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'[OT]: BGMicro GPS recievers'
2002\07\12@090413 by s.hutch

picon face


I bought two of the V5.10 units. Flashed them OK using 34057-62 which is NMEA
at 4800BPS, 8N1 (my sticker on the bottom had 34057-61)and used gpssk.exe from
http://www.shelor.net/Trimble_GPS site by Herbert Graf. The units communicate
with gpssk (after adjusting baud rate and protocol). Both units do not see any
satellites and all of the parameters are zeros in the upper window of gpssk. I
switched antennas around as well. Anything else I can try before sending them
back to BGMicro?


hutch

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2002\07\12@094304 by Herbert Graf

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> I bought two of the V5.10 units. Flashed them OK using 34057-62
> which is NMEA
> at 4800BPS, 8N1 (my sticker on the bottom had 34057-61)and used
> gpssk.exe from
> http://www.shelor.net/Trimble_GPS site by Herbert Graf. The units

       Actually that one isn't my site.

> communicate
> with gpssk (after adjusting baud rate and protocol). Both units
> do not see any
> satellites and all of the parameters are zeros in the upper
> window of gpssk. I
> switched antennas around as well. Anything else I can try before
> sending them
> back to BGMicro?

       How long have you let them sit? Do they have a completely unobstructed view
of the sky? The whole sky? Also do you have the Antennas pointed the right
way? (The mounting points face the ground). I have noticed that they won't
do anythign if they are too close to the ground, try putting them on a
cardboard box, see if that helps. TTYL

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2002\07\12@134447 by Jim

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Are you living/testing these uits directly in the
field of view of a PCS (1800MHz) site?

Jim


----- Original Message -----
From: <spam_OUTs.hutchTakeThisOuTspammindspring.com>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Friday, July 12, 2002 8:02 AM
Subject: [OT]: BGMicro GPS recievers


>
>
> I bought two of the V5.10 units. Flashed them OK using 34057-62 which is
NMEA
> at 4800BPS, 8N1 (my sticker on the bottom had 34057-61)and used gpssk.exe
from
> http://www.shelor.net/Trimble_GPS site by Herbert Graf. The units
communicate
> with gpssk (after adjusting baud rate and protocol). Both units do not see
any
> satellites and all of the parameters are zeros in the upper window of
gpssk. I
> switched antennas around as well. Anything else I can try before sending
them
> back to BGMicro?
>
>
> hutch
>

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2002\07\12@141246 by s.hutch

picon face
I do not see any towers around. I drove in to work with the antenna on the
dashboard, to give it some variety of sky...but only for 0.5 hrs worth. Maybe
I will park in an unused field for a few hours and take a nap waiting for it
to get a fix ;-). My antenna has a adhesive pad on the bottom (I assume that's
the bottom). Will 2 AA batteries do for the backup voltage?

hutch

On Fri, 12 Jul 2002 12:44:17 -0500 Jim <jvpollspamKILLspamDALLAS.NET> wrote:

Are you living/testing these uits directly in the
field of view of a PCS (1800MHz) site?

Jim


{Original Message removed}

2002\07\12@143822 by Herbert Graf

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-----Original Message-----
> From: pic microcontroller discussion list
> [.....PICLISTKILLspamspam.....MITVMA.MIT.EDU]On Behalf Of Jim
> Sent: Friday, July 12, 2002 13:44
> To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject: Re: [OT]: BGMicro GPS recievers
>
>
> Are you living/testing these uits directly in the
> field of view of a PCS (1800MHz) site?

       I didn't know that would be a problem? TTYL

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2002\07\12@144032 by Herbert Graf

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> I do not see any towers around. I drove in to work with the antenna on the
> dashboard, to give it some variety of sky...but only for 0.5 hrs
> worth. Maybe
> I will park in an unused field for a few hours and take a nap
> waiting for it
> to get a fix ;-). My antenna has a adhesive pad on the bottom (I
> assume that's
> the bottom).

       That "adhesive pad" IS the antenna, I think you've got your antenna pointed
the wrong way. The black mount part should face the ground, the pinkish
square in the middle of the silver plate IS the antenna (it is covered by a
white foam on one of my antenna's but is bare on the other), and should be
facing straight up.

