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RACAL- OMG what a confusing radio set - Printable Version

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RACAL- OMG what a confusing radio set - jcassity - 05-17-2018

made across the pond!! for the USA.

to be honest, watchig this vid total blew a brain fuse just watching the guy use this set.
you have to toally abandon what you normally would assume about tuning in stations. 

Seems like a lot of thougth went into this , then someone thought "TOO MUCH"!

https://www.bing.com/videos/search?q=hallicrafters+sx-42&&view=detail&mid=21BFC97B2D1BFAAE3AAD21BFC97B2D1BFAAE3AAD&rvsmid=587FFB22A69B41949BDD587FFB22A69B41949BDD&FORM=VDMCNR

RE: RACAL- OMG what a confusing radio set - Radioroslyn - 05-17-2018

If your in the market for a high performance rx give a good look @ a R-390 or R-390A. Built from '54-'84. Pretty complex set but modular construction so all of the sections unplug and unbolted for easy repair. Lots of info on line.  https://www.eham.net/reviews/detail/1634

RE: RACAL- OMG what a confusing radio set - jcassity - 05-17-2018

i see that model being brought up often when i was searching a hallicrafters sx-72,,,, i watched a few vids on the R390,,, man that one is likely out of my smarts!,,, but i suppose so would the sx-72! but something is pulling me to the sx72,, cant help it.

im just learning this tech,, and i suppose if i do take this kind of leap i can only learn.

RE: RACAL- OMG what a confusing radio set - EdHolland - 05-17-2018

The Racal is a very clever design, which achieved very high stability and good image rejection in a time long before frequency synthesis. I'd love to own one. The "Barlow-Wadley Loop" circuit configuration allows for a high first IF frequency, but cancels the oscillator drift with clever down conversion. The early Yaesu (FRG 7 and FRG7700) receivers, amongst others, use a similar circuit scheme.

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

More on the RA17:

https://www.electronics-notes.com/articles/history/radio-receivers/racal-ra17.php


Alignment, so I understand - and see in the video - is certainly not you're typical superhet procedure.

Cheers

Ed

RE: RACAL- OMG what a confusing radio set - EdHolland - 05-18-2018

Oh yes, and this radio makes a star appearance in this very famous movie scene.

https://www.youtube.com/watch?v=DoQwKe0lggw

Watch carefully behind the eponymous villain ;)

RE: RACAL- OMG what a confusing radio set - Arran - 05-18-2018

Quote "Prior to the introduction of the RA17, previous radios had typically used a free running variable frequency oscillator. Radios like the AR88 of 1940s vintage were still widely used and provided excellent performance in many other respects could not compete with the RA17.

Although free running variable frequency oscillators might be acceptable for low frequencies below about 3 or 4 Mc/s, as they reached frequencies towards the top of the range or 30 Mc/s or so, they would need to be periodically retuned, especially when receiving Morse or single sideband."

 This seems like a bit of a stretch to me, that may be true with the cheap sets with a pentagrid converter, but not with something like a National HRO, or Hallicrafters SX series set, it sounds like the article was written by a bit of a "fanboy". The older sets would not work with SSB perhaps but with code it was never an issue.
Regards
Arran

RE: RACAL- OMG what a confusing radio set - Radioroslyn - 05-19-2018

Right after the war Collins developed a platform using a very stable tuneable oscillator called a permeability tuned oscillator, pto (typically around 1.5 to 4.0mc) that would tune a 1mc segment. The output of this osc was mixed w/a crystal osc. When used as the local oscilltor signal it was hard to beat.The output is very stable like +/- 10hz from a cold start. The drawback is that each band was limited to 1mc tuning range of the pto. This was the industry standard from the late 40's thru the 70's in high end sw receivers and later in ssb transceivers. When ssb gained popularity in the 50's and 60's stability became very important drift of a couple 100 cys change the tonal qualities of the voice heard so you would have to retune the station every minute or so.
Receivers like the Collins 75A1, 51J series and R390/390A where icons of their time.

RE: RACAL- OMG what a confusing radio set - EdHolland - 05-19-2018

Arran - You have a point about the comments - and I think they don't quite reflect the qualities of the radio.

The emphasis on stability is important when considered in relation to the good IF image response rejection offered by the ~40 MHz IF band. This is where the ingenuity lies - although high frequencies are generated and used within the set to up-convert the incoming signals, any oscillator drift is cancelled again in the down-conversion scheme. One free-running oscillator is still required for the final mixer stage.

Much of the enthusiasm for these sets will originate from the fact that they were British, and we love our own stuff Icon_smile. I'd love to try out one of these sets, and know folk who have owned them in the past and remembered them fondly. They are a design classic that established a company which went on to design some really good communications equipment for military and commercial use.

Cheers

Ed

RE: RACAL- OMG what a confusing radio set - Radioroslyn - 05-20-2018

So Ed what do you think of the B-40 speaking of British sets? I kinda like the looks of it being a bit different. Have read they are dogs to work on.

RE: RACAL- OMG what a confusing radio set - EdHolland - 05-20-2018

I don't know a lot about them, but have seen them at museums. The "Lighthouse" design of the dial is wonderful, as to their performance, I can't comment. Would love to have a go on one Icon_smile