| |
ZL3AI > APRDIG 26.07.03 09:12l 198 Lines 9381 Bytes #999 (0) @ WW
BID : 1673-ZL3AI
Read: GUEST
Subj: TAPR Digest, Jul 23, 5/8
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<VK6HGR<ZL2BAU<ZL3VML
Sent: 030725/1336Z @:ZL3VML.#80.NZL.OC #:4981 [Chch-NZ] FBB7.00i $:1673-ZL3AI
From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: Running aprs in the car with a laptop - Use DC-DC conv!
From: <BobDonnell@arkalmus.com>
Date: Wed, 23 Jul 2003 10:12:21 -0700
X-Message-Number: 27
Actually, most modern inverters are actually two switch-mode supplies.
Typically, the inverter uses a switch-mode DC-DC supply directly from
the 12V input to create approximately 165 VDC, the equivalent
ground-to-peak voltage for 117 VAC. That switch-mode supply runs at
high frequency(20-2000 kHz), frequently with regulation, to maintain
charge in a capacitor bank. At the output of the capacitor band there
is a bridge array of high-voltage MOSFET transistors that are controlled
to switch the positive and negative sides of the capacitor bank
alternately between the "neutral" and "hot" connections on the output of
the inverter.
More elaborate schemes may modify the duty cycle of that output, to more
closely simulate a sine wave, depending on how much design effort and
parts cost is put into the inverter design. I've not investigated this
in depth, but there might even be some inverters out there that are
(essentially) class D 60-Hz amplifiers, using high-frequency pulse-width
modulation through a reactive network, to create a virtually perfect
sine-wave source.
So typical modern inverters, if inadequately supressed, couple
high-frequency square waves on to the source supply buss. And I bet
some can be seen on the output too.
The use of the switch-mode DC-DC conversion process with direct MOSFET
switching is what makes the modern inverters a lot more efficient than
their predecessors. But nothing beats the old inverter I used to have.
That one had a mechanical interrupter - a vibrator, like the tube mobile
rigs, of days gone by. But it was a much bigger vibrator! And a real
(and significantly heavy) transformer. And you knew if it was running -
you heard the buzz. Good thing, too - it took about 6 amps, 70 watts,
just to keep it running, with no load - this for a 175-watt inverter.
73, Bob, KD7NM
----------------------------------------------------------------------
Subject: RE: Running aprs in the car with a laptop
From: <BobDonnell@arkalmus.com>
Date: Wed, 23 Jul 2003 10:25:05 -0700
X-Message-Number: 28
Hi Jerry,
I discovered that my inverter (not a hugely expensive one) does affect my
VHF receive performance. The best way to tell is to find a repeater that
has a QSO in progress, and is a little scratchy - showing signs of a
somewhat weak signal. Turn the inverter off and on, and see if the signal
from the repeater becomes more scratchy - this is what will tell you if the
inverter affects your receive sensitivity. You can do the same with the
laptop and its power supply, and other interconnects in your system.
As an example, my DC-powered GPS (a Garmin GPS-III+) is the most obnoxious
noise source in my vehicle - and the signal is being coupled out on the
shield of the external antenna connection. The noise source is related to
the RS-232 data stream, and is probably the switch-mode power supply for
the NMEA serial output driver. I know this because the nature of the noise
is periodic at 1-second intervals, and changes between locked and unlocked
GPS receiver operation. About 10 turns of the coax for the remote antenna
through a ferrite toroid pretty well cleans this up.
Ferrite toroids (which are more effective, but harder to install than
split-core snap-on ferrites) on the interconnecting wiring for the inverter
and/or laptop switching supply are likely to help you in cleaning up noise
in your vehicle, in the HF spectrum.
And the price of the inverter doesn't really say anything about how well
RF-supressed the inverter is. I strongly doubt it's on the radar screen of
most manufacturers - mostly just us hams.
73, Bob, KD7NM
----------------------------------------------------------------------
Subject: RE: Add X-Port to TNC?
From: <BobDonnell@arkalmus.com>
Date: Wed, 23 Jul 2003 10:50:09 -0700
X-Message-Number: 29
Here are the issues that need to be resolved in doing this using this
part:
1) The unit runs on 3.3 VDC - not available in most TNC's
2) The serial data lines are not specified as running at RS-232 voltage
levels, and are most likely either 3.3 volt or 5.0 volt logic.
3) Because of 1 and/or 2, a PC board would be needed for mounting this
device and its associated voltage regulator.
