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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 11th Apr 2021, 7:28 pm   #21
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

By Jove, he's got it! (Rex Harrison, wasn't it?)

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 11th Apr 2021, 7:37 pm   #22
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

I was not yet born when that film was released. A few years later, I soiled my nappies...
regenfreak is offline   Reply With Quote
Old 26th Jul 2021, 5:20 pm   #23
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Just a quick update: I have come back to the FM valve tuner project after messing around with HF SSB receivers for a few months.

I built an oscillator test rig to test the performance and stability of the VHF valves:ECC85, 12DT8, 6BS8 and EC81 (Russian 6C11) as an oscillator. They all work fine on the test rig. The EC81/ 6C11 is an excellent UHF triode rated up to 750MHz. It gives completely flat oscillator output across the full range of frequencies when it was measured with a RF probe. Both the 6CW4 RF amp and ECC85 mixer/Rf AMP work well. In addition, the air gang tracks perfectly. However, I cannot isolate the root cause of ECC85 not oscillating well in the tuner, in spite of hours and hours of debugging. Therefore I started from a clean slate by building a minimalist 4-valve FM tuner with the line-up:

RF amp and mixer: 6N3P (USSR valve commonly used in FM and TV, the double triode has low noise and high transconductance.)

Oscillator: EC81 (6C11)

1st IF amp: 6BA6

2nd 1st amp/limiter: 6BA6

detector: ratio detector with diodes

The tuner works very well with good selectivity and sensitivity using an balanced ribbon indoor antenna. The IF transformers and ratio coils were stripped from a broken japanese FM radio. The dual air variable tuning gang were obtained from ebay. I think it was British made and was designed to track between 88MHz-100MHz. I was able to make it track perfectly from 88MHz to 108MHz after solving the compatibility mathematical conditions for the matched trimmers. Overall I am happy its performance as a mono tuner.


At the moment, I am working on my next project; a stereo tuner with the line-up:

Cascode RF AMP: EC88CC

Oscillator Ec81 (6C11)

mixer: 6CB6A

1st IF: 6BA6

2nd IF: 6BA6

1st limiter/3rd IF: 6AU6

2nd limiter: 6AU6

I will use a discriminator coil and broadband IF transformers to maximise the stereo audio fidelity. I omit AFC because it is not required in open chassis in which the temperature change is small. The 6C11 oscillator frequency is very stable.
Attached Thumbnails
Click image for larger version

Name:	A-FM-1.jpg
Views:	96
Size:	66.1 KB
ID:	238243   Click image for larger version

Name:	A-FM-2.jpg
Views:	84
Size:	86.7 KB
ID:	238244   Click image for larger version

Name:	A-FM-3.jpg
Views:	86
Size:	82.4 KB
ID:	238245   Click image for larger version

Name:	A-FM-4.jpg
Views:	79
Size:	89.5 KB
ID:	238246  
regenfreak is offline   Reply With Quote
Old 26th Jul 2021, 11:11 pm   #24
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

ECC85 have a nasty reputation for not lasting long and their gain falling. Usually the first thing to go is the ability of oscillators to start.

On the other hand, the number of double triodes suited for cascode use because of heater-cathode insulation for the running voltages of the upper triode, and also the need to keep cathode-heater capacitance down to prevent horrible coupling problems, is rather limited.

I stopped using valves for any new work a long time ago. The only valves being made revolve around hifi people and guitarists with fat wallets. Radio-type valves aren't being made and I see them as a dwindling resource, so I choose not to use any of them up and leave the remaining ones for servicing period equipment.

Sometimes transistors are the right answer.

They aren't products of the devil, they aren't harder to use. They're just different. You need more of them than you'd need valves to do the same job, but they're small, cheap and light on power so you can use as many as it takes. Like valves, they have limitations, so you have to design ways of evading them. The limitations are different to the limitations of valves, so there is culture-shock involved, but once you see the patterns in the different limitations of different devices it all suddenly becomes easier to undertand and easier to handle. It's all a lot simpler than it looks, once you get up the learning curve.y

As a piece of, um, shall we say micturition-artistry, I designed an audio power amplifier using as many transistors as possible but subject to the requirement that I could show that each and every one of them was doing something useful. It worked rather well and was a good joke with a friend who was designing a minimalist one. Bill's amp turned into a product at Linn (of Sondek fame) after he moved there. A small run of mine were built at HP. My prototype has been sitting in the corner of my lounge for 40 years. It's the size of a good picnic hamper.

