[TowerTalk] Calibrating antenna direction and using chokes with a beam

[K8RI]

On 10/25/2012 9:46 PM, Dan Hearn wrote:
> Here is a system which works for me and others in our ham club.
> Look in the newspaper for the times of sun up and sun down. Calculate the
> hours and minutes between. Divide this by 2 and that is the time of exact
> noon. At that time, look at the shadow of your tower or a vertical post and
> the shadow points to true north. Hopefully your newspaper has sunup/sundown
> times as ours does.

They are on the Internet for virtually any location.  Enter your 
coordinates and the times will come up.
Just do a google search on sun rise and sun set for your coordinates.

However, unless really directionally challenged, "over that way" is 
normally close enough for a 3L beam.  For dipoles, "over that way" is 
way more precision than required.

I've never bothered to get much more precise than "over there" even with 
a 7L monobander.


> 73, Dan, N5AR
>
> On Thu, Oct 25, 2012 at 5:58 PM, Mike <noddy1211 at sbcglobal.net> wrote:
>
>> There is going to be a website that will give your declination relative to
>> Magnetic North in ZL, I would go with that.  In California here finding a
>> strong station and adjusting the beam would be futile as the signal maybe
>> following a crooked path.  In California we are pretty much at 18 degrees
>> off Magnetic north, so it would make a difference to make the adjustment
>> for

All navigation charts I've seen (I'm a pilot) have magnetic deviation 
given for all areas on the chart. Or better yet, use Google Earth for 
your location. OTOH there are sites that will do it for zip code in the 
US and you can pick any specific date.

Here in Central Michigan I'm roughly 34 37 N by 84 20W the declination 
is about 7 4 W, negative.  Use a compass and subtract about 7 degrees.

In CA with 18 degrees (actually far N CA) positive you take the compass 
reading and "ADD" 18 degrees.

With the compass you have to be aware of local deviations at ground 
level.  The chart at the "compass store" completely ignores these while 
aviation charts do not.

However I like the sunup to sundown time divided by two and look at the 
shadow. Drive a stake in the ground at the tip of the shadow. (Not 
necessarily noon)  You can't get much more precise than that even with 
precision instruments. Just remember the shadow points North when you 
are North of the equator and South when South of the equator.

Done by zip code:  It'd be more precise by actual coordinates.
Today our sunrise is 804AM and sunset is 6:37 PM (1837). 
1837-804=1033/2=516.5  804+516.5=1320.5 or 1:20:30 PM for due North.

73

Roger (K8RI)


>> True North.
>>
>> You government is sure to have a website, but if not any serious navigation
>> website in ZL will have True north relative to your position.  Even my car
>> manual shows true north so you can set the car compass.
>>
>> Mike
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
>> Rick
>> Kiessig
>> Sent: Thursday, October 25, 2012 5:04 PM
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] Calibrating antenna direction and using chokes with a
>> beam
>>
>> I finished building my antenna (UltraBeam UB-50) and installing it on the
>> tower yesterday. Everything went reasonably smoothly.
>>
>>
>>
>> I tried to align the boom with true north before bolting it to the mast,
>> but
>> the result seems to be off by at least 10 degrees or so. I'm familiar with
>> the techniques for determining true north (although Polaris isn't visible
>> in
>> ZL), but I'm wondering if it's possible to do a more accurate calibration
>> by
>> measuring signal strength from a strong broadcaster with a known location
>> and a near-constant signal strength, over a range of azimuths. Then use the
>> center azimuth between two equal near-nulls on either side of the peak as
>> the calibration point. If this is viable, any suggestions for good station
>> to use as a target? Does frequency matter?
>>
>>
>>
>> What's the Best Practice with regard to using common mode chokes on the
>> feedline coming from a beam? I grounded the shield at the tower and again
>> outside the shack, with a lightning arrestor as well at the latter.
>>
>>
>>
>> Can't say I'm too happy with the way my rotator loop came out. I wrapped it
>> around the mast on top of the thrust bearing, but the TB has some bolts
>> that
>> stick out. Hopefully they won't grab or scrape the coax too much.
>>
>>
>>
>> I also have a UHF connector on one segment of LMR-600 that didn't seem to
>> go
>> onto a barrel connector as well as it should have. They are odd connectors
>> that have a very snug rotating collar, rather than the kind I'm used to
>> that
>> have a little up-and-down give in the direction of the cable. The center
>> pin
>> went in roughly 4 or 5 mm, but the collar hung up after only about two
>> turns. It's very snug (too snug), so I think the threads may have crossed.
>> I'm reluctant to take it apart now, though, since if the threads are
>> crossed, I may never get it together again, and it's a long segment of
>> LMR-600, which I don't have the tools or skills to replace connectors
>> myself. TDR on the line looks OK, and I did some TX tests at low, medium
>> and
>> high power, and didn't see any problems. I imagine I'm just asking for
>> trouble if I don't fix it, though, right?
>>
>>
>>
>> 73, Rick ZL2HAM
>>
>>
>>
>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2012.0.2221 / Virus Database: 2441/5353 - Release Date: 10/25/12
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
>