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Grimeton SAQ 17.2kHz Christmas Eve broadcast  

 
turretslug
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No, not a typo, a radio transmission that really is at a frequency slightly above PAL and NTSC line frequency and not 172kHz or 17.2MHz! From apparently (and believably) the only on-air operational Alexanderson alternator left in the world, it has been described as an alternator of power-station size and dentist-drill speed- something of an exaggeration in both ways but still reflective of quite an achievement that stretched the technology of its day in terms of power and precision, the high frequency output being achieved by using hundreds of reluctance gaps in the rotor.

https://en.wikipedia.org/wiki/Varberg_Radio_Station

http://whc.unesco.org/en/list/1134

This morning's transmission came in well here, using a very basic home-made up-convertor, based around the NE602 sand triode-hexode smile with peripheral components determined by what was plentiful here rather than application of science, fed from about 40 feet of random wire ("long wire" is utterly erroneous terminology with a 17.4km wavelength....) and feeding a Yaesu FRG-100 with 500Hz Collins mechanical 455kHz filter. Tune-up started at around 0740 GMT with a succession of letter "V"s interspersed with "SAQ" and key-downs of several seconds, the actual message coming just after 0800 (which I didn't copy or, shamefully, record!). The transmission appeared to cease around 0805, presumably in deference to both machinery life and the 'leccy meter. The clunkiness of converting 17.2kHz to first 4MHz, then 45MHz, then 455kHz and finally audio hasn't escaped me, I ought to come up with something simpler and thermionic for the next transmission in late June.

A fascinating glimpse into the world of pre-valve transmission techniques.

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Posted : 24/12/2016 11:52 am
Cathovisor
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Fascinating, and in a strange way, nice to know there is still one of these alternators running.

At the recent Gnosall auction, one of the lots was a veritable boat-anchor; a Soviet-era Wolna-K receiver, which is a marine receiver. The ranges on that tune down to 12kHz so it would have happily rx'ed that alternator.

Whilst I'd suggest your next frequency converter involved an ECH35 (6K8G if you must!) a bit of me thinks an ECH81 would do the job, as they've been proven to work at just 12V of HT.

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Posted : 24/12/2016 1:15 pm
turretslug
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In a sympathy for the underdog sort of way, I'd been thinking of a 7S7 or ECH42.... I rather like the loctal and rimlock series, the presentation was arguably mistimed and/or misconceived but the actual innards seemed to be mostly doing a good job (Oh, alright, someone said UL41, but there's an exception to every rule). The ECH81 often gets quoted as a good case of 12V kinda-working, but I wonder how well its predecessors also did at low HT? There's a cute wee LF (200-400kHz) beacon receiver, the BC1206, that was supposedly designed around minimum space/weight/cost usage in cramped WWII fighters that runs its loctals with HT of nominal 28V, the mixer being a 14S7. (Also notable for using the curious 28D7 double-tetrode, here in parallel single-ended mode but also used in push-pull, a valve supposedly inspired by the world of the 32V nominal "farm radio" where there was plenty of wind for the classic turbines and accumulators but the mains was a long. long way away indeed across the prairies.) Collins' R392, a classic piece of '50's US Cold War engineering-confectionery-for-the-sake-of-it also ran its valves straight from 28V supply- in this case, the use of 2 RF stages, 3 mixers and no less than 6 IF stages might suggest low gain at low volts but its full-beans HT (180V) rack-mount big brother the R390 does the same.

LF receivers can be interesting in an arcane sort of way- I wonder if the Wolna-K set uses tunable RC filtering on the 12-60kHz range in order to achieve 5:1 coverage, or if it is simply low-pass/band-pass filtered with 12kHz being the minimum achievable before the LO deafens the IF strip? Marconi's Atalanta uses tunable RC interstage, rather than tunable LC, in order to tune 25-100kHz in one go. Doing that with LC coupling would obviously need a tricky 16:1 range of either L or C, but only 4:1 with RC and the lower gain would be less important at those frequencies. Marconi's CR300 simply used a LPF on the 15-85kHz range. The Wolna-K has an aspect/presentation reminiscent of Murphy's B40 and B41 receivers, though without the wacky spiral "helter-skelter" tuning scale, presumably it's about as heavy....

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Posted : 24/12/2016 5:07 pm
Cathovisor
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turretslug said
The Wolna-K has an aspect/presentation reminiscent of Murphy's B40 and B41 receivers, though without the wacky spiral "helter-skelter" tuning scale, presumably it's about as heavy....  

I think I overheard suggestions that it was not going to leave its position on the stage at the village hall without a struggle...

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Posted : 24/12/2016 5:14 pm
Anonymous
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turretslug said
No, not a typo, a radio transmission that really is at a frequency slightly above PAL and NTSC line frequency and not 172kHz or 17.2MHz! 

Fascinating indeed!

