little pcb-mount CTs

I lucked out, in a recent visit to a local electronics-surplus store, and found a whole reel of very nice little surface-mount telco-coupling transformers which were apparently intended for PCMCIA V.90 modems. Bought a dozen or so to stuff into my junk-box.

They make very nice audio coupling transformers for "sound card modem" use in ham-radio applications (packet radio, PSK31, etc.).

I vaguely recall designing some basic rate ISDN equipment many years ago.

There were 2 standards for modulation, both providing 160kb/s. 4B3T (mapping 4 bits into three ternary symbols at 120kbaud) was popular in Europe. ISTR that there were more 4B3T ISDN lines than POTS lines in Germany. Or was that newly installed lines? I forget.

2B1Q (mapping 2 bits into each four level symbol at 80kbaud) was the other standard. 2B1Q doesn't have a spectral null at DC. It was important for the transformers to have good low frequency performance to avoid baseline wander. 4B3T didn't have this problem. Mapping 4 bits (16 combinations) into three ternary symbols (27 combinations) allowed room for some spectral shaping, including a DC null. The cost was a much wider bandwidth though (120kbaud vs 80kbaud for 2B1Q).

I had to design my own transformers. At the time, there was nothing available with the performance (both bandwidth and distortion) as well as supplementary insulation (as defined in IEC 60950) which was required to connect to a phone network. Most of the transformer manufacturers hadn't even heard of supplementary insulation. "How many kV is that?" they'd ask.

Regards, Allan

Ah, okay. I do something similar in modulating diode lasers--two secondaries in series-opposing between the current source and the laser, with the centre tap bypassed to ground. Zero DC magnetization, and the low laser impedance together with tight coupling keeps the power supply end from waving around too much.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

nor can you

rote:

's

.

-up

some dumb choices. Dissing me may not be particularly stupid, but dissing Joerg is exceedingly foolish.

gine that his own ideas on a subject could possibly be incorrect.

I don't find it difficult at all. If you find out that some of your ideas h ave been wrong - and admit it here, as I've been known to do - it doesn't t ake much imagination to conjure up the spectre of other ideas being wrong. The problem isn't so much a lack of imagination on krw's part, as an unwill ingess to contemplate the possibility.

In your case - of course - you haven't got a clue what's going on, so imagi nation doesn't come into it.

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Bill Sloman, Sydney

On Thu, 7 May 2015 19:09:43 -0700 (PDT), Bill Sloman Gave us:

Absolute bullshit.

555 argument is a perfect example of a proof that you are lying.

Really? If I though that there was a rational basis for your opinion I'd ask you to expand your argument, but since you've got no more idea than krw about what constitutes proof - or lying - it would be a total waste of time.

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Bill Sloman, Sydney

On Fri, 8 May 2015 01:10:22 -0700 (PDT), Bill Sloman Gave us:

You ARE a GODDAMNED, lying, retarded bastard, as you cannot even cite one instance of you admitting your absolute bullshit in here.

Not only can I do it, I've done it before. Search on "bill sloman" and "oops" and you'll get several examples.

The first one I found was on the 20th January 2014, in the thread "Emitter Follower + LPF Sine Convert for CD4060". It wasn't a particularly dramatic drop-off, but I certainly admitted that I'd been wrong.

It's probably not the most recent drop-off either. There was one on the 13/06/2014 in the thread "How do you test a 24Bit ADC" where I admitted that I'd posted a bad link, which is even more trivial.

I could probably find an embarrassing error if I looked hard enough, but it's late and I'm going to bed.

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Bill Sloman, Sydney

On Fri, 8 May 2015 08:40:19 -0700 (PDT), Bill Sloman Gave us:

Oh boy! BillyTard "posted a bad link" and cites *that* as one of his mistakes.

You are truly pathetic. Worse than the goddamned politicians and Tom Brady too. Fuck you.

You are not his type, DecadentLinuxUserNumeroUnoTard. Continue begging. Better luck next time.

On Fri, 08 May 2015 13:50:29 -0500, John S Gave us:

Leave it to a total retard to fail to grasp colloquial usage.

Continue trying, though I doubt you'll ever get it, being the thick skulled retard that you are. Better luck next life. That is if God lets you return as anything above a common slug, which is above where your brain currently operates.

Nice try though, chump.

It was certainly not what I'd intended to do, and I admitted that it was a mistake.

As usual, you missed the point, which was that I know I do make mistakes and I do acknowledge them. I don't make many and finding one that was big enough to make you happy required more work than you deserve.

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Bill Sloman, Sydney