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Feed line question for 2 meter LPDA beam

bevis

Member
Sep 28, 2020
65
22
18
55
I have never tried this so i wanted to get some input.

I have a specific need to use an ELK log periodic beam for 2m/70cm in a permanent installation that will be installed static.
I will never be turned. I need to use the lowest loss coax thats right for 2m.
The install will be 100 feet or less.
Power will be 50 watts or less.
Here is my idea.
I use LMR400 / Solid core RG8/ whatever .400/.500 OD coax as the main feed line up to the top of the mast that the ELK is going to be mounted to.
The ELK is less than 2lbs assembled and kinda delicate. The feed point is at the radiating end so theres no way i think you could use the big coax on that small beam out on the end of it without taking the chance that the coax destroys the beam from weight and flex.

Can i use a barrel connector at the end of the big coax run and then run a 5 foot piece of RG316 or RG400 ( something small and light ) out to the feed point on the Elk ? This is the only way i can think of to use low loss feed line and not take a chance of destroying the elk. I know that the barrel connection would have to be water tight. I dont know what the implications are of doing this.

Thoughts ?
Thanks
 

BJ radionut

Supporting Member and 6m addict
May 9, 2008
4,073
4,602
373
35 miles East of Indianapolis
Good quality barrel...Silver / Teflon grade... mil-spec ...is fine. w/short jumper. Then LMR400 at 100 ft for 2/440 is about the limit.
Plenum/Fire rated is 1.5 DB loss in that 100ft. @150mhz (3db+/440 Half your power and RX)
UltraFlex 400 =1.8 @150 MHz (3.5+DB @440)
Remember loss is both directions, not just power loss/RX also
Keep as short as practical. I would be tempted to go 1/2-inch Superflex but just me...I am changing out my LMR400max this spring on my 6m antenna to 1/2" Superflex >75ft...and changing 2m to 1/2" hardline...just me.
With indoor antenna, even slight loss will only disadvantage you more.
My 2 cents
All the Best
Gary
 

bevis

Member
Sep 28, 2020
65
22
18
55
Good quality barrel...Silver / Teflon grade... mil-spec ...is fine. w/short jumper. Then LMR400 at 100 ft for 2/440 is about the limit.
Plenum/Fire rated is 1.5 DB loss in that 100ft. @150mhz (3db+/440 Half your power and RX)
UltraFlex 400 =1.8 @150 MHz (3.5+DB @440)
Remember loss is both directions, not just power loss/RX also
Keep as short as practical. I would be tempted to go 1/2-inch Superflex but just me...I am changing out my LMR400max this spring on my 6m antenna to 1/2" Superflex >75ft...and changing 2m to 1/2" hardline...just me.
With indoor antenna, even slight loss will only disadvantage you more.
My 2 cents
All the Best
Gary
Thanks Gary
 

BJ radionut

Supporting Member and 6m addict
May 9, 2008
4,073
4,602
373
35 miles East of Indianapolis




Just some other ideas...Log periodic antennas typically have lower gain, than conventional Yagi's
Plus, feedpoint farther back on boom, where not issue like "tip" feed antennas


:ROFLMAO::love::cool:
 

bevis

Member
Sep 28, 2020
65
22
18
55
Well, I'm already in possession of 2 elks. If they don't do what i need them to do, I'll get yagi's. I really don't need the 70cm part of the equation but it's better to have it and not need it.
TY
 

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