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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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10th Aug 2017, 4:57 pm | #1 |
Heptode
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 998
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T1154 question
I have put together a brief article on using the T1154 for Tim Walford but he asks quite what Marconi did to the tx to try to prevent the chirping. I can see why the set chirps, but what did Marconi's do specifically to try to stop it? Anyone?
david |
10th Aug 2017, 10:43 pm | #2 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: T1154 question
What makes you think Marconi did anything to stop the tx chirping? Studying the schematic I don't spot anything that might be an "anti-chirp" measure.
Richard |
10th Aug 2017, 11:09 pm | #3 |
Heptode
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
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Re: T1154 question
No, nor me...I was led up the path!
D |
10th Aug 2017, 11:43 pm | #4 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: T1154 question
David,
well, the sort of things you might do to reduce chirping are: - fit a buffer/driver stage between the VFO and PA - provide a stabilised HT supply to the VFO - run the VFO at half (or some other sub-multiple) of the output frequency - ensure the VFO is in a totally screened (and filtered) metal box - don't key the VFO Marconi didn't do any of those things. Maybe someone else would like to suggest anything they can spot which Marconi did do to reduce chirp.....! My assessment of the T1154 is that it was a 1930s design which was tweaked somewhat to meet RAF requirements. But no major departure from the well known 1930s design principles were attempted. That is totally normal when the design time is told "we need this and this this......and we need it yesterday....." Wartime is often thought of as the time when the greatest technical advances are made. And that's true for brand new technologies - like radar for instance. For well established technologies - like radio comms - they tend to stand still, because no-one dares (or has the time to) try out new ideas. Richard |
11th Aug 2017, 7:22 am | #5 | |
Heptode
Join Date: Jun 2012
Location: Southeast Norfolk, UK.
Posts: 772
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Re: T1154 question
Quote:
I believe that there were two or more external crystal oscillators developed for the T1154, one by the Australian air force post-WW2. I did have circuits and info on the RAAF version but I can't locate them at the moment. A web search may throw up something. You don't hear many really "chirpy" signals on the amateur bands these days and no-one gives less than a T9 report when one does show up. The excellent G4FON Morse training program has a chirp facility as well as QSB/QRM facilities and a chirpy signal is, IMHO, easier to copy. True, a lot of the other stations on-air durig WW2 would have had chirp, hum, key clicks and drift but that may have actually been useful in mentally filtering the wanted and unwanted signals, hence the apparent lack of interest in improving the signal quality. Just a thought! 73 Roger/G3VKM |
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11th Aug 2017, 8:10 am | #6 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: T1154 question
Quote:
Of course this technique worked independently of any need to actually crack the encryption used! |
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11th Aug 2017, 8:13 am | #7 |
Heptode
Join Date: Jun 2012
Location: Southeast Norfolk, UK.
Posts: 772
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Re: T1154 question
David,
Ref external crystal oscillators for the T1154, as I mentioned above, I have now located the files and if you would like a copy let me know via P/M 73 Roger |
11th Aug 2017, 8:21 am | #8 | |
Heptode
Join Date: Jun 2012
Location: Southeast Norfolk, UK.
Posts: 772
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Re: T1154 question
Quote:
73 Roger |
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11th Aug 2017, 8:59 am | #9 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: T1154 question
I doubt whether crystals were introduced to the T1154 merely to cure the chirp. They were probably added to ensure operators got the equipment on to frequency. Many operators were barely competent to switch the equipment on - let alone get it on frequency.
Richard |
11th Aug 2017, 9:50 am | #10 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
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Re: T1154 question
My understanding was that these add-ons were popular with civilian airlines in the early post-war days. I don't think it was because the operators were no good. In an emergency you really don't want to be messing about with wavemeters etc. to get on frequency especially if the channel you are using doesn't carry much traffic to net onto.
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11th Aug 2017, 10:18 am | #11 |
Heptode
Join Date: Jun 2012
Location: Southeast Norfolk, UK.
Posts: 772
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Re: T1154 question
Yes, the info I have on external COs for the T1154 is all post-WW2, I believe. The wholesale coversion during wartime of T1154 stocks and the huge crystal bank needed to support it would have been very resource-hungry. Most likely, postwar the RAAF and civil users who had a/c like the York and Lancastrian felt that a simple add-on box and a few surplus crystals would improve their radio comms at moderate cost.
As to operator standards, surely post-war the airlines would have the pick of the bunch amongst those who wanted to stay in flying for a career? 73 Roger |
11th Aug 2017, 10:40 am | #12 |
Heptode
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 998
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Re: T1154 question
Interesting replies thanks. I was aware that fists were identified but it hadn't occurred to me that individual transmitters might be also. It reminds me of a QSO I once had on my 1154...I called CQ and the chap came right back with "that's an 1154!".
D |
11th Aug 2017, 10:48 am | #13 |
Pentode
Join Date: Apr 2011
Location: Swansea, Wales, UK.
Posts: 143
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Re: T1154 question
The full HT was applied to the MO which helps start the oscillator quickly. I once tried stabilizing the MO HT at about 220v with a zener string from the bottom of the dropping resistor. That made chirp much worse.
The drift after you start keying is more of a nuisance in my opinion so I made some mods which help a great deal. http://www.v-d-r.net\images\T1154 DRIFT MOD.pdf I have some before and after mp3s too. Some RST reports give T3, T7, and other numbers. It's always a pleasure to get for instance 579C then you know you're talking to someone of experience. 73, Andrew |
11th Aug 2017, 10:54 am | #14 |
Heptode
Join Date: Jun 2012
Location: Southeast Norfolk, UK.
