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ZL3AI > APRDIG 20.01.04 14:50l 192 Lines 8476 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
TAPR APRS Special Interest Group Digest for Saturday, January 17, 2004.
1. Re: Digital HF QRP?
2. Re: Digital HF QRP?
3. RXing Sats & Sapphire on 1/4 wave whip
----------------------------------------------------------------------
Subject: Re: Digital HF QRP?
From: WA8LMF2@aol.com
Date: Sat, 17 Jan 2004 03:55:57 EST
X-Message-Number: 1
In a message dated 1/16/04 6:14:08 PM Pacific Standard Time, wa7nwp@jnos.org
writes:
>Second, Pactor -- as the minimal requirement for Winlink -- is not common
>with the soundcard modem implementations.
This issue has been discussed endlessly on the MixW and other soundcard
lists. The problem is that the interrupt latency of Windows is too high to
produce the very precise millisecond-level timing need for Pactor and AMTOR
T/R switching.
>PSK31 is good for keyboarding. It's far too slow for real data
>operation.
Or for any data operation at all since PSK31 has no error detection -
checksum - ACK/NAK mechanism at all. There is no positive indication of
good/bad data at the receive end.
>Clover, Pactor 2 and 3, and QPSK15 on HF put the 1200
>baud AFSK we use in VHF to shame...
They acheive high data rates by using relatively wide-band (for HF data)
multitone modulation schemes that produce error-free high throughput. The
downside is that they require fairly hefty signal-to-noise ratios to work
well and acheive their rated throughputs. Which is hard to come by with a
QRP rig running into a lousy portable antenna. They are definitely not
weak-signal modes like PSK31 !
Transmitting the multiple simultaneous tones through an SSB transmitter
requires keeping the average power down to a tiny fraction of the peak
(keydown CW) power to avoid intermodulation distortion. This means that
you will have to run the '817 at something like 1 watt average output.
Stephen H. Smith wa8lmf (at) aol.com
Home Page: http://wa8lmf.com
Ham Radio/Mobile SSTV page: http://members.aol.com/wa8lmf/ham
APRS Stuff
http://members.aol.com/wa8lmf/aprs
----------------------------------------------------------------------
Subject: Re: Digital HF QRP?
From: "Gregg G. Wonderly" <gregg@skymaster.cytetech.com>
Date: Sat, 17 Jan 2004 08:50:52 -0600
X-Message-Number: 2
>>PSK31 is good for keyboarding. It's far too slow for real data
>>operation.
>
>Or for any data operation at all since PSK31 has no error detection -
>checksum - ACK/NAK mechanism at all. There is no positive indication of good/
>bad
>data at the receive end.
PSK31 sends streams of characters. There is no reason that those streams
of characters could not include FEC or at lease checksums. What would be
different is the sending and receiving encoding/decoding of the data before
display.
For email or other non-interactive data transmission, PSK31 should be great...
-----
gregg@cytetech.com (Cyte Technologies Inc)
----------------------------------------------------------------------
Subject: RXing Sats & Sapphire on 1/4 wave whip
From: Bob Bruninga <bruninga@usna.edu>
Date: Sat, 17 Jan 2004 17:57:49 -0500 (EST)
X-Message-Number: 3
The last two days, I watched the downlink from Sapphire on my 1/4 wave
(6") whip mounted on a sheet metal groundplane. To my surprise, both days
I was able to decode the packets at elevations down to between 15 and 20
degrees from Sapphire on my Kenwood D700. (My coax length to the radio is
only a few feet, so there is no coax loss).
As you have heard me say before, a 1/4 wave whip is a good antenna for
satellites because it's main lobe is elevated somewhat from the horizon
(5dBi) But I have also said for WEAK downlinks, that the 3/4 wave vertical
whip is better above about 25 degrees (over 7dBi), though worse below
that.
And the advantage of the 3/4 wave whip is that it is a 1/4 whip on 2
meters, so it is dual band and perfect when hooked to a dual band rig for
casual fixed antenna RX of satellites.
