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ZL3AI > APRDIG 03.04.03 12:07l 218 Lines 9100 Bytes #999 (0) @ WW
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Subj: TAPR Digest, Mar 29, 3/4
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Internet feed vs. FINDU.COM
From: "Jacob Tennant" <k8jwt@ntelos.net>
Date: Sat, 29 Mar 2003 16:41:43 -0500
X-Message-Number: 20
I was looking around today and found something funny(to me).
My local digi KB8CVP-7 shows up on FINDU.COM but not on the internet feed?
Also another digi KC8FWD-5 shows up on findu.com but no on the internet
feed.
Why is that? They are both being heard by a igate or internet station
somehow.
Jacob Tennant K8JWT
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Subject: Re: Internet feed vs. FINDU.COM
From: "Steve Dimse" <k4hg@tapr.org>
Date: Sat, 29 Mar 2003 21:50:49 +0000
X-Message-Number: 21
On Sat, 29 Mar 2003 16:41:43 -0500, Jacob Tennant wrote
>I was looking around today and found something funny(to
>me).
>
>My local digi KB8CVP-7 shows up on FINDU.COM but not on
>the internet feed? Also another digi KC8FWD-5 shows up
>on findu.com but no on the internet feed.
>
>Why is that? They are both being heard by a igate or
>internet station somehow.
The most likely cause is that there is a problem in the APRS IS that is
putting data on some servers but not all. This is generally due to a
misconfiguration in the hub that your local IGate is connected to (or
another upstream hub).
I get 5 or 10 messages a day like this (or less commonly the inverse "I'm
not on findU"), and I've long since stopped trying to track down the
specific flaws.
findU connects to servers simultaneously, in order to do the best it can
to grab all data that is out there, but no doubt some is still being
lost...
Steve K4HG
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Subject: XASTIR
From: "Phil Thompson" <philt@philt.net>
Date: Sat, 29 Mar 2003 17:02:02 -0500
X-Message-Number: 22
With all the hipe on the net about xastir, I thought I would give it a try
I have cygwin running on an 1.2Ghz PIII and I have Geotiff , and Imagemagic
compiled in
However, no mattter what I put in the /usr/local/xastir/maps directory,
whether it be tiff files, gif files or directories, the map chooser window
remains totaly blank.
I have performed the chmod on directory and files per the instructions.
Any thoughts on this one????
Also when xastir 1.1.4 starts, It requests I contact the author for a
registration number. I am running it on tcp/ip only. However I have been
unable to locate any method of contacting the author to obtain this number.
Phil Thompson VE3RD
E-Mail philt@philt.net
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Subject: RE: XASTIR
From: "Rich Garcia" <k4gps@arrl.net>
Date: Sat, 29 Mar 2003 17:20:03 -0500
X-Message-Number: 23
Have you tried to use another registration number from one of the other
applications ? I am not sure if WinAPRS number, MacAPRS, UI-View or such
validation would work.
Rich
Who just installed RH for the first time and actually got it to work! On to
Xastir now.
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Subject: Re: XASTIR
From: "Phil Thompson" <philt@philt.net>
Date: Sat, 29 Mar 2003 17:40:53 -0500
X-Message-Number: 24
Disregard previous message
I found callpass , created a registration number, now maps work
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Subject: Re: Transmitter combining.
From: Rich Osman <Rich@osman.com>
Date: Sat, 29 Mar 2003 16:56:23 -0600
X-Message-Number: 25
Bob,
With this small amount of isolation you are going to have significant
spurs generated in the PA at multiples of 25 Khz, so it will be MUCH
worse. There's no way you'll get any isolation out of a filter this
close. Based on what little I know of your probelm now, I'd suggest that
you at least consider two stage isolators at each TX output.
How much power do these downlinks run?
What modulation scheme is used?
What class of PA is used? (How linear?)
--
mailto:Rich@Osman.com http://www.rich.osman.com
Rich Osman; POB 93167; Southlake, TX 76092 (Near DFW Airport) ARS: N1OZ
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Subject: Re: Transmitter combining.
