Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly where
I want it several times now. After tightening things down and putting vinyl
electrical tape on all traps and section joints (where it seemed to make
sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections at
the traps, and so have been adding a stainless steel pipe-clamp connection
just above and below the trap for improved connection. Made things better I
thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing, so I'm
wondering if maybe I shouldn't be trying to tape up the traps at all - maybe
they are retaining water or something that is affecting the capacitance.
Each trap has a drain hole at the bottom, and the aliminium pole itself has
drain holes every now and then that I'm trying not to interfere with.

Is there a trick, or some practical experience here that you can share?

I've had a lot of fun experimenting with this in any case, but winter's
coming...

Thanks,

Kevin VE9-XYZ

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

On Fri, 24 Aug 2007 11:45:07 -0300, "Kevin Hastings"
wrote:

Is there a trick, or some practical experience here that you can share?

Hi Kevin,

Is this an elevated vertical, or ground mounted?

If elevated, do you have the transmission line choked at the
feedpoint?

If ground mounted, what kind of radials system do you have?

73's
Richard Clark, KB7QHC

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

"Kevin Hastings" wrote in message
...
I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly
where I want it several times now. After tightening things down and
putting vinyl electrical tape on all traps and section joints (where it
seemed to make sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections at
the traps, and so have been adding a stainless steel pipe-clamp connection
just above and below the trap for improved connection. Made things better
I thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing, so
I'm wondering if maybe I shouldn't be trying to tape up the traps at all -
maybe they are retaining water or something that is affecting the
capacitance. Each trap has a drain hole at the bottom, and the aliminium
pole itself has drain holes every now and then that I'm trying not to
interfere with.

Is there a trick, or some practical experience here that you can share?

I've had a lot of fun experimenting with this in any case, but winter's
coming...

Thanks,

Kevin VE9-XYZ




Kevin my Cushcraft (MushCraft (;-) R-7000 had a similiar problem. The trap
wires are aluminum and connect to the trap shell where a intermittent
connection would occur. Using a slightly larger screw and a star washer
cured the problem. Don't know if this applies to your ATV-5 or not.

Lamont

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

"Kevin Hastings" wrote in
:

I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly
where I want it several times now. After tightening things down and
putting vinyl electrical tape on all traps and section joints (where
it seemed to make sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections
at the traps, and so have been adding a stainless steel pipe-clamp
connection just above and below the trap for improved connection. Made
things better I thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing,
so I'm wondering if maybe I shouldn't be trying to tape up the traps
at all - maybe they are retaining water or something that is affecting
the capacitance. Each trap has a drain hole at the bottom, and the
aliminium pole itself has drain holes every now and then that I'm
trying not to interfere with.

Is there a trick, or some practical experience here that you can
share?

I've had a lot of fun experimenting with this in any case, but
winter's coming...

Thanks,

Kevin VE9-XYZ




Hi Kevin:

Don't cover up the vent holes. Water is a poor dielectric and will de-
tune the traps. Also it will promote corrosion.

John Passaneau W3JXP

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

Richard - this is ground mounted. with 15 radials as specified in the
manual - and when it works - it works well. Very low SWR and no RF in the
shack. But the traps change characteristics I guess.

Kevin

Hi Kevin,

Is this an elevated vertical, or ground mounted?

If elevated, do you have the transmission line choked at the
feedpoint?

If ground mounted, what kind of radials system do you have?

73's
Richard Clark, KB7QHC

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

Kevin Hastings wrote:
I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly where
I want it several times now. After tightening things down and putting vinyl
electrical tape on all traps and section joints (where it seemed to make
sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections at
the traps, and so have been adding a stainless steel pipe-clamp connection
just above and below the trap for improved connection. Made things better I
thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing, so I'm
wondering if maybe I shouldn't be trying to tape up the traps at all - maybe
they are retaining water or something that is affecting the capacitance.
Each trap has a drain hole at the bottom, and the aliminium pole itself has
drain holes every now and then that I'm trying not to interfere with.

Is there a trick, or some practical experience here that you can share?

I've had a lot of fun experimenting with this in any case, but winter's
coming...
========================
Earlier this week I have done a similar exercise with a Butternut HF9V
vertical, using a MFJ259B analyser. Initially I got nowhere,although
nothing was 'visibly' wrong.
However ,when stripping the antenna I found that because of dissimilar
metal corrosion (stainless steel bolts,nuts and washers to aluminium
tubing ) a white aluminium oxyde powder had developed in between the
stainless steel / aluminium contact areas . Following removal of this
and re-fitting all components the antenna can now be adjusted and tuned.
Sofar ,80 metres and 17metres are fine (SWR is around 1.5 : 1) ,the
other bands still to be done. When finished I'll cover all the spots
with above contact areas with (Finnigan's Wax Oil)
This wax oil is widely available in the UK and is primarily meant to
protect the chassis of cars . It is also very suitable for protecting
metal components of antennas especially in coastal areas near salt
water . My QTH is 30 metres (100 ft) from a salt water beach.

