Hopefully, you made it to Holiday World in Southern Indiana on your trip to
ride "The Voyage" roller coaster. We just recently had a 2-day coaster
enthusiast event there, called "HoliWood Nights", where we had two nights of
in-the-dark, full-throttle ERT (Exclusive Ride Time, after the general public
was kicked out for the evening) rides through the Indiana woods. After breaking
in all day for a couple of days, by 11-12:00 P.M., it was flying (as were the
two other wooden coasters, "The Raven" and "The Legend".) Maybe you were there?
Redefines the words "extreme ride". I have to go there at least a couple times
each Summer. And to Silverwood (in Idaho).
Truly Amazing.....
K7LJ
-----Original Message-----
>From: jeremy-ca <km1h@jeremy.mv.com>
>Sent: Jun 15, 2007 10:42 AM
>To: Ian White GM3SEK <gm3sek@ifwtech.co.uk>, towertalk@contesting.com
>Subject: Re: [TowerTalk] Balun question shield leakage
>
>Hi Ian, nice to here from you, its been ages!
>
>As far as the ship problem "Not at all" still holds. The network did not use
>PL259's, they are not even constant impedence. The installer used inferior
>cable but the proper F connectors for that cable and the ones we checked
>were all installed correctly.
>
>I was actually looking foreward to the catapult; I had been thru it 4-5
>times while on active duty and loved it. While traveling around the US on
>business I also made it a point to enjoy the latest and baddest roller
>coasters.
>
>
>----- Original Message -----
>From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
>To: <towertalk@contesting.com>
>Sent: Friday, June 15, 2007 4:39 AM
>Subject: Re: [TowerTalk] Balun question shield leakage
>
>
>> jeremy-ca wrote:
>>>>>We quickly discovered that the installing contractor ignored the specs
>>>>>and
>>>>>used cheap unbranded RG-11 with what looked to be around 75-80% shield
>>>>>coverage.
>>>>
>>>> Hmm. that's up to 450MHz, where the holes in the shield start to be
>>>> significant size (compared to HF) and, is it possible that some of the
>>>> problem might also be crummy connectors and crummy installation
>>>> practice?
>>>
>>>
>>>Not at all. Besides the range above 200 mHz wasnt even in use yet and
>>>most of the computer activity was terminal to CPU over modems in the
>>>5-50 mHz range.
>>
>> Helluva story, Carl! (It must really focus the mind to know that, one
>> way or another, you were going to leave that ship by catapult. )
>>
>> But Jim made two separate points there: the % shield; and also the
>> possibility of crummy installation practices. I don't believe a "not at
>> all" reply can cover them both.
>>
>> A 75-80% shield rating is only the visual % coverage. Its RF shielding
>> effectiveness varies with frequency. The lower in frequency you go, the
>> smaller the holes in a 75-80% shield become in terms of wavelength, and
>> the *more* effective the RF containment becomes. So leakage through the
>> shield at lower frequencies becomes *less* likely to account for RFI
>> running riot all over the ship.
>>
>> But it seems *very* likely that the bozos who used poor-quality cable
>> had also left behind several PL259s with the shields twisted right off.
>> Every one of those shielding gaps would transform the "shield" into a
>> fully functioning antenna with RF currents running all along the
>> outside.
>>
>> It seems quite likely that most of the solution was your all-round
>> better workmanship.
>>
>>
>>
>> On a more general point, I don't think we can ever dump lab tests and
>> practical performance into two separate compartments. Whenever we see a
>> difference, we've GOT to get our heads around some bigger picture, and
>> figure out the reasons why.
>>
>>
>> Finally, some practical shielding results from the different perspective
>> of European UHF TV:
>> http://www.wrightsaerials.tv/coaxcablequalityhmdim.htm
>>
>> Check out the whole www.wrightsaerials.tv site, and don't miss the
>> Rogues' Gallery!
>>
>>
>> --
>>
>> 73 from Ian GM3SEK
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
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>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
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