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ZL3AI > APRDIG 14.03.04 22:12l 242 Lines 9820 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
TAPR APRS Special Interest Group Digest for Friday, March 12, 2004.
1. RE: GPS Signal re-radiation
2. Re: Pre-emphasis / De-emphasis & D700 Question?
3. High speed data
4. Re: Pre-emphasis / De-emphasis & D700 Question?
5. Re: Pre-emphasis / De-emphasis & D700 Question?
6. Re: Pre-emphasis / De-emphasis & D700 Question?
7. Re: High speed data
8. Re: High speed data
9. Re: High speed data
10. Re: High speed data
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Subject: RE: GPS Signal re-radiation
From: "Kelly Cushing" <kellycu@comcast.net>
Date: Thu, 11 Mar 2004 21:21:15 -0800
X-Message-Number: 1
These articles might be of interest to you.
http://www.vancouver-webpages.com/peter/extant.txt
http://www.gpsnuts.com/myGPS/GPS/LEI%20tips%20tricks/Active%20antenna/active
_antenna2.htm
-----Original Message-----
Surely someone here on the list is doing this.
I need to feed GPS RF from the roof of this building - into an office.
It'll be used for testing... but the shell of the building currently
blocks GPS signals. I've seen at other facilities expensive GPS
equipment that relies on reradiation of the signal ... I figure someone
here has done it on the cheap... so that their GPS works fine inside.
I do not care that the summing node (antenna) on the roof does not
accurately reflect the position inside the building.. I just need the
GPS receivers to work.
TNX
ALOHA
AH6LS
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Subject: Re: Pre-emphasis / De-emphasis & D700 Question?
From: "Ernie Zingleman" <ks4q@zingleman.com>
Date: Fri, 12 Mar 2004 09:20:10 -0500
X-Message-Number: 2
In all my packet related activities, whether SEDAN nodes, DX Packet Cluster
RF infrastructure or APRS equipment, I've always tried to make everything as
flat as possible and have had good results.
Of course, for those of you that *WANT* to be purists, make sure that you
don't have 6dB pre/de-emphasis enabled on your TNC if you are feeding your
TNC audio into the front microphone jack of a typical 2 meter voice radio.
In that case, you pre-emphasize and then pre-emphasize again. Perhaps you
are then getting 12 db of pre-emphasis per octave. Of course, assuming
fidelity throughout the transmission and reception pathway, you might undo
it all at the other end assuming everybody is running 12 dB Pre &
de-emphasis too.
I'm not sure that the collective wisdom of the land mobile radio community
ever found any usefulness in 12 dB pre-emphasis....they settled on 6 dB per
octave. So, it raises the question as to whether folks in the packet
community truly are following the standard and whether it is useful.
On MFJ 1270Bs, I do the mod that Richard provides the link to (below). On
MFJ 1270C units, I put 'JMP J' in place. The header for this is located
near the 5 pin header for 'add-on' modems. This typically means that ONLY
the radio is adding pre & de-emphasis.
All higher level modulation techniques (such as 4 or 16 level FSK and
beyond) for Narrow band FM don't tolerate pre & de-emphasis...even if you
attempt to "UNDO" it at the other end. For these modulation techniques, the
modem puts out flat audio and the radio must handle it without doing pre &
de-emphasis....in other words bypassing the audio shaping that benefits
Voice communications.
By the way, I work in the commercial arena with equipment that does high
speed data...in excess of 43 kbps over a 25 kHz FM radio channel. The land
mobile community uses our equipment for sending high speed data over narrow
band radio. Typically, their equipment won't pass high speed data...so we
make our own radios & modems, and they all use a 'flat' approach to handling
audio.
Ernie KS4Q
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Subject: High speed data
From: Earl Needham <needhame1@yucca.net>
Date: Fri, 12 Mar 2004 07:33:48 -0700
X-Message-Number: 3
At 07:20 AM 3/12/2004, Ernie Zingleman wrote:
>By the way, I work in the commercial arena with equipment that does high
>speed data...in excess of 43 kbps over a 25 kHz FM radio channel. The land
>mobile community uses our equipment for sending high speed data over narrow
>band radio. Typically, their equipment won't pass high speed data...so we
>make our own radios & modems, and they all use a 'flat' approach to handling
>audio.
Wow! I can only dream of this I guess. Sounds like a bunch of hams home
brewing everything.
Ernie, could you provide a little more specifics on this system? It
certainly sounds interesting, and something APRS could possibly benefit
from. Just imagine an IGATE transmitting the entire APRS feed on 2.4 or
higher, and perhaps still room on the channel for local traffic!
