Topband: Supporting Ladder line

[donovanf at starpower.net]

Hi Rys, 


The terminationresistance of a BOG (including the loss in the 
ground rod and/or radials) is typically about 250 ohms. The value is 
non-critical, especially in the case of a BOG where most of the f/b 
ratio derives from the lossy ground in very close proximity to the 
antenna and not from the termination resistor. 


A 4:1 transformer works well for 75 ohm coax 
A 6:1 transformer may a better choice for 50 ohm coax, 
depending on the optimum termination resistance. 


In either case, the termination resistor attached to the unused coax 
(approximately 50 or 75 ohms) can be optimized to improve the 
front-to-back ratio. 


73 
Frank 
W3LPL 



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

From: "Ryszard Tymkiewicz" <rtym at ippt.pan.pl> 
To: donovanf at starpower.net 
Sent: Wednesday, January 10, 2018 9:55:34 PM 
Subject: Re: Topband: Supporting Ladder line 

Hi Frank... 
Yes I used to have reversible beverages even 15 years ago and of course I 
used these terminated resistors...but I was not sure about BOGs and RG-174.. 
now its clear..almost..why 6:1 transformer and not 4:1? (the end of your e-mail) 
..THANKS a lot 
Rys 
SP5EWY 






W dniu 2018-01-10 o 22:31, donovanf at starpower.net pisze: 



Hi Rys, 


Simply change the turns ratios of the reflection transformer and 
matching transformer to correspond to the approximate termination 
impedance and feed impedance. 4:1 transformers work well for a 
reversible BOG and a 9:1 transformers works well for an elevated 
Beverage. 


For a reversible Beverage, its very important that the unused coax 
be terminated in approximately a 75 ohm resistor. If you use a single 
coax feed, the switch box at the feedpoint must use a resistor to 
terminate the unused feed transformer. Its possible to optimize the 
termination resistor value to improve the front-to-back ratio, but the 
improvement is small especially in the case of a BOG. 


RG-174 has approximately 1 dB loss per 100 feet on 160 meters which 
is quite acceptable for a 220 foot BOG. You should use 6:1 transformers. 


73 
Frank 
W3LPL