[Skimmertalk] Antennas for Skimmer radios?
H Lawrence Serra
hlserra at sbcglobal.net
Sat Dec 24 12:59:49 PST 2011
Hi Dave-
I think we are in agreement, and yes, there can be better receive antennas than
transmitting antennas, such as beverages or magnetic loops which increase the
SNR in noisy locations.
But for the run of the mill ham, maximizing gain and reception angle generally
helps incoming and outgoing sigs-- especially if you don't have room for
beverages and stacked yagis.
>...suggested that we
>shouldn't necessarily try to optimize the receive antennas for CW
>Skimmer because a good receive antenna was likely to produce spots we
>couldn't work with our transmit antennas. That just doesn't seem at all
>rational to me when there is no way of knowing what the conditions are
>on the other end of the path.
This makes the point that optimizing your skimmer is very QTH- and propagation
zone- dependent. If you have a noisy QTH (like here) you need to do things that
reduce the noise on skimmer and on reception generally. I don't use RBN in
contests because for us out here, it is like drinking from a fire hose, and most
of the skimmer-dense east coast spots are completely irrelevant to San Diego
propagation. I use my local skimmer (because if I can hear 'em I can work 'em)
and Jack WA7LNW's up in a radio quiet zone, mile high in Utah, which has
similar, but not the same propagation as San Diego. (Even Bob N6TV's northern CA
skimmer has substantially different propagation than So. Calif. In any case, I
cannot hear or work many of the northern CA spots.) I filter my and Jack's
skimmers through VE7CC, and can always work almost everything spotted on my
bandmaps by these two skimmers.
Anyway, it is interesting to see what people are using and what their purpose is
for employing skimmers.
73, Larry N6NC
________________________________
From: David Gilbert <xdavid at cis-broadband.com>
To: skimmertalk at contesting.com
Sent: Sat, December 24, 2011 8:00:09 PM
Subject: Re: [Skimmertalk] Antennas for Skimmer radios?
Yes, path loss is, in most cases, symmetrical ... but the noise level on
each end (whether atmospheric or man made) is NOT likely to be the
same. VOACAP will show you that as well if you run the program for both
ends of the path using SNR as the variable. The S/N you get on one end
may have no bearing to the S/N you get on the other end even if the path
is symmetrical and the antennas on each end are identical. In any case,
the original comment from K3UK that I was replying to suggested that we
shouldn't necessarily try to optimize the receive antennas for CW
Skimmer because a good receive antenna was likely to produce spots we
couldn't work with our transmit antennas. That just doesn't seem at all
rational to me when there is no way of knowing what the conditions are
on the other end of the path.
Receive antennas and transmit antennas are NOT apples and apples. You
can get very good directionality out of a particular antenna and
therefore get very good signal/noise ratio, but that does not mean that
the antenna is efficient when transmitting. Think beverages and receive
loops.
Which receive antenna you use for CW Skimmer would of course depend upon
your purpose. If you are targeting a particular area for callsigns you
might prefer a directional antenna ... but it might not necessarily be
one that was also good for transmitting. If you want to monitor band
openings as the contest progresses you'd be better off with an
omnidirectional antenna. And if you want to feed CW Skimmer spots to
the RBN you might choose either, but more likely would choose an
omnidirectional antenna.
To regress a bit, K3UK based his premise on the statement:
"This based on the the theory ...if you hear
'em, you can work 'em."
That's backward anyway ... the old axiom is "You can't work 'em if you can't
hear 'em." Totally different, and would lead to a conclusion opposite of his.
Dave AB7E
On 12/24/2011 10:02 AM, H Lawrence Serra wrote:
> <Besides, you're talking apples and oranges. A receive antenna works
> <well when it maximizes the signal/noise ratio at this end of the path.
> <A transmit antenna works well when it maximizes the signal/noise ratio
> <on the far end of the path. Those are not at all the same things.
>
> Although there are skewed paths, and all send-receive paths aren't
symmetrical,
> actually, as a practical matter, they are generally the same-- apples for
> apples. If you look at VOACAP charts when doing antenna and terrain analysis,
> the take off (and receive) angles and the gain lobes generally benefit both
> incoming and outgoing signal strength.
>
> My point here is-- just like in contesting-- a mediocre omnidirectional
antenna
> is never a good idea, whether it's convenient to use or not. An active,
> omnidirectional antenna is convenient and easily matched across a broad band
of
> frequencies-- less work for mother. But for contesting, if you know where your
> bread and butter target areas are (producing most QSOs and MULTs) you want
> specialized directive gain antennas to amplify incoming and outgoing sigs to
> those target areas.
