UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Reply
 
Thread Tools
Old 15th Nov 2017, 9:21 pm   #21
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 9,041
Default Re: VHF or UHF?

"Supersonic" in those days meant pitched above the range of hearing

A heterodyne was (and is) a beat note created by mixing two signals together.

So a superhet beats a local oscillator with a signal to create a signal on a new frequency above the audible frequency range.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 17th Nov 2017, 9:30 pm   #22
johncoates
Triode
 
Join Date: Jul 2017
Location: Barnsley, South Yorkshire, UK.
Posts: 10
Default Re: VHF or UHF?

Quote:
Originally Posted by turretslug View Post
On a few pre-war sets, there was a 12-5m or thereabouts band referred to as "ultra short". Probably fairly quiet in most locations, unless you were in a 41.5MHz locale, was there much usage of 11m broadcasting then? I suppose it's all relative to what had come before, at some point someone (or some committee) with a tidy mind seems to have decided on spectrum delineation in decimal wavelength increments, hence the familiar 30-300MHz VHF, 300-3,000MHz UHF etc.- this demarcation would seem to have more application to abstract book-keeping than practical application to circuit techniques, propagation and so on.
Surely the 30-300 .... etc ..... derives from the velocity of radio waves at 300,000,000 (300 million) metres per second.
johncoates is offline   Reply With Quote
Old 17th Nov 2017, 9:47 pm   #23
johncoates
Triode
 
Join Date: Jul 2017
Location: Barnsley, South Yorkshire, UK.
Posts: 10
Default Re: VHF or UHF?

To be more explicit .....
A frequency of 200 kc/s (200,000 cycles per second) has a wavelength of 1500 metres.
Multiply the two together:
200,000 x 1500 = 300,000,000 metres / second.
johncoates is offline   Reply With Quote
Old 18th Nov 2017, 1:21 am   #24
Synchrodyne
Octode
 
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 1,811
Default Re: VHF or UHF?

Quote:
Originally Posted by emeritus View Post
According to the 1956 edition of the "ITT Reference Data for Radio Engineers", standardisation of frequency band designation seems to have been first agreed at the Atlantic City Radio Convention of 1947, although the CCIR later recommended that the use of such arbitrary names be discontinued.
Yes, the decadic classification system came out of the 1947 Atlantic City ITU Meeting. It was mentioned in Wireless World (WW) 1948 April, page 150 (with some deprecatory remarks about the series of superlatives used), and here is the pertinent page from the Annex to that ITU meeting.

Click image for larger version

Name:	ITU Atlantic City 1947 Annex p.15-E.jpg
Views:	23
Size:	40.5 KB
ID:	152422

Hitherto, it appears that the terms USW, UHF and EHF were both used for anything above 30 MHz (below 10 metres).

Terman used UHF in his 1943 book:

Click image for larger version

Name:	Terman Radio Engineers Handbook 1943 p.754.jpg
Views:	14
Size:	66.9 KB
ID:	152423

Sturley used both UHF and USW when discussing FM receivers (VHF) in Part II of his book. The 2nd Impression was published in 1948, and I suspect that the manuscript predated the availability of the outcomes of the 1947 ITU meeting.

In 1949 WW was still using EHF for Band II transmissions. In fact, I think that this (mis)use of EHF by WW was found even later than that.

Click image for larger version

Name:	WW 194906 p.221 BBC AP VHF FM & AM Tests.jpg
Views:	8
Size:	97.4 KB
ID:	152425

Although the ITU decadic system was essentially administrative, one may make a small number of approximate connections with radio wave behaviour. The international HF broadcasting bands, where long-distance skywave propagation is used, all fall into the 3 to 30 MHz range. The 75- and 11-metre bands represent about the lowest and highest frequencies that have utility for this purpose. Ground wave utility falls off below around 2 MHz, except over sea paths hence the 2 MHz marine band. So, from a little under 2 to a bit over 3 MHz is a transitional area, with more narrowly-based ground wave and skywave applications. The latter refers to NVIS propagation in the 120- and 90-metre tropical bands. Upper HF and lower VHF (into Band I) is also a transitional area.

The VHF-to-UHF transition is marked more by the change in circuit requirements, at least in the valve and early solid-state days. VHF techniques, such is in VHF TV tuners, worked up to about 220 MHz (valves) and maybe 250 MHz (solid-state), after which UHF techniques such as striplines took over. The technique frequency boundary was a bit below the classification boundary. One may see this for example in the Eddystone 990R (VHF) and 990S (UHF) receivers of the later 1960s. The 990R used VHF techniques and tuned up to 230 MHz. The 990S covered 230 to 870 MHz and had two front ends, one covering 230 to 510 MHz and the other 470 to 870 MHz. The latter was more-or-less a UHF TV front end; the former a UHF TV front end modified to cover a lower frequency range. Thus, one could infer that the frequency division point for the two receivers was chosen to suit the circuit techniques best matched to the frequencies respectively below and above that point.

