Xtal Substitute Solution

[Yorkie]

My remark as to ‘why would anyone want an 1155 other than to put on a shelf?’ was based on the fact that it wasn’t designed or intended to be used in a domestic environment – it was intended for airborne and seaborne communications and direction finding. To use it in a domestic environment requires extensive modification to a point at which it ceases to be an 1155 (though it may still look like one) and arguably, becomes a ‘donor set’.

The least that needs to be done is to build a power supply and an audio stage. Those can be external of course, but in the post-war years, the standard modification was to remove the DF section and to build in a valved power supply and audio stage. Indeed, to improve saleability as short-wave receivers, many ex-WD surplus firms sold them ready converted. There were also countless other improvements and modifications which featured regularly in PW, SWM, RSGB Bulletin (forerunner to Radcomic) to enable the 1155 to be used as a half decent short wave receiver. But as I say, it is then not an R1155 anymore.

Though unmodified, it met the needs of its designed purpose, it was nevertheless, a fairly basic superhet and even when much modified, will remain so. Hence, what it comes down to is a choice between collecting it and leaving well alone, putting in on display as an iconic radio of WW2, or as some might say ‘butchering it’ to convert it to a very average general coverage receiver.

There’s no doubting that most enthisists will agree that it is THE iconic radio of WW2, closely associated with Bomber Command, the appearance of which evokes romantic images in the minds of many, (particularly those of my vintage, it being the same age as me!), as the radio that 'helped win the war'. It was of course rushed into production to meet an urgent need. It didn’t exist until 1939 - equipment specifications and a contract were not given to Marconi until October 1939 to develop the required system as a matter of urgency. Air Ministry numbers T1154/R1155 were allocated to the equipment. Marconi was appointed the main contractor and the design team was lead by one of Marconi’s chief designers - Christopher Cockerell. (Later Sir Christopher, inventor of the Hovercraft)..

More than 80,000 T1154/R1155 were manufactured during the war for use by RAF and the other Commonwealth air forces. Some variants were also produced for the Royal Navy. Marconi engineered the 1154/1155 radio installation for Wellington, Whitley, Blenheim, and Hampden aircraft of Bomber Command, ground installations, flying boats etc.

It was in production well into the late 1940s.

They're not rare - there are countless thousands around - anyone who wants one can have one, but it will most likely not be in its original state and will need extensive complex renovation. (Hence, a starting price of in excess of £300 as stated in my earlier post).

So, fit for purpose? Yes indeed – for its intended purpose, which was not as a DX communications receiver for amateur use, and no matter to what extent it is modified, it will only ever be a single superhet, and hence, will have poor image rejection.

The Racal RA17/117 is an entirely different kettle of fish!

It's a high performance peacetime communications receiver designed in the 1950s for use by the likes of GCHQ for worldwide communications. It was not rushed into production to meet an urgent war need – it was ahead of its time. Really, it’s a bit unkind to the R1155 to speak of it in the same breath as if they are comparable, which clearly they are not, (except of course that they are both radios and both use valves. There, the similarity ends), though both met their design requirements and were fit for their intended purpose.

RA-17 & RA-117 receivers are based on the Wadley loop tuning system, making them quite complex for shortwave receivers. There are 24 valves in the RA-17 and 26 in the RA-117. The RA-17 is a triple conversion receiver, the RA-117 has 4 heterodyne conversion stages. These receivers have additional features expected of a high performance comms receiver, such as selectable-bandwidth IF, with crystal filters on the narrowest ranges.

Here's a little of the performance spec:

Tuning: Effective scale length of approximately 145 feet, i.e. 6
inches of scale length corresponds to 100 kc/s Frequency
increments remain constant over the entire range.

Calibration: A 100 kc/s signal derived from a 1 Mc/s crystal oscillator
having an accuracy of 5 parts in 10 million, providingcheck points
at 100 kc/s intervals.

Sensitivity: A1 reception, bandwidth 3 Kc/s; 1_V for 18dB signal-to noise ratio. A2 reception, 30% modulated, bandwidth 3
Kc/s; 3_V for 18dB signal-to-noise ratio.

Intermodulation: More than 100dB down for interfering signals at least 10% removed from the wanted signal.

Cross modulation: For wanted signal levels between 3_V and 1mV, an interfering signal 10 Kc/s removed and modulated 30% must have a level greater than 50dB above that of the wanted signal to produce a cross modulation of 3%. The ratio of wanted to unwanted signal is improved up to 10% of tune, at the rate of 3dB per cent.

Blocking: With similar conditions to those for cross modulation an
unwanted signal f2 must be 60dB greater before the audio
output of the wanted signal f1 is reduced by 3dB due to
blocking.

Selectivity: Six alternative I.F. bandwidths are obtained by means of
a selector switch. Filter details are:

-6dB -66dB
(1) 13 kc/s 35 kc/s
(2) 6.5 kc/s 22 kc/s
(3) 3.0 kc/s 15 kc/s
(4) 1.2 kc/s 8 kc/s
(5) 0.3 kc/s Less than 2 kc/s
(6) 0.1 kc/s Less than 1.5 kc/s

81-page manual on the RA 17/117 here:

http://www.qsl.net/m5aiq/manuals/ra117-nofig.pdf

The above remarks are just my own observations - I don't expect or mind one bit if others see it differently, and doubtlesss some will!

Waffled and dribbled Yorkie.