[KL7AA] Pilot Station school club station

Fri Oct 30 11:36:12 EDT 2015

True enough, but one of the advantages of a low horizontal loop antenna 
(approx 1 wavelength overall circumference, about 15 to 25 feet high) is 
that such antennas tend to radiate (and receive) "straight up" , so 
things like close in hills are not usually a problem.

Such an antenna operates as a NVIS  (Near Vertical Incidence Skywave) 
system, and as such sends a signal straight up to the ionosphere, where 
it is reflected right back down, and in the process covers a 300 to 500 
mile diameter circle centered on the originating station.   The 
performance of such an antenna can be as much as a 40 dB improvement in 
signal to noise ratio over a conventional dipole antenna at moderate 
heights.

At the same time, the antenna pattern for received signals is such that 
it has very little response to low angle signals, and thus rejects most 
man-made noise.

NVIS antennas of this type are used with great success on the 75 meter 
evening nets.  These are the Alaska Snipers net,  3920 kHz, 6:00 PM 
local time,   and the Motley Group, 3933 kHz 9:00 PM local time, both 
daily.

This same type of antenna has shown good performance for the 40-meter 
"Bush Net" , which meets daily at 8:00 PM on 7073 kHz.

If anyone needs construction details, I will be happy to provide them.

- Jim, KL7CC

On 10/30/2015 7:11 AM, David Heimke wrote:
> All good, but also Pilot Station is at the bottom of a hill and up against
> some steep terrain.  Something to keep in mind.
>
> -----Original Message-----
> From: KL7AA [mailto:kl7aa-bounces at mailman.qth.net] On Behalf Of Jim Wiley
> Sent: Friday, October 30, 2015 2:33 AM
> To: w5gfr1 at gmail.com; kl7aa
> Subject: [KL7AA] Pilot Station school club station
>
> Gordon -
>
> Hello from Anchorage.  It is encouraging to hear that you are taking on
> the project of assisting the students at the Pilot Station school.   I
> spent a fair amount of time in Western Alaska during the mid 60's, so
> perhaps some of my experiences will be of use to you.
>
> First off, Pilot Station (and most of Western Alaska) is part of an area
> where communication between "there" and the south-central portion of Alaska
> ("here") is difficult at best.  There are radio clubs in Nome and Bethel,
> both of which have a fair number of amateur radio operators.  It might be
> advantageous for you to contact some of those operators so as to establish
> some sort of "local area" communications net on the 75 or
> 40 meter bands.
>
> For both 75 and 40 meters, low horizontal loop antennas will provide
> fairly reliable "local" HF communications.   It will perform well for
> contacts with stations within 300 to 500 miles from your location.
>
> However, there are relatively few stations within this range, so contacts
> may still be somewhat difficult to come by.  When I lived in the Cape
> Romanzof area in the 60's, I actually had better luck with contacts with
> Russian and Siberian stations than I had with USA stations, but then I
> didn't have the advantage of knowing about the low horizontal loop concept.
>
> Contacts to South-Central (Anchorage, Palmer-Wasilla, Fairbanks, Kenai
> Peninsula),  on 75 and 40 meters, indeed any band,  will likely be difficult
> because of distance, and may be limited to Winter months only.
>
> Regular contacts using the 20 meter band, and 17 somewhat less dependable
> contacts on the 17 meter band will be possible, even plentiful, with the US
> West coast, Japan, and other Pacific Islands during most of the year.
> Because of the declining solar cycle, contacts on the 15, 12, and 10 meter
> bands will be difficult, and there may be
> times  when no stations will be heard.   I might even recommend that you
> put up a single-band (20 meters only) antenna.   Notice that I have not
> mentioned South Central Alaska for these bands.
>
> You mentioned that the Pilot Station school has a vertical antenna that
> does not seem to work very well.   One absolutely essential point when
> using a vertical antenna is that it must have a good ground radial system
> associated with the radiating element.  The absolute minimum ground radial
> system would be at least 16 radials, 32 will be better, with each radial
> being at least a quarter-wavelength long at the lowest band in use.  There
> is no room for a compromise ground screen when using a 1/4 wave vertical
> antenna.  Yes, some stations "get by" with much less, but they are typically
> (1) located much closer to the equator, and
> (2) much closer to other stations.  A station set up away from neighboring
> communities or at an extreme northern latitude (or both) absolutely must
> have a good quality grounding screen if they are to be successful.
>
> One possible alternative would be to use a half-wave radiator, which will
> ease the requirements for a radial system, but it will still not eliminate
> the need for a first-class ground system.
>
> Obviously, a half-wave radiator must be fed with a matching network, but
> that is fairly easy to accomplish.   Additionally, the half-wave
> configuration allows the use of elevated radials, and typically only 4 to 8
> are needed.  The radials operate somewhat differently when used with a
> half-wave radiator.  In this case, they are used to "decouple"
> the antenna from ground, as opposed to substituting for the missing half of
> the driven element.
>
> Next, using multiple vertical radiators gives you both "gain" over a
> half-wave dipole and the option of instant pattern switching.  A 4-element
> vertical antenna using the proven "4-square" configuration fed with
> Wilkinson dividers is an excellent performer, often (but not
> always) outpacing Yagi designs.  This configuration can be made very
> resistant to adverse environmental conditions, which are a constant problem
> in Western Alaska.  The use of a "pattern switch" allows instant changes of
> direction and avoids the problems associated with a mechanical rotor.
>
> Finally, keep in mind that a vertical antenna will  always be a low-angle
> radiator.  That means that it will perform best with contacts that are 800
> miles or more distant from your station. That means no Alaska contacts (most
> of the time)  with a vertical.  Not that closer range contacts will be
> impossible, just that signals may be weaker
> to_much _weaker the closer they are to your base of operations.   That
> is why I suggest the horizontal loop for contacts within Alaska.
>
> I hope this has been helpful.
>
> - Jim, KL7CC
>
>
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