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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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Old 14th Apr 2021, 9:17 am   #1
ian rose
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Default Airmec 864 comms rx.

Hello all
I have an example of the above unusual receiver of which [i understand] not many were made.
Although a little clumsy to use it performs well electronically.
It would be interesting to share thoughts with other member[s] about the receiver.
Regards to all
Ian Rose
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Old 14th Apr 2021, 9:33 am   #2
Radio Wrangler
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Default Re: Airmec 864 comms rx.

Hadn't known they'd done one.

The case and dial looks extremely like their signal generator. I wonder which came first?
Radiomuseum says this receiver is GPO approved for use in ships, so that presumably means it met the requirements of the period for a ship's main or second receiver.

As you have one, you might just be the main source of information on it.

Photos would be good.

David
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Old 14th Apr 2021, 10:47 am   #3
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Default Re: Airmec 864 comms rx.

I have a (very) faint recollection of this set- does it have a film-scale dial and ranging based on decadic capacitance swing, i.e. 3-10/10-30 style frequency bands with coverage from 30kHz to 30MHz? It would be interesting to know if it followed the "usual formulae" as regards aspects like the front-end/ type of mixer/ IF scheme and so on.

Colin
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Old 14th Apr 2021, 10:52 am   #4
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Default Re: Airmec 864 comms rx.

Here's a full page advert from Shortwave Mag.:

https://worldradiohistory.com/hd2/ID...rch=%22c864%22

Lawrence.
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Old 14th Apr 2021, 11:03 am   #5
turretslug
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Default Re: Airmec 864 comms rx.

Aha, thanks Lawrence- so rather than a 30-100kHz band, it did 15-45kHz for the long-range oceanic band, that would make sense. Sort of broadly comparable with the Marconi Atalanta then,

Colin
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Old 14th Apr 2021, 11:08 am   #6
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Default Re: Airmec 864 comms rx.

No problem, the year by the way was 1956.

Lawrence.
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Old 14th Apr 2021, 1:56 pm   #7
ian rose
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Default Re: Airmec 864 comms rx.

Thank you everyone.
My example exhibits some differences from the one in the shortwave mag, one of which is a much larger 'fine tuning' control, which may indicate it is a later model, although it does not have a centre zero marking. It is marked '0 to 100' Kc/s from right to left but is operational in the same way in as much that it is a calibration aid used in conjunction with a crystal controlled oscillator of 500 Khz and 100Khz minor markers in much the same way as the Racal R 17 series.
The RX was evaluated by the Royal Navy but was rejected for use due to the RX's 85 Khz IF frequency [as in the Atlanta which was also unusable by the RN] suffering from breakthrough from powerful comms to submarines which used that frequency. The RN also had a problem with the second IF of 100Khz because of the very powerful pulsed Loran nav. transmissions on that frequency. The RA17 and 117 were, as we know, taken by the RN in large quantities also having an IF of 100Khz with much better screening and filters with no operational problem.
In as much that the Airmec sported a 120 mm film scale of which one inch represents 1.2 Khz with calibration curser it was a pre-runner of the Racal series and I understand only about 200 were manufactured. It's a bit clumsy to use due its turret tuning to select bands so it seems to have been more suitable for fixed frequency work.
As Radio Wrangler says it seems to have been modelled on their signal generator which I guess came first.
The magazine ' Radio Bygones' published a two part critique of the set in Nos; 80 and 81 in Christmas and February editions 2002.
Ian Rose
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Old 14th Apr 2021, 4:52 pm   #8
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Default Re: Airmec 864 comms rx.

Airmec 864
Photos to follow when downloading from camera decides to work for me!
Ian Rose
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Old 14th Apr 2021, 5:30 pm   #9
G4XWDJim
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Default Re: Airmec 864 comms rx.

Didn’t Michael O’Beirne G8MOB write a review of it in Radio Bygones sometime in the 1990s. I can’t remember the exact date but I’m sure someone will.

Jim
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Old 15th Apr 2021, 1:27 pm   #10
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Default Re: Airmec 864 comms rx.

Pics follow of the Airmec 864.
the set was found in a shed in Hayling Island having suffered much from the salt atmosphere. I hope the block diagram answers 'Turretslug's' question and is legible.
Ian Rose
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Old 15th Apr 2021, 7:40 pm   #11
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Default Re: Airmec 864 comms rx.

