[time-nuts] GPS Antenna Feed Line Decision
kb8tq at n1k.org
Sun Sep 3 11:20:06 EDT 2017
The bigger issue with unsuspended cables is wind and weather. It’s not just a static weight issue.
When the wind blows the cable jerks around. You very much want to tie it off against the mast. You
also want a strain relief loop at the antenna.
> On Sep 3, 2017, at 10:44 AM, Artek Manuals <Manuals at ArtekManuals.com> wrote:
> LMR-400 is probably the best compromise , I doubt you will see any useful improvement in system performance as a result of the improved 1.5db loss characteristics of the larger cables. Losses due to atmospherics, ionospherics and multi-path will be an orders of magnitude higher than the additional 1.5 db of signal improvement with the larger cables. We are not talking comms with some guy in a space suit on Mars here :-)
> AS for walking the mast up I have done a number of installations of this sort and the use of a block and tackle at the eve point is not difficult, and will be appreciated more and more the older you get . Mechanical multiplicative advantages are easy to implement. Don't use block & tackles which can pivot since depending on the weave/braid of the rope they will twist around and bind.
> manuals at artekmanuals.com
> On 9/2/2017 7:48 PM, Clay Autery wrote:
>> Thanks for the response...
>> Not sure why you and the other guy both recommended RG-6 75-Ohm cable
>> and F-connectors, when the nominal impedance of literally everything
>> else in the system is 50 Ohm, including the antenna and the HP GPS
>> Distribution Amp.... And then adding N to F adapters?
>> Doesn't make any sense unless one has $$ as a top priority, already has
>> a spool of RG-6 quad shield, etc... but I specifically stated that $$
>> is not a top priority.... Not really even in the top 5 or 10...
>> The whole point of this exercise is to put up a semi-permanent SINGLE
>> antenna/feed-line install that will supply all 4 ports of the HP amp
>> with the least compromised signal within reason.... 4 now, and 8
>> whenever I can find the HP 8-way distro amp with external power input.
>> Strain relief solution: Really depends upon which cable stock I end up
>> using.... Obviously, the larger the cable, the more weight will be
>> suspended under the antenna (approx. 38 feet, depending on where I pull
>> the cable out of the mast at the bottom. (The mast is on a tilt-base of
>> my own construction.... which brings up a valid consideration. it is
>> already a chore to walk the mast up manually. The more weight added at
>> the top and inside the mast, the more difficult a manual walk-up will
>> be. I'd prefer to keep this a manual tilt for now... at least until I
>> add the tri-band vertical dipole)
>> LMR-400 would be less than 4 lbs total weight... I'd likely suspend the
>> cable by the connector alone. (although, it wouldn't be JUST the
>> crimp... The connector would have at a minimum, 1 layer of
>> adhesive-lined shrink tube... probably 2, with the second, overlapping.
>> Then a nice wrap of self-fusing tape and then electrical tape over that.
>> Even LMR-600 could be suspended by the connector alone, at 5 lbs max in
>> the 38 foot max vertical section.
>> I do have several methods of secondary suspension within the top (and/or
>> second) mast section though if I decide I need it.
>> Also prefer to keep all the connectors N-type as much as possible since
>> that is the station standard.
>> Clay Autery, KY5G
>> On 9/2/2017 6:07 PM, Mike Naruta AA8K wrote:
>>> Clay, you may wish to consider using a quality RG-6 with F
>>> connectors. Grounding blocks are readily available for the base of
>>> your mast and the entrance to your house. Also, off-the-shelf
>>> over-voltage protectors (Zap-Tech) are available. I even found an
>>> F-to-N adapter for the antenna on Amazon. Watch out for the ones with
>>> metric N threads though.
>>> For my 25 meter run I was going to use an existing one inch Heliax,
>>> but pulled a run of Belden RG-6 instead after learning that Trimble
>>> used RG-6.
>>> It worked well directly connected to a Trimble Thunderbolt; now it is
>>> connected to a Symmetricon 58535A GPS L1 distribution amplifier.
>>> My Blitzortung System Red station has been running fine in my attic
>>> (Michigan) on a Motorola 97 Oncore patch antenna fastened against the
>>> roof underside. It is looking through wood, shingles, and nails (and
>>> a tree and antennas and utility lines).
>>> How are you planning to do strain-relief on the vertical run of coax
>>> inside of your mast?
>>> Mike - AA8K
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