What type of circuit do I need to convert a weather radiosonde signal directly to audio?

[boylesg]

All I need is a simple circuit that converts a 401 to 403 MHz signal directly to audio so I can hear the radiosonde transmitting and know that I am nearby to it.

FM receiver? Good sound quality and all that is not a requirement so I gather it can be a quite simple circuit. I know a tank circuit will be required but I am not knowledgeable enough to know where to begin. So I need an example schematic.

 

[KlausST]

Hi,

Do a search for "SDR". Maybe this does what you need

Klaus

 

[boylesg]

Hi,

Do a search for "SDR". Maybe this does what you need

Hang on I have one of those - SDR-RTL module plugged into my Raspberry Pi.

I friend has a hand held radio that he can put into frequency mode where he just punches in the radiosonde frequency and you can hear it as a staticy beep beep beep.

That is all I want. I thought it would be a fairly simple discrete transistor circuit, starting with a simple tank circuit, that receives the signal and down shifts it to the audio range.

Is that not the case?

I thought it might be fun to try and build the circuit myself. I would just make it so I can swap out caps to change the frequency and with a trim cap to fine tune.

 

[KlausST]

Hi,

I´m an electronics designer for decades now. Rather deep in analog an digital measurement.
But I don´t feel able to build a "discrete" 400MHz receiver with mixer to get some useful audio sound.
For sure there are ICs, I had to read a lot of documents... and it may work. some day...

But when I see an SDR USB stick for about 15€ (you said no need for any good quality) then it simply makes no sense for me.

I don´t know about your 400MHz HF experience....and how much time, effort and money you want to spend....
I guess it´s possible.
But other members here have experience in this field. I´m sure they can give you better information than my "personal opinion".

Klaus

 

[boylesg]

Hmmmmmmm

A reply from Discord...

"because at those frequencies building things up on something like a breadboard isnt going to work"
"because the lengths of wire between your components have inductance, and that inductance starts to be enough to affect your circuits"
"which is enough to de-tune circuits at UHF"
"same with capacitance - adjacent veroboard traces have a few pf of capacitance between them"

Disappointing.

How do you pros protype UHF circuits then?

 

[danadakk]

Circuit board layout critical needless to say.

Agilent/HP and others have recommendations, Chip manufacturers typically also
have layout recommendations.

Pay particular attention to component characteristics, Caps, L's, their ability to
perform at UHF very challenging.

https://www.jlab.org/accel/eecad/pdf/050rfdesign.pdf

PCBs Layout Guidelines for RF & Mixed-Signal | Maxim Integra

See Maxim's guide for the design and layout considerations for RF and mixed-signal printed circuit boards (PCBs). It is applicable to all wireless and RF products.

www.maximintegrated.com

Regards, Dana.

 

[betwixt]

How do you pros protype UHF circuits then?

With respect to the issues mentioned. Prototyping at high frequencies means we construct with ground planes, short wires and even then pray before switching on! Breadboard is a definite non-starter, they are OK up to about 50MHz before serious problems occur. The length of all the interconnects and capacitance between them start to couple or de-tune circuits, think of a design then add capacitors between all the junctions and you will see the problem.

For short range, you might consider a super-regenerative receiver for ~400MHz, a two or three transistor design would be very sensitive yet quite simple to build. They primarily are AM receivers but you can recover some FM by using slope detection. Slope detection is where you recover a change in frequency by tuning off center so the signal is on the rising or falling edge of the passband. The nearer center it is, the more output you get so to a degree, modulation in frequency becomes a change in output signal.

Brian.