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Old 12th Jun 2019, 2:42 am   #1
Synchrodyne
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Default Dormer & Wadsworth (D&W)

I have some curiosity questions about the UK assembly maker Dormer & Wadsworth (D&W), of whom I don’t think that there has been much mention on this forum to date.

I know that D&W made solid-state FM front ends in the later 1960s and probably into the 1970s. Known users were Radford and Rogers, in hi-fi tuners.

Who else used D&W FM front ends? Were there any setmakers who used them as well as hi-fi equipment makers? Although I suspect that the Mullard modules were economically more attractive to the setmakers.

Did D&W start in the solid-state era, or did it have earlier activities with valve-based FM front ends?

What other radio/audio assemblies, if any, did D&W build?

And what eventually happened to D&W? I’d guess that the availability of FM front ends from Japanese sources such as Toko might have pushed it aside.

As to known users, Radford used the bipolar version of the D&W 341 4-gang model in its FMT2, and the 2 mosfet version of the 341 in its FMT3. (I think that the 2 mosfet 341 might have been an option late on in the export version of the FMT2.)

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Rogers used the 2 mosfet 341 in its Ravensbourne 2 FET tuner of 1968. It used a simpler D&W front end (model number unknown), 3-gang with mosfet RF amplifier and bipolar mixer, in its lower-priced Ravensbrook tuner of 1969.

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The 2 mosfet 341 was of the four-gang type with one RF amplifier, with a bandpass doubled-tuned input and a single-tuned interstage. This appears to have been the reverse of usual practice, which was to have a single-tuned input and a double-tuned interstage. For example, the Revox A76, which was an early benchmark supertuner, followed the usual practice, as did many Japanese products in the 1970s.

My understanding is that, at VHF at least (HF might be different), too much selectivity at the input compromises noise performance, even though it helps reduce large signal cross-modulation problems. Placing the bandpass at the interstage, where high selectivity is usable without worrying too much about noise effects, allows higher overall pre-mixer RF selectivity than would placing it at the input. Certainly VHF TV tuners, both valve and solid-state, usually had single-tuned inputs and bandpass interstages.

It is apparent that the D&W 341 was originally designed around bipolar devices, and later adapted to use dual-gate mosfets. Given that small-signal bipolar devices were known to have relatively poor RF performance, as compared with their valve predecessors when it came to cross-modulation and intermodulation effects, it could be that D&W thought that the better trade-off was to place as much selectivity as reasonably possible right at the input and accept the higher noise level. Then once then this was done, replacement of the bipolars by mosfets was done on a minimum change basis, meaning that the bandpass stayed at the input.

As to other users of D&W FM front ends, Sugden could be a candidate. This is the front end that it used in its R21/R51 FM tuner:

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It looks as if it could have been a varactor-tuned derivative of the D&W 341, retaining the bandpass input. Given that early implementations of varactor tuning were said to degrade cross-modulation performance, perhaps there was a case for the bandpass input where such were used.

The Sugden R21/R51 front end used different mosfets to those in the Radford and Rogers tuners, but this probably reflected the relatively quick progression in the early days. The RCA 40603 and 40604 were not gate-protected, and belonged to the 3N140 family. (Of which the variants and their nominal applications were the 40600 (VHF TV RF), 40601 (VHF TV MX), 40602 (TV 1st IF), 40603 (FM RF) and 40603 (FM MX)). The RCA 40822 was gate-protected, and belonged to the 3N187 family (40673 (all applications to 400 MHz), 40819 (to 200 MHz), 40820 (VHF TV RF), 40821 (VHF TV MX), 40822 (FM RF) and 40823 (FM MX).) I think that the gate-protected mosfets became available commercially late 1968 or 1969.