David

Oh, should have said, I have two FM tuners I'm playing with, one is one of the last Sony 'ES' series, the other is more interesting, a Revox B261, the manual is available on-line. This takes very different approaches. LC filtering and no ceramic filters. separate stages of limiting in the IF. An analogue pulse-count discriminator, and stereo decoding using several general-purpose ICs, not the usual one-chip wonders.
__________________
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 27th Jul 2021, 11:46 am   #25
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
ECC85 have a nasty reputation for not lasting long and their gain falling. Usually the first thing to go is the ability of oscillators to start.

In my case, the ECC85 is oscillating happily in my test rig but its output voltage vs frequency response is non-uniform. The components layout of FM tuner is very critical and an art form itself. i had a number of theories why is not oscillating in my first tuner but all of them have been proven wrong. The ECC85 would only oscillate if I connect a crocodile clip with a lead to the anode which is very puzzling for me.

Quote:
On the other hand, the number of double triodes suited for cascode use because of heater-cathode insulation for the running voltages of the upper triode, and also the need to keep cathode-heater capacitance down to prevent horrible coupling problems, is rather limited.
Thats why i will opt for EC88CC in cascode in my next adventure. It has higher transconductance than ECC85. Unlike ECC88, the miltary spec ECC88CC version has high voltage spec Vh-k for both triodes. The only disadvantage is that the EC88CC or ECC88 are highly sought after by the audiophiles who push up the prices to insane level.


Quote:
I stopped using valves for any new work a long time ago. The only valves being made revolve around hifi people and guitarists with fat wallets. Radio-type valves aren't being made and I see them as a dwindling resource, so I choose not to use any of them up and leave the remaining ones for servicing period equipment.

Sometimes transistors are the right answer.
I have been building transistor/IC AM and FM receivers for a year. In my heart, I prefer building valve receivers as i started off playing with valves before i learnt solid state electronics. I do not really care much about valve amplifiers and audiophile stuff etc. It s a pity the fat-walleted audiophiles drive up the prices of RF valves. I always look out for cheaper eastern europe/russian alternatives. A Mullard ECC88CC can fetch 40-50 while a Esatern european alternative would cost about 15.

Quote:
a Revox B261, the manual is available on-line. This takes very different approaches. LC filtering and no ceramic filters. separate stages of limiting in the IF. An analogue pulse-count discriminator, and stereo decoding using several general-purpose ICs, not the usual one-chip wonders.
Sounds very interesting. I will look for the schematic.
regenfreak is offline   Reply With Quote
Old 27th Jul 2021, 4:27 pm   #26
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 11,247
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
using as many transistors as possible
How many?
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Old 27th Jul 2021, 5:07 pm   #27
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

27 plus a couple of 3-terminal regs and four power supply rails. Sure I could have squeezed a few more in, but then some wouldn't have been quite so easy to say had necessary purposes. That's per power amp, of course.

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 30th Jul 2021, 4:59 pm   #28
John Caswell
Hexode
 
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 392
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

I have been reading this with a great deal of interest. Back in the early 60s I came across an article in the American Magazine "Radio Electronics April 1953" for a Long Distance FM tuner. having nothing better to do I decided to have a go at building this (fools rush in etc..what did I know about FM radio construction) My boss at the time, Bob, reckoned that we could do it together. It took about 6 months as we had to import a couple of valves from the US.
After much faffing about getting it stable (lotta gain built in) we finally had it running very satisfactorily. Its performance was quite startling, no good for FM stereo as IF bandwidth was quite narrow, but with the proverbial piece of wet string as an aerial, any signal passing was sucked in. When connected to a serious 8 element FM aerial long distance continental FM was eminently possible especially with Sporadic E conditions. I, in particular, learnt a great deal about RF earthing, component, positioning, screens across valve bases which has stood me in good stead in my later life, especially as I am now getting quite good at repairing/aligning Quad FM tuners.
A bit of a preamble for "regenfreaks" comment re an IF strip etc. I would think that a Quad valve FM IF strip would fit his purpose very well as it is complete strip with the mixer IFT mounted on it ready. It should be possible to find a valve FMT to butcher, and I think I may have one somewhere, will have a look and post back here If I find it.
Next thought I am pretty sure that the article will be in the American Radio Magazine website.

John

Last edited by John Caswell; 30th Jul 2021 at 5:07 pm.
John Caswell is offline   Reply With Quote
Old 30th Jul 2021, 5:05 pm   #29
John Caswell
Hexode
 
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 392
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Just had a look at the site, now called "worldradiohistory.com" yes it is there April 1953 and I also found the Quad FMT so if you want it "regenfreaks" PM me.

