It’s perhaps strange that there is little empirical data to allow activators to make an informed decision about which polarisation might perform best over different paths in different situations from a hilltop. Tom M1EYP and I decided a while back to make use of the RBN to compare antennas. Today we made a start.
We set up two antenna systems on The Cloud SP-015 and spent nearly two hours making test transmissions every 5 minutes. The antennas were a dipole at 6m AGL and an elevated vertical (top at 7m agl), both for 20m. They were about 150m apart.
To remove some variables we set our keying speeds and message formats to be the same and called at the same time. We both used 5 watts from FT-817s. We called 10KHz apart and swapped frequencies half way through.
The horiz versus vertical performance may depend on steepness at the summit operating position. Operating over a sheer cliff may yield different results than with a 5% gentle downgrade from the summit.
In reply to MM0FMF:
Hello,
"…Ooh, something techy. Excellent! "
I have two receivers on the Flex 5KA. If I sync both and have one receiver into my vertical (left ear) and the second receiver plugged into a hexbeam (right ear on headphones) = QSB is rapid variations of polarity. If I then phase the two antenna using ESC then the QSB is reduced. Not ‘technical’ I know but it is real time in terms of listening to two polarisations at the same time. Leaving a time gap allows too much time ~ propagation variation.
The horiz versus vertical performance may depend on steepness at the
summit operating position. Operating over a sheer cliff may yield
different results than with a 5% gentle downgrade from the summit.
It may, it may not. But does it? That is the question!
Well comparing the data properly is the way to go. I have no idea what Pete’s graph actually shows and the real analysis needs to be over specific paths. It also needs to take into account the SD of the results to show the error ranges - but surely a mathematician realises that?
Indeed, hence why I will do it. Just struggling to summon up the energy and motivation to do so at present. Something happened between the activation and now to put me in a heightened state of relaxation, not sure what…
I drive home, call in the shops to get some olives for my martini and
milk for everyone else and find a zillion posts!
If everyone else is putting milk in their martini you haven’t trained them properly.
No matter what the analysis comes up with it will only be a snapshot, conditions vary immensely and at the same time on another day the results may be completely different, so it will be interesting but inconclusive. I’ll be incommunicado in LD for five days from tomorrow but I look forward to reading the omnibus edition when I get back…
No matter what the analysis comes up with it will only be a snapshot,
conditions vary immensely and at the same time on another day the
results may be completely different, so it will be interesting but
inconclusive.
All true. Tomorrow I will run another series of tests. They will be focused on seeing how reliable the RBN data actually is. I will carry out the test at two arbitrary power levels (the actual levels don’t matter much). What will be carefully controlled will be the difference between the levels. It will be interesting to see how the RBN reports the test.
Short report of a similar experiment, not with complete statistics but mixed from RBN-figures, A-B-reports on air and receiving impressions.
20m-GP and 20m-dipole (fed @ 8m), not straight but not 90deg V-shaped. Antennas at a point on the hill where three directions offered three different contours: One direction very steep slope, one direction very gentle slope and one direction flat.
In the “steep slope direction” the dipole won with several S-units or two digit dB differences in RBN (be it more or less than 1000km).
In the “gentle slope direction” both antennas more or less the same with two A-B-tests on air giving some confidence in the results.
In the “flat direction” the GP won with more than one S-unit, but only three receiving impressions on the S-meter.
Of course more testing needed but at least no complete reversal of the gut feeling assumptions about those antennas types and their favourite slopes - so far
P.S.: Unscientific definition of steep and gentle: Steep is when you can not run down for some steps without falling
When you have some results comparing horizontal and vertical antennas can I ask if you will be hauling up several tens of feet of aluminium scaffold pole and some CB twiggery to see how that performs in comparison?
Maybe you could do a comparison of signal to weight ratio for this and other antennas?