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Re: T1154 question
David,
The document I have is a report published in July 44 by the RN on the radio aspects of Fortitude and the techniques used, a sort of basic intro for the senior officers, I suppose. The scope views are of a couple of RAF T1190 TXs and a US Navy set I can't recall, all are CW. Even in recent times it was possible to know if you were hearing a particular TX type. The KW-2000 transceiver has a keyed audio oscillator for CW generation, which gives it a very distinctive note, the last one I worked was Pat Hawker's. Back in the day, there were KW detractors who insisted the mode wasn't legally allowed by the licence conditions as it was "A2J" not A1! Interesting topic. 73 Roger Last edited by G3VKM_Roger; 11th Aug 2017 at 10:57 am. Reason: spelling |
11th Aug 2017, 11:09 am | #15 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: T1154 question
Quote:
You don't need to key either the MO or the AF oscillator, just switch the AF tone to the modulator only when the key's down. Also because there's a continuous transmitted carrier you can use simple carrier-derived receiver AGC like you would with voice-modulation; you can't do this with keying-the-carrier CW because the BFO usually swamps the AGC. "MCW" as it used to be labelled on the likes of 19-sets !! |
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12th Aug 2017, 1:00 am | #16 |
Triode
Join Date: Apr 2017
Location: Wellington, New Zealand.
Posts: 30
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Re: T1154 question
...but MCW is a much less effective mode than CW.
I've sometimes wondered why the RAF didn't specify crystal control for the T1154. Those click-stop arrangements were pretty clunky and required the erks to set them up afresh before each operation. This gave the listening Germans a pretty good idea about how big the raid was going to be. The frequency drift must have been terrible in a vibrating aeroplane. Maybe crystals were just too costly at that time- although most of the 1154s I've seen only have 4 or 5 freqs written on the front panel. |
18th Aug 2017, 9:52 am | #17 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: T1154 question
My guess is that the trouble with crystals during WWII was that they didn't allow any frequency flexibility. And that meant that some b****r would be on your frequency when you wanted to use it. Or even worse, the Germans turned up and jammed you.
Sets operating on VHF - like the TR1133, TR1143 and SCR-522 (US version of the TR1143) first started being used in the Battle of Britain (actually only the TR1133 at that date). But they would be range limited over the horizon of course. Fine for air-to-air comms, but air to ground would have had to rely on HF. And if you were flying over Germany and trying to talk back to the UK, you can imagine the potential for jamming - either intentionally or non-intentionally from all the enemy forces on the ground. Richard |
18th Aug 2017, 10:11 am | #18 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: T1154 question
Leaving crystals aside as a solution to chirp and drift, there is absolutely no reason why a VFO controlled set can't be stable and chirp free. It just has to be designed to do it. And no-one thought it important enough apparently when the T1154 order was placed.
There is an interesting history of the T1154/R1155 equipment here. It shows they were developed from existing Marconi equipment already in use by commercial airlines - that was the AD67 and AD77 transmitters, and the AD6872 receivers. As I said above, that is typical of wartime developments. Equipment is needed yesterday, and so no-one dares do anything other than meet what the specifiers demand. Engineers may well have known after 10 years of development that the 2 valve (MO-PA) layout had severe performance limitations. Outbreak of war is not the best time to be tiddling with "improvements"! Richard Last edited by trh01uk; 18th Aug 2017 at 10:35 am. Reason: Missing link |
18th Aug 2017, 10:16 am | #19 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: T1154 question
And I might add to my post above that new ideas rarely come from specifiers. They only know what has gone before, and therefore only ask for "the same again" but in blue or pink or some other very minor change. They have no idea what can actually be done or what it would take to do it. New ideas nearly always come from engineers, who bridge the gap between what is needed to get a job done and what the technology can actually provide.
An example of this from a related field is the request by the UK government in the early 30s, when they first appreciated that the UK would be totally open to enemy bombing from the air for a "death ray". In other words, beam so much radio energy at an incoming plane that it exploded or otherwise met a sticky end. When the engineers got the request, they quickly scotched that one as strictly for boys' comics. But they did come up with an alternative......RADAR. Richard |
18th Aug 2017, 10:31 am | #20 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: T1154 question
And to return strictly to the theme of this thread, another interesting "defect" of the T1154 is the complete absence of any HT regulation or smoothing in the transmitter. It was clearly intended solely for rotary power supplies, which were the only source of HT in the air.
But along comes another requirement for ground stations using the T1154/R1155 combo. And this needs an AC mains power system - the Types 114 and 115 power units. The Type 114 system is in fact two units - great big brutes just about liftable by one person, one weighing 65lbs and the other 55lbs. The interesting thing about these units is the extent of the smoothing systems employed. The receiver HT (210V), the transmitter HT (1200V) and the LT (7V at 13A) use double iron-cored choke smoothing. That is a choke followed by a capacitor twice over. A feature of a rectifier followed by an L-C filter is its stability with load variations. When you have to do it twice over, its usually because ripple on the supply is a serious problem. In other words the equipment being powered is overly sensitive to ripple. When I simulated the original 1200V power system, I got a peak-to-peak ripple voltage of around 1.2 volts, and that was stable over load current from 80mA to 200mA. The high performance of those mains power units points to the need to compensate the equally poor performance of the transmitter! Richard |