ELF was/is the only way to communicate with submerged submarines, so imagine my surprise when driving in northern Wisconsin (a land locked State about midway from Atlantic to Pacific coasts) to find an ELF transmitter station.

At the time I had no idea what it was, and quite frankly it only got my attention because I look out for interesting "street furniture" on boring road trips. Here we found "miles and miles" of "power poles" cut into a large forest. What could it be for?

In the 1980s we somehow managed without Google and Wikipedia, so I asked a fellow Ham radio operator.

Two watts ERP at a carrier frequency of seventy-six Hertz, from a one megawatt drive... 

At least you have about six months to brew a receiver in time for the next QSO

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Posted : 27/12/2016 10:11 pm
Katie Bush
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Every time I read this thread, I seem to conjure up images of early 'Marconi Wireless Telegraph' sets, and especially the RMS Titanic.

How far removed from the subject matter are Marconi's 'spark gap' transmitters?

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Posted : 27/12/2016 10:53 pm
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Katie_Bush said
Every time I read this thread, I seem to conjure up images of early 'Marconi Wireless Telegraph' sets, and especially the RMS Titanic.

How far removed from the subject matter are Marconi's 'spark gap' transmitters?  

The Alexanderson alternator is an AC mechanical generator that delivers sine waves (CW) to the aerial. I suspect it uses some form of OOK (On Off Keying) to turn that carrier into dots and dashes.

The spark gap transmitter, which shock excites a tuned circuit with an impulse (the spark), again it has OOK for modulation. Spark gaps pre-date the Anderson, and both were eclipsed by valves (early nineteen teens)

They're birds of a feather!

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Posted : 27/12/2016 11:16 pm
turretslug
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FordAnglia said

Two watts ERP at a carrier frequency of seventy-six Hertz, from a one megawatt drive...

That's the sort of thing that's made me wonder over the years just to what extent mains gets "transmitted" by happenstance, as it were. Certainly, there would be a fair amount of cancellation happening but there is such a vast network of overhead power lines that there must be some 50Hz "broadcasting" and field strength. Indeed,I found out not so long ago that there is a recognised field of forensic investigation that involves DSP'ing out the received mains hum present in any sound recording- even remotely-located mobile phone calls, battery-operated tape-recordings etc. -and matching the minute mains frequency fluctuations to grid records going a long way back to precisely time the sequence of events in investigations.The sort of thing that has me muttering, "Nah, no way, can't be true!"- until you find out that it's been long recognised and established in a quiet sort of way. After all, most of us have probably encountered the high-impedance, sensitive amplifier that was susceptible to buzzing from nearby fingers, poor connector contacts and so on, it's an extension of that principle.

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Posted : 28/12/2016 11:42 am
Cathovisor
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I'd heard about the mains variations being used in forensics; fascinating.

Forgive my lack of knowledge in the field, but could you receive Grimeton using 'direct conversion' with an AF oscillator and a suitable band-pass filter?

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Posted : 28/12/2016 1:05 pm
turretslug
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I can't see any reason why not to do that, it sounds like a rational and elegant route, really. Quite a few postings on the subject talk about simply feeding a random wire aerial into a computer mic. input or sound-card for spectrum display presentation and audio, I gather that there are even a few SAQ-specific programs out there! A few different angles/possibilities to the problem.

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Posted : 28/12/2016 1:19 pm
Cathovisor
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turretslug said
I can't see any reason why not to do that, it sounds like a rational and elegant route, really. Quite a few postings on the subject talk about simply feeding a random wire aerial into a computer mic. input or sound-card for spectrum display presentation and audio, I gather that there are even a few SAQ-specific programs out there! A few different angles/possibilities to the problem.  

The computer solutions are interesting, but complex and a computer is electrically very noisy.

I like the idea of your preferred choice - an ECH42/7S7 - doing the job. So a BPF of a few hundred Hz bandwidth centred on 17.2kHz and an ECH42 oscillating near same should work?

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Posted : 28/12/2016 1:34 pm
turretslug
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It does go against the grain, using complex modern tech to receive almost 19th century technology transmissions- but you could say the same about radar or X-ray machines!- crude, even brutish devices at heart but highly refined and added-to over the years.

The relatively conventional receiver route was easiest for me as I already had the highly-resolving receiver with narrow filter, so the basic up-converter(250kHz LPF, NE602, 20p MPU crystal, broadly-tuned 4MHz output load) was quick'n'easy, literally the diecast box was the most expensive bit. I had been a bit paranoid about noise, turning everything SMPSU-ish off and running receiver and converter from a lead-aid gel pack- but when the transmission was underway, turning all the usual suspects for LF hash back on made no discernible difference, so maybe 17.2kHz is too low for much of the grot that is such a pain at LW and MW.

