I know what I am going to say isn't talking about 160m, but pertains to a
vertical on the beach.
Quantifying, with anything but anecdotal data, the difference between a
horizontal antenna located inland versus a vertical on the beach would take
something more than a short experiment but here is another experiment that uses
RBN.
My son, ZF2DX, is living in Cayman Islands. I went down in May and we planned
to operate from the beach in the WPX Contest. On Friday I was in the process
of putting up some simple verticals when we were asked whether we would like to
join a small group at ZF1A. They would change category to M2 if we would
operate with them instead of operating separately with both in MS category. We
decided air conditioning would be nice and it would be fun to try to win the M2
category so I took down the verticals and we joined them.
Sunday afternoon when Kevin and I were finished with our operating time slots
we decided to go to the beach for about an hour, put up a 15m vertical with
only two radials, use 100w and then look at the RBN. ZF1A was on 15m using a
Yagi at 100 feet pointed toward Europe and 1200w power. We compared spots at
the same time to a large number of Skimmer stations. As I recall in some cases
we were in the range of -2 dB to -0 dB on some comparisons and in no case were
we down more than about 5 dB. Having both operated from the big station all
weekend, we both walked away from the beach before ever looking at the RBN with
the belief that it was a big improvement, just using a 12 foot vertical with
two radials. That belief was reinforced after we compared using RBN. If ZF1A
had been using 100w instead of 1200w and a single, ground mounted vertical with
any number of radials instead of the Yagi at 100 feet, I can only imagine how
much stronger we would have been.
I was converted into a believer and would not need specific quantitative data
to know that with very little effort I could put up some simple antennas on the
beach and be competitive with a large station with horizontal antennas located
inland. In fact give me about 6 dB over a single vertical on the waters edge
and you would need a very large station located inland to compete.
73...Stan, K5GO
Sent from my iPad
> On Aug 16, 2014, at 7:47 PM, "Juan EA5RS" <ea5rs@ono.com> wrote:
>
> As far as I know, skimmers are not signal-level coordinated, so strictly
> speaking, it only makes sense to compare measurements made by the same
> skimmer.
>
> Although not an expert in this field, I have performed some tests with
> skimmers, both under lab conditions as well as over the air.
>
> First, skimmers will not provide a signal power measurement, but a signal to
> noise ratio measurement. If the noise power does not vary with time (which
> need not be necessarily true), you could take the provided SNR as a measure
> of signal power relative to some constant noise power.
>
> But over HF channels (where signal levels follow a Rayleigh distribution),
> there is the additional measurement problem of fading. According to my
> observations, skimmers estimate SNR only needing a very short transmission,
> even shorter than a second. They will report SNR observed during that
> particular interval. But that level may have occured during a signal
> enhancement, or during a deep fade or anywhere in the middle. So
> measurements from the same station at different times, even only differing
> by seconds, may report SNRs differing several or many dBs. Let alone if you
> are trying to compare signals from two different stations, whose fading
> patterns are almost guaranteed to not coincide in time.
>
> All that said, skimmers provide a valuable tool for estimating signal
> levels, provided you are not trying to discern differences exceeding this
> "statistical noise". In my experience, you cannot rely on them for that
> purpose if you are looking for sub 5-10dB differences in ionospheric paths
> with 2 or more hops.
>
> 73,
> Juan EA5RS
>
>
> -----Mensaje original-----
> De: Topband [mailto:topband-bounces@contesting.com] En nombre de Hugh
> Valentine
> Enviado el: sábado, 16 de agosto de 2014 22:37
> Para: w8ji@w8ji.com
> CC: Topband@Contesting.com
> Asunto: Re: Topband: Modeling the proverbial "vertical on a beach"
>
> I am not a Skimmer expert, and am just asking. Question: Are all the
> Skimmers individually(and collectively) calibrated in concert? Can one rely
> on them for comparing scientific data and conclusion to prove or ascertain a
> point?Val
>
> ---------- Original Message ----------
> From: "Tom W8JI" <w8ji@w8ji.com>
> To: "Michael Tope" <W4EF@dellroy.com>, <topband@contesting.com>
> Subject: Re: Topband: Modeling the proverbial "vertical on a beach"
> Date: Thu, 14 Aug 2014 19:06:44 -0400
>
> I looked at comparative data from four or five contests.
>
> I'm too far out of the path and in distance (approaching 1000 miles
> different) to compare, but I was still interested in how others in the NE
> compared.
>
> If it was really 10-20 dB, shore locations would stand out like a sore thumb
> compared to inland locations. Everyone from around New England is about the
> same. Heck, K3LR is on the Ohio/PA border and does just as well or better
> than coastal stations in signal levels.
>
> 10 dB is completely undoable with antenna systems, once someone is at the 10
> dB threshold of gain over a dipole at optimal height (except on 160 where
> polarization is a player, and we have to compare vertical to vertical). 20
> dB would be beyond the world of magic.
>
> Understand I'm not saying there isn't a difference. I'm just saying it isn't
> an exaggerated difference that jumps out in the ways we use our systems.
>
> Watch skimmer yourself. It is entertaining to watch.
>
> 73 Tom
>
>
>
>
>
>
>
> ----- Original Message -----
> From: "Michael Tope" <W4EF@dellroy.com>
> To: <topband@contesting.com>
> Sent: Thursday, August 14, 2014 5:03 PM
> Subject: Re: Topband: Modeling the proverbial "vertical on a beach"
>
>
>> On 8/13/2014 6:28 PM, Tom W8JI wrote:
>>>
>>> But skimmer, which displays a relative level, does not show the level
>>> difference.
>>>
>>> Skimmer shows about the same peak levels, but the stations closer or over
>
>>> salt water paths (not localized salt water) have longer openings but no
>>> more level for peak level. Anyone can look at that.
>>>
>>> K3LR is about as strong into Europe, when I look at skimmer levels, as
>>> someone on the coast.
>>>
>>> The exceptions are people right next door to Europe (like VY1).
>>>
>>>
>>> 73 Tom
>>
>> Tom,
>>
>> How much skimmer data did you mine before establishing a firm conclusion
>> that the advantages of saltwater proximity are exaggerated?
>>
>> Myself, I think of how well AA7JV and HA7RY have done at various locations
>
>> using antennas that were very close to or in some cases literally in the
>> saltwater. The consistency of their topband signals compared to
>> Dxpeditions who were confined to inland locations seems to point to a big
>> advantage. I'll admit, however, that this hypotheses comes about from
>> anecdotal observations filtered through a mental lens that is biased
>> towards believing saltwater is a huge advantage.
>>
>> I think using skimmer is an excellent approach to this question provided
>> of course that you have mined enough data to filter out the statistical
>> noise.
>>
>> 73, Mike W4EF...................
>>
>> _________________
>> Topband Reflector Archives - http://www.contesting.com/_topband
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>>
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