Reception issue

[RecepAGulec]

Hi, I set up the PicoSDR receiver according to your application diagram (using the Pico2). I used a 74CBTLV3253 and an MCP6022, and since I powered both of them with 3.3V, I didn't use the 1kΩ and 470Ω voltage divider on the RPI Pico's ADC input. I used anti-alias filters on the MCP6022's outputs. I also used the 5-band LPFs you provided on the antenna input. When I power up the circuit, I only hear noise. I can't hear strong MW broadcasts or SW broadcasts. I swapped the IQ and used IQ correction, but unfortunately, I didn't hear any sound. I tried the RP2350 binary software, but the results were the same. What could I be doing wrong?

[dawsonjon]

Hi, that all sounds correct/reasonable. I'm sure its just something simple. I guess you don't have access to a scope so your best bet is to work through methodically checking everything. Are you able to bypass the filters for initial testing? Perhaps you could connect the antenna directly to the Tayloe detector to start with? Do you see the noise floor increase when you connect the antenna?

Best of luck, I'm sure you will get it up and running!

[RecepAGulec]

Let me briefly explain what I did:

1. Initially, I considered powering the circuit with a single Li-Ion battery and used a step-up buck converter that converts 3.7V to 5V.
2. Thinking that a buck converter might be noisy, I decided on a linear power supply.
3. Without LPFs at the input, I connected the antenna to the Tayloe mixer via first100nF and then via 10nF. (Of course, by applying the 1.65V from the 10k + 10k voltage divider to the Tayloe mixer via 1k.)
4. I also tried removing the OLED from the circuit, and the results were the same.
5. I replaced the opamp, the Tayloe mixer, and the Pico with new ones.
6. In answer to your question: Yes, the noise floor increases when I apply the antenna signal. The only thing I didn't do was remove diode D1. My application diagram is attached. picoRXei.pdf

[dawsonjon]

Cool,

Your schematic all looks good to me!

Without LPFs at the input, I connected the antenna to the Tayloe mixer via first100nF and then via 10nF. (Of course, by applying the 1.65V from the 10k + 10k voltage divider to the Tayloe mixer via 1k.)

On the schematic R9 is 82.5ohm, did you use 1k instead? I mention this because C11 acts as a short to ground, and in the past when I missed out R9 I ended up with symptoms very similar to what you are describing.

Initially, I considered powering the circuit with a single Li-Ion battery and used a step-up buck converter that converts 3.7V to 5V.

Perhaps a bit off topic, but couldn't you connect a single 3.7V Li-Ion battery to VSYS? The Pico works from 1.8 - 5.5. Maybe you have something else that needs 5?

Cheers Jon

[RecepAGulec]

I made a mistake when drawing the schematic. R9 is actually 1k. On the other hand, I used two Li-ion batteries connected in series, reducing the voltage to 5V using a 5V voltage regulator, and then applied it to the circuit. I have only one remaining concern: My circuit doesn't include an LNA. Can you receive the antenna without the LNA when you connect it to the circuit? 73

[dawsonjon]

I have had good results using a long wire atic antenna without an LNA. If you are using an indoor loop antenna an LNA is definitely needed for anything other than strong local stations.