> Will 2 AA batteries do for the backup voltage?

       The spec is 3V, 2AA's, assuming they are new should be OK. I'm using a 3V
lithium cell from a computer. TTYL

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2002\07\12@150323 by Jim

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I notice a problem with an OEM Motorola
unit that I have - the data starts to
degrade near a *known* active PCS site
that I have occasion to drive by ...

(GPS: 1575.42 MHz versus 1800/1900 MHz for PCS)

Jim

----- Original Message -----
From: "Herbert Graf" <mailinglistspamspam_OUTFARCITE.NET>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Friday, July 12, 2002 1:36 PM
Subject: Re: [OT]: BGMicro GPS recievers


> {Original Message removed}

2002\07\12@151221 by Herbert Graf

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> I notice a problem with an OEM Motorola
> unit that I have - the data starts to
> degrade near a *known* active PCS site
> that I have occasion to drive by ...
>
> (GPS: 1575.42 MHz versus 1800/1900 MHz for PCS)

       Hmm, interesting, I haven't noticed a similar effect traveling around my
area (which is at times adjacent to a 1900MHz PCS site), perhaps the
Motorlla module hasn't slightly looser front end filtering? Interesting.
TTYL

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2002\07\12@151806 by Jim

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Could be - I haven't explored the phenom
extensively, but noticed that the Moto
didn't perform as *crisply* around a
particular PCS site a couple of years
back. This particular Moto unit also
predates the fanout of PCS here in the
states ...

Jim

{Original Message removed}

2002\07\13@163233 by Benjamin Bromilow

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What's the general conscensus on these modules then? I'm keen not to miss
out ;) but if they are unreliable.....

So the general idea is
1) they need an unrestricted view of the sky
2) you have to leave them for a while to get a fix on the satellites- 5mins?
10 mins? longer?
3) ???

I'd like to fix one in my new kit car but if the LCD is going to display
"please wait" most of the time I'll make something else instead....

Ben

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2002\07\13@165201 by Michael Pettersson

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> What's the general conscensus on these modules then? I'm keen not to miss
> out ;) but if they are unreliable.....

I have today installed one in my car.
I'm using a different antenna then the one supplied because
the one I have have has a better housing.

> So the general idea is
> 1) they need an unrestricted view of the sky

Every GPS antenna needs this. I do not know if
these needs more then others. I have used the same antenna I'm now
using with another module and on the same spot.


> 2) you have to leave them for a while to get a fix on the satellites-
5mins?
> 10 mins? longer?

After a complete power down.. Could be an hour.
But when it is up and running it continuously transmits position just fine.

> 3) ???
>
> I'd like to fix one in my new kit car but if the LCD is going to display
> "please wait" most of the time I'll make something else instead....

Make sure the GPS always is "on". The power used by this module
shouldn't effect the battery on your car when you not use it.


Michael

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2002\07\13@170045 by Herbert Graf

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> What's the general conscensus on these modules then? I'm keen not to miss
> out ;) but if they are unreliable.....

       The ones I have are reliable.

> So the general idea is
> 1) they need an unrestricted view of the sky

       As with any GPS unit, they will tolerate some obstruction but you can
forget about getting good fixes all the time say at the heart of downtown
Toronto.

> 2) you have to leave them for a while to get a fix on the
> satellites- 5mins?
> 10 mins? longer?

       About 5 minutes, and only after a total power failure, if the battery
backup is maintained they reaquire quicker.

> 3) ???
>
> I'd like to fix one in my new kit car but if the LCD is going to display
> "please wait" most of the time I'll make something else instead....

       As long as you don't remove all power from them they come back with 5
minutes, often quicker. TTYL

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2002\07\14@103905 by Philip Pemberton

face picon face
Can anyone give me a BGMicro order code for these GPS modules? I'd love to
get one to play with before BG sell them all...

Later.
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2002\07\14@115541 by Herbert Graf

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> Can anyone give me a BGMicro order code for these GPS modules? I'd love to
> get one to play with before BG sell them all...

