Topband: WD-1A 2-way Beverage

[Roger D Johnson]

Lee K7TJR wrote:
> Hi Dave:    One look at the specs for WD-1A scares me. I do not see how one could successfully send any RF down one of these wires as a differential transmission line. That is exactly what happens, and what you need  in the reverse Beverage mode. The loss of WD-1A at 4kHz can be as much as 5 dB per mile by spec. Lets see thats about 1dB at 4kHz for the average length Beverage. 1000/5280 * 5 dB=~1dB. Using a simple 1 dB for each doubling (2^9 * 4khZ) of the  frequency as the spec chart shows, one can expect 9 more dB for a total loss of at least 10dB. It would likely be much worse than this in real loss figures for the cable at 2Mhz. 10dB  loss or more in the reverse direction would be very noticeable. I am not certain what it would do to the expected operation/pattern but I am sure it would affect the real versus theoretical termination resistance of the antenna as well. Some real loose approximations here! It is not hard to expect this when it has an approximate 70 ohm tr
ans
>  mission line impedance (my guess) and a pure DC loss resistance of 46 ohms in 1000 feet per side! 
> 
> So let me guess, you see 1 to 2 S-units (6 to 12 dB) difference in antenna gain forward to reverse?
> 
> Here is the specs when it was new. What it might be after 10 or 20 years maybe more is anybodys guess. 
> 
> Oh, and SWR would likely look pretty good as there is a lot of resistive loss here.
> 
> "http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-49104/dtl49104.pdf"
> 
> Personally, I would not use this wire. 
> 
> Lee  K7TJR Oregon
> 

Dennis made some actual measurements:

"However, be aware that the line loss is relatively high in the reverse,
transmission line mode. I tested this line extensively at 1.8 and 3.5 
Mhz using
approximately 10 watts of power and very well matched binocular core
transformers. I measured a net loss of 5.1 db for 502 feet of line on 
1.8 Mhz,
and 8.8 db for the 502 foot run at 3.5 Mhz. The loss in the reverse 
direction
goes up significantly at 7 Mhz and higher.

73, Dennis W0JX/8"

73, Roger


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