Frank GM0CSZ / KN6WH

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

"Kevin Hastings" wrote in
:

I've spent 2 months or so of tweaking an older Cushcraft ATV-5 5-band
vertical with a friend's MFJ analyser and have had this thing exactly
where I want it several times now. After tightening things down and
putting vinyl electrical tape on all traps and section joints (where
it seemed to make sense) it would look fine for a few days to a week.

Then the resonant points of some bands would shift up to no-man's band
seemingly overnight and stay there. I suspected poor screw conections
at the traps, and so have been adding a stainless steel pipe-clamp
connection just above and below the trap for improved connection. Made
things better I thought - now 1-2 bands are just out of whack again.

There's always moisture inside the trap when I disassemble the thing,
so I'm wondering if maybe I shouldn't be trying to tape up the traps
at all - maybe they are retaining water or something that is affecting
the capacitance. Each trap has a drain hole at the bottom, and the
aliminium pole itself has drain holes every now and then that I'm
trying not to interfere with.

Is there a trick, or some practical experience here that you can
share?

I've had a lot of fun experimenting with this in any case, but
winter's coming...

Thanks,

Kevin VE9-XYZ




Kevin,

In addition to the other responses at this time...

I note you used an MFJ analyser, not further described. Assuming it is
the MFJ259 or like...

Did your VSWR readings with proper transmitter reconcile with the MFJ?
If not, I would favour the transmitter VSWR readings over the MFJ (the
wideband detector in such instruments is too easily disrupted by other RF
sources to depend on them absolutely).

Regarding tape, remember that any measure that you take to prevent
ingress of water is also likely to prevent egress. Worse, you may not
prevent vapour being drawn into the trap, but may prevent condensate
leaving and so build a water trap. Drain holes aren't always as effective
as we would like (blocking for various reasons), but I would not obstruct
drainholes. Indeed, period clearing of drainholes is a good idea if
convenient.

I see others have raised the issue of the reliability of internal
connections in the traps, another common problems with those antennas.

Owen

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

There's always moisture inside the trap when I disassemble the thing,
so I'm wondering if maybe I shouldn't be trying to tape up the traps
at all - maybe they are retaining water or something that is affecting
the capacitance. Each trap has a drain hole at the bottom, and the
aliminium pole itself has drain holes every now and then that I'm
trying not to interfere with.


It's very difficult to hermetically seal a large surface-area container from
moisture ingress. What happens is that, on a warm sunny day the container
heats up, causing the inside air to expand , pressurize the container
somewhat, and leak out. Then a thunderstorm blows in and cools the container
suddenly , causing the inside air to quickly contract, pulling a vacuum and
consequently sucking in some of the humid outside air. The humid air that
was sucked in then condenses back to water, which remains trapped unless
some reasonable size 'weep' holes are provided at the lowest point.

The moral of the lecture is that, unless you have taken substantial measures
to guarantee a hermetic seal, you should have drain holes.

Joe
W3JDR

Cushcraft Vertical Trap Consistency - Is there a trick guys?
 

"W3JDR" wrote in news:OiLzi.1550$OM1.1000@trnddc07:


There's always moisture inside the trap when I disassemble the
thing, so I'm wondering if maybe I shouldn't be trying to tape up
the traps at all - maybe they are retaining water or something that
is affecting the capacitance. Each trap has a drain hole at the
bottom, and the aliminium pole itself has drain holes every now and
then that I'm trying not to interfere with.


It's very difficult to hermetically seal a large surface-area
container from moisture ingress. What happens is that, on a warm sunny
day the container heats up, causing the inside air to expand ,
pressurize the container somewhat, and leak out. Then a thunderstorm
blows in and cools the container suddenly , causing the inside air to
quickly contract, pulling a vacuum and consequently sucking in some of
the humid outside air. The humid air that was sucked in then condenses
back to water, which remains trapped unless some reasonable size
'weep' holes are provided at the lowest point.

The moral of the lecture is that, unless you have taken substantial
measures to guarantee a hermetic seal, you should have drain holes.

Now that was an original though posted in response to my post!