One point to make...
They are using vertically mounted 2-element SteppIR beams. Based on the
pictures I've seen, they may be phasing them as a broadside array as
well. Either way, they certainly have directivity... maybe too much if
they are phasing multiple beams without being able to steer them.
Larry N8LP
Tom Rauch wrote:
>>"Let's start with a technical consideration of which you
>>
>>
>should be aware. As you already know, we are using
>vertically-polarized antennas very, very close to salt water
>and with large radial fields. This makes our signal launch
>angle very, very low - quite a bit lower than most
>horizontally-polarized antennas on dry land. As a result,
>the K7C signal has been reported to be very loud on the
>receiving end. This doesn't mean, however, that you are just
>as loud here. All it takes is a couple of extra "hops" from
>a higher launch angle and your signal will change from an
>easy-to-work S5 to being undetectable. The K7C team has
>observed a number of occasions when it is obvious that you
>can hear K7C easily, but on our end the pileup is only an
>unworkable S-1 grumble. This is most pronounced at the
>beginning and end of an opening so you may be hearing us
>long before or after we can hear you. Marginal openings on
>the paths to Europe, the Middle East and Northern Africa may
>be enti
>
>
>> rely "one-way" - incredibly frustrating for you to have
>>
>>
>K7C be as clear as bell, but not hearing the most important
>DXer of all - you."
>
>
>
>
>>Does this explanation make sense?
>>
>>
>
>It makes no sense at all.
>
>
>
>>I would think that an antenna with a high angle of
>>
>>
>radiation on transmit would also favor signals with high
>arriving angles on receive.>
>
>That's the way it works, sort of.
>
>What people often forget is on receiving the ratio of
>response between signal direction and polarization and
>interference (noise/QRM) direction and polarization is what
>determines S/N ratio or ability to copy. Gain is for the
>largest part meaningless on HF receiving.
>
>Gain means everything for transmitting and directivity does
>NOT..the response pattern means everything for receiving and
>gain does not.
>
>That's why a -20dB gain receiving antenna with a good
>pattern works very well for receiving and really sucks on a
>transmitter. It's why a high gain transmitting antenna
>doesn't necessarily make a better receiving antenna.
>
>This is why feedline loss is virtually meaningless for HF
>receiving, but means a grat deal when transmitting.
>
>They are barking up the wrong tree with that explaination.
>The real problem is they have efficient omni-directional
>antennas that would have about the lowest directivity
>possible receiving noise and QRM from all directions, while
>many land based stations have antennas that have 5-10dB
>directivity (not necessarily gain).
>
>They are listening to a multitude of signals that bother
>each other. The other stations calling them are only focused
>on ONE signal that for the large part is in the clear rather
>than mixed with 1000 other signals.
>
><< The amount of signal attenuation on a signal arriving at
>a low angle at the station with the antenna transmitting
>with a high angle of radiation should be equally diminished.
>Therefore the station with the horizontal antenna over dry
>land should have trouble hearing hearing K7C as well.>
>
>That would be totally true in a noiseless world or two sites
>with evenly distributed noise.
>
>The limitation at HF is generally propagated noise, with
>either groundwave (in populated or congested locations) or
>skywave (in rural locations) setting the lower limit. The
>thing that sets the perceived signal level on receiving is
>the ratio of the accumulation of noise to the signal level.
>That S/N ratio relates only to antenna pattern, unless you
>have a very rare case where the receiver does not show a
>definite noise increase when the antenna is connected.
>
>About a year ago QST published an article about figure of
>merit for station improvements. The author used antenna gain
>as a factor for receiving. WRONG. Can't be used. (Of course
>point that out does nothing these days, since their mind is
>made up.)
>
>Pattern matters for receiving, and the FOM would depend on
>the direction(s) of noise or unwanted signals and the
>desired signal. Gain only applies to transmitting, and only
>gain at a useful angle for the path counts.
>
>In a very loose way they are probably correct, it is an
>antenna difference....but it is not for the reason they say.
>That reason makes no sense. The real reasons are:
>
>1.) People listening only have to sort out and focus on one
>signal. The other people have a lot of time to zero in and
>peak up everything and get focused on that one signal who's
>call they already know, they don't have to dig through a
>confusing mess. This fact alone makes several S units of
>perceived advantage (who gives a rare DX station that is S3
>an S3 report?).
>
>2.) K7C has an efficient antenna with a very poor pattern.
>About the worse they could have for working weak signals.
>
>3.) I'm sure many people calling them have very poor
>transmitting antennas, like dipoles at 20 feet. Some may
>even have GAP antennas, or other antennas with a good SWR
>but 20% or less efficiency.
>
>4.) The people in a pile up are in a mess of other signals.
>
>5.) They may not have the best weak signal receivers for
>sorting out multiple close-spaced stations at K7C.
>
>6.) K7C gets noise and QRM from all directions. Even a -5dB
>gain Yagi or dipole can have 10dB of directive advantage on
>receiving.
>
>73 Tom
>
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>
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>
>
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
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