>
> Out here in San Diego I use my skimmer as a second op in assisted class
> contesting. I want my skimmer to hear the most Europeans (or JAs, or South
> Americans) it can, so I can bang down the N1MM bandmap and work them quickly
>for
> points before the thundering herd from the clusters arrives. So I will add a
> 2-el yagi with wide beam width aimed 045 to cover NA and EU, and the Pacific
> islands off the back. Ideally, I would have stacked yagis in those directions
>to
> choose upper, lower or both depending upon arrival angle, but there is not
room
> here for that. Even though a 2-el yagi is not optimal, from experimentation
out
> here I know adding one aimed in the bread and butter directions makes a big
> difference in what my skimmer hears.
>
> I suppose as a mere propagation tool, an omnidirectional antenna produces
> omnidirectional information. But even for propagation study purposes, rotating
> gain antennas (a rotating yagi, or switched four square or phased verticals)
> would make more sense because it would hear more.
>
> 73, Larry N6NC
>
>
>
>
> ________________________________
> From: David Gilbert<xdavid at cis-broadband.com>
> To: skimmertalk at contesting.com
> Sent: Sat, December 24, 2011 6:23:58 AM
> Subject: Re: [Skimmertalk] Antennas for Skimmer radios?
>
>
> Yes ... that is exactly what we want from CW Skimmers. We want to know
> who's on the air and whether they can be heard at a particular
> location. It's up to everyone else to try to work them.
>
> Besides, you're talking apples and oranges. A receive antenna works
> well when it maximizes the signal/noise ratio at this end of the path.
> A transmit antenna works well when it maximizes the signal/noise ratio
> on the far end of the path. Those are not at all the same things.
>
> Dave AB7E
>
>
>
> On 12/23/2011 7:27 PM, Andrew O'Brien wrote:
>> I guess this brings up the question about the purpose of the skimmer
>> antenna. It seems to me that an active antenna such as the ones
>> mentioned in this thread , receive better than the antenna to be used
>> when transmitting. I always assumed that a station's receiving
>> skimmer antenna should be generally reciprocal to the performance of
>> the transmitting antenna. This based on the the theory ...if you hear
>> 'em, you can work 'em. Super skimmer antennas churning out "spots"
>> for the world maybe useful , but is that what we want from skims ?
>>
>> Andy K3UK
>>
>>> On Tue, Dec 20, 2011 at 3:31 PM, John Reilly<reillyjf at comcast.net> wrote:
>>>> I'm using a Pixel Magnetic Loop (RF Pro-1B) mounted at 10 ft; however,
>>>> it is surrounded by 25 ft houses! I'm planning to move my loop up to 25
>>>> ft plus next Spring to see if getting it at or above the houses will
>>>> improve performance. I also have a Clifton Labs vertical, but it
>>>> doesn't seem to perform as well as the mag loop.
>>>>
>>>> I also studied the N6TV stats and asked K3LR what they were using --
>>>> vertical(s) (I assume they are active). I use a QS1R.
>>>> - 73, John, N0TA
>>>>
>>>>
>>>> On 12/20/2011 12:09 PM, H Lawrence Serra wrote:
>>>>> Pete N4ZR suggested I put this out to the group:
>>>>>
>>>>> I would like to hear from skimmer ops on what ANT systems they are using
> for
>>>>> their skimmers.
>>>>>
>>>>> I am in the SW corner of the US, on the wrong (west) side of close-by Mt.
>>>>> Soledad and have roof space-limited ANTs. I use a PA0RDT active mini-whip
>> ANT
>>>>> about 5 ft above my roof for my SDR-IQ radio which feeds the skimmer. I
was
>>>>> surprised to see from N6TV's RBN stats that I have the lowest SNR average
>> for
>>>>> signals of reported RBN skimmers, and post only 1/5 the spots N6TV had and
>>>> 1/10
>>>>> the spots WA7LNW had from my part of the country.
>>>>>
>>>>> I have tried putting my 2-el Steppir yagi pointed 045T on the skimmer when
>I
>>>> am
>>>>> not contesting, and even that little extra gain results in more skimmer
>> spots
>>>>> from NA and EU. My plan now is to find a used A3 tri-bander that I can cut
>>>> down
>>>>> to a 2-el due to space limitations and because I want a broad beam width.
I
>>>>> plan
>>>>> to use a coupler to feed both the active mini-whip and the 2-el yagi to
the
>>>>> skimmer's feedline, so I don't have to mechanically switch ANTs when
>> SkimScan
>>>>> switches to the low bands at night.
>>>>>
>>>>> Anyway, I would be interested in what SDR or other radio you use, and what
>>>>> ANT(s) you use for your skimmers.
>>>>>
>>>>> 73, Larry N6NC
>>>>> _______________________________________________
>>>>> Skimmertalk mailing list
>>>>> Skimmertalk at contesting.com
>>>>> http://dayton.contesting.com/mailman/listinfo/skimmertalk
>>>>>
>>>>>
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