Other than that, any of the British hi-fi makers who were primarily audio specialists might well have been looking for third party help when it came to designing solid-state FM tuners. Leak’s difficulties in getting to the Stereofetic were well-documented in Stephen Spicer’s excellent history. I think it built its own front end as an integral part of the chassis, but based upon an intermediate RCA circuit. RCA went from all-bipolar to all-dual-gate mosfet FM front end circuits in four steps, namely single-gate mosfet RF + bipolar MX; single-gate mosfets RF & MX; single-gate mosfet RF & dial-gate mosfet MX; dual-gate mosfets RF & MX. It appears that somehow Leak got off at the third stop, not the final destination. Quad was quite late with its solid-state FM3 in 1971; whether that was a deliberate delay or circumstantial is unknown, but I think that its RF specialist, JD Collinson, had departed before then. Like Leak, it rolled its own FM front end as an integral part of the chassis, but it was probably based on the RCA two dual-gate mosfet circuit.

So Leak and Quad were evidently not D&W front end users. But there were other candidates, such as Lowther and Tripletone, and later on perhaps, Meridian. Armstrong I think had a history of doing its own RF work., so seems to have been unlikely to have used third-party front ends (although the 600 series might have been different.)

Possibly D&W would have been competing with not only German suppliers such as Görler, and later on Japanese suppliers, but also with those UK component and assembly makers who were active in the TV tuner market and who had also added FM front ends to their product lines. For example, it is known that Wharfedale used a German FM front end for its WFM-1 tuner of 1967.

Anyway, that was an interesting interlude in which D&W supplied high-performance solid-state FM front ends to the likes of Radford and Rogers.


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Old 12th Jun 2019, 6:36 am   #2
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Default Re: Dormer & Wadsworth (D&W)

There were also the Larsholt FM front-end modules that came along a bit later.

The noise issue in the front end was indirect. Designing the selectivity between the antenna socket and the first active device was a compromise. Go for more resonators, or use light coupling to achieve narrowness and the insertion loss went up. This loss acted as an attenuator, reducing your signal, reducing equally noise from the antenna, and adding thermal noise from the resistive effects of the losses of the filter components.

A quick fag-packet calculation woulb be that the loss of the filter in dB would add to the noise figure of the active device following it. but ireality's a bit worse than that. The antenna will see cold sky in half its field of view, and outdoor temperature ground in the other half, so overall its noise output is colder than the 290K assumed in noise figure definition. (This is why it's still worth pursuing noise figures down to 1dB and below) The losses of the input filter are at room temperature and so have a worse effect on the incoming signal to noise ratio than the simple loss in dB would suggest.

In later FM tuner designs the Q of varactor diodes is dramatically lower than that of mechanical variable capacitors, and they become the dominant limitation on resonator Q, no longer the inductor. So the losses of the input filter increase leading to more noise disadvantage unless heavier coupling is used to widen it. A wider filter lets more off-channel signals in to add up and clobber the first active device. Worse, the varactors themselves are non-linear. Narrower filters run their resonators at higher Q's and that scales up the signal voltages across the diodes. Intermod products rise disproportionately fast.

So designers go quite wide with varactor tuned front ends. High-Q filtering would be desirable, but it bites you at both ends of the dynamic range. You need a better active device as the RF amp.... lower noise helps, as does greater linearity at higher levels. The better linearity means narrow preselection is less needed and the low noise figure makes up for a little of the loss of the preselector filter.

A diabolical juggling game.

I developed my own spreadsheet for visualising the tradeoffs and balancing acts of a multi-stage receiver structure many years ago and I've fine-tuned it as I've used it to design various receivers over those years. It did the Agilent Noise Figure Analyser family, so it contributes to the noise figure values in most data sheets, that other people plug into their receiver-designing calculations

When you get to multi-dimensional compromises, there aren't any unique optimal solutions and RF design does become an art.

Artful Bodger would have made a good pseudo-name on the forum, or has it already been used?

David
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Old 15th Jun 2019, 9:00 pm   #3
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Default Re: Dormer & Wadsworth (D&W)

When I was designing Band II FM rebroadcast receivers I did some literature searching to try to establish the "noise-field" which a terrestrial antenna might see. I recall a figure of 4dB for quiet locations: in cities man-made noise is considerably higher. Figures for medium-wave are such as to make an RF person weep.

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Old 15th Jun 2019, 10:17 pm   #4
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Default Re: Dormer & Wadsworth (D&W)

The Cambridge Audio T55 is almost certainly another candidate, the circuit diagram of the front end looks identical to the one shown above for Sugden R21/R51. The transistor and varicap diode types are identical too.

