Topband: Bury beverage wire?

[donovanf at starpower.net]

Hi Martin, 


Matching transformers aren't necessary for your 160 meter Beverage 
b ecause your coax is only five meters long, b ut its probably best to 
use a pair of transformers. I ts likely that the loss in the matching 
transformers will be very slightly greater than the mismatch loss 
through only five meters of coax. If you don't use transformers, 
use 75 ohm high velocity factor foam dielectric coax such as RG-6 
cable TV coax. 


If you use matching transformers, it isn't necessary to precisely 
match them to the Beverage, a pair of 6:1 transformers will work fine 
with 75 ohm coax. Because one dB of additional loss isn't a significant 
consideration in a 160 meter Beverage, you can use either a binocular 
core or toroid ferrite core with either isolated windings or auto 
transformer winding. It isn't worth the trouble of building low 
loss transmission line transformers for Beverage antennas. 


The antenna side of each matching transformer must be connected to a 
ground rod. Grounding the coax side of each transformer shouldn't 
matter because the coax is so short. I'd ground the coax shields 
since common mode isn't an issue with only five meters of coax. 


My favorite Beverage transformer is the W8JI 2:5 turn ratio Beverage 
matching transformer using a FairRite Products 2873000202 Type 73 
ferrite binocular core. I use either telephone wire from an RJ-11 
telephone cable, wire from a Cat 5 Ethernet cable or 30 AWG wirewrap 
wire. 


https://www.w8ji.com/core_selection.htm 


73 
Frank 
W3LPL 


----- Original Message -----

From: "Martin" <dm4im at t-online.de> 
To: topband at contesting.com 
Sent: Wednesday, January 17, 2018 4:10:04 PM 
Subject: Re: Topband: Bury beverage wire? 

Thanks to all. 
I had a few direct responses to my inquiry. 
I should haver better described the situation by expressing that it is 
not a driveway, but rather an opening in a fence separating 2 lawns. I 
just had no words for it in english. 

One guy came up with the idea to thread the wire through tennisballs and 
bury it in a conduit, so no portion of the wire would touch ground or 
the conduit. 

This seems like a good idea, but isn't just burying coaxcable , leaving 
the shield open and only use the center conductor about the same, 
without a bunch of unknown parameters? 

Another suggestion was to bury coax and start the antenna after the 
opening. Excellent, but last resort, because this would only allow a 
180m long antenna. Still better than no antenna and better than most 
hams can do. 

W3LPL came up with what i think is the best idea: 
Bury coax with high VF and put transformers on both ends. 
This leads to another question: 
What ratio do i wind the transformers? 1:9 at the feedpiont, 9:1 at the 
beginning of the coax, 1:9 at it's end where the wire continues? Or do i 
measure the impedances to calculate a ratio? 
Do i put in a ground rod at each end of the coax to connect the 
transformers? 
Do i connect both sides of the transformers to ground? 

If i get this to work, i have a 230m-235m long antenna with 5m of it 
under ground. 

Any input? 



-- 

Ohne CW ist es nur CB.. 

73, Martin DM4iM 
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