[TowerTalk] Buried HF/VHF feedlines

Sun Jul 26 16:48:43 EDT 2020

There should be a saying - "there is no such thing as too large a coax 
junction box."  ;)  Antennas & towers seem to propagate after a few 
years.  I absolutely wouldn't used buried boxes.

If you are pulling Heliax then a big box is needed to manage the bend 
radius.  It takes at least 3 folks to pull it - reel payout, conduit 
feeder and lubricant applier, and puller. More if you are pulling 
several cables.  Maybe a capstan for a long pull.  The flat pull tape is 
cheap, strong, doesn't twist, and easy to attach.  Klein pulling grips 
with swivels are the pro approach to the cable or bundle attach point. 
Buy the large radius conduit sweeps (90d elbows) 24" minimum. Two 90d is 
the usual maximum, if more bends are needed then they need to be very 
large radius.  There are heat sleeves made to bend schedule 40 PVC, it 
takes a bit of practice to get it soft enough to bend but not toasted 
(really, it turns brown) PVC.

My favorite end junction box (other than a small shed) is an office 
counter height steel cabinet.  Only the already welded ones which cost a 
little bit more.  Available in 48" and 36" wide.  Toss the shelf.  A 
couple of coats of exterior latex and my 48" has no rust and no water 
inside after 4 years.  Easy to cut holes with common hole saws for the 
conduit hubs.  Chafe collars are a must (I've demonstrated why).  I now 
have a 36" on order to replace a fiberglass real enclosure that is too 
small for a new tower conduits.

The Carlon boxes 4x4 to 12x12" are ok for control cables/AC.  Electrical 
enclosures are available in a huge range of sizes but bring your wallet. 
  A new 48" fiberglass likely more than $1k vs $300 for the office cab. 
Used ones with wrong holes are easy to fix with 1/4" acrylic and caulking.

Grant KZ1W

On 7/25/2020 17:15, Jonathan - KE0YBL via TowerTalk wrote:
> Thanks, appreciate the local feedback. Not to get too off topic, but I'm planning to run the conduit to pull boxes/hand holes on each end, then short runs to the shack and tower. Water management, easier pulls, etc.
> 
> Does anyone have recommended boxes? Sprinkler boxes seem pretty junky as far as lawn mower tires etc. Proper Oldcastle concrete boxes are a bit overkill price wise. Other favorites? Also other techniques for coming up from below frost level into the box? Presumably just gradual slope and into the side as with most other stuff..
> 
> Thanks,
> 
> Jonathan
> 
> -------- Original Message --------
> On Jul 25, 2020, 6:55 PM, Kevin Kidd wrote:
> 
>> A few observations...
>>
>> Splices are "weather proof" not water proof and should never, ever, ever,
>> ever, never be placed below grade or in a flooded conduit. They will too
>> often leak hanging on a tower, they will always leak underground /
>> underwater.
>>
>> I have pictures of 3in Air Heliax compressed to about half that diameter
>> after freezing in a shallow, water filled, steel conduit in a MN swamp.
>>
>> Hardline is waterproof and direct burial as long as it hasn't been spliced
>> or damaged. Bury the coax or conduit below the local frost line and don't
>> splice it and you will be good for years.
>>
>> Good luck,
>>
>> Kevin C. Kidd, CSRE/AMD - WD4RAT
>> kkbclists at kkbc.com <kkidd at kkbc.com>
>> Lawrenceburg, TN
>> KK Broadcast Engineering - AM Ground Systems Company
>> www.kkbc.com -- www.amgroundsystems.com
>>
>> On Sat, Jul 25, 2020 at 1:26 AM Jonathan - KE0YBL via TowerTalk <
>> towertalk at contesting.com> wrote:
>>
>>> Hi All,
>>> I feel like this has been done to death - and yet, the Internet has really
>>> been notoriously awful with misinformation for me the past few weeks. I
>>> appreciate your thoughts as I work through this!
>>>
>>> I'm putting up a new tower primarily for HF and maybe some VHF. Given my
>>> ideal location is some ~350ft+ from the shack, I've been waffling back and
>>> forth as to whether to remote the radios in an enclosure, or bring Heliax
>>> back. I'm leaning toward the Heliax route.
>>>
>>> I'm working with an experienced (decades) climber/tower company in my area
>>> (Minnesota), who has used 7/8" Heliax for $1.50/ft. This seems reasonable,
>>> and a fraction of new, thus making my project seem doable. Sadly may
>>> require an underground splice due to lengths, but one battle at a time. I'm
>>> open to other sources for such things.
>>>
>>> Herein lies the rub -- my climber's experience has been (and probably
>>> yours as well) that directly burying this in our frozen tundra eventually
>>> results in crushed cable through thawing and freezing. I'm considering 3"
>>> or 4" HDPE conduit/innerduct to alleviate that, but given I'll need to go
>>> through a valley, condensate will condensate in the dip no matter what I
>>> do. I could perhaps drop the conduit down 36+" deep to avoid the frost
>>> level, but it'll still be sitting in water (albeit not frozen at that
>>> depth) without active moisture management in the run (fan, nitrogen (ugh),
>>> whatever - not feasible).
>>>
>>> I feel like at this point I'm really overthinking it. Fiber to the tower
>>> and radios in a box would be much easier, but less desirable - but now I'm
>>> really torn.
>>>
>>> I appreciate your feedback immensely,
>>>
>>> Jonathan
>>> _______________________________________________
>>>
>>>
>>>
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