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Old 15th Jun 2019, 11:12 pm   #5
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Default Re: Dormer & Wadsworth (D&W)

I've just completed a service on a Clarke & Smith 959 schools radio. This has a D&W FM
front end, with the output fed to a Mullard module. By replacing a couple of ceramic
caps with high quality trimmers I have extended the band to 108 MHz for which I will
make a replacement FM tuning scale. I was surprised the local oscillator was 10.7 MHz
low of the signal frequency. Performance is excellent.

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Old 16th Jun 2019, 1:40 am   #6
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Default Re: Dormer & Wadsworth (D&W)

Thanks for the Cambridge T55 (candidate) and Clarke & Smith (959) additions to the list of D&W FM front end users.

That the Cambridge T55 and Sugden R21/R51 front ends were identical strongly indicates that they were third-party units, and I think adds some weight to the notion that they were from D&W.

The Clarke & Smith case is interesting in that as a Mullard Module IF strip was used, one supposes that a D&W front end was chosen over the more obvious Mullard Module because it had better performance. Lower cost seems less likely as major producer Mullard was probably in a position to match competitor pricing as required.

Oscillator-low (infradyne) operation was in fact the original BREMA recommendation in respect of the 10.7 MHz FM IF. As oscillator-high (supradyne) was the norm in the USA and elsewhere, I suspect though that many UK makers, with the export market in mind, followed this pattern. Clarke & Smith might have been more UK domestic-market oriented. I’d guess that D&W would have supplied its FM front ends for either infradyne or supradyne operation as customers required.

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As to tuning range, the Radford and Rogers FM tuners had full coverage, 87.5 or 88 to 108 MHz. Initially anyway the Sugden R21/51 covered the “European” range 88 to 104 MHz. Presumably the D&W front ends could be configured to suit.

D&W was very early in adopting dual-gate mosfets for FM front ends. Whether it also went through an intermediate jfet stage in the transition from bipolars is unknown, but the available evidence suggests not. The use of jfets in FM front ends preceded the use of dual-gate mosfets by around a couple of years.

The FET front end option for the Radford FMT2 was available by the time of the Audio Fair 1967, a year after the model was first introduced. The working assumption is that this was the D&W mosfet unit, although it might have been otherwise.


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On the other hand, Mullard seems to have been slower in adopting fets for its FM front ends, and I think that it started with a jfet RF amplifier.

Eddystone used a Mullard FM front end in its 1002 broadcast receiver of 1972. This was shown in the schematic as an all-bipolar, 3-gang, varicap-tuned unit. Oddly, it was followed by two dual-gate mosfet IF amplifiers before the CA3089 FM IF subsystem IC. Assuming that Eddystone preferred to use a Mullard unit, one imagines that it would have used a mosfet-based unit had such been available, but absent that accepted what Mullard had available.

The replacement for the Eddystone 1002, the 1570 of 1978, also used a Mullard FM front end, shown as the UM1181 without circuit details on the schematic. I understand that the UM1181 had a dual-gate mosfet RF amplifier, although I have not seen the full circuit. In this case the front end output went directly to a TDA1071 subsystem IC.

As Larsholt has been mentioned, here is the schematic for its 8319 FM front-end. This was of the single-RF stage, four-gang type with a bandpass interstage.

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Old 16th Jun 2019, 11:34 pm   #7
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Default Re: Dormer & Wadsworth (D&W)

Another possible candidate for having used a D&W front end was the Tripletone FM Mk II of c.1970. In the Gramophone magazine review, it was described as having front end that was completely shielded within a metal box, which suggests a proprietary unit rather than an in-house design. It had 3-gang capacitor tuning with a dual-gate mosfet RF amplifier and bipolar mixer. This description was similar to that of the D&W unit used in the Rogers Ravensbourne.


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Old 26th Jun 2019, 3:32 am   #8
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Default Re: Dormer & Wadsworth (D&W)

Here is the Cambridge T55 FM front end, with the Sugden R21/R51 circuit for comparison:

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I think that the T55 dated from later in 1972, so it was a bit later than the R21/R51, which were from 1970-71.

