Francophones

I popped into a local TV and radio dealer quite recently and asked for a yard of dial cord. The girl behind the counter had not the first idea what I was talking about.

I went back and forth between the text and the schematics to try and clear up some inaccuracies in the text. Comparing with the original German text, the G->F translator did an honourable job, in fact.

I believe you have a VNA. I'd use that instead of a wobbulator. You won't need the diode detector then. You'll need a high-Z probe though. You'll also need an oscilloscope to observe the audio amplifier input (to adjust the discriminator).

Jeroen Belleman

But not with those all-important abbreviations!

Yes, I do have a couple of lab grade VNAs, but I really don't see how they could be used to good effect in this situation? Surely a wobbulator is king here? Attempting to use a VNA would just create another set of obstacles AFAICS because I would really require a fixture to get meaningful results and getting a fixture for this specific transistor radio would mean building one, which is for me right now totally impractical (not to mention massive overkill!)

Maybe you should first build a dim bulb tester. Among other things, it would enable you to re-form the power supply caps it old gear and save an explosion or three. :-)

Many hits on a Google search, here's the first one:

I did actually build one a few years ago with swappable bulbs for different loads. Two problems, though:

I think that you might have to add a third one in future - finding an incandescent bulb to use!

Yes, getting harder as time goes by, so I stocked-up in advance and put a couple of dozen aside while they were still widely available. I would imagine the oven types will still be around for a few more years, anyway - and they tend to be more robust.

For many purposes you can ignore the difference between the 50 and 75 ohm impedances (and 60 if you ever come across any). However, be very aware only BNC 50 and 75 ohm connectors are mutually mechanically mateable (yes - they really are!). I don't know if any others that are.

Not recommended. The center pin differs, a 50 Ohm BNC pin is thicker and may damage a 75 ohm BNC. I'm cautious, most of my below 1 GHz equipment is 75 Ohms (from CATV company), the rest is 50.

Arie

It is the N connector the center pin is different. The BNC pin is the same. It is the ammount of dialectric (insulation) in the BNC that makes it a 75 or 50 ohm connector.

In the US anyway, there is an alternative, to use only bulbs intended for industrial uses, meaning other than 120 Vac. Like 130 Vac.

Joe Gwinn

N connectors are good, but the fact that 75 and 50 Ohm connectors are similar enough to mate, but not nearly enough to do so without damage or malfunction is perverse. When I took charge of the electronics lab, it took a while to sort them out and to eliminate the victims of mismatched matings. (I was always amazed at the sheer quantity of connectors in a busy lab.)

For BNCs, there *is* a difference, but it doesn't usually matter. I kept 50 and 75 Ohms separate, but when put to the test, many

In a pinch, BNC and N can even mate between them. I'm not sure if that's deliberate or accidental.

Jeroen Belleman

For most of its length, the male BNC 50 ohm pin is actually the same diameter as the 75. However, the tip of the 50 pin is fairly 'blunt', while the 75 is more pointed.

I guess that if you are particularly clumsy while you are inserting a 50 male into a female 75, it might just be possible to have the blunter male pin a bit off-centre, and catch the side of the female receptacle, and splay it. However, despite 43 years working in the CATV industry, I failed to achieve this!

The real difference between the two impedances is that the amount of PTFE dielectric in the 75 has been minimised in order to increase (with some difficulty) the Zo from 50 to 75 ohms. IIRC, the 50 has a more-uniform structural RLR, so it the better connector at the higher frequencies.

In message snipped-for-privacy@news.eternal-september.org>, Ralph Mowery snipped-for-privacy@charter.net writes

Indeed. A 75 ohm N male (thin pin) inserted into a 50 ohm female (fatter receptacle) results in a non-connection. A 50 ohm N male (fat pin) inserted into a 75 ohm female (thin receptacle) results in a splayed (and usually wrecked for future use) receptacle.

Yes - the 'innards' are essentially the same. IIRC, the BNC innards also mate with C-connectors. I think it's deliberate. After all, its the innards that carry the RF.

I don't think that's quite right. The diameter of the inner and outer conductors has more influence on Zo than the dilectric thickness.

A type N male will also mate with a BNC female.

Cheers

Phil Hobbs

I doubt they'll be able to replace the oven illumination easily (unless they mount the bulb on the outside and use fibreoptics to bring light to the inside!). I was surprised a few months ago when I bought a new microwave oven to find it had an LED lamp which illuminated the inside. I would have thought that with around a kW of microwave energy being generated that would have been a pretty hostile environment for an LED lamp. Obviously, though, they had the screening well sorted out. I suppose that I shouldn't have been surprised as the timing and display circuitry have been around for years and hasn't been affected by the RF energy or switching spikes.