John
John Caswell is offline   Reply With Quote
Old 30th Jul 2021, 6:54 pm   #30
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 10,403
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

As far as front-ends are concerned, it could be worth looking at the circuits used on early Pye mobile-radio stuff [Valve-receiver Vanguards/Cambridges from the very-early-60s]. These had to be RF-tough - particularly the 'police' versions operating around 96-101MHz when there were nasty broadcast-stations running 100Kw or so less than 10MHz away.

I built various 144MHz converters back in the early-70s; a 6CW4 Nuvistor - neutralised - was the go-to front-end back then. One thing we learned was that maximum RF gain and lowest noise-figure did not coincide: HT voltage was significant - the 6CW4 seemed to be happiest with a mere 80 Volts anode voltage.

I also used the A2599 - http://www.r-type.org/exhib/abn0002.htm - and A2521 - http://www.r-type.org/exhib/abn0004.htm - with success - though it has to be said the appearance of Texas Instruments' GM0290 germanium VHF/UHF transistors [and the TV-tuner-oriented AF139/239] made life a bit easier.
Attached Thumbnails
Click image for larger version

Name:	amp.jpg
Views:	40
Size:	36.1 KB
ID:	238503  

Last edited by G6Tanuki; 30th Jul 2021 at 6:59 pm.
G6Tanuki is offline   Reply With Quote
Old 31st Jul 2021, 10:44 am   #31
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
Just had a look at the site, now called "worldradiohistory.com" yes it is there April 1953 and I also found the Quad FMT so if you want it "regenfreaks" PM me.
Thanks John. I will check it out. I purchased the Quad FMT service manual last year just to study the schematic. I never own or repair the Quad...I am such a nerd

Quote:
As far as front-ends are concerned, it could be worth looking at the circuits used on early Pye mobile-radio stuff [Valve-receiver Vanguards/Cambridges from the very-early-60s]. These had to be RF-tough - particularly the 'police' versions operating around 96-101MHz when there were nasty broadcast-stations running 100Kw or so less than 10MHz away.
Thanks I will check. After researching many cascode FM front end designs, I have already settled with the E88CC cascode with USSR 6C11 oscillator and 6CB6A mixer. The attached drawing of is my component layout of my FM stereo tuners (E88cc, 6C11, 6CB6A, 6BA6,6BA6, 6AU6,6AU6). I have the habit of mapping out the components on paper before i build anything. I am collecting components and will start making the chassis. It is hard to find triple gang air variable capacitor. So I may have to strip the triple gang from the 6C4 tuner.

In the USA, 6BS8, 6BZ7 were used in some high ended tuners. For british design, the Troughline Stereo III used ECC88 in casode.


Quote:
I built various 144MHz converters back in the early-70s; a 6CW4 Nuvistor - neutralised - was the go-to front-end back then. One thing we learned was that maximum RF gain and lowest noise-figure did not coincide: HT voltage was significant - the 6CW4 seemed to be happiest with a mere 80 Volts anode voltage.
I destroyed one 6CW4 by applying 90V to the plate. In the datasheet, 90V B+ should be OK. I think ideally B+ should be around 70V for 6CW4. The biggest problem with 6CW4 is that the sockets are very over priced. It is possible to wire a pair of 6CW4 in cascode in my next project, but I dont fancy spending the money...


Quote:
I also used the A2599 - http://www.r-type.org/exhib/abn0002.htm - and A2521 - http://www.r-type.org/exhib/abn0004.htm - with success - though it has to be said the appearance of Texas Instruments' GM0290 germanium VHF/UHF transistors [and the TV-tuner-oriented AF139/239] made life a bit easier.
Thats interesting. Thanks. In all FM cascode designs that i have seen, there are always either inductive or/and capacitive neutralising network between the lower and upper triode. In the simplest neutralising network deisgn, a RFC is used to link the lower and upper triodes in which Cak, Cgk and the RFC form a low pass pi-filter.
Attached Thumbnails
Click image for larger version

Name:	fm stereo.jpg
Views:	34
Size:	62.2 KB
ID:	238535  

Last edited by regenfreak; 31st Jul 2021 at 11:04 am.
regenfreak is offline   Reply With Quote
Old 31st Jul 2021, 1:38 pm   #32
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
I have been reading this with a great deal of interest. Back in the early 60s I came across an article in the American Magazine "Radio Electronics April 1953" for a Long Distance FM tuner. having nothing better to do I decided to have a go at building this (fools rush in etc..what did I know about FM radio construction) My boss at the time, Bob, reckoned that we could do it together. It took about 6 months as we had to import a couple of valves from the US.After much faffing about getting it stable (lotta gain built in) we finally had it running very satisfactorily. Its performance was quite startling, no good for FM stereo as IF bandwidth was quite narrow, but with the proverbial piece of wet string as an aerial, any signal passing was sucked in. When connected to a serious 8 element FM aerial long distance continental FM was eminently possible especially with Sporadic E conditions. I, in particular, learnt a great deal about RF earthing, component, positioning, screens across valve bases which has stood me in good stead in my later life, especially as I am now getting quite good at repairing/aligning Quad FM tuners.
I have looked at that article on page 58:

https://worldradiohistory.com/Archiv...cs-1953-04.pdf

It is a badass project that would require a 5 gang variable capacitor, 6BZ7 cascode with untuned, broadband front end, a rather unusual 6J6 push-up tuned RF amp, 6AH6 tuned RF amp, 6C4 oscillator and 6AB4 mixer. The extra 6AH6 pentode would add lots of gain for DX in expense of more noise. Then there are six IF transformers (back-to-back capacitive-coupled double-tuned IFs) and a cascaded 6AU6 limiter!!!

Last edited by regenfreak; 31st Jul 2021 at 1:50 pm.
regenfreak is offline   Reply With Quote
Old 31st Jul 2021, 4:06 pm   #33
John Caswell
Hexode
 
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 392
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Well yes, I agree with all you say, but I wouldn't call it a badass project, at the time it was pretty hot tuner which was really what we were interested in.
Took some effort to tame it, poor construction techniques on my part, I was just an apprentice, but soon got my act in gear, after much ear bashing both figuratively and literally, those were the days!!
I didn't offer the info for you to build it, so much as ideas. For instance we made the tuning gang out of 5 individual ex gov variable caps with flexible/isolating couplers between each stage to avoid common coupling through the shafts, all sorts of filter chokes for the heaters, IFT were easily available, as was pretty well everything else. For me a very worthwhile exercise in techniques and construction.

John
John Caswell is offline   Reply With Quote
Old 31st Jul 2021, 4:51 pm   #34
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Amateur radio publications used to talk of 'VHF' construction techniques and UHF ones as distinct from normal radio construction as practised at HF.

But they failed to explain that the construction technique was NOT a function of what frequency you wanted it to work at. Rather it was a matter of what frequency range did you want to ensure it didn't oscillate in.

An unstable stage has the remarkable super-power of mucking up your wanted reception no matter what frequency it takes off at. So the choice of construction style comes down to what frequency ranges does the active device have the ability to self-oscillate in?


In a conversation with Ian, G3ROO, a very experienced and excellent home constructor, he was discussing buying a spectrum analyser. He'd said that it didn;t need to go much above 30MHz, because he didn't build things for any higher. I explained that the purpose of such an instrument is to confirm that something is only creating the intended signals, and that the analyser therefore must cover enough frequency range that you can be comfortable that there is unlikely to be unwanted stuff above its capability. Even HF stuff can take off at hundreds of MHz, so an analyser covering to 1GHz or so is sensible.

Your circuitry must not only succeed in doing the things it is supposed to do, it must also fail to do all the things it must not do. This latter is the bigger deal. Almost infinite unless you can justify some limitations. DeMorgan doesn't quite fit RF logical thinking

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 31st Jul 2021, 5:17 pm   #35
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
But they failed to explain that the construction technique was NOT a function of what frequency you wanted it to work at. Rather it was a matter of what frequency range did you want to ensure it didn't oscillate in.

An unstable stage has the remarkable super-power of mucking up your wanted reception no matter what frequency it takes off at. So the choice of construction style comes down to what frequency ranges does the active device have the ability to self-oscillate in?


In a conversation with Ian, G3ROO, a very experienced and excellent home constructor, he was discussing buying a spectrum analyser. He'd said that it didn;t need to go much above 30MHz, because he didn't build things for any higher. I explained that the purpose of such an instrument is to confirm that something is only creating the intended signals, and that the analyser therefore must cover enough frequency range that you can be comfortable that there is unlikely to be unwanted stuff above its capability. Even HF stuff can take off at hundreds of MHz, so an analyser covering to 1GHz or so is sensible.

Your circuitry must not only succeed in doing the things it is supposed to do, it must also fail to do all the things it must not do. This latter is the bigger deal. Almost infinite unless you can justify some limitations. DeMorgan doesn't quite fit RF logical thinking
This is very true. At VHF frequencies, self-oscillation or regeneration occurs easily with either capacitive coupling between electrodes inside the valves due to stray capacitance, or inductive coupling due to stray inductance of the wirings. Therefore, the component layout and wire dressing become an art form with lots of nuances practiced by manufacturers. The usual goal is to have the shortest distance between points and minimal interactions or feedback between RF/IF/AF stages. To remove the RF energy feedback along the B+ lines and heaters, RFC chokes are used extensively in VHF. It is desirable to keep the IF gain stage low and use valve shields to prevent self-oscillation.
regenfreak is offline   Reply With Quote
Old 31st Jul 2021, 6:59 pm   #36
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Even split into many stages, you still wind up needing the same amount of gain in the IF.