In terms of general circuitry, the T55 could be said to have been an early “plateau” model, having dual-gate mosfet RF and mixer stages, and using the “industry standard” CA3089 IF processor (which dated from the second half of 1971) and the MC1310 PLL stereo decoder (which dated from early 1972). The Sugden R21/R51 started life with a discrete decoder, later changing to the MC1310. It also had a discrete IF strip, which I don’t think was ever upgraded.

On about the last step to the plateau was the Quad FM3. In original form it had the two dual-gate mosfet front end, IF strip using the TAA661 IC, and the MC1305 non-PLL IC decoder. It was updated in two stages, firstly with the MC1310 in place of the MC1305 and secondly the CA3089 in place of the TAA661.

Models such as the Leak Stereofetic and Rogers Ravensbourne and Ravensbrook were further back down that staircase from all-bipolar discrete to the plateau. The Ravensbourne was early in having the two-mosfet front end (courtesy of D&W) and had the early Fairchild IC-based IF strip using a µA703 cascade and a ratio detector. The Ravensbrook had an early RCA IC-based IF strip, namely the CA3012/CA3014 combination (which actually predated the µA703). Both had discrete decoders. The Ravensbourne was later updated, but I am not sure of the details.

Returning to D&W front ends, it occurred to me that the Goodman’s models of the later 1960s and 1970s might have been candidates for using them, but a look at the schematics for the Stereomax, Module 80 & 90 and One-Ten models does not show any correlation. The Module 80 & 90 and One-Ten models all had front ends using jfet RF amplifiers, so they might have been of German origin. The German makers seemed to favour jfets during that period.


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Old 26th Jun 2019, 4:32 am   #9
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Default Re: Dormer & Wadsworth (D&W)

Back in the day, I wasn't aware of D&W and I thought that all those British tuner makers were making their own front ends, so they must have their own RF designers. Engineers are dangerous beasties to keep in captivity, particularly design engineers, at the best of times. They'll laugh at management decisions, see straight through personnel department shenanigans, and generally cause disruption. RF design engineers are by far the most dangerous. They know that no-one else understands what they do, thinking it's some form of black art. They do practical jokes. They design what they want to do, not what they were told to do. Disruption is elevated to mayhem. The electronics industry never saw more beards and VWs until Unix hit town. I can now understand the attraction of bought-in front-ends.

What I did wonder about was where all the innovation came from. The answer I saw was the semiconductor firms. What became the norms in FM tuners came from the applications notes of RCA for dual-gate MOSFETs, CA3089 and CA3090. Motorola for varactor tuning and MC1310. Philips ar the time were producing reference designs around bipolars saying that they represented the best performance on low DC bias currents - clearly thinking of portable. radios, not hifi. Ceramic filters came along and became standard features. Did this come from Murata/Kyocera? or were Brush-Clevite the initiators? Murata were certainly the winners.

D&W were but a step in this food-chain... the trickle down from apps notes.

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Old 26th Jun 2019, 10:41 am   #10
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Default Re: Dormer & Wadsworth (D&W)

Quote:
Originally Posted by Radio Wrangler
The antenna will see cold sky in half its field of view, and outdoor temperature ground in the other half, so overall its noise output is colder than the 290K assumed in noise figure definition. (This is why it's still worth pursuing noise figures down to 1dB and below)
True for UHF, but at VHF there is more noise coming from somewhere else? I seem to recall reading somewhere that at 100MHz there is little point in going for a noise figure below about 3dB.