From: WA8LMF2@aol.com
Date: Sat, 29 Mar 2003 18:05:16 EST
X-Message-Number: 26
In a message dated 3/29/2003 1:16:08 PM Pacific Standard Time,
bruninga@usna.edu writes:
>ANyone do this for a living and can comment on the desired transmitter
>separation?
Any RF from one transmitter that finds it way back into the final amp of
another TX in the same band is going to create horrible amounts of IMD. The
final amps normally operate very non-linearly (class C for most FM amps) and
will act as an excellent mixer for the two (or more freqs). This problem
occurs constantly on crowded sites here in the west, where you may have
20-30 transmit antennas on a single tower and 5-10 towers within a
quarter-mile circle on a particular mountain peak. And on the ground almost
everywhere in cellular systems .
The transmitter frequency separation required is determined entirely by the
amount of selectivity in the final amplifier tuned circuits and matching
networks. In the tube era, one actually had H-Q resonant peaked tank
circuits in the driver and final stages of transmitters that produced
significant selectivity against signals a few few hundred KHz or a MHz away.
Today's solid state PAs are almost universally broadband amplifiers with
just a lowpass filter with a cutoff somewhere between the band in question
and the second harmonic. There is essentially NO inband selectivity at all.
Or if there are resonant tank circuits, they are connected across
high-current, low-voltage (i.e. lo-Z) semiconductor amplifier device and are
typically have a very low loaded Q (i.e. extremely broad).
[ Contrast the difference between the classic tube "boat anchor"
Motorolas and GEs that could not be crystaled for two freqs separated by more
than a few hundred KHz on 2M (or a meg or two on UHF), with modern
solid-state boxes like the D700 that will (with the magic diode cut) TX with
full power from 138-to-174 MHz and 430-to-480. ]
Since modern solid-state transmitters have virtually no internal in-band
selectivity in the PA stages, you must provide it with external devices. The
TX separation you will require will be determined almost exclusively by the
cost, complexity (and because this is a spacecraft, size and weight) of the
external networks you choose to use.
I would guess you would have to take the approach used in cellular systems
and some trunked radio systems (where you routinely have 5-10 transmitters in
band that need to be coupled to a limited number of antennas). Each TX
output passes through a TX ferrite circulator (think of it as a "diode" for
RF that allows RF to pass one way but not the other) and then passes through
one or more extremely hi-Q cavities before being joined with a 4- or 5- or
6-sided tee into a common line leading to the antenna The idea is to
increase the return loss from any TX output back into the final amp of any
other TX to AT LEAST 40-50 dB.
In cellular systems, attenuator pads of 8-10 dB are often inserted between
the TX output and the circulators, to ensure that the circulators look back
into a perfectly-flat non-reactive non-frequency-sensitive load to absolutely
maximize their performance (and to add another 10dB of return loss. This
means that a 25-watt TX will typically put out only about 2 watts to the
antenna (which is still about 8-10 time the power of the talkback from the
typical wimpy cellular handset). Horrendously lossy, but you get a very
clean spectrum even with dozens of transmitters on the same tower. [ I
believe this intentionally-very-lossy approach is used on some aircraft and
naval radio installations where you have a lot of close-spaced channels being
used simultanously. ]
In the UHF systems I am most familiar with, each leg (transmitter) of the TX
combiner used a single cavity about the size of 3 one-gallon paint cans
stacked (i.e. very large diameter full-wavelength). This type of cavity
allowed us to combine 3 transmitters into one antenna with about 1 MHz
spacing. [ This was a low-loss system combining 100W transmitters and
delivering about 70-80W on each channel to the antenna common point.
Circulators but no pads were used. ]
In a similar 800 MHz system, four 100W transmitters were combined into
each antenna with cavities about the size of a single gallon paint can with
minimum frequency separations of about 1.5 MHz. (The 800 MHz cavity Q was
higher and the percentage selectivity greater, because the
diameter-to-length ratio of the cavity was higher. )
Stephen H. Smith wa8lmf @ 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
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