Advice needed for experimenting with simple RF circuits.

[biastee]

BAT63 and TLC2652

Hi KJDS,
What are the advantages (& disadvantages if possible) of this topology? Thanks.

[apblog]

BAT63 and TLC2652

Thanks for the diagram.  I took the liberty of checking your previous posts and that method of biasing a diode is really clever.  I'm looking forward to trying this circuit, and also trying to understand the temperature compensation aspect.

Not sure exactly what you want to do with "square waves"...

I think the technical term might be "on/off keying".  It's how my weather sensors transmit data. It might be manchester encoded, not sure yet.

It’s possible to hit around 700-800MHz dead bug fine. Don’t expect the circuit to work twice though.

I'll be happy enough to see it work once!

[bd139]

Got a few minutes to write this up now.

I don't think this is a viable approach to building a receiver for the first time reciever builder. Basically this is building a 432MHz crystal set which is fraught with problems. The issue is that there's no selectivity, the detector isn't at all sensitive and there's no gain stage and everything is done at the carrier frequency which is extremely high. Even a basic direct conversion receiver needs a selective front end, quality balanced mixer and a massive amount of gain. I would start at a much lower frequency and build something to a block diagram. Try a simple HF band receiver. Also learn to work to block diagrams rather than schematics first. Entire RF systems are usually described as block diagrams before anyone even picks up the soldering iron.

If you want to receive on 432MHz as a first time builder it's important that you keep the UHF portions COTS and 50 ohms throughout which is difficult without using commercial parts. Ergo use commerical parts.

The minimal receiver I would build for 432MHz without using a COTS IC is as follows. That kills off a lot of problems like impedance matching, downconverts the signal to 4.915MHz (cheap crystals here if you need filters!) and will actually work.



Edit: LO should be 427.085. I was clearly drunk in charge of the calculator earlier

[apblog]

Thanks for taking the time to create that diagram and post a write up. 

I know that building a non-selective crystal set with makeshift wiring at 432MHz is pretty dumb.  I am having a bit of fun with idea though, and it's nice to get a feel for the problems involved and also for the basic technology.  I'll probably muck around with it a bit more and then move on to a more practical approach.

The more I read, and the more I experiment, I am looking forward to doing correctly, with a mixer, LO, and all. 

[apblog]

The minimal receiver I would build for 432MHz without using a COTS IC is as follows. That kills off a lot of problems like impedance matching, downconverts the signal to 4.915MHz (cheap crystals here if you need filters!) and will actually work.

What do you think of the following RF parts list for implementing your diagram?

Code: [Select]

BFTC-415+    LTCC Band Pass Filter, 330-500 MHz   
GALI-74+     Low Noise MMIC Amplifier, DC to 1 GHz  (both input and IF amp)
ADE-751H+   Double Balanced Mixer   
RDP-2150+   Lumped LC Diplexer, DC-10 /40-2150 MHz
And of course the SIS-570 you mentioned.  I'm still looking at the options for that part.

I'm curious why you mentioned that 4.915MHz is a common crystal frequency.  I don't understand why a crystal is needed as part of the IF amp and detector.

[bd139]

I haven't reviewed the parts TBH. I would probably use Minicircuits parts and toko filters.

You don't /need/ a crystal filter but you can build an extremely tight (down to 200Hz) bandpass filter with crystals. It depends what you intend to receive.

4.915 because it's dead easy to build the IF stages at this frequency and build decent IF filters with crystals if you need to do that. Higher frequencies require specialist layout and parts. Lower frequencies are impractical. Some IFs are a PITA like 10 and 12MHz which seem to be sensitive to other things in the vicinity which are clocked at those frequencies.

[radiolistener]

I ordered one of these last week (RTL-SDR-V3) and it just came yesterday.  I haven't figured out the software yet.  It did come with a nifty antenna kit though. 

Congrats! This is very nice SDR receiver for the price.
It also can receive short wave 1-14.4 MHz with pretty good quality.
You're just need to select in the ExtIO settings window Direct Sampling: Q input
To get back to usual VHF/UHF mode, select Direct Sampling: Disable

the best software is HDSDR
http://www.hdsdr.de/

You will need to install drivers:
1) install libusb from zadig: https://zadig.akeo.ie/

2) place ExtIO_RTL2832.dll into HDSDR folder:
http://hdsdr.de/download/ExtIO/ExtIO_RTL2832.dll

Here is instruction: http://hdsdr.de/RTLSDR_with_HDSDR.pdf

[apblog]

You don't /need/ a crystal filter but you can build an extremely tight (down to 200Hz) bandpass filter with crystals. It depends what you intend to receive.

That's interesting.  It occurs to me that with tight bandpass filters you could make a receiver that demodulates multiple channels at once within the 433 MHz band, while only having one VHF/mixer section.  That's useful for me because my temperature sensors transmit on 3 different frequencies.

4.915 because it's dead easy to build the IF stages at this frequency and build decent IF filters with crystals if you need to do that. Higher frequencies require specialist layout and parts. Lower frequencies are impractical. Some IFs are a PITA like 10 and 12MHz which seem to be sensitive to other things in the vicinity which are clocked at those frequencies.

More research to do... 

the best software is HDSDR

Thanks for the tip!