My First receiver:Recommendations-part_1

[froten]

Hello All,

I'm planing to start building my first project in RF circuits, a SW radio receiver (3-30MHz). I have small experience with RF design so I'm trying to get some help through this forum.

In this post I would like to get some recommendations on the overall design, building blocks, suggested circuits, links and projects.

Since it is the first receiver, it doesn't have to be a high performance, can be Battery or line power operated, and all transistor since IC's are difficult to optain in my city. Any idea is welcome.

Thanks in advance for any help.

 

[RadioRon]

This is an ambitious project, but a good choice in general. I hope you are ready to learn a lot as this may be hard at times.

My first SW receiver was built from a kit when I was in school, but when building this kit, I learned about how to build it, but not how it works, and I didn't learn as much as I would have liked. So building from scratch may be better, but you should start with a proven circuit. We need to look around for an article in a ham radio magazine that describes a complete project, and it will be difficult to find something that uses no ICs. So, the search should begin with looking in older magazines and handbooks.

We have to restrict the search to those circuits that are fairly simple, but at the same time avoid those that are too crude. In my opinion this means to stick to the tried-and-true superheterodyne structure, or consider a modern direct conversion type. Avoid the regenerative receivers. We assume that the only kind of modulation you care about for now is AM. It is possible to add SSB later on if you like. Don't bother with FM for now.

It may be wise to consider a modular approach, where the major subsections are built on their own boards and then cabled together. This allows you to perfect one subsection at a time, although it does mean more construction work. Whether this is a good idea or not depends on the design, but keep it in mind.

 

[MikeMl]

Don't overlook the Radio Amateur's Handbook, and other ARRL publications.

 

[froten]

Thanks RadioRon for your helpful replay.

I started looking in some old magazines like EPE and trying to get a proven and tried project.

I will consider the modular approach and will create new post in the forum for each stage or module during my work. I'm thinking also about using superheterodyne designs as I have read alot of material about thier design and theory of operation.

For now, I'm thinking about using BJT or FET transistors , where I will use a tuned circuit at the input of a BJT mixer with tuned collector circuit to IF freq, followed by two tuned stages for IF amplification and then an envilope detector, but any other idea is wellcome.

Thanks again for any help

 

[Nigel Goodwin]

You would probably do better looking in Practical Wireless, rather than EPE, as EPE (Practical Electronics) rarely did radio projects.

The ARRL or RSGB Handbooks are a good place to start - however, much of the old radio components are difficult or expensive to source these days.

Many years ago you even buy suitable coils and transformers, no doubt someone will come along and mention the name (I've it forgotten now), which allowed you to easily build both valve and transistor multi-band radios. The front end coils came on B9A bases, with metal screening cans, and you could have pluggable coils to change bands (using B9A sockets) or switch them as normal.

 

[rfs100]

Hell, back when I was in High School, more than 30 years ago the parts were expensive,and difficult to find...not to mention complicated to build for a beginner.

Dont be afraid to go the kit route, especially in RF circuits...a well designed PCB does wonders for stability,and specs.
You will still learn as much by building a Kit, without the aggrivation.
My first receiver was a Radio Shack Shortwave P-Box kit....regenerative....so it was a TON of fun to tune.

https://www.google.ca/images?hl=en&...itle&resnum=4&ved=0CDgQsAQwAw&biw=783&bih=363

 

[rfs100]

**broken link removed**
Man, I never realised the tons of receiver kits out there...Google it

 

[Nigel Goodwin]

**broken link removed**
Man, I never realised the tons of receiver kits out there...Google it

That's just a direct conversion receiver, for SSB or CW - they are VERY simple, yet work amazingly well.

 

[rfs100]

Sigh....alas, the best radio kits in the world are long gone...kits like the Radio Shack Globe Patrol and especially the Heathkit sw-17 that I built...etc. Its unfortunate that a lot of people have never had the experience of building a Heathkit...they were a absolute joy to put together, and once they were together you usually had a pretty good item too boot!

 

[Nigel Goodwin]

Sigh....alas, the best radio kits in the world are long gone...kits like the Radio Shack Globe Patrol and especially the Heathkit sw-17 that I built...etc. Its unfortunate that a lot of people have never had the experience of building a Heathkit...they were a absolute joy to put together, and once they were together you usually had a pretty good item too boot!

I once built a Heathkit FM Stereo Tuner, the guy who bought it decided he couldn't do it, and paid me to!

Beautiful kits, but even back then they were VERY expensive - and couldn't possibly be viable now. I used to love looking through the catalogue and dreaming

 

[rfs100]

I once built a Heathkit FM Stereo Tuner, the guy who bought it decided he couldn't do it, and paid me to!

Beautiful kits, but even back then they were VERY expensive - and couldn't possibly be viable now. I used to love looking through the catalogue and dreaming

I also eagerly awaited the seasonal Heathkit cataloge, as well as the Edmund Scientific and the Radio Shack catalogue (our town was so small...we didnt even have a Radio Shack!!!!!!)
My dad was best friends with the head electronics techs at his work, and they both were great at helping me out. They bought EVERYTHING from Heathkit ( 2 elderly British gentlemen living in a small house in Kapuskasing, both their wives had died, and no kids...what the hell else did they have to spend their money on???)
They actually bought the Heath/Zenith Color TV kit, and allowed me to assemble it. I was over at their house every night working on it for about 2 months. It was stressful, because I was a perfectionist, and they double checked every solder joint I made. It worked the first time we plugged it in. I remember it was shipped freight in about 10 seperate boxes. Hell, they didnt even ship the cabinet until you called them and said you were almost finished building the kit.The case was SOLID WALNUT...NO VENEER....floor model. I dont remember the actual weight, but it took 4 grown men to get it into the hiouse. Hell, the picture tube required 2 guys to carry it in its shipping crate!
They actually bought and built the "portable" (about 100 lbs!!!) Heath/Zenith Tv for their bedrooms as well.
Im certain that I drove these 2 poor old guys crazy...I was over at their house watching MY TV every night.