Quote:
In later FM tuner designs the Q of varactor diodes is dramatically lower than that of mechanical variable capacitors, and they become the dominant limitation on resonator Q, no longer the inductor. So the losses of the input filter increase leading to more noise disadvantage unless heavier coupling is used to widen it. A wider filter lets more off-channel signals in to add up and clobber the first active device. Worse, the varactors themselves are non-linear. Narrower filters run their resonators at higher Q's and that scales up the signal voltages across the diodes. Intermod products rise disproportionately fast.
When I designed a DIY FM tuner (with varicaps) I think I went for Q=40 single-tuned from the antenna into the dual-gate MOSFET RF stage and Q=80 double-tuned into the diode DBM. I have no idea how optimised that is, but it seems to work OK.
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Old 26th Jun 2019, 11:39 am   #11
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Default Re: Dormer & Wadsworth (D&W)

Re post no. 10

G8HQP_Dave: Yes, there is more noise than thermal at 100 Mc/s and lower. It is cosmic noise emanating mainly from our Galaxy - At 100 Mc/s typically it is about 1000 deg Absolute reaching as high as 10,000 deg Absolute towards the Galactic centre, with higher values at lower VHF frequencies.
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Old 27th Jun 2019, 2:55 am   #12
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Quote:
Originally Posted by Radio Wrangler View Post
What I did wonder about was where all the innovation came from. The answer I saw was the semiconductor firms. What became the norms in FM tuners came from the applications notes of RCA for dual-gate MOSFETs, CA3089 and CA3090. Motorola for varactor tuning and MC1310. Philips ar the time were producing reference designs around bipolars saying that they represented the best performance on low DC bias currents - clearly thinking of portable. radios, not hifi. Ceramic filters came along and became standard features. Did this come from Murata/Kyocera? or were Brush-Clevite the initiators? Murata were certainly the winners.
With the ceramic IF filters for consumer equipment, Clevite does appear to have been the initiator in the early 1960s, at least for AM applications. But by the time they came into widespread use for FM tuners and receivers, say 1969 give or take, Murata was probably the dominant supplier, and by then I’d expect doing its own R&D.

RCA’s several steps along the road from all-bipolar to all-dual gate mosfet front ends were mentioned in post #1.

The use of jfets in FM front ends turned out to be something of a side-story. TI could have been involved as a proponent, although not the only one. It did pursue the use of jfets in TV front ends, but that was not productive, although the specific drawbacks, whilst being deal-breakers for the TV case, were manageable for the FM case. But by 1970 it was advocating the use of dual-gate mosfets in FM front ends.

In respect of the development of integrated FM IF strips, RCA was a major contributor but not quite as dominant in early innovation as it was in the dual-gate mosfet case. It went through several intermediate steps before it got to the CA3089. In coarse terms, and referring only to the FM-oriented ICs (not those with a TV-sound orientation) these were the CA3012/CA3014, the CA3043, the CA3075/CA3076. The CA3089 was the first RCA own-design FM IC to include quadrature demodulation. Fairchild had previously introduced a rudimentary form of quadrature demodulation in its µA717, but Sprague was the first to use a balanced six-transistor tree for the purpose, in its ULN2111A. This spawned many lookalikes, including but not limited to the SGS TAA661 and Siemens TBA120. RCA’s master stroke was to develop a complete subsystem, inclusive of auxiliary functions, in an IC that included a quadrature demodulator and had extra gain as compared with what had gone before.

Sprague had also noted that the six-transistor tree had multiple uses, and Motorola took this on board in a big way. One of its several early applications was in the MC1304/5 stereo decoder IC, which I think established Motorola’s prime position in this field. RCA was first with a PLL-type stereo decoder, but Motorola followed this very quickly with its own MC1310, which became the dominant type. I’d guess that Motorola built on its established position, added to which its decoder did not require the use of an inductor, whereas the CA3090 did. Anyway, the equipment makers seemed happy enough with using an RCA/Motorola combination rather than an all-RCA set of ICs. Fairchild also introduced a PLL stereo decoder, the µA758. I am not sure whether this just preceded or just followed the MC1310, but in the literature it has often been treated as an MC1310 variant/derivative, perhaps not because that is what it was, but because of Motorola’s dominance.

During the 1970s, once the plateau had been reached and refinement rather than significant innovation became the mode, both RCA (CA3189) and Motorola (TCA4500) offered improved ICs in their respective fields, but Hitachi and Toko moved into dominance, each offering successively improved versions of both the CA3089 and MC1310, with some selective innovations such as pilot-tone cancelling decoders. Toko was by then a major coil and IFT supplier, and also offered block filters for pots-decoder filtering, birdie filtering, etc.

