[TenTec] OT: Openwire/Window Line and Bad Wx

Sat Aug 3 18:01:31 EDT 2013

I hope this does not add to the confusion too much. However...

  Radials really only apply to quarter-wave verticals.  The reason is 
that the radials  allow the field to act as though is is a half wave 
antenna, although the bottom half is virtual.  A half-wave vertical only 
requires a ground.  There is no question that at 40 meters and below, it 
is not easy to put up a a half-wave vertical and so, depending on how 
the vertical is constructed, and which bands are covered, radials may be 
needed to create or maintain the desired pattern.  Although I have not 
seem this, it would seem to me that for multi-band verticals, there 
should be some isolation of the radials in order to maintain the desired 
pattern for the upper bands.

John  /  WA1JG

On 8/3/2013 12:18 PM, Darrell Bellerive wrote:
> It is not just the quality of the ground, but rather the proximity to 
> the ground. Ground losses are present for a low horizontal antenna
> regardless of the quality of the ground.
>
> For a vertical antenna, the ground quality is what matters, hence the
> need for radials.
>
> Model a dipole in free space and note the maximum and average gain of
> the antenna, then model the same antenna at 0.05 wavelength above
> perfect ground and compare the gain. Changing the ground quality from
> perfect to normal to poor will also influence the loss.
>
> At low heights the radiation pattern will totally change from free 
> space, with most of the radiation going straight up. Not necessarily a 
> bad thing on 160 and 80 metres.
>
> One of the tricks for tropical shortwave broadcasters is to bury a 
> radial under a dipole and then optimize the height of the dipole to 
> get the desired radiation pattern. Usually these stations are looking 
> for a coverage area within a few hundred miles of the station, and a 
> radiation pattern directly up is what is desired.
>
> Darrell Bellerive
>
> On 08/03/2013 08:17 AM, k6jek wrote:
>> How big are the ground losses?  Are they the difference between an
>> EZNEC prediction over perfect ground and what it says over average
>> ground assuming average is what you have? Is it the difference
>> between the model's prediction of impedance over perfect ground and
>> what you actually measure as Bob Orr said in his book years ago, for
>> example, the model says the impedance should be 35 +jx  over perfect
>> ground and you measure 50 +jx,  at the feed point, that's 15 ohms of
>> loss?
>>
>> Jon
>>
>> On Aug 3, 2013, at 7:46 AM, Darrell Bellerive wrote:
>>
>>> 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 at karinya.net> To: "Discussion of Ten-Tec Equipment"
>>>> <tentec at contesting.com> Cc: "Phil Sussman"
>>>> <psussman at pactor.com>; "Bob McGraw - K4TAX" <RMcGraw at 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 at 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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>>>>>>
>>>>>
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>>>>
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