Re the 11-metre HF broadcasting band, as best I can determine, it stayed unchanged after the ITU 1947 meeting, although some other HF bands were expanded slightly. So, it probably had some, but perhaps not much use before then. But I don’t think that it was ever used all that much. It depended upon sunspot cycles, and maybe was usable for about 3 or 4 years out of 11. When it was open, the major user seemed to be the BBC WS on 25.75 MHz – perhaps about the only used in the early 1990s.


Cheers,
Synchrodyne is offline   Reply With Quote
Old 18th Nov 2017, 8:53 pm   #25
turretslug
Nonode
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 2,057
Default Re: VHF or UHF?

In the UK at around that time, RSA on 25.79 MHz, RFI on 25.82 MHz (the French broadcaster, not the interference!) and VOA on 26.04 MHz were all strong, clear and dependable presences during the day, with a few others appearing more rarely and faintly. Further into the formal VHF definition between 30 and 32 MHz, harmonics of 19m stations could be found, usually faint but often clear. The strength and readability of the fundamental having little relationship to that of the harmonic, presumably propagation from site and the harmonic suppression (or otherwise) of sender and aerial systems having greater bearing.

Re. circuit techniques, I can't help thinking that VHF considerations could be said to come into play by 20 MHz or so- many HF receivers that followed traditional LF/MF/HF architecture of multiple band-switching around a single set of active devices looked to be pushing things by this point with stray capacity, stray inductance and poor L/C ratio of a system centred around a large-value, wide-ratio gang capacitor all presenting design headaches. The very few turns of the highest frequency band inductors set against a mass of band-change wiring links shows that this format was on its edge. After this point, the idea of dedicated front-end modules for a particular frequency span with hard-wired tuning elements and active devices looks wise- the wartime GEE receivers with a choice of 4 plug-in modules spanning around 20-85 MHz being a classic example. Having said that, turret formats could allow a single set of active devices to give at least adequate performance with choice of several sets of tuned circuits to 200MHz+ but frequently with bespoke expense and bulk, the (I think) US-originated Band I/III TV tuners being a mass-produced exception. Perhaps, as you say, circuit technique boundaries could be said to be more like 20-200MHz for VHF with UHF above this point- thus we have the 225-400 MHz "UHF" airband. A further delineation might be where stripline techniques give way to cavity techniques.
turretslug is offline   Reply With Quote
Old 20th Nov 2017, 7:41 pm   #26
Synchrodyne
Octode
 
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 1,811
Default Re: VHF or UHF?

20 MHz was also approximately the point where aerial noise had declined to the point where receiver front end noise became dominant in terms of defining overall performance. Some HF receiver makers, both in the commercial and consumer domains, used “VHF” valves in the RF amplifier/1st RF amplifier position in order to obtain good noise factors in the 20-to-30 MHz range. Most common I think was the use of high-slope, sharp cutoff VHF pentodes, such as the 6AK5, Z77, 6F1, etc. Occasionally high-slope, remote cutoff VHF pentodes such as the EF85 were used, and late in the valve era the cascode RF amplifier (e.g. ECC189) was found. Another approach was the use of a grounded-grid triode (or triode-strapped pentode) with aperiodic input as an RF pre-stage.

Conversely, some tunable VHF and VHF-UHF communications receivers tuned below 30 MHz, usually to somewhere in the 20 to 30 MHz range, for example 25 MHz in the case of the ICOM R7000. That I think is an indication of the pseudo-VHF nature of that frequency region.

The technology required for TV tuners probably helped push the envelope both in the VHF and UHF cases. In the early 1950s, VHF TV tuners went to 216 MHz or so at a time when few VHF communications receivers went that high. Eddystone had planned 210 MHz for the 770M, but couldn’t get it to work properly so settled for 165 MHz with the 770R. The range above that was left to the 770U, using UHF techniques, and that went only to 500 MHz, whereas UHF TV tuners of the time went to around 900 MHz. For the 500 to 1000 MHz range, Eddystone offered the highly specialized 770S, which was originally described as an EHF receiver, although it was being described as UHF by the early 1960s.

Returning to the original question, a reasonable deduction is that RMorg uses “UHF” according to its apparent pre-Atlantic City 1947 meaning, which referred to anything above 30 MHz. That meaning may have been established by customary usage in that period rather than by formal definition.

RMorg also uses another old convention, namely tuned circuit count. Apparently, that was a sales feature in Germany in the immediate post-WWII period, as noted in this Wireless World 1950 November item. Note that the FM band was still being referred as the EHF band. (It looks as the WW editorial staff were being a bit stubborn about adopting the Atlantic City designations.)

Click image for larger version

Name:	WW 195011 p.418 Radio in Germany.jpg
Views:	8
Size:	88.3 KB
ID:	152595

Tuned circuit count was not unknown in the UK, though. Dynatron’s late 1940s/early 1950s tuner-control unit combinations, such as the T69, T99 and T57, were designated according to valve count and tuned circuit count. So, the T69 had six valves and nine tuned circuits. The count evidently included the oscillator tuned circuit.


Cheers,
Synchrodyne is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 10:25 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.