Amplifer Design

Most UK kettles are 3kW although there is a trend towards 2.4kW for new portable appliances as the full 13A load stresses the fused plugs somewhat. Much more of a problem with electric fan heaters than kettles which typically only present a load for a couple of minutes at most.

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Regards, 
Martin Brown

Not at all. I just checked the rating label on my "electric kettle". (Almost every household in the UK has one of these.) Mine is rated at 220 - 240V, 2500 - 3000W.

Most UK household mains supplies are about 240V single phase and have a main fuse rated at 80 or 100A. Larger houses often have

3-phase 240V (phase to neutral) at 100A per phase.

(The "official" voltage is 230V but this is just for harmonisation purposes with the rest of the EU. The specified tolerances allow the real voltage to be around 240V for most areas.)

John

2400 W is only 10 A steady state i.e. 24 ohm resistance.

Unfortunately the cold resistance is quite low, until the resistor reaches nominal operating temperature, so the cold start current can be much larger than 10 A.

Well I'm mightily relieved you said that, Win, because I do happen to have a very large amount of both polarities in stock. THANKS!!! :)

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...

The RTL-SDR (listening) community seems to think that this genuine "RTL-SDR v3 Blog" version is very much better than the cheap generic TV dongles that have the same chipset. Ok, I grant that it has a TCXO and the "Q-branch" mod for HF listening, but...

What else is it about this specific dongle that makes it better? If you know and have time to answer, of course...

Clifford Heath

Just wondering if I should try to match pairs by Beta as closely as possible. I have a nagging suspicion I really should make that extra little bit of effort.

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SDR is pretty amazing for its size and cost, but in terms of sensitivity and selectivity you really cannot beat good old fashioned physical components built specifically for the purpose: rock solid silver mica capacitors and carefully cut and trimmed, temp-stabilised quartz crystals for frequency control; large, open wound, well-spaced gold plated inductors for high Q tuned circuits. You'll never successfully emulate qualities like those in software. NEVER!!

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Yes, I know and agree about SDR (though it can do other things that are very complex in discrete, like order-100 filters, etc). I asked about this specific RTL2832U dongle being supposedly better than other ones. I'm amazed at the fan-dom it has garnered, being a crappy little 8-bit thing on USB.

Although this is an old design, it adheres well to the BJT design philopsohy I learned in the late 60s. Which is to rely on accurate Ebers-Moll transconductance characteristics, and stay away from the uncertain beta, and similar aspects of a transistor, in the circuit design. So you don't need to match beta, Vbe, or other perameters.

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 Thanks, 
    - Win

It could be as low as 22 ohms when cold. but I can't see an xtra half-amp making a big difference.

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  When I tried casting out nines I made a hash of it.

On a sunny day (Thu, 17 Oct 2019 09:38:31 +1100) it happened Clifford Heath wrote in :

Well I have the time, nyways what is time .. relativity.. OK As with everything (like cars) people have preferences. Indeed the TCXO is great, But .. you can specify angt frequency error in rtl_sdr with the -p flag to compensate. When you have the thing warm up for some time even without TCXO the drift is maybe 2 ppm (for my old ones that is). For most purposes that is fine. I have a rubidium reference (ebay) and cheched the ebay TXCO sticks against it, and for one I added a 1 ppm correction (assuming the rubidium is exact). Good enough for me. As to sensitivity I am not sure, seems much the same to me. I did GPS with the E4000.