       Hmm, looks like it's to late. The part number was ACS1394, it was located
on the "last minute additions" page, but it's not there anymore and a search
reveals no match. TTYL

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2002\07\15@024900 by Pic Dude

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Uh-oh... I feel a GPS black-market coming on.  I'll have
to hang on to mine for a bit then. :-)

Cheers,
-Neil.



{Original Message removed}

2002\07\15@051338 by Alan B. Pearce

face picon face
>So the general idea is
>1) they need an unrestricted view of the sky
>2) you have to leave them for a while to get a fix on
>the satellites- 5mins? 10 mins? longer?

Well these two factors are common to any and all GPS units. Typically thay
will not work inside a building because the building materials have too high
an absorption at the 1.5something GHz they use, and it takes a while for the
receiver correlator to lock onto enough satellites in view to obtain an
accurate position fix.

From a cold start, most documentation seems to talk in terms of 10 minutes
to get an accurate fix, but if it is possible to feed the receiver some info
about its current position first, then this can be reduced.

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2002\07\15@052814 by Benjamin Bromilow

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Looks like I might have missed the boat :(
The units aren't in the new catalogue and they're no longer on the "last
minute additions"....
Oh well, c'est la vie

Ben

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2002\07\15@053851 by Alan B. Pearce

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>Looks like I might have missed the boat :(
>The units aren't in the new catalogue and they're no
>longer on the "last minute additions"....
>Oh well, c'est la vie

It can be worth checking ebay and the like.

Picked up a Trimble OEM unit for about 2/3 the price of the lowest cost new
unit I have found in the UK. Yet to take delivery of it though, the seller
is as slow as .....

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2002\07\15@063958 by Michael Pettersson

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Does anyone know if the BGMicro GPS transmitts information on speed?
I'm using it in NMEA mode and I get the location transmitted but
it seems that I don't get the speed informationen (and heading).

Is it possible to set what data the gps should transmit?

/regards

Michael Pettersson
sm6xog

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2002\07\15@095509 by M. Adam Davis

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The GPSSK has an NMEA mode that allows you to set what strings it should
ask for each second.

IIRC the sveesix can be programmed to automatically send certian NMEA
straings every second as well.

You only get meaningful heading and speed when moving, but it is there.

-Adam

Michael Pettersson wrote:

{Quote hidden}

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2002\07\15@122442 by Michael Pettersson

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It looks like that the GPS does not send speed information.

Is it possible to make it transmitt this information.
If it is, how do I do it and with what software?

/regards

Michael
sm6xog


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2002\07\15@162346 by Peter L. Peres

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On Mon, 15 Jul 2002, Alan B. Pearce wrote:

>>So the general idea is
>>1) they need an unrestricted view of the sky
>>2) you have to leave them for a while to get a fix on
>>the satellites- 5mins? 10 mins? longer?
>
>Well these two factors are common to any and all GPS units. Typically thay
>will not work inside a building because the building materials have too high
>an absorption at the 1.5something GHz they use, and it takes a while for the
>receiver correlator to lock onto enough satellites in view to obtain an
>accurate position fix.

The funny part being that they won't work even inside the attic of a wood
thatched house, even less in a tile hatched one. I don't know if it's the
nails, or the humidity and treatment chemicals in the wood. Trees stop it
pretty well (ONE tree should be enough). Of course I think that the
military have means to get better signal. I don't think that they need to
poke a hand out of a trench under fire to get a fix ;-).

Peter

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2002\07\15@185446 by Jim

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Peter wrote:

  "The funny part being that they won't work even
   inside the attic of a wood thatched house"

Do you have the antennas pointed up? <grin>

There has to be a reason - since in my wood-frame
house my old '94 era Magellen will lock and display
position *inside* - as will several JRC OEM GPS
modules that I've worked with.

I have found that the 'thermal reflective plastic
window film' (I believe they use some sort of
vapor-deposited metal on this co-called 'plastic')
used on the windows of tall modern office buildings
won't pass a GPS signal - I had to look for a break
in the 'plastic' in order to test GPS devices in the
office!

