[Fwd: TR and RF problem of the computer: Solutions]

Fri, 14 Feb 1997 18:33:32 +0300

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Date: Fri, 14 Feb 1997 13:46:23 +0100
To: oh2mm@nettilinja.fi
From: SM7PKK <mats.persson@mbox2.swipnet.se>
Subject: Re: TR and RF problem of the computer:  Solutions
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Hi Ville,

Instead of using the CNY-17 I would suggest you use the Darlington
Opto-couplers instead. They can be driven by the port much easier and thus
you never need the transistor. We have used this setup at the local club
for our multi-station several times both for CW keying aswell as to control
our home made voiceboxes on SSB.

Fx TIL 113

I have also found ELFA Sweden selling a special kind of Ferrite beads that
are especially made for the 9 pole D-sub aswell as for the 25 pole. These
ferrite beads have 9 resp. 25 holes in them shaped as the pinning on the
connectors. Thus you can pull the leads through the bead and then solder
them then slide the Ferrite piece all the way out to the already soldered
wires and thus get the RFI -prevention directly at the connector. This
toogether with a shielded D-sub cover will take care of intereference to
and from the computer very well. Especially if these kind of beads are used
at both ends. 

73 de Mats SM7PKK

At 20.44 1997-02-12 +0300, you wrote: 
>>>>

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

SM7PKK			E-mail: mats.persson@mbox2.swipnet.se
Mats Persson		The SM7PKK DX-Pedition Site- http://home1.swipnet.se/~w-17565
Zenithgatan 24 # 5		PLEASE NOTE THAT THE SITE HAS MOVED!!!
S-212 14 Malmoe		DON´T USE CALLBOOK ADRESS IT´S WRONG!
Sweden			CW !!

P.S My logs are open forever.. ever.. ever..

I do not want to receive any MAILORDER offers of any kind to my e-mail
address!!!!

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