DigiTIA receiver

By | March 27, 2017

The guys at the Solder Smoke podcast have inspired me to do a bit more solder melting and this is the result – a CW/SSB HF receiver for 40m band. It is a bit “al fresco”, with no case, built on a piece of copper clad with modules stuck down using a double sided tape.

DigiTIA receiver

Detail of the main board

The rig is “half-DigiTIA” – there is no transmitter. I am not planning to add one because I live in a rental apartment and don’t have neither space for a proper antenna nor a local HAM license (too lazy to do the paperwork).

The receiver is very simple, using the 3 termination independent amplifiers (the purple modules in the photo) as described by Wes Hayward W7ZOI. I have only built them using surface mounted parts to make them smaller and they are not bidirectional because I don’t need that for a receiver.

Termination Insensitive Amplifier

TIA, as designed by Wes Hayward, W7ZOI

The mixers are ADE-1 from MiniCircuits – also SMD parts, but they fit perfectly on a small off-cut of stripboard as a carrier.

The VFO and BFO are using Si5351 clock generator module from Adafruit, driven by an ATMega328 micro and a small OLED display module. I have adapted the code used by Pete Juliano N6QW to use the more recent U8G2 library by Oliver Kraus because the Adafruit one didn’t work correctly with my module. My display is slightly different and the text was not displaying right.

Si5351 VFO/BFO

The receiver uses 11.997450 IF – that is the frequency most of my 12MHz crystals matched on, so I have used that frequency for the IF – digital VFO/BFO make it trivial to move the IF as required. The crystal filter could use some tweaking but it works well enough.

The audio was a bit low, so I have used an NE5532 opamp as a low noise preamplifier and I am feeding it into a classic LM386 audio amplifier. The LM386 has separate power supply for now because it likes to break into loud oscillations otherwise – the power supply decoupling and grounding are not ideal.

The input has a bandpass filter for 40m, I have used the same design as used in the BitX transciever, by Ashhar Farhan VU2ESE.

BitX40 bandpass filter

And how does this contraption sound? Well … judge for yourselves – there was a CQ WW WPX Contest – SSB contest going on, so the band was pretty busy. This from northern France, using a magnetic loop hanging on the wall in an apartment:

 

8 thoughts on “DigiTIA receiver

    1. Jan Post author

      Hello,

      What tips do you need? I am using the normal 60/40 leaded solder and around 300-320 °C on my ERSA Nano. Nothing special at all.

      Jan

      Reply
  1. Nigel Young

    Jan, I realize i’m a bit late to the party here, but then I stay longer 😉
    Now, I notice you used the AD-1-24 mixer, I just purchased some of these and when they turned up they had the -24
    number on them. I did a bit of research and I can find no data sheet for this. I was expecting just the AD-1.
    There seems to be some opinion based on blogs in the bitx website that these are internally wired differently.
    I don’t see for the life of me why it should make a difference since it is balanced right?
    You look to have wired yours as per the mini circuits spec sheet for the AD-1 .
    So, am I getting my knickers in a twist with this or not being your design obviously is working fine.
    Nigel

    Reply
    1. Jan Post author

      Hello Nigel,

      The mixers are actually ADE-1+ and if you look at the photos of my board you will see the markings on mine are also AD-1-24.

      Personally I would trust more the manufacturer’s datasheets than some random forum posts or blogs – it is not rare that people make wild guesses or completely wrong conclusions. Also, who knows what they have got – a lot of people get fake/knock-off parts from eBay or AliExpress and then they wonder.

      According to Minicircuits, ADE-1+ comes only in a single variant (the difference between ADE-1 and ADE-1+ is that the latter is RoHS compliant, using different plating on the leads, the parts are otherwise the same) and single pinout, so who knows what folks on those blogs are talking about …

      Ultimately what matters is – does it work? You can verify the wiring also by flipping the part upside down and looking – mine are not potted and you can see the coils inside.

      Jan

      Reply
  2. Nigel Young

    Thanks Jan,

    Yes, I got mine from Ali, being in NZ means a huge post cost for us stuck out here. Mine are as you describe, they are unpotted and it is clear to see the terminations. They were talking about the pinouts are a mirror opposite to the ADE 1 and that the -24 was a special order etc etc, it is clear from the datasheet that it should not matter which port you use since they are identical. This is what prompted me to search a little further and……came across your blog.
    Fantastic stuff Jan, I do like the variety of topics. Any how you have stopped me going stir crazy and doubting myself.
    I was a bit concerned since I already designed a PCB and the thought of having to re route it gave me sheer terror.
    PCB design software is a painful experience if you don’t use it often.

    Thanks again Nigel

    Reply
    1. Jan Post author

      You are welcome.

      I am not sure where did they get the mirror opposite bit because Minicircuits has no such component on their website … So either they have a weird knockoff part or something else.

      Whether the ports are completely identical is difficult to say – I have no means to measure it but at HF it likely doesn’t matter even if there were minute differences. ADE-1 is good for up to 500MHz I believe, so there it could be different due to parasitics of the leads inside at such frequencies.

      Good luck with your project,

      Jan

      Reply

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