I had thought of using said 7S7 fed to the main 85kHz IF strip of my Eddystone 750, as this has variable-bandwidth mechanical IFT coupling down to CW bandwidth, thus an LO tunable around a few kHz of 70/100kHz should find SAQ. At least that would be fewer conversions and a more appropriate IF/technology. Talking of LF receivers and direct conversion, I'm surprised that there isn't more publicity about using the technique below LW (say), as all the narrow-span tuning range division gets clunky and long-winded as the octaves go lower.Just as an example, the CR100 receiver spans nearly 20MHz on the highest 11-30MHz band but only 100kHz on the lowest 60-160kHz band. The Eddystone 850 gets quite silly, with a slow-motion tuned 10-20kHz band. Maybe there are more elegant LF/VLF reception approaches, but they remained heavily-veiled in the bowels of submarines.... Not as appealing on the second-hand market as more mainstream coverage sets anyway.

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Posted : 28/12/2016 2:19 pm
Cathovisor
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I don't know if you've seen this:

http://eddystoneusergroup.org.uk/Data%20Sheets/Spec%20Sheet%20850-4%20Nov%201968.pdf

- but the price of the 850/4 is rather eye-catching, shall we say!

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Posted : 28/12/2016 2:57 pm
turretslug
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Ulp. Blimey, that appears to equate to over 5k today! Eddystone were a funny outfit (and I say that in full awareness of the danger of lynching by their die-hard afficionados), I never quite understood how they stayed in business so long. Actually, I've a pretty good idea- by relying on the near-mandatory patriotism and innate conservatism of government departments blessed with the cosy frisson that comes with near carte-blanche ability to sign cheques guaranteed by other people. The mechanical detailing, precision and sturdiness of some of their stuff can sometimes be second-to-none, almost the Kudelski of radios, but the actual electronic design is often unexceptional, been-there and even behind the curve. In other words, an uninformed person tasked with signing a purchase order probably thought, ooh, this is heavy and neatly built with smooth tuning- it must be hot poop, how quickly can you deliver? A more technically aware and critical presence might have denied them the order.

They also seemed to compensate for the machined castings and precise brassware by using some distinctly average electronic components, I suspect from what I've seen that a substantial amount was surplus or end-of-life acquisition. Certainly, the advice with any acquired Eddy is to stand by for a session of weeding out drifted R's and degraded C's.

The 850 is pretty ordinary and pedestrian in its design, a goodish MW radio topology with LF coilset. Other makers of that era had appreciated the fact that as you get closer to 0Hz (and 10kHz is perilously close in IF skirt selectivity terms!), the careful use of balanced mixers becomes pressing to stop the IF strip getting deafened by the LO and its close-in noise spectrum (eg, Racal's RA37 LF converter(12-980kHz) with its 2x 6F33 suppressor-grid controlled pentode balanced mixer, tweakable for AC and DC balance.)

Whilst the 750 here is one of the favourites for its mechanical construction competence, that doesn't blind me to its compromises and shortcomings- that, too, was a pricey set for what it offered, it seems to have sold in relatively small numbers and was eventually repositioned in Marconi HR100 guise as a shore-station watch receiver (a term which always seemed to have a "damning with faint praise" aspect to it).

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Posted : 28/12/2016 4:41 pm
Cathovisor
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I've heard similar accusations laid at Marconi's door; it was remarked to me that they were a high-quality metalwork company that just happened to put electronics inside their beautifully-made boxes!

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Posted : 28/12/2016 6:33 pm
raditechman
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Missed it again, I always forget about this transmission.

I think the web sdr at Twente may go down to 17.2 kHz

http://websdr.ewi.utwente.nl:8901/

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Posted : 29/12/2016 9:07 am
turretslug
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One thing I've been on the lookout for for a few years (in a fairly casual way, which'll be why I haven't found one yet...) is one of the 19kHz block LPFs that used to be used on the L + R outputs of posher FM tuners in pre-pilot cancel days- I believe Ambit used to do them. These typically had a multi-element LC network to bite sharply at 19kHz plus, but were careful to have minimal effect below that to avoid poisonous comments in the hifi press. One of these would seem to be a Good Thing at the input to a SAQ-(and GBR etc!) specific receiver/converter, as opposed to a wider-appeal converter with LPF at the top of the LW band. As with any LC block filter, they're a little fussy about terminating impedance (ISTR around 3k3 - 4k7 or so) but something like an input source- or emitter-follower using a small power FET or video DA output-type transistor and slight gain collector-loaded following stage buffering the high-impedance aerial into the filter and then to the mixer would keep things hygenic.

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Posted : 29/12/2016 10:18 am
Cathovisor
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turretslug said
One thing I've been on the lookout for for a few years (in a fairly casual way, which'll be why I haven't found one yet...) is one of the 19kHz block LPFs that used to be used on the L + R outputs of posher FM tuners in pre-pilot cancel days- I believe Ambit used to do them

I'm not entirely sure, but I think I have a few of those - they were in a box up in the loft (the contents of which is now in a storgae unit - still), NOS Philips stock. I will try and get to them before the summer.

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Posted : 29/12/2016 12:35 pm