After watching these kind of results for months and months until I was
bleeding from the eyeballs, I came to some conclusions.
1) There are calm steady propagation nights, and there are wildly varying
propagation nights. The former is like a windless night, and the latter
windy. The latter is FAR more common. The former can tell you all kinds
of things.
2) On calm propagation nights, shorter distances, equivalent to one hop,
will compare antennas very well, without worrying about further insight.
But you need to watch measurements for a decent period to make sure things
are steady. Most nights steady doesn't describe anything. I haven't seen
a steady night on 160 for a while now.
3) On normal varying propagation nights, you can tell a great deal in a
contest where you have an evening and wee hours full of spots. If you get
a graph on your station vs another station at a single RBN (use spot
analysis tool on the RBN web page) and filling in the dots you see what
appears to be a string of mounds with deep fades, graph the high points of
the mounds. Ignore things that look like spikes in the graph. This gets
you a comparison of two close stations, where the differential in that
direction will repeat as long as the stations don't change equipment and
antennas. It appears to be good to a dB or two. If you see persistent
differences of four or five dB or more, accounting for power, then you have
an reliable difference that has something going on
feedline/antenna/matching to cause it.
It is quite surprising how many times these accounted-for-power differences
exceed ten dB. It is surprising how many times before and after changes
vs. an unchanged local will amount to 7 or 10 and even 15 dB. There ARE
seemingly endless ways to run up surprising, severe by any definition,
losses not predicted in models, or in literature, or in common parlance.
If the improvement in performance is 8 plus or minus 3 dB, that is STILL a
severe improvement regardless of the fuzzy accuracy, and it will make a
difference to the DX. With care, RBN easily gives you that.
Still waiting for someone to build a $25 dollar RF field strength meter
that does not have the "diode problem": A meter, that even if 1 mV/m on
the scale is plus or minus 100%, whatever 1 mV/m on the display actually is
reliably repeatable, and so will still show CHANGE in power level to a
reliable 1% accuracy. Elecraft??? Wayne???
Until everyone who has an SWR meter has that FS meter, we are still going
to be on the short stick detecting smaller losses and accumulating small
improvements to max out the dB, and doing poorly in accumulating an
accurate modern acumen for circumstances of the common man.
In the meantime, we definitely can help the fellows with undetected
unexpected huge loss problems, and measure significant changes reliably
with RBN. If the numbers are there, you are. If not, you're not.
73, Guy.
On Thu, Nov 29, 2012 at 12:13 PM, Jim Brown <jim@audiosystemsgroup.com>wrote:
> On 11/29/2012 2:55 AM, Larry Gauthier (K8UT) wrote:
>
>> Especially on 160 meters, results varied widely from day-to-day; even
>> from hour-to-hour. You may find the same is true by looking back through
>> the history of spots for your old antenna as you compare it to your new
>> antenna.
>>
>
> I strongly agree. This spring, I used W6CQZ's JT65 RBN to try to compare
> two 160M antennas in real time. I did so by calling CQ for one sequence on
> one antenna, then the next sequence (2 minutes later) on the other antenna,
> and repeating that for at least an hour. On a typical evening, I got
> reports from receivers in MI, IN, and PA, (as well as some much closer)
> with QSB that was at least 2-3 times the difference in dB of the predicted
> difference between the two antennas. I put the numbers in a spreadsheet
> and carefully averaged them, and even after six or eight runs, was not able
> to establish that I was seeing the difference the model predicted.
> Depending on how the timing of the sequences correlated with the timing of
> the QSB, I could see the predicted 2dB advantage or not.
>
> 73, Jim K9YC
>
>
>
> ______________________________**_________________
> Topband reflector - topband@contesting.com
>
_______________________________________________
Topband reflector - topband@contesting.com
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