Hi Roger!
Good to hear you again. All you say is true with HF antennas. On the
other hand, what about VHF and higher?
Looking around I've found a bunch of stuff on optimizing and
qualifying antennas by using solar/cosmic noise. Every explanation
(makes a bunch of sense) that I've read says that the characteristics
(f/b, g/t)of the antenna are necessary to proceed with the
measurements.
As it's been said bunches of times, the figures provided by
manufacturers are suspect at best.
K3NG has an arduino rotator control project that has a sun tracking
feature, which almost automates the qualification process, if I
understand the process correctly.
What to do?
Constructing an antenna range is a possibility. There is a "how-to" in
a piece of software called HDL (horn, dish, lens).
Is this worth it? Time is fun to waste but I'd like something to show for it.
Norm n3ykf
On Thu, Dec 11, 2014 at 7:51 PM, Roger (K8RI) on TT
<K8RI-on-TowerTalk@tm.net> wrote:
> As I see it:
> There are several absolutes in antenna gain and many probably, might, maybe,
> could be attributes.
>
> The two absolutes are the 2.1 db dipole to Isotropic source (I've been a ham
> since 61 and the books have always listed that figure) and gain measurements
> are only true for the test range where they were made. Hence even though
> the manufacturer may be honest and make an honest attempt at measuring gain
> figures in all axises, comparing one manufacturers antennas against another
> manufacturers antennas from advertized data only gives ball park figures and
> tells me little about how they will perform in my installation.
>
> Doubling the number of antennas theoretically doubles the gain which is an
> additional 3 db for each doubling although it's unlikely due to losses in
> feeding and matching that this will be achieved. Losses in the additional
> coax can be substantial.
>
> Even with computer modeling of the installation, the inputs must be accurate
> and few if any know the ground characteristics near or far to any great
> precision.
>
> The radiation pattern at vertical angles is a crap shoot. You are playing
> the percentages for atmospheric conditions that will match the maximum
> signal radiated will be at the most desirable angle to match those
> conditions. That's why the contesters have stacks that allow them to select
> the antenna height that lets them put the maximum signal into the desired
> range/distance.
>
> As most of us have both budget and land constraints that limit us to the
> number, size, and height of our antenna(s) It's unlikely we can depend on
> equaling the performance in the advertized figures. Often for 40, 75, and
> 160, a simple wire antenna, or vertical will out perform all but the largest
> and/or sophisticated antenna or array.
>
> I've had extremely good luck with sloping, center fed, half wave dipoles.
> compared to some stations running Yagi antennas at reasonable heights. Many
> times the first word in the response to my call, is "Wow". Yes, I do run
> QRO, but the best sounding signal out of my tetrode amp is at, or around the
> legal limit so there is little incentive for pushing beyond the legal limit
> for that extra 1 db and those tubes are expensive.
>
> --
>
> 73
>
> Roger (K8RI)
>
>
> ---
> This email has been checked for viruses by Avast antivirus software.
> http://www.avast.com
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|