The other factor that I don't think has been mentioned is ground loss of
the transmitted signal. For horizontal antennas, antenna height is the
major factor, and for vertical antennas, radials.
The impact of ground loss on a low horizontal antenna on the 160 and 80
metre bands will be significant compared to feedline losses. A dipole at
25 to 30 feet above ground for 160 metres is only 0.05 of a wavelength
high. As a horizontal antenna is lowered below 1/4 wavelength above
ground, ground losses increase significantly.
Remember though that lots of hams make lots of contacts with low
dipoles, and any antenna is better than no antenna. So like Bob has
stated, striving to eliminate that last dB of feedline, tuner, or balun
loss may be insignificant compared to other factors. We need to be
mindful of our complete system of transmitter power, losses,
propagation, etc. and the impact each has on our transmitted signal.
73, Darrell VA7TO
Darrell Bellerive
On 08/03/2013 06:37 AM, Bob McGraw - K4TAX wrote:
Steve et al:
I'm not saying that loss does or does not change with the vinyl type
window line between wet and dry. I do agree with your results in that
loss does increase with a wet line as opposed to a dry line. I also
agree that loss is greater per unit at 28 MHz vs. the same length of
line at 1.8 MHz or 3.8 MHz regardless if the line is wet or dry.
My point, with today's receivers, in most all cases the atmospheric
noise and man made noise will mask any receiver internal noise and will
easily overtake any loss in the transmission line. However, the loss in
the transmission line will affect the NF of the receiver, which on HF is
of little significance. In many cases, we worry about 2 or 3 dB loss
in the transmission line but run the attenuator of 10 dB to 20 dB at the
input of the receiver. Now on transmit, that point makes a different in
the power arriving at the antenna. Again, typically less than 1 S unit
on the other end. To that point, most of the time I run the Argonaut VI
at 10 watts and can work about any station I hear, regardless of line loss.
True open wire line, by definition, is two conductors supported only at
the source end and the termination end, drawn taught, and without any
spacers. This of course is a real challenge to make work reliably in
practice unless one uses large conductors and spaced at 6" to 18" and
used at lower frequencies and typically with very high power in the near
megawatt range. We used this feed line approach in some of the
commercial SW stations to which I attended. Some of these feed lines
were each several thousand feet in length. All of this is far beyond
the scope of most ham installations.
I would like to see more data on dry line vs. wet line from natural
cause as opposed to "wetted" line. I use the vinyl covered line with
66% of the web spacers removed. {Remove 2, leave 1, remove 2, leave
1.} I see little change from wet to dry on HF.
73
Bob, K4TAX
----- Original Message ----- From: "Steve Hunt" <steve@karinya.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Cc: "Phil Sussman" <psussman@pactor.com>; "Bob McGraw - K4TAX"
<RMcGraw@Blomand.net>
Sent: Saturday, August 03, 2013 8:01 AM
Subject: Re: [TenTec] OT: Openwire/Window Line and Bad Wx
We're talking here about reported changes in loss that - if true -
would be equivalent to a 5dB change between dry and wet on a 100ft of
ladderline feeding a doublet on 10m.
Are you folks trying to tell me that 5dB makes "little to no difference"?
Steve G3TXQ
On 03/08/2013 13:27, Phil Sussman wrote:
Bob is right! In the end, propagation will dictate. External
conditions have more of an effect than the subtle differences
over which we have control.
Sure we can increase efficiency, yet the results are subtle.
It all depends upon whether the band is open, eh?
Well said, Bob!
73 de Phil - N8PS
------
Quoting Bob McGraw - K4TAX <RMcGraw@Blomand.net>:
As I said in my closing remark in an earlier post:
"I realize that we'd like to eak out every dB we can, but in the
end, it
makes little to no difference on HF."
If one can match the load, using what ever means and equipment, then
energy will be transferred. On receiving, atomospheric and man made
noise will overtake any losses in the antenna system and will over
ride most all receiver noise.
73
Bob, K4TAX
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