Jim


{Original Message removed}

2002\07\15@210426 by M. Adam Davis

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Peter L. Peres wrote:

>The funny part being that they won't work even inside the attic of a wood
>thatched house, even less in a tile hatched one. I don't know if it's the
>nails, or the humidity and treatment chemicals in the wood. Trees stop it
>pretty well (ONE tree should be enough). Of course I think that the
>military have means to get better signal. I don't think that they need to
>poke a hand out of a trench under fire to get a fix ;-).
>
>Peter
>
>
>
The sveesix I got was from an auto application.  Being 6 channel (IIRC)
units and probably made for auto applications they expect a good view of
the sky.  Once they get a good lock and get a current almanac they work
great, though.

The sveesix is not exactly a high performance GPS unit.

-Adam

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2002\07\16@032929 by Alan B. Pearce

face picon face
>Peter wrote:
>
>   "The funny part being that they won't work even
>    inside the attic of a wood thatched house"
>
>Do you have the antennas pointed up? <grin>
>
>There has to be a reason - since in my wood-frame
>house my old '94 era Magellen will lock and display
>position *inside* - as will several JRC OEM GPS
>modules that I've worked with.
>
>I have found that the 'thermal reflective plastic
>window film' (I believe they use some sort of
>vapor-deposited metal on this co-called 'plastic')
>>used on the windows of tall modern office buildings
>won't pass a GPS signal - I had to look for a break
>in the 'plastic' in order to test GPS devices in the
>office!

Any timber is a good absorber of RF signals, even down to HF. The New
Zealand Forestry Service used to have mobiles on their vehicles somewhere in
the 5-8MHz region IIRC, and noticed significant reductions in signal
strength out in the pine forests. The actual losses will depend on a number
of other factors such as moisture content, and exact wood type, but it will
always be there.

A typical microwave absorption (not a power load) consists of a wedge shaped
piece of wood in a lump of waveguide. I have often figured that the best way
to make a stealth motor vehicle to minimise detection by traffic speed
cameras is to have the panels covered by wedges of a nice soft wood like
balsa, shaped into wedges that would act as waveguide beyond cut-off at the
relevant frequencies :) OK the car would look odd, but you wouldn't get many
traffic tickets. :)

If you are able to receive the GPS signal inside your house then the
cladding on the house must be something other than wood.

There is of course another gotcha in all this. I am not sure what the
absorption frequency of water is, but I suspect that the GPS transmissions
are not in this range, as it would foul up location finding in wet weather
if it was, and as this is a military originated system, I suspect they would
choose a frequency with minimal losses under these conditions.

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2002\07\16@135141 by miked

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Should be in the VTG message, in knots and km/hr
>
> Does anyone know if the BGMicro GPS transmitts information on speed?
> I'm using it in NMEA mode and I get the location transmitted but
> it seems that I don't get the speed informationen (and heading).
>
> Is it possible to set what data the gps should transmit?

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2002\07\16@135558 by miked

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These guys, http://www.astrotoo.com , have some Motorola Encore GT+s from a
track tracking system(they also have the HF TX). NO ANTENNA. They have
some on eBay;
cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1366966836
Also check the Excess Inventory sale at;
http://www.synergy-gps.com/
who are a major Motorola GPS dealer.
{Quote hidden}

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2002\07\17@034422 by Michael Pettersson

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> Should be in the VTG message, in knots and km/hr

These guys, http://www.astrotoo.com , have some Motorola Encore GT+s from a
track tracking system(they also have the HF TX). NO ANTENNA. They have
some on eBay;
cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1366966836
Also check the Excess Inventory sale at;
http://www.synergy-gps.com/
who are a major Motorola GPS dealer.

> >
> > Does anyone know if the BGMicro GPS transmitts information on speed?
> > I'm using it in NMEA mode and I get the location transmitted but
> > it seems that I don't get the speed informationen (and heading).
> >
> > Is it possible to set what data the gps should transmit?

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2002\07\17@035721 by Michael Pettersson

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> Should be in the VTG message, in knots and km/hr

It is.. but it seems that most softwares uses this information from the
RMC message.. one this unit dosn't seem to transmitt.

The only ones transmitted seems to be GGA and VTG.
Is it possible to make the unit transmitt more messages?

