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PA2AGA > HDDIG 23.12.99 04:32l 210 Lines 6884 Bytes #-9640 (0) @ EU
BID : HD_99_323B
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Subj: HamDigitalDigest 99/323B
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Subject: HamDigitalDigest 99/323B
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connections when plugging in/out or fondling with the connector to find
the spot of good ground contact.
Normally there is a small regulator on the card to provide the voltage,
and it is short-circuit protected. It could run a little hot when left
shorted all the time.
A better recommendation seems to always use AC-coupling on the soundcard
inputs, so if you use a transformer, put a (say 1uF) nonpolarized cap
in series. Or a resistor of sufficient value to reduce the current,
and small enough in relation to the input impedance. 4k7 or so.
In fact, this is always a good thing to do. When I make connections
to transceivers for 9k6 modification, where AC coupling is a bad idea,
I always put in a small series resistor directly at the connection point,
to avoid damage to the transceiver when the outgoing lead is shorted to
ground or to small voltages like +5 or +12. Better to have some percent
of signal loss than a blown-out 3357.
Rob
--
+----------------------------------+--------------------------------------+
| Rob Janssen pe1chl@amsat.org | WWW: http://www.knoware.nl/users/rob |
| AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU |
+----------------------------------+--------------------------------------+
>.
------------------------------
Date: Tue, 21 Dec 1999 00:46:31 GMT
From: longbch@my-deja.com
Subject: FA: MFJ 1278 Multi-mode Data Controller (Packet, RTTY, CW, FAX)
For Auction: MFJ 1278 Multi-mode Data Controller (Packet, RTTY, CW,
FAX)
See the auction at:
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=221981939
This package includes:
- The MFJ-1278 multi-mode controller
- AC adapter power supply
- Owner's Manual (Includes troubleshooting, calibration, and schematics)
- 2 Microphone cables with 5-pin DIN male connectors
(one is wired for a Kenwood TS-430S)
- MFJ Packet Starter Pack pamphlet
- Fast-Start manual (not pictured)
- 3.5" floppy of the MFJCOMM 3.0 software. This is the DOS program
that communicates with the unit.
The 1278 will operate the following modes:
- VHF packet
- HF packet
- Baudot
- AMTOR
- ASCII
- CW
- Weather Fax
I will try to answer any questions, please don't hesitate to e-mail me.
Thanks
Sent via Deja.com http://www.deja.com/
Before you buy.
>.
------------------------------
Date: Mon, 20 Dec 1999 11:23:56 -0600
From: "George T. Baker" <w5yr@worldnet.att.net>
Subject: ground loops and audio isolation transformers
Hamish, I use a fairly old but still workable Heathkit Monitorscope
(SB-610) to examine the output r-f envelope of the PSK31 transmitter
under TUNE (no modulation) and TWO TONE (idle) conditions.
The effects of any extraneous signal content are immediately evident as
waveform irregularities. If the unwanted signal components are of any
level at all, the power ratio between TUNE and IDLE will depart from the
ideal 50% value.
Any scope of sufficient vertical bandwidth will suffice to do envelope
examination. The old Monitorscope just happens to be rather convenient
for the purpose. Critical examination of the IDLE waveform readily
identifies any distortion due to overdriving, etc.
72/73, George
Fairview, TX 30 mi NE Dallas in Collin county
Amateur Radio W5YR, in the 54th year and it just keeps getting better!
R/C since 1964 - AMA 98452 RVing since 1972
Hamish Moffatt wrote:
>
> Rob <NoEmail@NoWay.com> wrote:
> > I think the main problem may be related to the fact that I use a laptop.
> > The laptop has an external power supply with a two prong plug. It is not
> > grounded well (like most laptops).
>
> Interesting. How can you detect that you have a ground loop?
> I have audio and PTT connected directly from my Toshiba laptop
> to my IC-726 rig and haven't noticed any problems.
>
> Hamish VK3SB
>.
------------------------------
Date: Mon, 20 Dec 1999 18:21:34 -0500
From: "Bob Lewis" <aa4pb@erols.com>
Subject: ground loops and audio isolation transformers
> How can you detect that you have a ground loop?
Listen to the signal on another receiver. The ground loop will cause
60 Hz hum on your signal. In addition to the ground problem, you also
have to be careful not to overdrive the rig or otherwise inject any
distortion into the signal. One way is to look at the waterfall
display of another receiver/computer setup or have a friend report on
your signal. Distortion will cause multiple lines (more than the
normal two in idle) on the waterfall and a low IMD number. Be careful
that the other receiver is not distorting the signal. With some
back-to-back testing I did here, I found that switching from slow to
fast AGC on my IC761 caused a 15 dB degradation of the IMD.
>.
------------------------------
Date: Sun, 19 Dec 1999 17:11:00 -0500
From: "Bob Lewis" <aa4pb@erols.com>
Subject: ground loops and audio isolation transformers
Must be related to the rig's mike input circuit in some way I guess.
I've used two different computers and two different lap tops with two
different rigs (Icom and Elecraft) in all combinations, all with
direct connections and no hum. Or, I'm just lucky.
Rob <NoEmail@NoWay.com> wrote in message
news:Yla74.199109$5r2.503872@tor-nn1.netcom.ca...
> Hi Bob,
>
> I also use short cables (abt 3 feet) between the sound card and
rig.
>
> I think the main problem may be related to the fact that I use a
laptop.
> The laptop has an external power supply with a two prong plug. It
is not
> grounded well (like most laptops).
>
> The ground loop problem is not that bad but it is there. The
solution is to
> use audio isolation transformers which SOME radio shack stores keep
in
> stock.
>
> Many SSTV programs for sound cards now recommend that you use these
> transformers just to be on the safe side. Some people just prepare
cables
> with the transformers in them since the transformers are really
small.
>
> But the audio isolation transformers won't be much good for real
ground loop
> problems unless you also isolate the PTT circuit using opto
isolator. Not a
> big deal. It will just cost you a dollar or two more in parts.
>
> I don't know why lots of Hams use a simple transistor for PTT
switching from
> the computer's serial port. Using an opto isolator is just as
simple and
> provides true ground isolation.
>
> 73's
> Rob
> VA2FB
>
> "Bob Lewis" <aa4pb@erols.com> wrote in message
> news:83j8k1$2m4$1@bob.news.rcn.net...
> > Just curious. When you have the ground loop problem are the radio
To be continued in digest: hd_99_323C
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