The arrival of fully electronic tuning towards the end of the 1970s, which required changes to the IF ICs, apparently provided an opportunity for Sanyo to emerge as a major force, at least somewhat displacing Hitachi and Toko. National Semiconductor also entered the FM IF IC field with its LM1865 family, which was innovative in having an on-board IF pre-stage and providing dual-bandwidth front end AGC.

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Originally Posted by Radio Wrangler View Post
D&W were but a step in this food-chain... the trickle down from apps notes.
My guess is that D&W may have started with say a Mullard-based all-bipolar design, although the double-tuned bandpass input option might have been its own idea, in order to get better resistance to spurious responses for the hi-fi market. Then it followed the RCA application notes when it came to converting its circuits to use one or more dual-gate mosfets. (I think that the European semiconductor makers were asleep in the late 1960s when it came to developing and applying dual-gate mosfets.) After that it followed the Motorola application notes when it came to adapting its circuits to use varicaps.

It also reasonable to assume that D&W saw a market opportunity for FM front ends that were somewhat better than those offered by Mullard, and suitable for use in hi-fi tuners. It could have been a niche that was not addressed by the “major” TV front end makers, such as AB Metal Box, Plessey-Brayhead and Cyldon. In the valve days, some of these at least also offered FM front ends, but these appear to have been of the basic one-valve, two-gang variety that was probably at best marginal for hi-fi applications. And with solid-state TV front ends, they stayed with bipolars well beyond their “best by” date, so even had they FM offerings, they probably would not have had the mindset necessary to make the change to mosfets – perhaps some NIH at work. D&W’s main competition in the 1960s may have been the German makers such as Görler.

From this distance looking back, D&W is very obscure. It is the sort of organization that “Hi-Fi News” magazine just might have written about back in the days before it went off the rails, and had quality columnists such as Austin Uden, but as yet, there is no on-line archive for this magazine.


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Old 27th Jun 2019, 3:02 am   #13
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Quote:
Originally Posted by SteveCG View Post
G8HQP_Dave: Yes, there is more noise than thermal at 100 Mc/s and lower. It is cosmic noise emanating mainly from our Galaxy - At 100 Mc/s typically it is about 1000 deg Absolute reaching as high as 10,000 deg Absolute towards the Galactic centre, with higher values at lower VHF frequencies.

Here are some charts showing atmospheric and cosmic noise distributions. They are from a 1955 paper on TV tuners, but I don’t think that the universe has changed all that much in the intervening time.


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Old 27th Jun 2019, 8:13 am   #14
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There is another factor in addition to NIH syndrome that has been at work in many companies over most of time.

They do not want to release onto the market a new product with some new technology because they fear it will cannibalise sales of their existing product, their cash-cow.

The error in this decision is that once a new technology is starting, if you do not introduce it yourself and thereby cannibalise your own products, there will soon be a competitor along to do it for you.

Some firms really were too dim to see the inevitability of the loss of surpassed technologies. Others could see it, but were financially trapped without the cash flow to more regularly update their product lines.

It's one of natures wonders how a firm can be made up of some quite bright people, yet the composite entity can behave in some rather disappointingly stupid ways. I guess it's a case of having so much momentum going in some direction, that by the time they realise it's silly, they can't stop it

Of course, it's too easy for us to judge, looking back with 20-20 hindsight.

I sometimes wonder about Clive Sinclair, sitting in his C5 prototype, didn't he feel just a bit too vulnerable? His potential customers did.

Studying the mechanisms behind failed products and missed opportunities can be fascinating. I wonder if the history of our times will be written in these terms, or will future historians not be able to get themselves out of the Monarchs, politicians and wars groove?

Philips has a long history of innovation and haven't been scared of upstaging their own products, so sticking with bipolars too long has to be NIH.

By the way, semiconductor firms seem to be dropping dual gate mosfet transistors as fast as they can. We seem to be exactly at the end of their era. Trying to find something to equal them for easy AGC, low cost and plentiful gain is proving difficult. Some 12v parts linger, but the 5v families are almost all gone.