> >
> > Does anyone know if the BGMicro GPS transmitts information on speed?
> > I'm using it in NMEA mode and I get the location transmitted but
> > it seems that I don't get the speed informationen (and heading).
> >
> > Is it possible to set what data the gps should transmit?

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2002\07\17@141139 by Peter L. Peres

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On Mon, 15 Jul 2002, Jim wrote:

>Peter wrote:
>
>   "The funny part being that they won't work even
>    inside the attic of a wood thatched house"
>
>Do you have the antennas pointed up? <grin>

Why ? ;-)

No, really, I mean an old wooden house which has no insulation in the roof
and an equally old brick house with (French) tiles on the roof. I suppose
the tiles are stealth material ;-). On the front porch you get immediate
lock on 4-5 sattelites. Go inside, bzzt.

Peter

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2002\07\17@142244 by Jim

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Someone's 'theory':

    "If you are able to receive the GPS signal
     inside your house then the cladding on the
     house must be something other than wood."

Real world:

Brick veener exterior (MORE absorptive/reflective to
uW's than wood), standrard wood framing, roofing of
4'x8' plywood sheets topped  with 'composition'
shingles -

- and GPS receivers are *fully* able to function.

Your example involving 'pine forests' involves a
LOT more in the way of lossy material which a
typical land-mobile 2-way system would and see
using terrestrially-bound just barely above
the surface-of-the-earth signals.

   "Any timber is a good absorber of RF signals, even
    down to HF."

Any truth to the rumor that old hams used to use
wood sticks dipped in parafin (sp?) as spacers
on their open-wire twin-lead feedlines?

I guess there're no thruth to the rumor that lumber
used in construction if kiln-dried to some single-digit
moisture value either ...

I need an explnation, too, as to how I can pick up SW
as well as AM broadcast band signals equally inside
and outside inside of my house too.

(It seems that 'mother nature' is un-informed as to the
proper behavior of EM waves in an urban environemnt.)

Okamura, where are you when we need you?

Jim

{Original Message removed}

2002\07\17@143547 by Jim

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'Why?' you ask?

Because your experience seems to indicate that WOODEN
houses seriously impede GPS L1 "L band" signals and *I*
am pointing out that my experience has been different ...

BTW - I've got a good six inches of blown fiberglass
insulation in my attic *and* a veneer of solid brick
on the exterior of th house to a height of 10' or so.

I think the GPS NAVSTAR program office is cutting the RF
output power for areas outside the Western Hemisphere (and
*in* areas of conflcit) on the GPS L1 freq and the
C/A code - while leaving P-code and GPS L2 (for exclusive
use by the military and qualified ueers) at normal power
levels ...

Jim

{Original Message removed}

2002\07\18@042427 by Alan B. Pearce

face picon face
>I mean an old wooden house which has no insulation in the roof
>and an equally old brick house with (French) tiles on the roof.
>I suppose the tiles are stealth material ;-). On the front porch
>you get immediate lock on 4-5 sattelites. Go inside, bzzt.

Tiles are sure stealth material when it comes to this. I think you will find
the tiles are glazed only on the outside surface, and so the inside surface
being porous can absorb moisture. This stands a real good chance of being
the equivalent to operating underwater as far as the signal is concerned
unless the roof is being exposed to hot Mediterranean sun or perhaps Arizona
desert summer, not sure where you are.

You don't say what the roof material of the wooden house is.

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2002\07\18@043507 by Alan B. Pearce

face picon face
>    "Any timber is a good absorber of RF signals, even
>     down to HF."
>
>Any truth to the rumor that old hams used to use
>wood sticks dipped in parafin (sp?) as spacers
>on their open-wire twin-lead feedlines?

Well a couple of sticks of timber to support an antenna is a considerable
amount less thann a whole forest of trees with the antenna down among them.
As I understood it the parafin was a water proofing treatment. :)

{Quote hidden}

Again the amount of timber is a lot less than a forest of trees, and growing
trees have a fair amount of moisture in them - part of the reason that house
timber needs to be kiln dried :)

>Your example involving 'pine forests' involves a
>LOT more in the way of lossy material which a
>typical land-mobile 2-way system would and see
>using terrestrially-bound just barely above
>the surface-of-the-earth signals.

