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[KM4AH]

I have a 75 meter dipole up 80 feet on a utility pole.
I feed it with about 375 feet of LMR400.
Three hundred feet is buried in conduit.
The squirrels have ruined my coax where it goes up the pole.
I was going to just replace the entire run, but a friend suggest I just switch it over to ladder line where it comes out of the 10 foot stick of PVC and save the 300 feet of LMR400 in conduit.

Any thought on this ?

[W9IQ]

You would need to analyze the impedance transformation that the section of ladder-line will have on the feedpoint impedance. This likely will create a high SWR in your coax. You will also need a balun at the transition which will introduce some additional loss and transformation.

I would just run some PVC up the pole to protect the coax from the tree rats.

- Glenn W9IQ

[AI5BC]

Another option is to splice in a smaller coax going up the tower inside EMT. 80 feet of coax @ 75 meter band loss is low, you would not sacrifice much loss using a smaller coax going up.

[WB6BYU]

Using 600 ohm open wire line to replace 75' of coax
results in an SWR over 100 : 1 on the rest of the coax.
Even on 80m, that makes at least 10 dB loss in the
coax.

We can quibble about details, but you get the ideas that
just swapping the ladder line for the coax isn't necessarily
a good idea if efficiency is important.

With a half wavelength of ladder line, however, it would be
much more efficient.


If the dipole is already matched, I'd just replace the chewed
part with another piece of coax.  A splice using two plugs
and a barrel connector isn't going to make any significant
difference.

[KM4AH]

Thanks. I can replace the entire length for $350 with an aftermarket LMR 400 provided I can get it pulled through without breaking anything. I could go with ladder line all the way, but I really don't want to look at it.
Just curious.

[N0GV]

Run heavy emt up the pole. Cut and splice the cable at the ground. Use N connectors and cover the entire splice with adhesive lined heat shrink 4" past the connectors on each side to keep it waterproof.

Buy a .22 and a book of squirrel recipes. .22 shorts won't go thru the heavy wall emt at 50 yards - now you are looking at meals and a conversation....



Grover

[N8NK]

Buy a .22 and a book of squirrel recipes. .22 shorts won't go thru the heavy wall emt at 50 yards - now you are looking at meals and a conversation....



Grover

If tree rat isn't to your liking, bring 'em up here to Michigan. There are 20' alligator gar pike in the Great Lakes.. and the tree rats make most excellent bait. They sink nicely to the bottom, you see...
Fun thread. Intesting thread. Be well all...
Blowzo the Humble Ham
dit dit

[WA3SKN]

Are you using the antenna for multi-band operation?
And why not just put a connector on the good part of coax and replace the 80 ft of damaged coax?  You might put it in some conduit this time.  Is any of the 80 ft salvageable?
Now you could put a remote tuner at the base of your utility pole and then use the ladder line plan.

-Mike.

[VR2AX]

I'd try scattering acorns away from the base of the pole.

Only a marksman can reliably hit a very small moving target at 50 yards without CD. Maybe treat the acorns with something..

[W1JPP]

I only run 100 watts. When I had my 450’ horizontal loop and now my current 160m dipole, i ran ladder line to outside the shack, connected to a 1:1 balun and immediately after that, the balun to my external ah-4 tuner. Both the balun and tuner I mounted on a board. Then coax from the tuner into the shack to the rig.

Mostly I wanted multi band use.

I have other coax fed antennas and other “tuned” dipoles and tuned vertical delta loops (20m and 40m and 10m)

All the others have come down over the years as after many times and years of doing a/b tests I found the ladderline fed performed equal to or marginally better than the dedicated coax fed resonant antennas.

I avoided ladderline for 20 years hearing many of the hypothetical horror stories. When I lived in maine it wasn’t uncommon for 60’ of my ladderline as it made its way to my house running a couple feet off the ground to be buried under 3’ of snow and ice. All worked fine.

Even for my portable setup, I use ladderline from the top of my portable fiberglass mast, down to a 1:1 balun to an ldg rt-11 tuner and then coax to my rig. I can use random lengths (avoiding some lengths) and get on multiple bands.

[N0GV]

Had a rat problem once, an air rifle and the neighbor's hunting dogs ended it.... Perhaps chaining fido in the yard near the pole would work too. Fun for him and exercise for the tree rats. Hosting a pine marten family would also help....

[KM4AH]

Are you using the antenna for multi-band operation?
And why not just put a connector on the good part of coax and replace the 80 ft of damaged coax?  You might put it in some conduit this time.  Is any of the 80 ft salvageable?
Now you could put a remote tuner at the base of your utility pole and then use the ladder line plan.

-Mike.

Usually 3.915 , almost exclusively.  I have a 40 meter dipole and a decent tri-bander on 70 feet of 45G.

Just not fond of barrel connectors.

I have a Nye Viking MB-V that just sits on the desk for looks. And, I was thinking I could use a 9 to1 balun.

But, I think the simplest solution is just buy a reel of coax.  I don't have the ladder line anyway and would have to buy that.

[KM4AH]

Had a rat problem once, an air rifle and the neighbor's hunting dogs ended it.... Perhaps chaining fido in the yard near the pole would work too. Fun for him and exercise for the tree rats. Hosting a pine marten family would also help....

I sat in a tree in the Bob Marshall Wilderness and watched a Pine Marten.  What a cool animal.

[KA4WJA]

Randy,
Unless you have some pretty hearty squirrels, maybe you have some imitation LMR cable?
Are you sure you have Times Microwave LMR-400?  Or is it LMR-400uf?  Or LMR-400-pvc?  Or is it imitation LMR-400, of some kind?

The reasons I ask are:

--- actual LMR-400 (and Davis Bury-Flex) has a stiff/smooth PE (polyethylene) outer jacket....and, I've found my squirrels will gladly chew on PVC jacketed cable (like RG-213/214, etc.) but they avoid gnawing on my PE-jacketed Davis Bury-Flex.  (and, this has been the case now for more than a decade)

--- actual LMR-400db has the same PE jacket, along with the flooding-compound-gel inside (which does a good job of keeping water out, when the jacket is pierced....and, has the additional advantage that critters don't like the taste and/or it sticks to their teeth, etc....so, they stop chewing on the cable quickly)

---  LMR-pvc has (obviously) a PVC jacket and is loved by squirrels.

--- LMR-400uf has a thremoplastic-rubber jacket (and, I'm not certain how that tastes to squirrels)

--- imitation LMR-400 could have any jacket...


The solution to many hams' problems with low-loss flexible cables, that they need to keep critters from chewing is using Davis Bury-Flex, as it has a stranded-center-conductor (like LMR-400uf), but also has a stiff/smooth PE outer jacket (like real LMR-400 has)....


Just saying, have a close look at what cable you have and what cable you're thinking of buying to replace it with...


And, while I understand your concerns over "barrel connectors", if you use a real Amphenol (or KIngs) brand PL-258, they should handle a few KW on 75m with no problem....imitation Amphenol, no-name-brand, etc., I wouldn't trust in ANY situation! 


Remember, you do get what you pay for. 


Hope I helped?

73,
John,  KA4WJA

[KM4AH]

It's an off brand LMR400.  They all indicate a PE jacket.  I really can't complain, it's been in use 15 years or so. Mostly my fault for leaving some excess looped up for them to sit on.