Extension of FM band

[nicholasachurchman]

Hi,

All valve FM receivers I have seen only go upto 100MHz on the FM band. When was the band extended to 108MHz and were any valve receivers made which cover this upper section ?

Regards,

Nick

The only British valve receiver that I can think of off the top of my head that covers 88-108 MHz (or should that be M/cs?) is the original version of the Hacker Mayflower, from 1960, which still sounds great on FM (or, again, should that be VHF?) today. The Mayflower II only went up to 104 MHz. There were sets from other countries, such as Germany that also had the full range, and there were certainly some hi-fi tuners such as those made by Armstrong which had extended tuning (my Armstrong 526, though a very early solid-state model, is calibrated between 86 and 109 MHz).
It wouldn't have been until the late eighties that any broadcasting took place is the upper part of Band II though, before that it was used by the police, hence many British manufacturers made sets that only went up as far as about 100-101 MHz.

Tez.

[Sideband]

Hi Nick_C.

I have one valve radio that covers the full VHF band from 87.5 to 108 Mhz. It is a Stella set ST160A (made by Philips) and was manufactured sometime in 1960. To be fair it is based on a Continental design but was sold in limited quantities by specialist outlets. Other VHF valve sets I have only cover up to 100Mhz and these are pre- 1960 sets. One set (Baird 301 made in 1955) only covers up to 95 Mhz! Of course this was OK at the time because there were only three stations operating, the highest being the Home Service (now Radio 4) on 93.5 Mhz in the London area. It probably was not until 1970 that radio's were made with extended VHF bands as soon after (around 1973) 'local' FM and commercial stations started broadcasting above 95 Mhz.


Rich.

[quantum]

Once you get into the early 1960s you get valve sets which cover the upper part of the band (for example, the Pye 1202 gave 86-108mhz and the McMicheal MS204 gave 88-110mhz) but I agree that when you only had the three BBC channels on VHF there wasn't much need for the higher part of the band.

I remember as a lad watching an episode of Z Cars where they had to give false messages over the car radios as the villains were listening into the police messages on the upper part of the VHF band with a large radiogram (very clear too, much better than when I listened in on my parent's Cossor set!)

[nicholasachurchman]

Hi,

If I understand this correctly, within the UK there was no restriction on making sets that covered this upper part of the band.

I had assumed the home office had restricted this part of the band and at some point in the past said OK folks, you can now makes sets that cover this extra section.

Also with the FM (or VHF!) band as busy as it is today its difficult to imagine just three stataions transmitting.

Thanks for all the information. Much appreciated.

Nick

[paulsherwin]

I'm not sure of the details here, but AFAIK originally the FM broadcast band was only defined up to 100MHz right across Europe. It wasn't illegal for manufacturers to cover up to 108 and some did, where a design was intended for export as well as domestic European markets. The band was extended to 104MHz in the early 60s and 108 in the late 60s.

As others have commented, it took some time for countries to clear the extended band of non-broadcast services. I remember listening to the police dealing with the Brixton riots as late as 1983 when I lived in South London.

I believe it is still illegal to listen to any non-broadcast transmission under the Wireless Telegraphy Act.

Best regards, Paul

[Station X]

I sometimes operate or repair construction machinery made in the Far East. This sometimes has an FM radio fitted as standard, but it is useless in the UK, because if I remember correctly the coverage is from 70 to 90 MHz.

In the UK it is only legal to listen to Licensed Broadcast Stations, Radio Amateurs and Standard Frequency Transmissions such a MSF.

I can remember listening to the Emergency Services in the upper part of the FM band from the late 50s through to the late 80s. Some of these transmissions were AM, so slope detection had to be used on the FM receiver. The better the radio the worse the reception was.

Graham.

[quantum]

The old USSR used to have unusual FM frequencies as well - their FM band operated between approx 65-74mhz. It did mean that they could use simpler front ends, an ECH81 type valve would work as a frequency changer at these frequencies in a conventional circuit.

In Quarrington's Radio Circuits and Data there is a circuit of a FM receiver using a 6K8 as the FC, plus three IF stages - voltage regulation is used on the osc anode and screen of the 6K8, I assume to prevent drift. However, how efficient a 6K8 is at 100mhz is open to question...mind you, the book was published in 1949!

[Sideband]

A 6K8?

Good heavens! They were not the quietest of frequency changers on AM especially when you got up into the high shortwave bands. I wonder what the s/n ratio was at VHF?

Rich.

[TrevorM6TSE]

Much as it maybe IS illegal to listen to the police...Scanner users will be disappointed that by the end of 2005 " Airwave " the police TETRA based system will be all accross the UK. It's just gone live where I live. It's digital, based at Celluar frequencies and.. un scannable!

[paulsherwin]

TETRA also famously knackers up TV reception:

http://www.wrightsaerials.tv/Tetra.htm

Best regards, Paul

[ppppenguin]

Wright's aerials have a great web site! Lots of modern and historic aerial stuff.

[TrevorM6TSE]

I know this is off subject (sorry Paul!!) but is Tetra the same as " Dolphin " ??

Taa

[Hybrid tellies]

Thanks Paul for that link to that wonderful site. A few of us at work have spent a few happy moments trawling through this site.
So Tetra is not only causing health concerns but upsetting tv reception as well
Going back to the FM subject, were we the only country clever enough to share a broadcast band with emergency services such as the police?

[newlite4]

A few months ago, I bought an American Wards Airline 15BR-1535B AM/FM receiver from a collectables shop in Bath. This dates from around 1952 and covers 88 to 108 MHz. It has variable capacitor tuning as opposed to the variable inductor tuning which is much more common in early British and continental VHF sets. This set contains eight valves .The output and rectifier are octal types, the others are B7G.
In contrast, I have been restoring an early British kit built FM tuner from about 1957 which only covers 88 to 95 MHz .
Neil Deacon

[paulsherwin]

were we the only country clever enough to share a broadcast band with emergency services such as the police?

This was normal practice across Europe. Various emergency services started using frequencies above 100MHz in the 50s and once established it was quite difficult to move them - the radio systems needed replacing completely.

When I was on holiday in France in the early 80s I noticed frequencies around 88MHz were still being used to control traffic lights!

Best regards, Paul

[jim_beacon]

Neil,

that wouldn't be the Jason Kit tuner would it ? (Wireless World design)

I have one, and it needs about 30 minutes to warm up and be stable - unless you go near it, or let a draught blow across it!

The tuning range is adjustable to any where in the band, by altering the turn spacing of the RF and oscillator coils, or by moving any of the wires under the chassis! I wonder how many of them actually worked in the 50's?

Jim.

PS somewhere I have a book that covers the building of the tuner in both local and fringe (extra EF91) versions, and also the Osram 912 amp (I guess that makes the valves Z77 instead of EF91).

[newlite4]

Jim, the valve line up in this one is ECC85 front end followed by two EF85s in the IF strip and two diodes forming the detector. There is also an EZ80 rectifier and an EM80 magic eye. It may well be a Jason kit but the design does seem to be rather basic and the layout is rather untidy, it is prone to instability. There are no chassis markings but the FM front end is, I think, of Philips manufacture.
Neil Deacon