[TowerTalk] perspective

Tom Rauch W8JI@contesting.com
Thu, 20 Jul 2000 13:20:59 -0400


George wrote:

> The way I see it is this:

> The world is a noisy place at HF frequencies.  This noise comes
> from all directions - it can be worse in some directions.
> At HF you are limited by the noise seen by the antenna.

Yes indeed.

> If a signal is above the noise you will be able to hear it.
> 
> If the signal is below this noise then an increase in gain
> in the direction of the signal will increase the noise
> by the same amount.

Yes indeed.
 
> Have a VERY quiet location. 
> (This worth more than most know.)

In a quiet location, the noise level increases a lot when the band 
opens. It's about a 20 dB change here from day to night on a quiet 
winters night on 160 meters! On occasion I can hear DX stations 
during the daytime here but there is no chance they can hear me. 
That's because the noise and signal have dropped in proportion at 
my end, but at their end the noise is high (it's dark) while my signal 
is weak (it's daylight over part of the path from me to them).

Propagated noise is the big equalizer that makes having a very 
quiet rural location not such a big deal over a suburban location.    
 
> Use an antenna with a very good pattern - so that it rejects
> the noise from every direction except the one you want to hear.

That's it. You need the maximum noise null to signal response 
ratio you can get, independent of gain (except for the consideration 
that the signal can't be taken into the systems internal noise).
 
> When you design an antenna for HF you want to get a good 
> pattern - even if it means giving up some forward gain.
> You will not hear the 1 or 2 db improvment in forward gain
> but you will hear an improvment if you can make the pattern
> better thus rejecting unwanted noise.

We should all say amen to that! Too often we look only at forward 
gain, yet the F/B and F/S ratio is much more important to receiving.

I'll take an antenna that trades pattern null depth for gain any day of 
the week.
 
> Now to go back to the quiet location - most of us would 
> improve our hearing ability more by spending the time to 
> find a quiet location than by debating about minor changes in
> the antenna system.  If you can't move - then you need to
> be spending your efforts getting rid of ALL of the power
> line noise, electric fence noise etc.

When you find that quiet location, you'll notice that antenna pattern 
is more important than ever. That's because ALL of the noise will 
come from intentional and unintentional transmitters scattered all 
over the world, and you'll need a wide deep null in every direction 
except the one you want to view.

Then when you do that, you'll miss callers that are in the null. It all 
equals out unless you are working fixed directions.

Too many people pay attention to gain, and not enough consider 
pattern.


73, Tom W8JI
w8ji@contesting.com

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