--------------------------------------------------
From: "Ed Muns" <w0yk@msn.com>
Sent: Friday, January 08, 2010 2:55 AM
To: "Jim Thomson" <Jim.thom@telus.net>; <towertalk-bounces@contesting.com>;
<towertalk@contesting.com>
Subject: Re: [TowerTalk] 340N + mag 520...how close can you get them ?? / Al
mast
> The biggest issue is detuning of the 20m Yagi by the 80 dipole. This can
> be greatly reduced by opening the feedpoint on the 80 when operating on
> 20. This is easily done with one of the relays in the 80 band-segment
> relay box.
>
> Ed - W0YK
### The 80m rotary dipole will inline with both the 20m and 40m boom
below it. IE: at right angles to both the 20 and 40m yagi's. I
would have thought that this alone would eliminate any potential 80/20m
interaction ?? How does the 80m dipole resonate on 20m anyway . 20m
isn't exactly the 3rd harmonic of 80m. That being said, apparently per
K6JRF... who has the Create brand 80m dipole [albeit 56' long] sez his
does resonate on 20m.. and also 15m... go figure.
## I do have the F-12 relay switch box.... [ 6 x coils and 3 x P+B DPDT
relays] I don't understand how shunting various coil combo's will open
circuit the 80m dipole ? As a side note... I was not impressed with the
12 ga THnn wire used.... and re-wound all 6 x coils with 8 ga magnet wire
[ polyimide.. you can also get it in 6ga.. both from planet wire] .
However, a simple spst vac relay could easily accomplish what you
stated... open one side of the feed point. I could open both sides as well.
This entire mess is used in conjunction with an array solutions switch
box... [ 1 in ......6 out, all 7 x connectors are 7-16 din type] On
this AS remote switch box, all un- used ants have their center conductors
grnded. The AS box can easily be modified with on extra relay..... so one
could have the choice of either floating or grnding all un-used ant
ports... any relay that is de-energized. In my case, the AS box will be
mounted to the mast.
## I don't particularly like the coil /relay 8 x segment switch box
setup.... and will try another method.... and use one of my spare 10-1050
pf motor driven ceramic vac caps... inserted in series with the hot leg of
the feed point... and re-tune the dipole for aprx 3500 hz. Then by
reducing C.... the resonance point of the dipole will keep moving UP in
freq. On paper, it should tune the entire 3500-4000 band.
## I have also replaced the stock 12 ga Alumo weld LL wires with 10 ga
alumoweld wires. [I had a 500' roll of it]. I'm also seriously thinking
of adding capacity hats on each end.... just past the LL insulator. F-12
calls em ..'T-bars' on their new sigma 80m els. I extrapolated between
their 56' el.. and their 78' ele ....... and came up with aprx 21' T
bars........ one per side. On paper, it appears that the stock 18 ohm
feed point will be raised up a bit.... maybe as high as 30 ohms. Either
way.... the helical hairpin coil across the feed point will step the
18-30 ohms UP to 50 ohms. I don't know if this has been attempted
b4.... using LL wires in conjunction with T bar loading ?
## as a side note, for any of you that use F-12 80/40m switch box's with
the 2/4/6 x coils and P+B /deltrol DPDT mech relays in em. I have had
the relay contacts either go wide open, or high resistance.. and that's
brand new. I solved the problem by silver plating all the contacts with
'cool-amp'....... and then also coated the contacts with ..'conducto lube'
[ grnd up silver powder in grease, made for contacts, etc] both
available from cool amp in Ore...... problem solved. I also put heat
inside the box.. and also silica gel desiccant.. and seal the box's tight.
F-12 used nema box's.. which have a rubber gasket around em.
Tnx for all the help..... Jim VE7RF
>
>
> Sent from my BlackBerry
>
> -----Original Message-----
> From: "Jim Thomson" <Jim.thom@telus.net>
> Date: Fri, 8 Jan 2010 01:22:26
> To: <towertalk@contesting.com>
> Subject: [TowerTalk] 340N + mag 520...how close can you get them ?? / Al
> mast
>
> gents
>
> F-12 claims you can install another HF yagi, or tribander, etc,
> including 15m.....within 1 meter [ 39.37"] of the F-12 340N.
>
> Is this true? Seems like very short spacing to me. I'd like to
> install the F-12 EF-180B [ 80m rotary dipole] at the top of the mast
>
> then the F-12 mag 520 below it.... then the F-12 340N at the bottom of
> the mast. I don't want to use any more mast than required to do the
> job.
>
> The proposed mast is 2.875" OD 6061-T6 Aluminum [sched 80].. which
> is .276" wall thickness. I worked out the section modulus
> 1.33622 x 40 ksi yield strength = 53,448 inch lbs..... [or 4454 ft lbs]
> ... which is plenty strong enough. I have no clue what the actual
> deflection
>
> will be towards the top of the mast.. in say a 70 mph wind.
>
>
> Another option was to use 2.875" OD 6061-T6 al mast... [sched 40]..
> then stuff some 2.375" sched 80 inside of it. Total wall thickness
> in that case is
> aprx .405" .. and section modulus is increased to aprx 1.70541
> 1.70541 x 40 ksi = 71,016 inch lbs [ or 5918 ft lbs] Again ,. I have
> no clue what the
>
> actual deflection is, in a 70 mph wind.
>
> I'd like to use something like a 10.5' mast [ out the top of the
> tower]... with the 340N, just 1' above the bearing.... then the 20m yagi..
> 4' above the 40m,
>
> then the 80m dipole 3' above the 20m yagi. LL truss bar would be
> another 2.5' above the 80m dipole. = 10.5'
>
> On paper, none of this should interact. Can one realistically install a
> 520 just 4' above the 40m yagi.. with no interaction on either yagi ???
>
> Plan B for a mast, is to use 2.875" OD 1026 DOM.. with 1/4" wall
> thickness. Section modulus = 1.244131..... x 89 ksi = 110,743 in lbs
>
> or 9228 ft lbs. 1026 dom is cost prohibitive right now, esp with
> shipping costs, etc. 6061-T6 is readily available here in town. I
> already have 20' of
> 2.875" 6061-T6 [ sched 80]
>
> To test the 6061-T6... I proposed to install it to my deck, horizontally..
> with XXX feet sticking out in mid air....then start adding weight at
> the extreme end
>
> and and also along it's length .. and measure the deflection. If there
> is some on line calc that depicts deflection, that would be even better.
>
> Is my plan feasible.... or am I out to lunch on this one ??
>
> Later........... Jim VE7RF
> _______________________________________________
>
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>
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