None of these are huge, insurmountable problems. However there are other
solutions, already packaged, that don't require special hardware. A number
of companies already make fully standalone ethernet/RS-232 boxes that can
be powered from regulated or unregulated supplies, so no design or
construction is required. If you've got to build a board to implement the
Lantronix part, you're going to spend some significant time getting to the
working end of the project. And you're likely to pay a premium to get that
which is needed to build one up, as a one-(or few)-off project.
http://www.moxa.com/product/Serial_Device_Servers/1_Port/NPort_DE_211.htm
is a unit I've used sucessfully to interface to the RS-232-based controller
in a product my company has manufactured and sold. While it doesn't use a
web page for configuration, it works adequately using a telnet client, and
it's well documented. It will support automatic connection and link
maintenence between two uning, over a network, allowing easy creation of
what appears to be a long RS-232 cable, via an existing network. It also
allows connection of its power source via pins of the RS-232 cable, in
addition to the supplied coaxial power connection on the side of the box.
So the power source connection can be made as physically reliable as the
DB-25 connector - always a plus in a mobile environment.
No, I don't work for these folks. I just had a need for ethernet/internet
to RS-232 remote operation, and this unit was one of the most cost
competitive off the shelf solutions I turned up, at the time. I've seen
re-branded versions of this companies' products from other manufacturers
too. And they're available from electronics distributors.
73, Bob, KD7NM
----------------------------------------------------------------------
Subject: Re: GPS thoughts
From: "Scott Miller" <scott@opentrac.org>
Date: Wed, 23 Jul 2003 11:12:30 -0700
X-Message-Number: 30
Hey, hiking boots are a common sight in data centers around here. Well, so
are combat boots, but that's usually because they're military people.
Though we did have one civilian employee who had to keep pushing the dress
code... I think they finally said something to him when he showed up in
black combat boots, khaki shorts, and a Hawaiian shirt.
Seriously, on the GPS thing, I've now got three of the $50 Digitraveler GPS
receivers. I'm planning to pull one out of its case and sew it into a
pocket on the top of my daypack. It'll connect to a TT3 and optionally to a
Palm m125 carried in a front pocket for display purposes. I just testing
the m125 with it today and it works pretty well - the display is comparable
to the Garmin eTrex series, and it's got a multimedia card slot for
expansion.
Hopefully this will fix the problem I've had with the eTrex Legend where I
can't ever find a convenient place to carry it where it can still see the
sky. The m125 can be shut off completely and stowed in a pocket without
affecting the receiver. And one of these days I'm going to have to try the
Palm APRS software.
Scott
N1VG
----- Original Message -----
From: "Mark Fellhauer" <sparkfel@qwest.net>
To: "TAPR APRS Special Interest Group" <aprssig@lists.tapr.org>
Sent: Wednesday, July 23, 2003 10:00 AM
Subject: [aprssig] Re: GPS thoughts
>strapped to my back. I suppose I could wear hiking boots all the time,
>but I'd look funny in bowling tournaments or at funerals/weddings... :)
----------------------------------------------------------------------
Subject: Mobile power
From: "Scott Miller" <scott@opentrac.org>
Date: Wed, 23 Jul 2003 11:24:43 -0700
X-Message-Number: 31
I've got a laptop with a thrashed screen and no battery - I think I'll try
hooking it straight up to 12 volts just to see if it'll power up. Now if
only they'd use something more rugged than coaxial plugs for power.
Here's another mobile power question... most of my stuff runs on NiMH AA
batteries. GPS, digital camera, tracker, radio, and so on. When I'm out
camping for awhile I can go through a lot of them, and currently my choices
for charging are a 4-cell solar charger, or an inverter driving a 110v
desktop charger with two banks of two cells. The solar charger is
unreliable and inconvenient because it can only charge groups of four, and
the inverter setup is bulky and inefficient. What I'd really like is a 12v
charger. Something with an 8-cell capacity and no larger than 2-cell banks.
Does such a beast exist? Or does anyone have a good charger schematic?
Also, I just picked up an 85 AH deep cycle marine battery at xxxxxx for
about $45. I'm thinking of building a mobile power cart with a 400 watt or
better inverter built in, along with voltage and current meters. It might
go in a large ammo can or other army surplus container... if anyone's got a
similar setup with pictures on how they did it, let me know...
Thanks,
Scott
N1VG
----------------------------------------------------------------------
Read previous mail | Read next mail
| |