Exactly, there is an almighty amount of lossy material in a forest, and IIRC
I said there was a noticeable loss of signal strength, but this does not
mean a total loss at HF, which is why your house is not a total RF shielded
faraday cage :)

But the fact still remains that the higher you go in frequency, the more
likely losses will arise from sources you do not expect, which is one part
of the reason that good RF engineers are regarded as dealing in black magic
by those who are not initiated into the inner circle :)))

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2002\07\18@134047 by Barry Gershenfeld

face picon face
>Any truth to the rumor that old hams used to use
>wood sticks dipped in parafin (sp?) as spacers
>on their open-wire twin-lead feedlines?

I imagine this is true.  After all, the RF in a feedline
is supposed to stay in the wire and is not supposed to
radiate.   And an open-wire feedline is mostly air.

>I guess there're no thruth to the rumor that lumber
>used in construction if kiln-dried to some single-digit
>moisture value either ...

It probably is, coming out of the kiln.  But unless you
can seal it from moisture, the effect doesn't last.

>I need an explnation, too, as to how I can pick up SW
>as well as AM broadcast band signals equally inside
>and outside inside of my house too.

AM is 1 MHz.   SW is 10 MHz.  GPS is 1575 MHz.   Microwaves
behave a lot differently than "short" waves.

>Brick veener exterior (MORE absorptive/reflective to
>uW's than wood), standrard wood framing, roofing of
>4'x8' plywood sheets topped  with 'composition'
>shingles -
>
>- and GPS receivers are *fully* able to function.
>

GPS works in my house, and it worked in a building made
of concrete and steel.  The reason:  BIG WINDOWS.   If
there's any doubt, take a look at *which* satellites
are in view and how that correlates to the direction
your windows face.

Barry

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2002\07\18@145831 by Peter L. Peres

picon face
On Thu, 18 Jul 2002, Barry Gershenfeld wrote:

>>Any truth to the rumor that old hams used to use
>>wood sticks dipped in parafin (sp?) as spacers
>>on their open-wire twin-lead feedlines?
>
>I imagine this is true.  After all, the RF in a feedline
>is supposed to stay in the wire and is not supposed to
>radiate.   And an open-wire feedline is mostly air.

Yeah, right. There are three sets of Maxwell equations. One for
conductors, one for air, and one for paraffinated wood sticks ;-). I liked
the part at 'it's not supposed to radiate'.

>>I guess there're no thruth to the rumor that lumber
>>used in construction if kiln-dried to some single-digit
>>moisture value either ...
>
>It probably is, coming out of the kiln.  But unless you
>can seal it from moisture, the effect doesn't last.

They boil them in pitch and/or paraffin for that purpose, when coming out
of the kiln. Nowadays they use more modern processes and other
impregnating materials, the ones quoted above are very very combustible.

>>I need an explnation, too, as to how I can pick up SW
>>as well as AM broadcast band signals equally inside
>>and outside inside of my house too.
>
>AM is 1 MHz.   SW is 10 MHz.  GPS is 1575 MHz.   Microwaves
>behave a lot differently than "short" waves.

It's a power budget thing. Wood is often impregnated with plastic using
low frequency RF (see dielectric heating). That's about 1MHz but at
>1kW/m^2. The power budget for GPS and most space->earth segments is very
poor.

{Quote hidden}

Here I did not even have one sattelite inside. A one-sheet window dropped
the signal strength bar on a visible satellite by half. I assume this is
linear so it would be 6dB down.

Peter

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2002\07\18@145835 by Peter L. Peres

picon face
On Thu, 18 Jul 2002, Alan B. Pearce wrote:

>>I mean an old wooden house which has no insulation in the roof
>>and an equally old brick house with (French) tiles on the roof.
>>I suppose the tiles are stealth material ;-). On the front porch
>>you get immediate lock on 4-5 sattelites. Go inside, bzzt.
>
>Tiles are sure stealth material when it comes to this. I think you will find
>the tiles are glazed only on the outside surface, and so the inside surface
>being porous can absorb moisture. This stands a real good chance of being
>the equivalent to operating underwater as far as the signal is concerned
>unless the roof is being exposed to hot Mediterranean sun or perhaps Arizona
>desert summer, not sure where you are.

