[TowerTalk] Balanced Feedline for Ground Mounted Vertical?

[jimlux]

Richard (Rick) Karlquist wrote:
> Joe Giacobello wrote:
>> If one had to install a ground mounted vertical as far as 2,000 feet 
>> from the shack and wanted to avoid the expense of using low loss coax, 
>> could a balanced feedline be used as an alternative?  The idea would be 
>> to run the balanced feed line to the base of the antenna and connect to 
>> the antenna through a current balun.  The input to the feedline and the 
>> antenna would be matched by means of a balanced tuner in the shack.
>>
>>lower loss than the hardline.  You can look at aluminum wire vs copper. 
>   It's just a cost thing.  Physics vs money.
> 
> I happen to have used 4 AWG insulated stranded aluminum.  Evidently,
> the insulation and stranding haven't hurt me in the loss department,
> as the loss is close to the theoretical loss, which is in the tenths
> of a dB on the low bands.
> 

I would think that given the half mile run, you should give serious 
thought to aluminum (unless someone gives you the mile of copper wire) 
or copperclad steel (depending on the frequency.. as long as the skin 
depth is much less than the cladding thickness).  Maybe even aluminum 
clad steel.  Aluminum is about 60% the conductivity of copper, so 
considering it as a "tube", if you go 60% bigger diameter, you'll have 
the same loss. Whether buying 2.5 times the volume of aluminum is 
cheaper is something you'll have to check. On a raw materials basis, 
almost certainly, but wire prices only follow metal prices on a lagging 
basis, and because so much copper wire is used, there are anomalies.

(Copper/Aluminum density 9/2.7.. about 3..  Copper price is about $2/lb, 
aluminum about $0.65/lb.. also about 3, so for the same volume, copper 
costs 9 times what aluminum does.  For the same loss, aluminum will cost 
about 1/3 what copper does)

I second Rick's comment about tuning at the antenna... and maybe you 
could figure out a matching network that does the transformation to your 
open wire line impedance, rather than transforming to 50 ohms, then from 
50 to 450 or 50:800.  You'll still need a transformer at the shack, 
probably (or, you could use your tuner to do the transformation..)