[Elecraft] OT: Re: KPA500 mobile?

[Fred Jensen]

Well, one of the side benefits of this list ... lots of smart and 
knowledgeable people.  A summary and then it can pass into the archive ...

1.  The first of "my" tunnels is in Newcastle CA [between Auburn and 
Sacramento  on the old US40 and Lincoln Hwy route] and was constructed 
sometime around the end of the 19th/beginning of the 20th centuries.  
It's not quite 1/4 mile long.  There is no visible wire or radiax in 
it.  The hill it runs thru is full of water and you get leaked on when 
driving thru it, even in summer.

2.  In the early 80's, the company I worked for then had a contract to 
rehab the communications for the Bay Area Rapid Transit system.  We used 
a 300 ohm twinlead with a hollow core about 2 1/2 in in diameter along 
the ceiling of the tunnels and underground sections.  It was 150 MHz 
land mobile stuff and the twinlead was fed from a combiner that put 5 or 
6 transmitters into it [train control, fire, security, etc.]  It worked 
very well. Aligning the combiners [which actually looked a bit like a 
still [:-) ] was a bear in the equipment spaces in the tube under SF Bay 
but it worked well.  They also wanted 800 MHz simulcast throughout the 
service area, a requirement probably still waiting for a real solution.

3.  Other than under bridges, in canyons, beside heavily forested roads, 
and in the garage, where it's obvious the path to the satellite(s) is 
blocked, we don't experience any XM drop outs. She's going to drop the 
subscription, it's expensive and my new Honda Ridgeline has become our 
travel vehicle, but she's had it since 2013.

4.  I've wondered if there wasn't some sort of waveguide effect in 
tunnels.  For BART, one of the many problems we had with simulcast was 
that it leaked into the tunnels, even as far as the bottom of the 
Transbay tube.  I don't know the XM satellite frequencies but I thought 
they occupied some spectrum abandoned by the Cellphone industry.

5. [Bonus Factoid]: The pine forests of the Southeast US are opaque to 
800 MHz.

Thanks for all the ideas and peripheral info.

73,

Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn



On 4/15/2017 10:40 AM, Clay Autery wrote:
> I would think it would depend almost entirely on the orientation of the
> tunnel...   (and satellite reception azimuth).
>
> First, the longest of those two tunnels is only 425 feet or so.  The
> other is significantly shorter (southbound).
> The tunnels are oriented generally north/south which is the preferred
> direction IF you have to monitor geosynchronous satellite transmissions
> from overhead...  sort of).
> You are right on the edge of a large body of water, which while not
> brine, has better conductivity than the soil around the lake.
> Significant potential for reflections off the high ground on almost all
> sides....
>
> Don't know where that first tunnel is, so I can't comment.  But if you
> gotta hear in a tunnel.... those two would be great candidates...
>
> 73,
>
> ______________________
> Clay Autery, KY5G
> MONTAC Enterprises
> (318) 518-1389
>
> On 4/14/2017 10:47 PM, Fred Jensen wrote:
>> Semi-related curiosity regarding shielding.  My wife's car has
>> Sirius/XM radio.  It usually loses contact with the satellite driving
>> under Interstate bridges and the like.  Likewise in the garage.  OTOH,
>> at our previous home there was a tunnel through a small hill, perhaps
>> 1/4 mi long.  The XM worked fine through it. There are a pair of
>> tunnels at Cave Rock next to Lake Tahoe through a granite mountain.
>> XM works fine through them too.  Anyone know why?
>>
>> 73,
>>
>> Fred ("Skip") K6DGW
>> Sparks NV USA
>> Washoe County DM09dn
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