Only, they ARE exposed to the Mediterranean sun all the time. I'm in
Israel. And they are not glazed on either side. French tiles are very
thick (up to 1") and solid, large things. I think that they evolved from
the Roman kind, except these are factory made.

In my limited experience many (many) 'household' ceramics do not pass the
'microwave test'. This includes some saucers and bowls that get hotter
than the food inside them. Apparently it is dead easy to have impurities
in the ceramic which cause high losses at high frequency.

>You don't say what the roof material of the wooden house is.

Slats, probably treated with pitch and something else. It's a shed really.
Maybe the dope they treat the wood with to prevent fires and insects
feeding on it does something to the signal. There is no insulation. Just
nails to keep the slats on.

Peter

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2002\07\18@181118 by Jim

flavicon
face
  "which is why your house is not a total RF
   shielded faraday cage :)"

It's NOT even close for well into the VHF and
UHF range I'm afraid to inform you ...

I think you've read one too-many ill-informed text
book on this subject ...

I've been there - and done most of this - from AM
Broadcast freqs through VHF and UHF 2-way radio including
cellular/cell site propagation studies ***and***
actual crane tests/firld strength measurements with
the highest freq worked at being Ku band on a RADAR
project  ... other projects included some original
GPS gear - we at TI did one of the original HDUE
(High Dynamic User Equipment) receivers for the
military during GPS field trials in 1978 ...

.. so, please, - *do* spare me the lecture about the
black arts. The black arts are what I deal in, what
I have dealt in and will continue to deal in ...

(Okamura - where are you?)

Investigation of Modified Hata/Okamura Propagation Models:
http://www.aca.gov.au/frequency/spps/0102spp.pdf

Jim

{Original Message removed}

2002\07\18@183026 by Jim

flavicon
face
Barry wrote:

     "GPS works in my house, and it worked in a
      building made of concrete and steel.
      The reason:  BIG WINDOWS"

Insufficient in some cases *IF* those windows are
heavily tinted in some cases (as I wrote a day or
two ago) when metallic-desposited heat-reflecting
film is applied ...

One of my former employers rented a multi-story
building that had been retrofitted with heavy
plastic tinting on the windows. NO GPS signal
inside.

I *did* manage to find a break in one of the applied films
on one edge - and positioned my GPS antenna there - got
enough signal to work with ...

There are also "GPS extenders" (much like the active
cellular bi-directional 'extenders') available for
providing GPS signals where *none* sometimes naturally
occur - like in close-fitting metal hangar (that has
been designed to be somewhat RF tight to start
with - for instance where 'classified militrary
projects' are in play) with the doors closed.

A simple:

  antenna---> RF Amp --> Re-rad antenna

does the trick in that case.

The one place on this earth I *have* had bona-fide
problems with GPS propagation was down in the hills of
Tennesee - driving on one of the Interstates that runs
deep down into some of those 'hills'. The old '94
Magellean wasn't too keen on providing coordinates
all the time ...

As to my 'needing an explanation' why SW was receivable
inside a house - Barry, that was a rhetorical
question - not a *real* question ...

Jim


{Original Message removed}

2002\07\18@183941 by Jim

flavicon
face
Peter penned:

  > Yeah, right. There are three sets of Maxwell equations. One for
  > conductors, one for air, and one for paraffinated wood sticks ;-). I
liked
  > the part at 'it's not supposed to radiate'.


You've never seen a 'launcher' style RF
power transmission system have you Peter?

Comprised of a single 'conductor' ...

BTW - open-pair conductors are still in use by hams
for feeding some of the higher input-Z antennas in
the HF range ...

Of course, tht's NOTHING compared to using simple twisted
pairs such as 100BaseT CAT5 wiring ...


    "Here I did not even have one sattelite inside. A
     one-sheet window dropped the signal strength bar
     on a visible satellite by half. I assume this is
     linear so it would be 6dB down."

I think you have other factors at play here, up to
and including defective equipment and 'energy
efficient' windows that do not pass RF ...