Thanks- there was an interesting and evolving post-war middle-ground in comms receivers between those that followed the very traditional and relatively straightforward route set by the trail-blazing HRO and cemented by the AR88 et al (e.g Murphy B40, Eddystone 680/730, GEC BRT400) and the sophisticated and very expensive 1MHz-per-span pace-setters like the Racal RA17 and Collins R390. Some of these middle-ground sets took advantage of dual-conversion to provide incremental tuning, and it looks as though the Airmec was a good example of this trend with a particularly wideband 800kHz IF.

Perhaps Airmec felt that, having invested design and tooling effort in the turret mechanism and other metalwork for their signal generators, branching out into receivers with turret bandchange would bring worthwhile extra return and that the marine market was a promising field. It certainly looks to have been a particularly large set, with an RA17 almost dwarfed beside it!
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Old 15th Apr 2021, 7:48 pm   #12
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Default Re: Airmec 864 comms rx.

Airmec acquired by Racal in 1969 ;

https://gracesguide.co.uk/Airmec
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Old 16th Apr 2021, 8:39 am   #13
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Default Re: Airmec 864 comms rx.

Quote:
Originally Posted by turretslug View Post
Thanks- there was an interesting and evolving post-war middle-ground in comms receivers between those that followed the very traditional and relatively straightforward route set by the trail-blazing HRO and cemented by the AR88 et al (e.g Murphy B40, Eddystone 680/730, GEC BRT400) and the sophisticated and very expensive 1MHz-per-span pace-setters like the Racal RA17 and Collins R390. Some of these middle-ground sets took advantage of dual-conversion to provide incremental tuning, and it looks as though the Airmec was a good example of this trend with a particularly wideband 800kHz IF.
I think so. Also, meeting the GPO marine requirements probably pretty much meant using an “intermediate” layout during the valve era. The frequency coverage requirements essentially outruled single-conversion with a single IF, given that it would need to be placed somewhere south of 100 kHz. Single conversion with a dual-frequency IF strip, as in the IMR 54, was possible, but perhaps unwieldy in that all selectivity options had to be provided at both frequencies. Double conversion, with single conversion on some of the lower frequency bands seems to have been the favoured landing place. The front end selectivity requirements would have made upconversion difficult in respect of front end tuning tracking in the mechanical tuning era.

Even into the early solid-state era the need for unusual layout seemed to persist. The Eddystone EC958 was designed inter alia to meet the GPO requirements, and was variously triple-, double- and single-conversion; with low IFs (i.e. not upconversion) having been a deliberate choice. Normally the RF input was bandpass above 1.6 MHz, single-tuned below, but the marine version (EC958/5, aka Marconi Nebula) required bandpass down to 54 Hz to meet the GPO specifications. The Marconi Apollo (MWT N2050) marine receiver was double-and single-conversion with low IFs, even though Marconi had used upconversion for the preceding solid-state H2001 Hydrus compact ISB/SSB point-to-point receiver. So one assumes that the Apollo layout was a deliberate “horses-for-courses” choice, and not simply a carryover of valve-era practice. The Marconi N2020 not-quite-all-solid-state naval receiver of the same era was also triple or double conversion with low IFs.


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Old 16th Apr 2021, 9:11 am   #14
ian rose
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Default Re: Airmec 864 comms rx.

Thank you everyone. I read all the info with great interest.
In response to 'Turretslug's' comment on physical size. It is, I suppose, an unusual shape and does not have the depth of say RA17 or AR88.
dimensions are; Width; 48cm. Depth;only 27cm [including handles] Height; 40cm. Whereas;
RA17; Width; 48cm. Depth; 52cm [including handles but excl. plugs at rear]
Height; 27cm
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Old 16th Apr 2021, 9:19 pm   #15
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Default Re: Airmec 864 comms rx.

It's actually smaller than the RA17 on bald HxWxD volume, though the sloping top of the RA17 might make its actual volume similar.
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Old 17th Apr 2021, 11:23 am   #16
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Default Re: Airmec 864 comms rx.

Hi All,
A place I worked in the late 60's had an Airmec Wave Analyser - the same basic instrument as the receiver and the signal generator all based on the turret band change and film scale tuning mechanism.
It was used to look for spurious outputs from HF transmitters - spectrum analysers being narrow band jobs in those days.
The tuning mechanism was horrible - stiff and lumpy - and made tuning from 1 to 30Mhz or more an absolute chore, making the test very unpopular amongst the team. As the most junior engineer I got to do it a lot!
Happy Days
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