Thanks,
Earl
Earl Needham, KD5XB, Clovis, New Mexico DM84jk
SETI@Home: 11399WU/7.4yrs
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Subject: Re: Pre-emphasis / De-emphasis & D700 Question?
From: Jeff King <jeff@aerodata.net>
Date: Fri, 12 Mar 2004 14:43:18 -0600 (CST)
X-Message-Number: 4
Quoting Ernie Zingleman <ks4q@zingleman.com>:
>Of course, for those of you that *WANT* to be purists, make sure that you
>don't have 6dB pre/de-emphasis enabled on your TNC if you are feeding your
The spec for FM is 6db/per octave. How you get there is a exercise left to
the reader. Perhaps the TNC manufacturers added it because some FM radios
where not following the spec? In any case, you need to verify, that between
the combination of TNC radio, that you are as close as possible to 6db/per
octave.
>All higher level modulation techniques (such as 4 or 16 level FSK and
>beyond) for Narrow band FM don't tolerate pre & de-emphasis...even if you
>attempt to "UNDO" it at the other end. For these modulation techniques, the
>modem puts out flat audio and the radio must handle it without doing pre &
>de-emphasis....in other words bypassing the audio shaping that
>benefits Voice communications.
AFSK and FSK are not the same thing. The "A" in AFSK means audio. You want a
flat path for FSK and GMSK.
More to the point, you want everyone on the channel running the same thing,
and in the case of Bell 202 AFSK 1200 baud packet, that is the voice
standard, and it is 6db/per octave.
Please take a look at those links I posted.
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Subject: Re: Pre-emphasis / De-emphasis & D700 Question?
From: "Ernie Zingleman" <ks4q@zingleman.com>
Date: Fri, 12 Mar 2004 16:07:17 -0500
X-Message-Number: 5
Jeff,
I was already familiar with the material before you posted it. I've used it
as a guide for setting deviation levels.
Since there is a fuss over everyone maintaining 6 dB pre/de, I guess it is
good that I pointed out that if they are already doing it in their radio,
they don't need to do it in their TNC too! :-) Most of them have probably
been too enthusiastic and are now running 12 dB
But I guess that most are oblivious to this and will continue to be. What
can I say, we all have an opinion, Right?
By the way, since you say that AFSK implies 6 dB pre/de and FSK does not,
should I be concerned when I run RTTY? :-) Oopps that is yet another
definition of what AFSK and FSK mean! Besides, that is not FM.
Before we continue this thread any further, I'd like to make the suggestion
that people concern themselves with the deviation of the 2200 hertz tone
more than anything else. Therein lies the most room for improvement in
communications efficiency.
Ernie KS4Q
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Subject: Re: Pre-emphasis / De-emphasis & D700 Question?
From: Jeff King <jeff@aerodata.net>
Date: Fri, 12 Mar 2004 16:33:47 -0600 (CST)
X-Message-Number: 6
Quoting Ernie Zingleman <ks4q@zingleman.com>:
>Since there is a fuss over everyone maintaining 6 dB pre/de,
Fuss? Naw.... I just think manufacturer's need to maintain specifications
and ham's shouldn't give them a pass. The spec for FM voice radios is 6db
per octave. It would be a fuss if I was getting bent out of shape with a
radio that had 5 or 7db per octave, the radio being discussed had 0 db per
octave. It has a serious problem that needs to be addressed. Hence I posted
the link for a fix.
>But I guess that most are oblivious to this and will continue to be.
>What can I say, we all have an opinion, Right?
Again, the spec is 6db per octave. That is not an opinion. Now, if you want
a opinion from me, my opinion is hams should not accept equipment in the
marketplace that is poorly designed or doesn't meet specification.
>By the way, since you say that AFSK implies 6 dB pre/de and FSK does not,
>should I be concerned when I run RTTY? :-) Oopps that is yet another
>definition of what AFSK and FSK mean! Besides, that is not FM.
If you are squirting audio into the mic jack of a FM rig, then yes, you
should be concerned, in particular if you are concerned about
interoperatbility. AFSK means AUDIO FSK, similar to the old Bell 103 and
Bell 202 modems. The FSK modulation is converted into audio tones, so it
has much more in common with voice then with FSK. In fact, the whole reason
that it is converted to audio is so it can pass via voice grade circuits.
>Before we continue this thread any further, I'd like to make the suggestion
>that people concern themselves with the deviation of the 2200 hertz
>tone more than anything else. Therein lies the most room for improvement
>in communications efficiency.
Right, that was in the links I posted. And the reason your suggesting 2200
hertz, is that with pre-emphesis, that is the first tone that would get
clipped.
I don't see where we disagree on anything Ernie.
-Jeff
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