David
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Old 27th Jun 2019, 9:18 am   #15
G8HQP Dave
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Default Re: Dormer & Wadsworth (D&W)

Groupthink is alive and well in a boardroom near you. One dominant person with a bad idea (or a lack of good ideas) can steer a whole organisation down the wrong path. Mix in some mergers and demergers, which almost always destroy value (except for the accountants and lawyers).
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Old 2nd Jul 2019, 5:35 am   #16
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Two of my opening questions were:

Quote:
Originally Posted by Synchrodyne View Post
Did D&W start in the solid-state era, or did it have earlier activities with valve-based FM front ends?

What other radio/audio assemblies, if any, did D&W build?
The answer to the first question is given by this advertisement from Practical Wireless (PW) 1966 May:

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Similar advertisements ran through to 1969, but apparently not beyond.

Thus, D&W was active in the valve era,

That the advertised assembly was an FM front end (of the single-valve type) with an attached AM two-gang tuning capacitor shows that the D&W product line extended at least a little beyond FM-only front ends.

I’d guess that Haverson Surplus had acquired remaining stock of D&W valved FM front ends following the change to the solid-state type by D&W’s customers.

The Haverson description “beautifully designed and precision engineered by Dormer & Wadsworth” to some extent was probably marketing speak “purple prose”, but suggests that they might have been better than comparable run-of-the-mill units aimed more at the setmaker market.

Radford might have been a user of D&W valved FM front end. Its FMT1 model is known to have had a separate tuning head of the one-valve (ECC85) type, and it is almost certain that this would have been a proprietary unit. It does seem a little odd that a single-valve FM front end – essentially a lowest common denominator type – would have been used in a high-performance tuner that had a four-stage IF strip and a wideband ratio detector, but that may have reflected the non-availability of higher-performance units from third-party sources. Those UK FM tuner makers who used two-valve front ends probably “rolled their own”, and in many cases integrated them into the chassis rather than mounting them as a separate screened unit. (Although the Dynatron FE2 (used in the T10A and I think the T11) was a two-valve separate unit.) Of the UK-made single-valve units available to Radford, the D&W may have been seen as the best of the bunch.

Be that as it may, it does appear that with the arrival of the solid-state era, D&W took the opportunity to rise above the standard performance level, with 4-gang models and early adoption of the dual-gate mosfet. (Whether it ever got to 6-gang models with 2 RF stages, as did the Japanese suppliers and Ambit in the UK is unknown).


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Old 2nd Jul 2019, 7:38 am   #17
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I've just been looking around and found Short Wave Mag May 1971 on the American radio history site. I even remember the trio advert on the front cover!

Inside is an article "Versatile Sub-Modulator" by A H Dormer G3DAH C.Eng FIERE. and a column "The VHF Bands" by the same.

The article is about a very hybrid (valves + JFETs + Plessey SL600 series ICs) FM modulator for a KW2000. If this is the Dormer of D&W, then he seems to have interests in VHF and FM. The VHF column ran to 5 pages.

There is a Wadsworth in the same issue, G3OLP in Todnmorden selling a DX100U and, wait for it! a DST-100.

This might be the right Dormer, but I'm not sure about Wadsworth. Not a common name, though.

There is a wing commander A H Dormer in the RAF list, group 90 (signals) Radio warfare 12 April 1955. RAF Medmenham, Marlow, Bucks.

Even with SWM's page rate and all those pages, Mr Dormer would still need a day-job.

Once you start searching, heaven knows where you wind up... I've just spotted a Scottish VHF convention 1969 piece with a photo of David Guest GM3TFY, who I worked with for many years, and someone getting presented with the Jock Kyle trophy, which many years later sat on my mantelpiece for a year. It's a small world!

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Old 3rd Jul 2019, 3:33 am   #18
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Default Re: Dormer & Wadsworth (D&W)

Thanks for that. I’d say that it’s better than even odds that A.H. Dormer was the Dormer in D&W.

His comment at the end of the SWM article – about using the Plessey SL620 and SL630C ICs in a modulator circuit - is interesting: “Although circuits have been published in the past showing use of these IC’s [sic] for compression purposes, they seem to have been taken directly from the manufacturers’ data sheets which, in practice, are not always suitable for amateur use.”

