:04 PM
> > 
> > Tom/Chris,
> > 
> > Do either of your Telerex 40 meter beams have solid rod stainless steel
> element
> > tips? Dean Scarborough, KS8S used to have two 40M329 stacked at 90' and
> 180'.
> > As I recall, he had a problem with the stainless steel tips breaking off
> of the high
> > antenna. The stack never played very well, but his steel guys were not
> broken
> > up at all, so I suspect that this might have been part of the problem. 
> > 
> > Mike, W4EF...............................
> > 
> > ----- Original Message ----- 
> > From: "Tom Rauch" <w8ji@contesting.com>
> > To: <towertalk@contesting.com>; "Chris Kepus" <ckepus@calweb.com>
> > Sent: Monday, January 08, 2001 2:52 PM
> > Subject: Re: [TowerTalk] Telrex 40 M Beam restoration
> > 
> > 
> > > Hi Chris,
> > > 
> > > > I am in the process of restoring a Telrex 40M329 beam.  I would like
> to
> > > > contact anyone with experience with this beam and especially someone
> who
> > > > is still using this fine antenna. 
> > > 
> > > I have a 40M346 or whatever the long boom 40 meter antenna is. 
> > > You really need to check some things on that antenna, if it is 
> > > anything like mine.
> > > 
> > > Telrex used two types of elements. The piece going to the boom is 
> > > OK, but the next taper has a single wall really thin tubing element 
> > > (as I recall something like .038 wall). Some beams use two thin 
> > > walls sleeved.
> > > 
> > > I strutted the elements on mine with tarred nylon supports, but that 
> > > wasn't enough. After a few  $400 trips by a crane to repair 
> > > elements, I just totally rebuilt the elements using normal 6061T-6 
> > > .058 wall aluminum with a normal element taper.
> > > 
> > > Now the antenna has finally lasted six months without a repair.
> > > 
> > > I also found the stock balun was junk. It had a small coil of coax 
> > > and a hunk of house wire in the balun. This balun is probably 
> > > different than yours, since my antenna has a 50 ohm feed it uses a 
> > > 1:1 balun. I replaced it with a homebrew balun. You probably don't 
> > > have the same balun, but the obvious design flaws in my antenna's 
> > > factory balun make me wonder how good the other baluns are. I 
> > > have no idea if the other baluns are OK, just that the factory 1:1 
> > > balun that came with my antenna was poor.  
> > > 
> > > The director tuning was OK, but the reflector on mine (using factory 
> > > elements) was far too low in the band. When I shortened the 
> > > reflector, F/B ratio became around 40 dB or more (measured) 
> > > compared to a pathetic 15-20 dB stock at the band center. Your 
> > > antenna is different, and may be OK. 
> > > 
> > > The antenna worked OK with factory reflector settings, but I found 
> > > them more for feedpoint impedance than F/B ratio. When I reset 
> > > the reflector (by watching F/B on a test tower 500 feet away) the 
> > > feedpoint was way off.
> > >  
> > > > Also I am interested if anyone has tried using this beam on 20M by
> > > > altering the feed system and using an antenna tuner?
> > > 
> > > I don't see any easy way to do that, I think you'd be asking for 
> > > trouble.
> > > 73, Tom W8JI
> > > w8ji@contesting.com
> > > 
> > > --
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> > > Problems:                 owner-towertalk@contesting.com
> > > 
> > > 
> 

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