AW: [TowerTalk] 5 db required to see?

[Gerhard Burian]

Dear Pete,

A few thoughts to signal differences:

Might be the situation you described was at the edge of propagation, just
before the band was closing. There is a focusing effect of the ionosphere
due to quite different reflection heights which results in a highly spotwise
reflection with very strong signals and others with quite low signals. Also
strong QSB is a sign for this. To show this simulations can be done with
PROPLAB software in the single ray mode.
An other effect of quite big differences in signals between two stations
with same power is possible with antennas of different angle of the main
lobe. There is tilting effect on the rays on multihop propagation towards
steeper angles of about 1 degree after 4 hops. So if a station is radiating
with 8 degree on the upper side of the main lobe the signal will arrive with
9 degree, lets say at the lower side of the main lobe of the receiving
antenna. The other station is transmitting with 9 degrees from the lower
side of the main lobe and this ray will arrive at 10 degrees at the first
station. This might be close to the first null allready!

Best regards
Gerhard OE3GBB

-----Ursprüngliche Nachricht-----
Von: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]Im Auftrag von Pete Smith
Gesendet: Sunday, May 28, 2000 5:09 PM
An: TOWERTALK@contesting.com
Betreff: Re: [TowerTalk] 5 db required to see?



At 06:10 AM 5/28/00 -0600, n4kg@juno.com wrote:
>ABSOLUTELY !  Hearing the little guys with horrible
>locations and/or antennas is what makes the difference.
>
>It never ceases to amaze me to see the difference in
>signal strength between the DX stations you hear CQing
>and the guys who answer YOUR CQ's.  Sometimes it's
>as much as 40 dB, even on the high bands.  This goes
>WAY beyond power differentials which might be 10 to
>12 dB.  The QRP'ers with modest antennas are louder
>than the bottom layers of 100 W guys and poor antennas
>and/or locations.

It would be really interesting, sometime, to measure just how far below 0
dBi some of these weak stations must be, at least for a given arrival
angle.  Yesterday afternoon, just before European sunset, I was running
stations on 10 meters, and found signal strengths ranging from S9 + 20 to
not moving the s-meter on my TS-930.  Conservatively, that must be 60 db.
Even allowing 20 db for power and 15 dbi for antenna variations that still
leaves what... maybe 25 dB... for location, antenna height, etc.

>
>No one has even mentioned local and/or atmospheric noise
>considerations so far in this discussion.  That can be even
>more important than a dB or two of antenna gain.  This may
>also explain why many of the East Coast guys prefer
>antennas with high F/B ratios.  It helps them hear the
>weaker stations on crowded bands.

Not just F/B but also F/S.  You guys to our South and Southwest keep
sending us thunderstorms!
>
>For hunt and call operation, I prefer low F/B ratio antennas
>to pick up the occassional multiplier to the South or West.


>
>On 40M, hearing those incredibly weak Europeans through
>the QRM and QRN is the biggest limitation.  My Beverages
>are quieter than my beam or former 2L Delta Loop but often
>the signals are then too weak to copy.  No wonder W3LPL
>and W4AN (among others) use Phased Beverages with
>additional gain for receiving on the low bands (including 40M).

If gain, per se was the story, counldn't you just jack up the preamp?  I
think a more likely explanation for that design choice is the narrower
pattern, which yields a higher SNR.  For most of the big stations, I'm sure
that SNR, rather than sheer gain, is the limitring factor on the low bands.



73, Pete Smith N4ZR
n4zr@contesting.com



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