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Old 9th Oct 2006, 7:12 pm   #1
adibrook
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Default Simple SW Receiver.

After reading the article about the canteen radio on the the spy radio thread...it got me thinking.

After reading some stuff about regens on the net, i get the impression that a regen can recieve CW, SSB and normal am transmissions. AND on the SW band the tuning coil is only about 13 turns.

I got the impression that a SW regen can look somethgin like this.

http://img.photobucket.com/albums/v4.../shortwave.gif

Its pretty much like a normal AM regen, but with much less turns on the coil. 10 for the tank circuit and 3 for the feedback.

If i was to build this, than i shoudl be able to listen to all sorts of amature activily...right?

Allmost any rf pentode will work here i think...maybe a EF80 or EF91?

Thanks.

Last edited by Station X; 11th Oct 2006 at 10:11 am.
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Old 9th Oct 2006, 7:29 pm   #2
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Default Re: simple SW reciever.

Yep, that's basically it. If the radio will work on MW you just need to fit another coil with fewer turns. You do need to be a bit more careful with construction at the higher frequencies.

Lots of similar circuits here: http://vintageradio.me.uk/radconnav/valvetrf/

Any HF valve should work in this sort of circuit. Often a number of related types will have the same pinout, so you can experiment with different valves. For example, EF80, EF85, EF89, EF183, EF184 all have the same pinout (there are probably more too )

Paul
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Old 9th Oct 2006, 8:22 pm   #3
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Default Re: simple SW reciever.

Hi Adi,

the position of the cathode tap is quite critical, and will probably need some experimentation. Try looking for a copy of the Practical Wireless "Atlantic Two" circuit, it is a two valve set based on your circuit, and works very well. (I wound coils for mine on a 35mm film container).

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Old 9th Oct 2006, 9:45 pm   #4
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Default Re: simple SW reciever.

Quote:
Originally Posted by adibrook View Post
If i was to build this, than i shoudl be able to listen to all sorts of amature activily...right?
Not really.

The main problem with the regenerative radio like you show is that they will literally work with any combination of components. That is if by 'work' one means they can be brought to oscillate.

But the brutal truth is that most old designs are pretty useless, seen with the requirements we today may in mind.

Quote:
Originally Posted by adibrook View Post
Allmost any rf pentode will work here i think...maybe a EF80 or EF91?
Use as 'dull' a pentode as you can possibly find, like an EF86. Yes, that is an audio valve and it will work perfectly for this RF application. You do not want a 'hot' valve like an EF89 or - worse - an EF183 or EF184. Regeneration control will be much too tricky to control.

For a regen to actually work for SSB reception on SW it needs to be built bulletproof, Ie. mechanically really, really rigid and with a very good bandspread mechanism on the variable capacitor.

The coil data depends on the capacitor you intend to use.

Here is the link to the thread from the last time you asked the same question, complete with my answers.

Frank N.
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Old 9th Oct 2006, 10:13 pm   #5
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Default Re: simple SW reciever.

Frank, I think it's clear that Adi doesn't want to build a highly optimised regenerative receiver for real amateur radio use, he wants to knock something together using bits and pieces from his junk box

I tend to have a similar attitude

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Old 9th Oct 2006, 10:23 pm   #6
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Default Re: simple SW reciever.

Hi paul,

Yeah, I sort of gathered that much.

Trouble is that is a fairly pointless exercise IMHO. If the coil only has 10 or so turns, then it will run at a fairly high frequency. Combine that with junkbox construction technique, and it will be useless.

Not just 'unstable' or 'beginner quality'. Useless. A waste of time.

If such a receiver should be able to reproduce intelligible SSB transmissions, then it has to be 'optimized'. Mind you, the optimization is mostly a combination of component values and a few circuit details and not in particular added complexity. This combined with brutal mechanical strength and shielding.

No-one said anything about 'nice' or 'polished'.

Frank N.
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Old 9th Oct 2006, 10:39 pm   #7
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Default Re: simple SW reciever.

I agree it won't do very well with SSB. If the objective is to listen to SSB and CW amateur radio, a simpler solution would be to build a BFO using a spare IFT. This could use a valve or a transistor. You then just use a normal domestic radio with SW coverage, and adjust the BFO frequency to beat with the IF frequency of the radio. Transistor circuit here: http://www.hanssummers.com/radio/superdrg/bfo/index.htm

There's no harm in building the regen and seeing what happens though

Paul
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Old 9th Oct 2006, 10:52 pm   #8
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Default Re: simple SW reciever.

