[TowerTalk] 80 m 4-square high SWR with no obvious reason why - using COMTEK ACB-80

kq2m at kq2m.com kq2m at kq2m.com
Thu Jul 14 22:44:08 EDT 2022


Hi Ignacy,

Thank you for your reply.  I use gloves for most significant physical 
tasks to protect my hands. The strange part is that unlike almost every 
other splinter that I have ever gotten, I did not feel this at the time 
and can't even imagine what I did to get it.  It was in the morning and 
I was not doing anything in my house that would have been a risk to my 
fingers.  The cause will remain a mystery.

I know that DX Engineering also has a 4-square but I am not familiar 
with what is different about it or why you feel it is superior to the 
Comtek.  If I were to get it, would the cabling or the length of the 
coax phasing lines be any different?  I would appreciate any specifics 
that you can provide.

Tnx & 73


Bob, KQ2M


On 2022-07-14 06:42, Ignacy Misztal wrote:
> Bob,
> Terrible problem with the splinter. We nearly always to remember to do
> certain tasks with gloves, but sometimes we forget.
> 
> If money is available, the dxengineering 4sq is way above that of
> Comtek. If you can reuse the controller, the switching unit is almost
> half price of the complete package.
> 
> Ignacy NO9E
> 
> On Thu, Jul 14, 2022, 00:29 <kq2m at kq2m.com> wrote:
> 
>> My apologies to all for the extreme delay in responding.  I got a
>> long
>> wood splinter under my pointer finger  nail and it got infected and
>> ballooned rapidly necessitating a visit to my internist and then to
>> a
>> hand surgeon who had to cut open the nail and remove some skin and
>> the
>> splinter.  Unfortunately he had to cut it open again 10 days later.
>> As
>> you can imagine it was a mess, extremely painful and almost
>> impossible
>> to type with the multiple layers of bandages.  5 trips to the hand
>> surgeon and 3 weeks later it is finally mostly healed.
>> 
>> Many thanks to NO9E, NA6O, W5JMW, W4EF and N3AC for their thoughtful
>> and
>> very helpful responses.
>> 
>> I had checked the coax, control cables, dummy load, Wire elements
>> and
>> feedlines just to be thorough and everything looked fine.  And then
>> I
>> opened the ACB-80 relay box and spotted a fully charred relay and
>> partly
>> blackened circuit board and then noticed that the other two relays
>> next
>> to it either had significant corrosion or lichen growth inside, or
>> both.
>> Whatever was on the relays likely caused the relay immolation but
>> it
>> was surprising to see given that the relay unit was held in place
>> with
>> antenna ports facing down and then that was placed under a large
>> heavy
>> duty plastic bin to prevent water, leaves, etc. from getting inside.
>> 
>> I am sending the relay unit back to DX Engineering for service along
>> 
>> with the control box.  My understanding is that there is currently a
>> 6 -
>> 8 week backlog for repairs.  The unit is 27 years old.  It would be
>> great to be able to get another 10 - 15 years out of it.  I won't
>> need
>> it after that.
>> 
>> 73 and thanks for all of your help and information!
>> 
>> Bob, KQ2M
>> 
>> On 2022-06-27 14:17, Ignacy Misztal wrote:
>>> If a mismatch in the 4 SQ should cause high dumped power but
>> little
>>> SWR change, it suggests that the Comtek box has a problem.
>>> Perhaps during testing with the elements out of order something
>> has
>>> fried.
>>> Comtek has a reputation of less reliable relays. My 2 year old
>> Comtek
>>> stack match stopped switching and a KW sent to the stack fixed the
>>> issue.
>>> Ignacy NO9E
>>> 
>>> On Sun, Jun 26, 2022, 19:23 <kq2m at kq2m.com> wrote:
>>> 
>>>> Hi,
>>>> 
>>>> Before WPXCW one month ago, my wire 80M 4-square using the COMTEK
>>>> ACB-80
>>>> was working very well, with ~ 1500 W out and 100 w reflected at
>> 3.5
>>>> mhz
>>>> and ~ 1500 W out and 50 w reflected at 3.7 mhz.  The F/S and F/B
>> wer
>>>> 
>>>> excellent and about as predicted when the DX station signals were
>>>> low
>>>> angle.
>>>> 
>>>> Between then and now (one month) we had two violent windstorms
>> and a
>>>> few
>>>> nasty T-storms, with gusts approaching 50 - 60 mph but tame
>> compared
>>>> to
>>>> what it has been through in the past.  2 wire elements broke off,
>>>> the
>>>> F/B and F/S disappeared and the forward power dropped to ~ 800 w
>>>> with
>>>> 350 w reflected from from 3.5 - 3.7 mhz.  That's normal and to be
>>>> expected.
>>>> 
>>>> However, when I fixed the two elements today, while the F/B and
>> F/S
>>>> improved somewhat, the forward/reflected power did not go back to
>>>> the
>>>> usual values. That is NOT normal.
>>>> 
>>>> I checked each of the connectors and continuity at the bottom of
>>>> each
>>>> element and everything appeared to be fine. I checked all the
>>>> phasing
>>>> lines and they appeared normal.  All the elevated radials were in
>>>> the
>>>> air at their normal elevations.  I could not find anything wrong.
>>>> There
>>>> was one sketchy looking connection on the  feedline to the shack
>> and
>>>> I
>>>> made a new connection with a new Amphenol pL259, but there was -
>>>> still ~
>>>> 800 w forward 350 w reflected from 3.5 to 3.7 mhz.
>>>> 
>>>> I seem to remember something like this happening about 10 years
>> ago
>>>> with
>>>> high reflected power and loss of F/B and F/S as a result of
>> multiple
>>>> 
>>>> COMTEK external relay box cold solder joints that were not
>> obvious.
>>>> DX
>>>> Engineering checked it out found the cold solder joints (that
>> COMTEK
>>>> did
>>>> NOT find) and fixed them and priority shipped it back to me so
>> that
>>>> I
>>>> would get it before CQWWCW which I did!  But the F/B and F/S was
>>>> worse
>>>> then than it is now so I am not sure that it is the same thing.
>>>> 
>>>> What is striking to me is that the forward power has uniformly
>>>> dropped
>>>> and the reflected power has uniformly risen across the entire
>> band
>>>> as
>>>> though the entire array was detuned by 500 khz, suggesting
>> something
>>>> 
>>>> systemic.  I suspect that the problem is in the relay box but I
>>>> can't
>>>> figure out what may be causing this.
>>>> 
>>>> Has anyone experienced a similar problem with their ACB-40,
>> ACB-80
>>>> or
>>>> ACB-160?  Does anyone have any idea of what to do look for next?
>>>> 
>>>> Tnx & 73
>>>> 
>>>> Bob, KQ2M


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