Wes Stewart wrote:
However, compare something like Andrew LDF4-50 to Wireman 554 and you
find that the "lossy" coax has a loss of 0.48 dB/100' @ 50 MHz and the
"low-loss" ladderline has a loss of 0.41 dB under the same conditions.

Hi Wes, let's say I'm trying to choose between the two.
Wireman 554 is about 25 cents/foot. How much did you say the
Andrew LDF4-50 costs? :-) (LMR-1700 is about 8 bucks/foot.)

Here's another way to look at things for multi-band non-
resonant antenna lengths. The feedpoint impedance for
that type antenna may vary from a low of about 50 ohms
to a high of about 7500 ohms. To minimize SWR for all
conditions, Z0 should equal the square root of those
two values or 612 ohms. Given 600 ohm open-wire line,
the SWR shouldn't go much above 13:1 for the open-wire
line but may go as high as 150:1 for the coax. I don't
know about you, but I would rather run with a maximum
SWR of 13:1 rather than a maximum SWR of 150:1.
--
73, Cecil http://www.qsl.net/w5dxp

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On Tue, 05 Apr 2005 11:28:46 -0500, Cecil Moore
wrote:

|Wes Stewart wrote:
| However, compare something like Andrew LDF4-50 to Wireman 554 and you
| find that the "lossy" coax has a loss of 0.48 dB/100' @ 50 MHz and the
| "low-loss" ladderline has a loss of 0.41 dB under the same conditions.
|
|Hi Wes, let's say I'm trying to choose between the two.
|Wireman 554 is about 25 cents/foot. How much did you say the
|Andrew LDF4-50 costs? :-) (LMR-1700 is about 8 bucks/foot.)

Typically I buy it at hamfests for $1.00/ft. I have about a dozen
short lengths that I bought just for the connectors for $20.00. I
also have "in stock" a 110' length of LDF5-50 (7/8") that I paid a guy
in San Diego $200 for and a friend brought home to me for free. I've
been saving this for a new EME antenna....someday.

|
|Here's another way to look at things for multi-band non-
|resonant antenna lengths. The feedpoint impedance for
|that type antenna may vary from a low of about 50 ohms
|to a high of about 7500 ohms. To minimize SWR for all
|conditions, Z0 should equal the square root of those
|two values or 612 ohms. Given 600 ohm open-wire line,
|the SWR shouldn't go much above 13:1 for the open-wire
|line but may go as high as 150:1 for the coax. I don't
|know about you, but I would rather run with a maximum
|SWR of 13:1 rather than a maximum SWR of 150:1.

Who's talking about multiband non-resonant antennas? I prefer to
operate with SWR = 2.0. I can bury my line, strap it to the tower,
run it through a hole in the block wall without heartbreak and the
only concern I have with rain is that we don't get enough.

Furthermore, I don't have concerns with breakage or degradation from
UV and the only tuner I need is the one built into the plate circuit
of my Drake L-4B.

Wes Stewart wrote:
|Here's another way to look at things for multi-band non-
|resonant antenna lengths. The feedpoint impedance for
|that type antenna may vary from a low of about 50 ohms
|to a high of about 7500 ohms. To minimize SWR for all
|conditions, Z0 should equal the square root of those
|two values or 612 ohms. Given 600 ohm open-wire line,
|the SWR shouldn't go much above 13:1 for the open-wire
|line but may go as high as 150:1 for the coax. I don't
|know about you, but I would rather run with a maximum
|SWR of 13:1 rather than a maximum SWR of 150:1.

Who's talking about multiband non-resonant antennas?

Usually, anyone considering ladder-line for the feed
system. If the antenna is single-frequency with a 50
ohm feedpoint, there's not much of a reason to even
consider ladder-line except for very long runs.
--
73, Cecil http://www.qsl.net/w5dxp

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