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Originally Posted by paulsherwin View Post
I agree it won't do very well with SSB. If the objective is to listen to SSB and CW amateur radio, a simpler solution would be to build a BFO using a spare IFT.
Must admit I haven't tried something along those lines. Though in general my main objectives for 'simple' CW/SSB receivers are stability and bandspread, both of equal importance. You need to be able to set and hold a frequency to within less than 100Hz, something I'm not certain all commercial SW receivers will do. The requirements are much less stringent for AM reception.

Quote:
Originally Posted by paulsherwin View Post
There's no harm in building the regen and seeing what happens though
Of course not. That is as long as you aren't too discouraged from further experimentation if it doesn't live up to expectations. My first ECC81 regen was hurled together in a hurry and worked accordingly, yet I'm still here.

Frank N.
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Old 10th Oct 2006, 12:57 am   #9
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Talking Re: simple SW reciever.

Just for what it's worth - and to give a little encouragement here - many, many years ago, I built a simple regen receiver from a design published in Practical Wireless. IIRC it used a 6BR7 as the detector and a triode-pentode (an ECL xx variant) for the AF stage. (In TRF notation, a 0V2 + rectifier). With plug-in, pre-made coils, I had a lot of fun listening to Radio Amateurs on 80m. / SSB with it. OK, so it wasn't up to double-conversion s'het. standards with rock-solid stability, etc. Moreover, I'm not aware that SSB signals of those days required any less exotic kit for their reception than the Amateur SSB signals radiated today - but that dear little radio was:
(a) cheap & simple - no exotic test gear required;
(b) as a novice, it got me started;
(c) I learnt a lot;
(d) it was fun!

So let's not be too discouraging to Adi, no?

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Old 10th Oct 2006, 6:10 am   #10
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Default Re: simple SW reciever.

Quote:
Originally Posted by G8DLH View Post
I'm not aware that SSB signals of those days required any less exotic kit for their reception than the Amateur SSB signals radiated today ...
No disagreement. 80m is a good place to start, both from a propagation point of view and also with regards to signal strength and the ease of obtaining suitable stability.

But Adi will need a good more than 10 turns on the main coil to hit 3.5MHz.

Frank N.

Edit: When I talked about the requirements of today, I was thinking mainly about the amount of traffic and the signal strengths often encountered near the SW BC bands. A receiver with a 10KHz wide front end will not be very pleasant to use on a packed 80m band.

Last edited by YC-156; 10th Oct 2006 at 6:32 am.
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Old 10th Oct 2006, 1:06 pm   #11
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Default Re: simple SW reciever.

Quote:
Originally Posted by YC-156 View Post
That is as long as you aren't too discouraged from further experimentation if it doesn't live up to expectations. My first ECC81 regen was hurled together in a hurry and worked accordingly, yet I'm still here.

Frank N.
Experience shows that Adi is rarely discouraged by anything!

You carry on Adi - from experimentation comes knowledge

Regards,
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Old 10th Oct 2006, 1:47 pm   #12
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Default Re: simple SW reciever.

I just thought that maybe if a guy can build it covertly in a concentration camp out of a canteen and a random stolen parts and 12v HT, it cant be that hard. I appreciate that i'm brobably dumber than that guy...but i DO have a good selection of parts, valves, 250v ht and no guards watchign me.
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Old 10th Oct 2006, 2:30 pm   #13
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Default Re: simple SW reciever.

Quote:
Originally Posted by adibrook View Post
I just thought that maybe if a guy can build it covertly in a concentration camp out of a canteen and a random stolen parts and 12v HT, it cant be that hard. I appreciate that i'm brobably dumber than that guy...but i DO have a good selection of parts, valves, 250v ht and no guards watchign me.
People did build amazing things in POW camps during WW2 using smuggled parts. I suppose they had plenty of time on their hands though

I'm sure you'll be able to make it work - just throw it together and see what happens. You'll certainly be able to pick up broadcast stations both on SW and MW if you wind the right coil.

Lots of people built these things as their first radio project in the 50s and 60s (after the obligatory crystal set of course).

Paul
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Old 10th Oct 2006, 3:32 pm   #14
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Default Re: simple SW reciever.

