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G8MNY > TECH 26.03.20 13:32l 107 Lines 5065 Bytes #999 (0) @ WW
BID : 50002_GB7CIP
Read: GUEST
Subj: Diamond X500 Colinear Repair
Path: IW8PGT<IZ3LSV<I3XTY<I0OJJ<I0OJJ<GB7CIP
Sent: 200326/1126Z @:GB7CIP.#32.GBR.EURO #:50002 [Caterham Surrey GBR]
>From g8mny%gb7cip.#32.gbr.euro@i0ojj.ampr.org Thu Mar 26 12:30:41 2020
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Mar 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This old high gain 200W dual band colinear aerial ended up being internally
water logged, and with water ending up in the coax, after passing through the N
connector (the only way out!).
Lost of preparation was needed to take it down as it was at 30ft up, on the to
of the pole on a chimney. Then dismantle it (not loosing which part is which)
and test each component for failure, clean up, repair all the parts etc.
It is made in 3 sections:-
BOTTOM SECTION
This has two aluminium tubes, outer one has two mast support clamps. The inner
tube is held in position with bolt (unless corroded solid as my one was!).
Inside is a machined up brass N socket connector disk, that screws into the
inner tube. (corroded solid).
The disk supports a PTFE insulation stalk where the 4.5 turn matching coil is
wound. It is tapped in the middle by a 10pF C from the N socket, and the top of
coil tuning has a 1.5pF C to ground. The coil tuning capacitance is also to the
inner tube! The inner tube has the bottom fibreglass pole bonded inside it.
Radials
Bolt
-------=================== Fibreglass tube painted white .----__
_³³Coil __~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _
N[_ _////_[__]----------------\\\\---------[]\\\\\\\\\\\[]-------[_]
con ³³ 2 caps __________________________________________________ __
-------=================== '----
Outer Tube with Ferrule jointer
2 mast clamps and water seal
The internal 1/8" brass rod aerials has a 70cms 8 turn hard copper phase coil
and longer 2m 61 turn coil on a fibre rod, spaced along the aerial.
The rod joiners are either a stainless clip or brass ferrule, and screw or a
hex grub screw.
Sponge (sticky draft excluder) is wrapped around any part that could touch the
fibre glass tube as a vibration spacer.
MIDDLE SECTION
This is thinner and has 2 ferules and seals for inter tube joining. Inside is 2
x 6 turn coils separated by a mechanical capacitor boss and the rods to a 61
turn coil.
__.----. Fibreglass tube painted white .----__
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _
----------\\\\------[c]------\\\\---------------[]\\\\\\\\\\\[]-----[_]
___________________________________________________________________
~~'----' '----~~
TOP SECTION
This is thinner still, and has a metal top cap. It has 1 ferrule and seals
for inter tube joining. Inside there is a joiner feeding a rod & 2x 6 turn
coils separate by a mechanical capacitor boss, and the long top rod.
__.----. Fibreglass tube painted white __
~~~~~~~~~_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~³metal
----------[_]------\\\\------[c]------\\\\----------------------- ³top
___________________________________________________________________³cap
~~'----' ~~
THE REPAIR
After undoing the ferrules, the water came out, and inner wire jointing screws
were undone to free up the upper 2 sections.
I had to cut the outer tube off with an angle grinder, to free it from the
inner tube. And that slot not only freed it, but let me see the brass disk
thread, which I was able to leaver out and undo the hex grub screw freeing the
bottom loading unit from the rods.
On testing it I found it resonated OK. But above 2m and 70cm until I added the
inner tube again, so the wet coil and 2 caps were still OK!
I polished up all the copper coils, brass rods, joiners and line caps with a
wire wheel. Then greased up all joints, aluminium soldered up any loose crimp
joints. And I replaced the sponge vibration spacers.
The fibreglass tubes were not cracked, but needed a spot of paint, to prevent
there was no way any water could get out other than down the N connector!
To stop any further water problems, I carefully drilled a 2mm drain hole in the
brass disk near the N connector avoiding the 2 small 1kV caps.
REASSEMBLY
Initially done for RF testing to see if it all still worked. SWR 1:12 in the
middle of 2m. The tests repeated again after spraying any corrosion metal
protection on the aerial components. and final assembly.
On re-errecting the aerial @ 30ft in the clear it worked very well, compaired
to a backup loft 9ft triband colinear.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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