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PA2AGA > HDDIG 05.12.99 14:17l 174 Lines 7385 Bytes #-9661 (0) @ EU
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Date: Sat, 04 Dec 99 23:34:13 MET
Message-Id: <hd_99_305B>
From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 99/305B
X-BBS-Msg-Type: B
All,
(especially to Scott, Trish, Cortland, John, Wb4ogm, Mark, Hamish,
George)
I believe I am zeroing in on the source of the computer generated
interference. I believe it is as some of you suggested, the SMPS
(switching) power supply internal to the Toshiba. Apparently the
switching speed is 110 khz. I am not even sure 110khz is considered RF.
At any rate, I suspect the 110 khz follows the 110 vac wiring path into
the Icom tranceiver. So I suspect I am looking for a way to eliminate
the offending 110 khz signal somehow along the 110 vac wiring path,
(computer power cord, etc). This helps narrow coming up with alternative
solutions considerably. If you have ideas I'm all ears.
I have written the following letter to the folks at the Toshiba Tech
Dept.
To Toshiba,,
Thanks for your help this morning. If you will recall, I described to
you an RF radio interference problem which I am having with my Toshiba
Tecra 500CDT. The interference which the computer is generating prevents
me from using my ICOM 728 Amateur Radio transceiver to communicate
within the 6.5 to 8.5 mhz frequency spectrum. I understand this
interference may be in violation of FCC Part 15 re electronic
device/radio interference.
To recap the situation, I have a Toshiba Tecra 500 CDT computer. I
bought it in December of 1996. The three year warranty is up December
31st of this year. I have recently begun using my computer in the same
room with, and in conjunction with an amateur radio high frequency SSB
tranceiver. The transceiver and computer are in close proximity, 2-4
feet.
The problem is that the computer generates a significant amount of RF
interference, at many frequencies, enough to interfere with reception,
from about 6.5 to 8.5 mhz in the HF frequency spectrum. I have done some
preliminary testing and have tried some fixes but so far the problem and
interference persists.
There is a law which manufacturers of electronic devices and electronic
devices must be in compliance with. The law requires that any electronic
device may not cause interference to other devices or services. It is
FCC Rule Part 15. The FCC's Part 5
compliance ID number is CJ6UK333. The decal on the bottom of the unit
references the law and the FCC ID number.
1. The interference seems to be generated by the CPU or internal power
supply. I understand the internal power supply in the
Tecra is an SMPS (switching type) power supply operating at 110 khz. The
interference caused by turning on the computer when it is plugged into
the 110 vac house current supply. It dissappears when the computer's
power cord is removed from the 110 vac house current receptacle and is
left to run on it's internal battery. Turning on the computer creates
90% of the interference. The LCD screen lighting adds another 10% of
measureable S unit noise level on the Icom 728 transceiver signal
strength meter.
2. The frequencies where the majority of the interference appears are
between about 6.5 mhz and 8.5 mhz and the interference
appears independently at many different frequencies and spaced about 110
khz apart. Ie interference frequencies are 7070, 7180, 7290, 7400,
7510, etc.
3. The noise is stopped if the computer is turned off or put in
"suspend" mode and powered down.
4. Noise is significantly reduced, (perhaps acceptable), at freqs lower
than 6.0 mhz, and higher than 9 mhz
5. I have tried connecting, the computer's rear metal computer port
jacks to the the Icom 728 chassis. This helps to
reduce the interference by perhaps 5-10%
6. Have tried ferrite chokes / cable clamps on the computers data cable
and the computer's 110 vac power cord. The effect on interference is
negligible
7. I have tried unplugging the 110 vac power cord. The effect on
interference reduction is dramatic. Interference is reduced 90%.
8. I have seen somewhere where someone suggested trying rf bypass caps
to bleed off unwanted RF energy. Is this a solution?
Given the frequency of the signal, 110 khz, and the fact that turning
off the computer power supply stops the interference the
power supply is likey the culprit. Also there is a question in my mind
as to whether the interferring signal is being radiated. The
RF ferrite chokes clamped on to the 110 vac power cord appear to have no
effect on the level of interference. I believe the 110 khz signal is
primarily being conducted along the 110 vac wiring path to the HF
tranceiver, rather than being radiated, leading me to believe something
could be done to eliminate the signal somewhere along its wired path,
capacitors?, specialized filter circuit?.
Thank you for your suggestions with respect to this problem. If you
believe you can service and repair the problem, and can
describe your proposed solution, I will be happy to ship the unit to you
for such repair. If the problem is inherent in the computer or it's
internal power supply by design, and is irreparable, we shall have to
take alternative steps.
The Serial Number of the unit is #11689286. The Part Number is
#PA1221U-T2A. The Toshiba Registration Number is #5997388. Toshiba Case
Number is #1837689.
Thank you,
Bob Cook
>.
------------------------------
Date: Wed, 24 Nov 1999 18:48:04 -0800
From: "Cathryn Mataga" <cathryn@junglevision.com>
Subject: good 9k6 pkt rig ?
Okay, my antenna is one of those Cushcraft dual band yagis. It's
like $69 or something. It's on an archerotor, that's on
2 5 foot masts on the roof. Maybe 25 feet off the ground in the
flats of Berkeley, which is a slight grade to the SF bay.
Though lately, I've had the antenna pointed one way all the time,
so I'm thinking of fixing that beam on another mast I have, and
using the rotor for something else. Except it's just too cold to
mess with it, nowadays.
w6yx in Palo Alto, has a pretty good site, I understand
on side of Black Mountain, that looks over most of the East Bay and South
Bay, as I understand it.
I'm pretty sure paccomm can put in crystals for whatever pair you want.
So, the split should be no problem.
Seems to be the common wisdom, that putting amps on 9600 baud
channels isn't such a good idea, since the T/R switching slows things
down -- though I'm just repeating what I've read and heard from others
around here. I have considered running more power, though, to avoid
'hidden transmitter' issues with stations farther south in San Jose. That
is I want to blast out enough juice to keep their carrier detect going,
even if they don't copy me. Though right now the channel is pretty quiet,
so this isn't a huge issue.
I think, if you want more power, the way to go is with the Mitek's err,
I forget the other brand that people modify, but these guys put out
near 80 watts.
I do know that the station on other end runs 3 watts into
a vertical, and I was initially worried about this, being 30 miles
away and all, but it seems to basically work. I initially planned
to move the radio up on the mast, if I had any trouble, figuring I'd
To be continued in digest: hd_99_305C
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