[TowerTalk] [YCCC] guy placement questions

Dick Green WC1M wc1m at msn.com
Tue Apr 11 20:14:16 EDT 2006

I believe the interaction was only with the 4-el SteppIR. 

> -----Original Message-----
> From: Mike Bernock [mailto:mbernock at comcast.net] 
> Sent: Monday, April 10, 2006 7:11 PM
> To: wc1m at msn.com; 'Tower'; 'YCCC'
> Subject: RE: [YCCC] guy placement questions
> Dick,
> I have a 40M2 (M2 40M, 2 ele) at 98' sharing a mast with a 3 
> ele SteppIR at 90'. There was no noticeable effect on VSWR on 
> any band on the SteppIR when the 40M2 was installed above it. 
> I made some before and after ground wave checks (around a 
> mile away), on all SteppIR bands (20M - 6M), comparing 
> forward gain and F/B in both the normal and 180 flip modes. I 
> only recall recording a slight drop in F/B on 15M (normal and 
> 180 mode) after the 40M beam was installed. I have some 
> scribblings from this test safely filed somewhere... I will 
> post them, if I can find them. Hope this info helps.
> -- Mike, N1IW
> -----Original Message-----
> From: yccc-bounces at yccc.org [mailto:yccc-bounces at yccc.org] On 
> Behalf Of Dick Green WC1M
> Sent: Monday, April 10, 2006 2:05 PM
> To: Tower; YCCC
> Subject: [YCCC] guy placement questions
> Background: I've got a permit for 100' of Rohn 55 that will 
> support a three-stack of 4-element SteppIR yagis and a 
> 40-2CD. The 40-2CD will be on the mast and all three SteppIRs 
> will be on TIC rings. HFTA shows that 90'/60'/30' spacing is 
> best for the stack from my location. Not too long ago, a 
> TowerTalk poster said models he did for SteppIR showed 
> interaction between the 40-2CD and the 4-el SteppIR on 15m 
> (some) and 17m (significant.) At least 15' of separation is 
> needed to minimize the interaction. If the top SteppIR is at 
> 90', then the 40-2CD should be at least five feet up the mast (105').
> Question 1 - Guy elevations: Rohn specs call for guying at 
> 33', 63' and 95'.
> The stack models fine at 96'/64'/34', so this would be a 
> reasonable choice.
> In that case, the 40-2CD would be 10' up the mast, at 110'. 
> In both cases, the 40-2CD will be 15 feet above the top guy. 
> Are there any structural advantages/disadvantages between 
> having 10 feet of tower and five feet of mast above the top 
> guy versus five feet of tower and 10 feet of mast above the top guy?
> Question 2 - Mast length: In the 90'/60'/30' case, I would 
> put eight feet of mast above the top section (40-2CD five 
> feet up, boom struts three feet
> higher.) In the 96'/64'/34' case, I would put 13 feet of mast 
> above the top section (40-2CD ten feet up, boom struts three 
> feet higher.) At the two proposed guy placements, how much of 
> the mast should be inside the top section (i.e., how far down 
> should the rotor be?) Is it best to have the rotor close to 
> the top guy point? If so, I would need 20' of mast in both 
> cases. True?
> Question 3 - Guy radius: The SteppIRs need at least 25' of 
> turning radius (24' plus one foot for the TIC ring.) The 
> middle SteppIR will probably not clear the top guy if the guy 
> radius is at the Rohn nominal 80'. If I put the guys 85' out 
> (slightly over the spec of 80% plus or minus 5%), then I'll 
> get about 3 feet of clearance. If I put the guys 90' out, 
> then I'll get about 5 feet of clearance. How do I compute the 
> expected sag in the guy wires?
> (Note: The plan is to use phillystran guys.) Does 3 feet 
> leave enough margin? Does 5 feet leave enough margin?
> Thanks in advance for any learned answers to these questions!
> 73, Dick WC1M
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