That suggests that although he might have been guided by the semiconductor makers’ application notes in designing FM front ends, he also put his own interpretation and ideas into them. I imagine that he would have been able to provide a cogent rationalization for placing the bandpass at the input rather than at the interstage.

Interesting that he used the TIS88 jfet for the microphone preamplifier and its “emitter follower”. This was TI’s contender for TV front end use in the late 1960s, and did find application in some FM front ends (I think B&O used it, for example). One wonders if D&W offered say a TIS88 cascode RF amplifier option for its 341-series FM front end.


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Old 12th Jul 2019, 2:27 am   #19
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I have found an odd reference to Dormer & Wadsworth in Elektor magazine 1976 March. This was in a constructional article for a TV sound tuner that also received FM, using both a TV front end and an FM front end whose respective outputs were the converted to 6 MHz for further processing. In respect of the front ends it was said:

“The internal circuitry of the front ends will not be described as these are commercial units and the circuits will obviously depend upon the manufacturer.

“A word of warning would not come amiss at this point. There are on the market vast quantities of scrap TV front-ends, and as many of these are of dubious quality they are best avoided. It is advisable to obtain a front-end from a reputable manufacturer such as Toko, Dormer & Wadsworth [my emphasis], or at the very least a new, boxed, surplus front-end from a reputable TV manufacturer. The problem does not arise to such as [sic] extent with the front end of FM radio, as there are less scrap ones on the market”

From that one could reasonably infer that both Toko and D&W also offered TV front ends as well as their probably more well-known FM front ends. That would not be surprising in the Toko case, although I have never seen mention of it. But it could well have made TV front ends for those Japanese TV makers that did not wish to build their own. On the other hand, with D&W I have the impression that it might have been oriented to relatively small production runs that might have made it uncompetitive when it came to TV front ends. I think that the TV front-end business was somewhat cut-throat, requiring a melding of both precision engineering and low-cost mass production techniques.

Still, in view of the Elektor comment, the question needs to be asked – has anyone here ever come across a D&W TV front end?


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Old 12th Jul 2019, 5:55 am   #20
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Until you mentioned them here, I hadn't known they existed. I'd seen Larsholt ubits in some magazine projects, I knew about the Mullard modules, and were there ones by Gorling (sp?) in some German/Austrian radios?

In the 1990s, analogue TV was still dominant and cable system operators wanted to add a quality monitoring system to look at the VITS (Vision inserted test signal) that is added in one of the unused lines. From this you can get bandwidth, diff gain and diff phase, etc.

They wanted a test box to demodulate and test each channel in turn, and if a fault persisted long enough to not be a glitch, to fire up a modem and 'phone home' with a report to some central monitoring facility.

The reason for all this was the advertisers. Advertisers had long argued that not all parts of a distribution network got good enough quality all the time, and used this supported by ad-hoc monitoring to argue down the price of running their ads.

There must have been sufficient money dependent on this for getting the cable firms interested in thorough network monitoring. Quality parameters, not just signal presence.

An R&D project at HP repackaged video digitiser and CPU cards that existed in spectrum analysers with a TV tuner/demod module for the TV standard of the target market.

We found a series of tunerr/demods from Philips with variants for each of the standards we had to cover. Then our problems began. Philips provided samples freely, but thereafter Philips did not want to deal with us. We didn't want the sort of quantities a TV setmaker used. "Go through a distributor!" we were told. The distributors were no better. They didn't handle this product range because setmakers dealt directly with Philips. The distributors would be delighted to deal with us, but as Philips would only sell to them in units of a pallet-load, the distributors imposed the same requirement on us. They would have no other customers for them.

Anyway, analogue TV distribution was drawing to a close and interest was fading. Add in the Philips problem and although the project was just on the threshold of full production, it was quietly withdrawn from the catalogue. If this sounds like a lame product, it was worse than that. Truly accursed would be accurate. A safety recall hit the units which had gone out. All the units were got back, except one which no-one could trace.

I got dropped in to manage the project part way through. I have an enduring urge to run at the mention of 'tuner', and a tendency to avoid Philips parts of any type.

David
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