Peter Voelpel wrote:
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of jimlux
> Sent: Donnerstag, 30. Oktober 2008 15:21
> To: Towertalk Reflector
> Subject: [TowerTalk] repeating the N0AX/K7LXC studies
>
> Is there any interest in repeating the studies? It's a huge amount of work,
> but technology has advanced, both in antennas and in measurement technique.
>
> Seems to me that the big resource consumer is getting and assembling the
> antennas (and then disassembling and shipping back to whoever loaned/rented
> them). The thought of a multi week antenna assembly fest makes my
> fingertips hurt to contemplate it.
>
> With a bucket truck and suitable test site (which I might happen to have
> available) the antenna raising/lowering would be pretty speedy. Maybe you
> could do one antenna a day. (From sitting on the ground next to the tower,
> hoisted up and mounted, spun for the measurements, then brought down).
>
> Maybe a temporary tower or a crane.. Now that I think about it, the latter
> sounds attractive. You could put a rotator with a sort of universal plate
> mount on the top (or in a 120 foot telescoping boom lift), bring it to the
> ground, bolt the antenna on, raise it up.(the bucket truck is controllable
> from the ground) No high work at all (which is always slow). It's not all
> that expensive to rent a lift for a week.
>
>
> (or actually, we essentially have this on the antenna range at JPL..A big
> boom that can erect and has a precision rotator on the end of it. We use it
> for testing VHF and UHF antennas with a huge log periodic or horn as the
> probe. I wonder if we could permission to use it?)
>
> Jim, W6RMK
>
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> If not having the 2nd antenna in the mainlobe, either to receive the test
> signals or to transmit one, all results well be misleading and it might
> happen that the worst antenna gives the best result.
> That 2nd antenna postion must be pretty heigh.
> Lets say the antenna to be tested is at 10m height for the 20m test, then
> the other antenna 100m away must be about 55m up!
>
The advantage of living in Southern California is that we have lots of
really tall, steep sided mountains. It's easy to arrange a probe antenna
a few km away that's essentially on a 100s of meter high tower.
Or, you do the NBS/NIST reflection range thing and do the measurements
at multiple heights and distances over the measurement range.
For instance, at JPL, our range sits on top of a very steep sided knife
edge ridge above the lab, several hundred meters above the surrounding
terrain in most directions. We have transmitter sites on hillsides or
tops several km away over a valley. Not ideal for HF, because there IS
still stuff around, but pretty good. At least there's airconditioning
and bathrooms and the cafeteria.
But, we could also go out to some garden spot like Danby dry lake, which
is almost perfectly flat and uniform for some 10s of km in all
directions. There's a 3000m high mountain range adjacent with roads on
which a team could operate a HF source for testing. However, Danby (and
places like it) are horrible places to spend any amount of time (I used
to go out there when I worked for the special effects company to shoot
car commercials, etc.)
Jim, w6rmk
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