Adi, go ahead and try it out, it's true you learn from experimenting, and you can always develop the circuit if need be. If you don't try then you'll never find out. As a few people have said on this forum, you can have a lot of fun just throwing a basic circuit together. I still do this from time to time, even though I've been through it all before in my teens. I think it's to rebel against the fact that everything has to be so complicated nowadays.

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Old 10th Oct 2006, 4:44 pm   #15
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Default Re: simple SW reciever.

One of the first regen sets I made was from a circuit I found in a library book. It used a 6Q7 with a 6v lantern battery for heaters and a 90v battery for HT. The coil was wound on the cardboard tube from a toilet roll (in fact I think there were two placed close to each other for regeneration and you just moved then together or apart to adjust it). It was built on a wooden base and was really a 'junk box' contraption. However it worked really well and whilst it can be said that it was not stable in any sense of the word (you could tune it by putting your hand close to the valve) it was very instructive and gave me hours of pleasure. I seem to remember using a 500pF tuning capacitor instead of the 320pF specified and to my pleasure, I found that it also allowed the set to cover the HF end of medium waves which in those days included Luxembourg, Light programme, Radio Caroline, and Radio London. Yes I had great fun with that set!


Rich.
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Old 10th Oct 2006, 8:02 pm   #16
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Default Re: simple SW reciever.

Adi
have a look at this link it may well inspire you
http://www.zerobeat.net/qrp/powradio.html

Jay
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Old 10th Oct 2006, 8:46 pm   #17
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Default Re: simple SW reciever.

Quote:
Originally Posted by adibrook View Post
I just thought that maybe if a guy can build it covertly in a concentration camp out of a canteen and a random stolen parts and 12v HT, it cant be that hard. I appreciate that i'm brobably dumber than that guy...but i DO have a good selection of parts, valves, 250v ht and no guards watchign me.
Err no Adi, that is not what I was trying to imply.

You specifically asked if a shortwave receiver using a very small coil would work for receiving SSB and CW, specifically ham radio signals. My answers to that is 'no', because I doubt it could be made sufficiently stable to be worth the effort. My thinking was that with a coil that small, you would end up running at a very high frequency and/or your tuning capacitor would cover a *very* wide frequency range. In either case you would find it very difficult to either hold or tune narrow band signals.

The POW radios didn't receive very narrow band signals and they didn't try to use a tiny coil, that is the difference. They were listening to AM. If you want to receive ham SSB signals, then I'd personally go for the 80 or 40 m band as Al suggested, using a larger coil and having a few thoughts toward bandspread of the tuning cap.

I'm not trying to dissuade you, only suggesting that you may want to pause just a sec and choose a few key components carefully. Unless of course you want to make it harder for yourself than it has to be.

Frank N.

Edit: Follow up coming, needs additional explanation.
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Old 10th Oct 2006, 8:50 pm   #18
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Thumbs up Re: simple SW reciever.

Quote:
Originally Posted by adibrook View Post
. .. I appreciate that I'm probably dumber than that guy...but I DO have a good selection of parts, valves, 250v ht and no guards watching me.
"Dumbness" - like "beauty" - is relative. You can play a guitar and have a capability with Morse . That's more than a lot of people have - myself included. Moreover, Adi, you have a little thing called "enthusiasm" - and an inquisitive mind - like education, something that can never be taken away.

Best wishes for your project.

Al / G8DLH
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Old 10th Oct 2006, 8:59 pm   #19
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Cool Re: simple SW reciever.

Inspired. I'm truly inspired. And just for the hell of it + nostalgia, I'm going to design and build my own TRF / 0V2 !
I'll aim at the Amateur Radio 80m. band - & see how it develops.

BTW This is my idea of a "constructive" comment on this Theme!

Watch this space!

Al / G8DLH
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Old 10th Oct 2006, 9:19 pm   #20
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Default Re: simple SW reciever.

I've certainly built a regen receiver capable of receiving 160 metre and 80 metre SSB transmissions. However it used tansistors rather than valves. An OC170 and an OC71. It should have used a Denco 3T Blue coil, but I wound my own using a borrowed Grid Dip Oscillator to check the frequency range.

I've just dug out the circuit and article from Practical Wireless dated November 1966.

A homebrew project was far more satisfying to use than bought in equipment, even though it might not have beeen as good. It was certainly cheaper.

How about trying to build a replica HAC (Hear All Continents) receiver? Some information can be found here:-

http://home.wxs.nl/~meuls003/hac/hac.html
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