I have 2 of the ebay TCXO ones, rtl_test shows this on the laptop: ~# rtl_test Found 1 device(s): 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Found Rafael Micro R820T tuner Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

Then I have a very old no TCXO one that one runs on a Raspberry Pi receiving AIS (ship data): root@raspberrypi:~# rtl_test Found 1 device(s): 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Found Rafael Micro R820T tuner Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

So that one looks a lot like the same chip, but no TCXO, corection needed +46 ppm

Rx AIS with the one: rtl_fm -f 161975000 -p 46 -s 48k -r 48k | aisdecoder -d -h 127.0.0.1 -p 10123 -a file -c mono -f /dev/stdin And then I have an old nice E4000 with a wider frequency range: ~ # rtl_test Found 1 device(s): 0: Generic RTL2832U (e.g. hama nano) Using device 0: Generic RTL2832U (e.g. hama nano) Found Elonics E4000 tuner Supported gain values (14): -1.0 1.5 4.0 6.5 9.0 11.5 14.0 16.5 19.0 21.5 24.0 29.0 34.0 42.0

That one has a few ppm error too, but the larger frequency range is great, I rebuild it mounting the PCB in a dycast box. E4000 tuner is maybe harder to find these days, no TCXO.

So it depends. For testing I just always use a TCXO one.

Very nice things to have, one in use to receive data from a cheap 433 MHz wireless weather sensor mounted outside under the garden table uses 'rtl_433' software. Planes with 'dump1090'.

Note the harmonic factor button, say you have 144 MHz, just press it to 2 and you see 288, 432, etc etc tells you a lot about your filtering :-) In the olden days in broadcasting we used to test the eurovision audio lines with 1000 Hz, and then measure the amplitude of 2000, 3000, 4000, etc .. do the math and get distortion. No scope in the world ... ! That also works for MHz..

Just scan the spectrum, last week I was searching for some interference, came from a HDMI cable...

On a sunny day (Wed, 16 Oct 2019 23:39:41 -0000 (UTC)) it happened Cursitor Doom wrote in :

No T-Ford either! Again, do you have a cellphone?

Thanks, Win, that's a real plus, believe me. I'm carrying out some other tests in the odd minutes I get between the phone ringing and various people calling and have ascertained the

*actual* fault appears to be in one of the preceding stages. So at the moment, it looks like there's nothing wrong with that "partially C-E shorted bjt" - it's simply being driven into saturation by a chain of cause and effect from an earlier stage where the true fault *does* lie. I'm guessing this is not unusual when you have directly-coupled stages like these, which I'm not so much accustomed to dealing with. I'll be investigating further over the next 8 hours as and when time and interruptions permit and will report back in due course.... Thanks again for your invaluable assistance!

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Same here! Far too much stuff in fact. Well, if you're not too far away why not pop over and meet up at the next one? And don't worry - I'm not gay! :-D

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Yes, of course. HATE the damn thing, but there's no avoiding them. What are you driving at, dear boy?

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Domestic supplies are variously rated at 40A, 60A, 80A and 100A. 40 is comm on in 1&2 bed flats. There are also pre-war 30A supplies still in use, even in houses where one would expect much better. In my limited experience of the latter they coped with way above 30A well enough.

230v is the nominal voltage only - the target voltage is still 240v.

NT

On a sunny day (Thu, 17 Oct 2019 08:00:46 -0000 (UTC)) it happened Cursitor Doom wrote in :

So, now I am curious, where are you located then? or is that only known to Russian agents ;-)?

I am all the way in the north of the Netherlands, 'Friesland'. Well now anyways, lived all over the place.

On a sunny day (Thu, 17 Oct 2019 08:13:45 -0000 (UTC)) it happened Cursitor Doom wrote in :

In that cellphone there is a lot of precision RF stuff, filtering etc, mostly integrated in one chip that is smaller than even one of your mica caps... If you like 'precision' filtering, then I have a super-conducting filter from a cell[phone tower here.... At 70 degrees Kelvin the R of the inductors is zero, so the Q is enormous, that filter is attenuating any out of band signals in the cellphone band (in the tower).

also a bit of a boat-anchor :-)

Elsewhere in Yurp. It'll take me 48hrs to get to that hamfest so there's no excuse for you not to make the effort from your position "just up the road." :-)

Believe me, it's not the Russians you need to worry about.

Ah yes, I know it well (the location anyway). So that's a date then! Next March at the hamfest. I'll be wearing a red carnation, bright orange flared trousers and a tinfoil hat. See you there! :)

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