Jim



{Original Message removed}

2002\07\18@190711 by Peter L. Peres

picon face
On Thu, 18 Jul 2002, Jim wrote:

>Peter penned:
>
>   > Yeah, right. There are three sets of Maxwell equations. One for
>   > conductors, one for air, and one for paraffinated wood sticks ;-). I
>liked
>   > the part at 'it's not supposed to radiate'.

>You've never seen a 'launcher' style RF
>power transmission system have you Peter?

Never seen a Tesla exhibit, sorry.

>Comprised of a single 'conductor' ...
>
>BTW - open-pair conductors are still in use by hams
>for feeding some of the higher input-Z antennas in
>the HF range ...
>
>Of course, tht's NOTHING compared to using simple twisted
>pairs such as 100BaseT CAT5 wiring ...

Has anyone measured the emissions of an office building wired up like this
during office hours ? I think that you could find it using a df radio
in a thick fog or something ;-). BTW I'm a great fan of 10Base2..

>     "Here I did not even have one sattelite inside. A
>      one-sheet window dropped the signal strength bar
>      on a visible satellite by half. I assume this is
>      linear so it would be 6dB down."
>
>I think you have other factors at play here, up to
>and including defective equipment and 'energy
>efficient' windows that do not pass RF ...

Look, there is nothing fancy here. It's a bog plain single sheet 3mm cheap
glass window in a ~90 year old one storey brick house. It was reasonably
clean on the day I 'measured' it. I'll probably try the microwave test on
a piece of roof tile. I'm curious if it could be used as a crucible to
melt metal in the microwave ;-) The brick the tiles and the windows in
this house kill the GPS signal very dead.

Peter

PS: I hope you realise that glass is a very bad insulator at RF unless
formulated to be that. Most commercial glass, as in windows, bottles,
ashtrays etc, is totally loaded with various metal oxides and more exotic
elements to make it cheaper to manufacture, tint it, etc etc. Those metal
oxides are often the same ones as used in high loss ferrite cores (hint
hint). The microwave test will tell the truth (more or less).

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2002\07\18@210844 by Josh Koffman

flavicon
face
Shot in the dark here, but perhaps your windows have leaded glass in
them?

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

"Peter L. Peres" wrote:
>
> Look, there is nothing fancy here. It's a bog plain single sheet 3mm cheap
> glass window in a ~90 year old one storey brick house. It was reasonably
> clean on the day I 'measured' it. I'll probably try the microwave test on
> a piece of roof tile. I'm curious if it could be used as a crucible to
> melt metal in the microwave ;-) The brick the tiles and the windows in
> this house kill the GPS signal very dead.

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2002\07\18@222552 by Dale Botkin

flavicon
face
On Thu, 18 Jul 2002, Jim wrote:

>    "which is why your house is not a total RF
>     shielded faraday cage :)"
>
> It's NOT even close for well into the VHF and
> UHF range I'm afraid to inform you ...

Amen.  I run an HF dipole under a rather thick all-wood roof (plywood,
with cedar shakes on top) and can tell you it doesn't absorb squat.  I'm
all-QRP (low power), and most people are quite surprised when they that
find out.  I'll have the V/UHF J-pole up there in a week or two, followed
in a few months by the satellite setup of VHF and UHF beams.  I can assure
you I won't be able to detect a difference between inside and outside.

Dale
(n0xas)

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2002\07\19@040207 by Alan B. Pearce

face picon face
>The one place on this earth I *have* had bona-fide
>problems with GPS propagation was down in the hills of
>Tennesee - driving on one of the Interstates that runs
>deep down into some of those 'hills'. The old '94
>Magellean wasn't too keen on providing coordinates
>all the time ...

I have heard of folk going out in the hills and believing their GPS when
down deep in a valley, but the position being reported was incorrect,
because the valley happened to be in line with the flight path of one
satellite, and only one other satellite was visible to the receiver, or
something like that.

I don't remember the exact details of the problem, just that deep valleys
(including those between tall central city buildings) can be a problem which
one needs to be aware of.

The problem that arises when modern man gets dependant on technology,
without realising the limitations of it. :))

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