[TowerTalk] K7C - One-Way Propagation?

[Tom Rauch]

> "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