 

[transistor495]

I once built a Heathkit FM Stereo Tuner, the guy who bought it decided he couldn't do it, and paid me to!

Heathkit what kit?..you guz were so lucky to have those goody stuffs in the past where we guyz were not on earth hm

Especially audiodude might have bought and made some pretty old tube goodies

This pic is a very eye-catching one about that boy. It is always fun to have an interested kid nearby when doing stuffs or we were like that at childhood.

 

[froten]

Thanks all for all the help.

I have done some RF circuits in the past and read a lot of text books and web pages put still lacking practical experience, therefore I'm starting with this project at the transistor level.

I have downloaded many old receiver circuits (two are attached) which I'll try to build a similar receiver (with NPN transistors). I choice these circuit because of low parts count, low current and because I understand the circuit theory of operation. and I'm starting with the mixer circuit.

any advises are welcome.

appreciate ant help.

 

[froten]

I would like to know:

1) What is the sensitivity required to build a SW receiver? or what is the expected RF signal value at the input of the mixer? is it in the range of 1uV, 100uV or 1m?

2) What is required gain from the mixer to the detector? 60db,80db or more?

3) What is minimum RF signal value at the detector diode? do we need more 0.7V for the diode to work?

 

[flat5]

If you can afford it you really should get a copy of "The ARRL HandBook". A used copy from 1970 till now should do.
Any of the early years makes good reading though. You may find one in a public library but often they are stolen.

When I built a 80-40 meter ssb receiver (~1977) I used the 1968 ARRL book and some issues of Ham Radio Mag. for ideas.

Needed sensitivity depends on the freq. range you are receiving. Lower freqs. have more atmospheric noise.
Too much sensitivity brings other problems. This is true for the rf, mixer, if, detector, audio sections of the receiver.
For a silicon diode provide more than .7 volts, yes. By that point it's hard not to

 

[RadioRon]

Thanks all for all the help.

I have done some RF circuits in the past and read a lot of text books and web pages put still lacking practical experience, therefore I'm starting with this project at the transistor level.

I have downloaded many old receiver circuits (two are attached) which I'll try to build a similar receiver (with NPN transistors). I choice these circuit because of low parts count, low current and because I understand the circuit theory of operation. and I'm starting with the mixer circuit.

any advises are welcome.

appreciate ant help.

These examples are very good. They are relatively simple designs, but they have all the necessary elements of a reasonable receiver. The difficulty in these is that there are very few suppliers left these days for these types of IF tranformers.

 

[RadioRon]

I would like to know:

1) What is the sensitivity required to build a SW receiver? or what is the expected RF signal value at the input of the mixer? is it in the range of 1uV, 100uV or 1m?

2) What is required gain from the mixer to the detector? 60db,80db or more?

3) What is minimum RF signal value at the detector diode? do we need more 0.7V for the diode to work?

1) I think you should plan for a sensitivity of 1 uV for 10 dB SNR. This would be the value at the input terminal. I recommend that in your first radio, you do not integrate an antenna into the radio, but leave that to be external and instead provide a terminal at which it can be attached. You will have to decide what input impedance the terminal will have. You can choose any impedance, but as you look at other designs you will find that many receivers use a standard impedance of 50 ohms.

2) and 3) the amount of gain that you need will depend on the sensitivity of the AM detector. Once you know that, you can work back from that point to the antenna terminal. For the type of detector shown in the schematics you found, the voltage depends on the type of diode. The 1N295 is an older model of Germanium diode and nowadays many people use the 1N34 instead. This type was popular as a detector because it requires much less voltage than a silicon diode. You might look up the diode curve and find that the forward voltage at which it rectifies is a function of current, ( 1N34A Diode Performance ) . For this reason, it is best to arrange so that the diode has a high impedance load to minimize the current through the diode. In this way, the detector might function well with voltage as low as 200mV.

With these figures, you can calculate the gain required will be about 106 dB. This is fairly high, so i wonder if my numbers are a bit too conservative. It is not uncommon for an AM receiver to have gain of at least 80 dB for weak signal use on short wave bands.

 

[TULLIO]

regenerative receiver

Hello froten: see : Cq radio amateur 310 spanish, is the last regenerative receiver of Charles Kitchin.

 

[audioguru]

I can't remember the sequence of my first projects.
A Heathkit vacuum tubes stereo amplifier. An Eico vacuum tubes FM tuner then later when FM stereo was invented a vacuum tubes stereo mutiplex adapter for it. A Heathkit vacuum tubes oscilloscope that still works. A transistorized voltmeter. An SQ surround-sound adapter. Two LM3915 bar graph circuits. An FM transmitter. Etc.

I never made a shortwave radio or Ham transmitter. I used the telephone instead.

 

[BobW]

A radio receiver can be one of the most rewarding electronics projects ever. However, I would stay away from a superhet as a first project. There are a lot of complications in a superhet that aren't apparent at first glance. I suggest a regenerative receiver as a first project. They are extremely sensitive, but much simpler to build.

As an example, a very quick internet search brings up:
https://www.qsl.net/wb3gck/pipsqk.htm
And lots of others with on the net.
I'd stick to something with no more than 3 transistors (excluding audio amp section).