Multi-superhets can evade the problems associated by leakage around high-gain strips by choosing to have some of the gain at one intermediate frequency, and the rest at the other.

Any feedback by leakage from the overall output to the overall input is on the wrong frequency and causes no trouble. It's like the frequency-shifting howl-round suppressors used on PA systems, though there the shift is rather small.

In designing a receiver, gain is cheap, dirt cheap nowadays. Selectivity is expensive and screening is very expensive.

Designing a receiver to receive a chosen signal isn't particularly difficult. It's designing it to not also receive everything else at once is where it gets difficult.

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 31st Jul 2021, 8:04 pm   #37
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
In designing a receiver, gain is cheap, dirt cheap nowadays. Selectivity is expensive and screening is very expensive.
The Silicon Labs DSP chips have changed everything and will kill all off all expensive, dual-conversion hardware-based designs used in narrow banded FM transceivers in the near future. With DSP architecture, it is much cheaper to have multiple conversions. For example, the Tecsun PL-880 DSP has quad conversions for the FM broadcast band (triple conversion for the AM, SW and SSB):

1st IF: 55.845 MHz
2nd IF: 10.7 MHz
3rd IF: 45 kHz
4th IF: 128 kHz

My Tecsun R-9700DX has dual conversion and is one of the remaining few analogue multiple -band receivers that is still in production and it is considered to be a strong performer in term of FM selectivity and sensitivity
regenfreak is offline   Reply With Quote
Old 31st Jul 2021, 10:54 pm   #38
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,354
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

A lot of receivers nowadays use I/Q mixdown from the incoming signal frequency into a pair of 1-pole lowpass filters, a bit of variable gain and then a pair of ADCs. ADI and all the usual semiconductor firms have had products out for some time. Last I looked, the Lime chips seemed amongst the best.

BUT

The dynamic range is rather limited. The synthesisers with on-chip VCOs and fairly basic Frac-N technology are noisy. Quite a bit of incoming bandwidth hits the ADCs. Also the cancellation of racing I and Q pthes against each other is limited. Fancy calibration helps, but not enough.

The HF transceiver currently set up in my radio shack up-converts to an IF in the 60MHz region (carefully more than twice 30MHz) where it has three sets of crystal filters (AM/FM, SSB, CW) then it mixes down to just above audio for its single ADC. Things do NOT go I/Q in the analogue sections, that happens only in nice, precise, digital processing. The synth is a multiloop one.

There is a preselector with switched inductors and a switched C, 2C, 4C, 16C etc network. All switched by relays!

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 31st Jul 2021, 10:57 pm   #39
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Just come across the schematic of MARANTZ 10B stereo FM tuner:

http://zilla.li/Resources/PDF/Marant..._Schematic.pdf

It has EC88 in cascode, six sets of three-pole Butterworth filters to replace conventional double tuned IF filters (see attachment) and CRT scope, Wow!!!!

The center LC element of the Butterworth has a shunt resistor to widen the bandwidth for FM stereo, I guess.
Attached Thumbnails
Click image for larger version

Name:	Marantz10B-butterworth.jpg
Views:	32
Size:	37.6 KB
ID:	238591  
regenfreak is offline   Reply With Quote
Old 31st Jul 2021, 11:13 pm   #40
regenfreak
Hexode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 379
Default Re: DIY FM tuner with 6CW4 nuvistor and ECC85

Quote:
A lot of receivers nowadays use I/Q mixdown from the incoming signal frequency into a pair of 1-pole lowpass filters, a bit of variable gain and then a pair of ADCs. ADI and all the usual semiconductor firms have had products out for some time. Last I looked, the Lime chips seemed amongst the best.
I purchased a cheap and cheerful Xiegu G90 20W SDR transceiver ( i can't afford to buy anything else. I only paid 320 new directly shipped from China). It uses 24 bits direct sampling. I am new to the technology. My understanding is limited. I was reading the I and Q mixer theory.....I +iQ plane...spiral... heavy stuff. I was reading this ARRL paper

https://www.arrl.org/files/file/Tech...0708qex013.pdf
regenfreak is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 2:53 am.


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 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.