To see the PLOT (as measured) of gain versus elevation angle for the 3/4
versus the 1/4, see: http://www.ew.usna.edu/~bruninga/g34-14.jpg
The 2 or more dB advantage of the 3/4 wave is clear. But it gives up
performance below 25 deg. TODAYS's observation that there is adequate
signal from Sapphire to capture and decode packets on the 1/4 whip down to
15 or 20 degrees, then says that we dont need the higher gain at the
higher elevations for this satellite as I thought, and that the 6" whip
(with no coax loss) is adequate (if you stick with UHF only).
Again, this is not recommended for the average user of satellites who
should use a Beam, but this *is* important for people establising
unattended SATGATES designed to just pick up what they can whenever the
satellites comes into view without having to keep motors running and
Tracking programs constantlly in use.
The plot above is EASY to make by anyone with only a GPS and PC. Just
scale your model antenna to 1575 MHz and hook it to your GPS. Then just
monitor the output of the GPS which reports every 2 seconds the AZ/EL and
Signal strength of all GPS satellites. Then just average and PLOT the
results.
My SIGPLOT.BAS program does this automatically and is what made the above
plot. (SIGPLOT.bas is included in every copy of APRSdos in the PROGRAMS
directory)... and is mentioned near the bottom of the web page below.
de WB4APR@amsat.org, Bob
APRS SATELLITES http://www.ew.usna.edu/~bruninga/astars.html
If you're still reading, my antenna is simply a 6.5" piece of wire stuck
through a hole in the top of one of those green steel boxes you see in
neighborhoods to cover Cable TV junctions. The box sits on the flat roof
at work and provides about a 1 foot by 2 foot groundplane. Inside the box
is the AMP/Preamp to make up for the 150' coax run to my office. This
preamp is NOT a super dooper Satellite low-noise amp, but just the kind
they put in AMPS to make up for the switching loss in the T/R relays on
receipt. My guess is that a Kendood D7 or D700 directly connected would
do as good or better.
Then all you run down to the shack is just 3 wires to the serial port.
No coax. My APRSdos program APRStk, then auto tunes the kenwood to every
amateur sat that comes over, sets the band, accounts for Doppler, and sets
the TNC to 1200 or 9600 baud. Throughtout the day I hear AO27, SO50,
Sapphire, PCsat, ISS, LO19 (CW on an FM rig(yuk)), UO22 and anything else
that is radiating and I have in the tracking list.
Of course if you want to HEAR the voice ones then you also have to run 2
more wires for the speaker... and of course, its such a waste to put your
kenwood on the roof too, but its the only rig that lets me control all
this from the serial port:
TNC baud rate (1200 or 9600)
Which Band the TNC is connected to for TX and RX separately
Which band the dual band rig is on (it is really 2 dual RX's)
What the frequency for each satellite is
TUning the rig during passes for Doppler (5 KHz steps for FM only)
Capturing packets from any packet satellite
Hearing Voice from all of them.
The ONE thing I need still need to implement is a "mute" command so that
the program will turn off the speaker when the 9600 baud satelites come
over, because they are just noise... But for my application for showing
students whenver ANYTHING is in view, I dont need the MUTE..
Oh yes, the program then also can TURN any $50 TV rotator to track any
satellite too via two bits on the LPT1 printer port. But I am not using
that right now... And lastly ,it displays a grapic on the bottom of the
screen showing a timeline versus elevation of all satellites that will be
in view in the next 2 hours, so, from across the room, a quick glance will
alert you to all activty coming up without touching a key..
Im not pushing my APRStk, its kind of old and crude, but it works, and it
plots anyone with a position too. But I sure wish someone else would use
these ideas to put these traking NEEDS in some good windows software...
1) Controls the simple TV rotators
2) Commands the Kenwoods and internal TNC
3) Captures all UI packets and displays any position reports on the map
4) Displays the bottom line graphic of all sats in view for next 2 hours
for instant visualization of what is to be happening in space in your
area in the next few minutes..
5) and does all of this automatically.
Bob
---
END OF DIGEST
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