Re: Connecting coax in wet weather

Conrad, PA5Y
 

Mark et al.

Thanks for the tips. I will use Denso I think, once I find a local source. Mark's recommendations seem to make sense to me and while I can live (and do) without Eastenders I don't want to be forever messing about with coax. I am already sick to death of it ūüôā

73

Conrad




From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Mark GM4ISM via Groups.Io <gm4ism@...>
Sent: 05 October 2019 21:20
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Connecting coax in wet weather
 
Hi All
To be clear
A tight layer of PVC tape is still required over the self amalg.  Denso cannot really  be used to compress the self amalg.  That compression is, I believe, an important factor in sealing the joint.
 
 
To summarise what is done in my professional world.
we expect to apply 4 layers in effect
1 good layer of¬† self amalg with little stretch. This extends 1‚ÄĚ beyond the¬† end of the connector and any boot
2 a layer of stretched self amalg  over the top of the 1st layer
3 a layer of tightly wound PVC tale extending¬† 1‚ÄĚbeyond¬† the self amalg
4 a layer of Denso¬† extending 1‚ÄĚ beyond the PVC
 
Good practice is to then smooth down the surface of the denso with added grease if necessary, by hand.  Twisting so as not to accidentally undo the connector.
 
Messy job but  it will last for years.
 
This practice is  not  unique to the broadcast world, though some don’t apply the denso and put more PVC on.   I have tried this ( For several years over a large number of sites) and  despite the possibility of  water becoming trapped under the PVC I did not observe an increased failure rate.  Standard practice as above, including denso was formalised  many years ago in my organisation. 
 
 
Denso directly applied on self amalg results in a horrible mess after a time and while I have no direct evidence of degradation, I think there  is some long term change to the amalg tape due to the oils in the Denso. This is much reduced with the PVC layer
 
As a useful side effect that layer of PVC make taking the denso off much less messy. 
 
My organisation must have upwards of 2000 antenna systems  that use this waterproofing regime. Each may have on average 10 joints.
If the joints leaked, many people could loose Eastenders, Radio 1 or other  critical services.
The technique was developed before my time in the industry and I have not been able to substantially improve on it.   Investigating  where water  did get in  concluding that if done properly and with care, these joint have a very good MTBF
 
On last point 
Self amalg is a variable  substance.   If it doesn't instantly stick to itself under brief applied pressure such that you cant pull it apart  back to the individual layers, it probably wont keep water out!
 
As it is, I don’t use Denso on my amateur systems, just self amalg and UV stable PVC
 
Mark GM4ISM
 
 
 
Sent: Saturday, October 05, 2019 7:30 PM
Subject: Re: [UKMicrowaves] Connecting coax in wet weather
 
Dear Paul,
 
To answer your questions:
 

Regarding your statement

I am unconvinced on wrapping plastic insulating tape over self-amalgamating

Please could you explain  as I have been using this method for approaching 50 years and from this thread others adopt the same methods

To follow Mark‚Äôs statement that "PVC tape does not contribute much to the waterproofing.‚ÄĚ my observation is that water gets in under the insulating tape and is trapped there, contributing to leakage. Thus it is better to use Denso tape and if Denso tape is used, no PVC tape is needed to protect the self-amalgamating tape from UV.¬†

now frowned upon by most operators for H&S reasons, joints protected by the DTELS method of self-amlagamting tape

could you please explain DTELS

DTELS- the Home Office Directorate of Telecommunications- privatised in 1994.
 
Regards,
 
Alwyn
 
_____________________________________________________

Alwyn Seeds, Director
114 Beaufort Street (Management) Company Ltd.,
114 Beaufort Street,
London,
SW3 6BU


114 Beaufort Street (Management) Company Ltd., Registered in England and Wales: No. 02797775 Registered Office Address: 114 Beaufort Street, London, SW3 6BU
______________________________________________________
 

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