TR and RF problem of the computer: Solutions
Ville Hiilesmaa
oh2mm@nettilinja.fi
Wed, 12 Feb 1997 20:44:37 +0300
------------33CE5900292F3
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset=us-ascii
Like K4MA and others, I have experienced a lot
of RFI to the computer when using TR with a
linear amp at OH0MM, EA8EA and PY0FF.
The symptom is the same: paraller port used for keying is
locked in a permanent key-down position. The
locking can happen with only 80 watts output.
At all these three QTHs I mentioned
some of the antennas are very close to the shack.
I've used laptops only, a Dell 386SX
and a Panasonic CF-41 Pentium.
I agree that ferrite chokes and optoisolation help,
but sometimes this is not enough. In that case, a
ground lead will help.
The remedies in detail:
1. FERRITE CHOKES on ALL leads attached to the laptop,
I use the rectangular ferrite stuff (which can be opened, don't
remember the brand name). Use separate ferrite for each lead.
The chokes must be very close to the laptop (no more than one inch).
Note that the power cable and the paddle cable must be choked, too.
In some instances two chokes in series is needed for a single cable,
in particular, for 160M.
2. Use of OPTOISOLATING TRANSISTORS
for the keying line and for the PTT line.
Optos are very small, cheap, and provide a complete
galvanic isolation between the laptop and the radio.
I use CNY-17.
The circuit is simple and fits inside a parallel port connector.
Some laptops give too low voltage to properly
switch the light diode inside the CNY-17 .
In this case, an additional 2N2222 will
help. (I can FAX the circuit, if you need).
3. GROUNDING THE CHASSIS of the laptop directly to the
chassis of the linear amp. Necessary in some cases, not always.
Use a very short (about 2 to 3 ft.) direct ground wire from the
laptop to the amp. This is the ONLY ground connection between
the laptop and the rest of the rig (other leads being opto-isolated).
(It looks like the internal wiring of the laptop picks up RF
so that choking external leads isn't always enough).
4. USE KENWOOD's IF-232C INTERFACE
to control the TS-850 frequency, RIT, etc. via the serial port.
The IF-232C is a small black (and expensive!!!) box
and it also uses photocoupler circuits which provide
electrical isolation between the computer and the rig.
I don't have any experience of rigs other than TS-850.
I've not used packet and don't know how much RF
the packed connection wires would pick up.
I've never used CT in a contest, so can't comment on that, either.
Good luck!
Ville, OH2MM
------------33CE5900292F3
Content-Transfer-Encoding: 7bit
Content-Type: text/html; charset=us-ascii
<HTML><BODY>
<DT> </DT>
<DT>Like K4MA and others, I have experienced a lot </DT>
<DT>of RFI to the computer when using TR with a </DT>
<DT>linear amp at OH0MM, EA8EA and PY0FF.</DT>
<DT>The symptom is the same: paraller port used for keying is</DT>
<DT>locked in a permanent key-down position. The</DT>
<DT>locking can happen with only 80 watts output.</DT>
<DT> </DT>
<DT>At all these three QTHs I mentioned</DT>
<DT>some of the antennas are very close to the shack.</DT>
<DT> </DT>
<DT>I've used laptops only, a Dell 386SX</DT>
<DT>and a Panasonic CF-41 Pentium.</DT>
<DT> </DT>
<DT>I agree that ferrite chokes and optoisolation help,</DT>
<DT>but sometimes this is not enough. In that case, a</DT>
<DT>ground lead will help.</DT>
<DT> </DT>
<DT>The remedies in detail:</DT>
<DT> </DT>
<DT>1. FERRITE CHOKES on ALL leads attached to the laptop,</DT>
<DT>I use the rectangular ferrite stuff (which can be opened, don't</DT>
<DT>remember the brand name). Use separate ferrite for each lead.</DT>
<DT>The chokes must be very close to the laptop (no more than one inch).</DT>
<DT>Note that the power cable and the paddle cable must be choked, too.</DT>
<DT>In some instances two chokes in series is needed for a single cable,</DT>
<DT>in particular, for 160M.</DT>
<DT> </DT>
<DT>2. Use of OPTOISOLATING TRANSISTORS</DT>
<DT>for the keying line and for the PTT line.</DT>
<DT>Optos are very small, cheap, and provide a complete </DT>
<DT>galvanic isolation between the laptop and the radio.</DT>
<DT>I use CNY-17.</DT>
<DT>The circuit is simple and fits inside a parallel port connector.</DT>
<DT>Some laptops give too low voltage to properly</DT>
<DT>switch the light diode inside the CNY-17 .</DT>
<DT>In this case, an additional 2N2222 will</DT>
<DT>help. (I can FAX the circuit, if you need).</DT>
<DT> </DT>
<DT>3. GROUNDING THE CHASSIS of the laptop directly to the</DT>
<DT>chassis of the linear amp. Necessary in some cases, not always.</DT>
<DT>Use a very short (about 2 to 3 ft.) direct ground wire from the </DT>
<DT>laptop to the amp. This is the ONLY ground connection between</DT>
<DT>the laptop and the rest of the rig (other leads being opto-isolated).</DT>
<DT>(It looks like the internal wiring of the laptop picks up RF</DT>
<DT>so that choking external leads isn't always enough).</DT>
<DT> </DT>
<DT>4. USE KENWOOD's IF-232C INTERFACE</DT>
<DT>to control the TS-850 frequency, RIT, etc. via the serial port.</DT>
<DT>The IF-232C is a small black (and expensive!!!) box</DT>
<DT>and it also uses photocoupler circuits which provide</DT>
<DT>electrical isolation between the computer and the rig. </DT>
<DT>I don't have any experience of rigs other than TS-850.</DT>
<DT> </DT>
<DT>I've not used packet and don't know how much RF</DT>
<DT>the packed connection wires would pick up. </DT>
<DT>I've never used CT in a contest, so can't comment on that, either.</DT>
<DT> </DT>
<DT>Good luck!</DT>
<DT> </DT>
<DT>Ville, OH2MM</DT>
</BODY>
</HTML>
------------33CE5900292F3--