ATS25 AMP

[G8PTN]

As a user of the ATS25-AMP, please see a summary of my findings below.

On inspection of the PCB, an inferred simplified block diagram of the additional RF circuitry is shown attached.

These functions have not been characterized.
- Impedance selection: 50Ω, HI-Z.
- Filtering: Low-Pass and Band-Pass.
- Low Noise Amplifier: LNA.
Note: There appears to be an HF low-pass filter (i.e. sub 30MHz) in the HI-Z path and therefore selecting HI-Z whilst receiving VHF (WFM) is not appropriate.

General
The firmware shipped on the ATS25-AMP is a hybrid version of V.16 and is not available for download.
Updating to a later version is therefore at the user’s risk.

The ATS25-AMP is not officially supported by the Harduino firmware, mainly due to the points below.
- The ATS25-AMP DIGI Decoder may not function correctly at low battery voltages.
A possible workaround is to add a low power 5V boost circuit such as a charge pump to power the Digi Decoder circuitry.

- The ATS25-AMP may show backlight flickering and/or reboots at low battery voltages.
This is the case for most of the ATS25 receivers, apart from the ATS25 Max Decoder.
The Max Decoder uses a high power 5V boost converter feeding the 3V3 on-board regulator.

Note: At battery voltages greater than 3V3, the nominal performance of the ATS25-AMP appears to acceptable and therefore provided the battery is topped up, it should operate as expected.

73, Dave

[G8PTN]

Hi,
I have updated my ATS25 AMP to V4.2 AIR beta.
The installation was fine and "ATS25 AMP" was selected in the setup on the receiver.

Everything appears to be working correctly, but I have noticed a minor issue.
Switching between various options seems to result in the wrong values for the SI4732 GPO1 and GP02 signals.

Example 1:
If a “HAM” band is selected, switching to a broadcast band via the “BAND” option (or entering a frequency outside the ham bands) causes the GPO1 control signal to be set to Logic ‘1’. This effectively selects the FM filter RF path and results in no signal to the AM input of the SI4732.
Switching back to a “HAM” band, the GPO1 signal remains at logic ‘1’. If a different “HAM” band is then selected requiring GP02 to change, the GP01 signal is then set back to logic ‘0’ which is the correct state.

It seems that any similar selection causes the same invalid setting of GPO1.
Ham band > Broadcast band
Broadcast band > Ham Band
Ham band > CB
Etc…
Apart the case when switching to “CB” it is possible to work-around the issue as described above.

A basic truth table for correct operation is shown below.

73, Dave

[Binns]

G8PTN, Thanks for the feedback, I'll check it out.

[G8PTN]

Hi,
I have tested the updated V4.2 AIR beta release 15.04.2024 and it seems to have fixed the issue with the filter selection.
Thanks very much.
73, Dave

[G8PTN]

A general question on the pseudo NFM for CB and 10M.
I did a quick test, with CB band, AM mode selected on the ATS25-AMP and with the TinySA set to AM modulation a clear 1kHz tone was received.
With NFM selected on the ATS25-AMP and with the TinySA set to NFM modulation, no tone was received.
I did not experiment with the RF levels, so perhaps it is just a sensitivity issue.
Does the pseudo NFM use the same RF path into the SI4732 as AM?
73, Dave

[Binns]

A general question on the pseudo NFM for CB and 10M.
I did a quick test, with CB band, AM mode selected on the ATS25-AMP and with the TinySA set to AM modulation a clear 1kHz tone was received.
With NFM selected on the ATS25-AMP and with the TinySA set to NFM modulation, no tone was received.
I did not experiment with the RF levels, so perhaps it is just a sensitivity issue.
Does the pseudo NFM use the same RF path into the SI4732 as AM?
73, Dave

Please provide the connection diagram of the mixer in your receiver so that I can understand if it works correctly

[G8PTN]

Please provide the connection diagram of the mixer in your receiver so that I can understand if it works correctly

Hi,
Perhaps that is the problem. I have not implemented any mixer.
It looks like I wrongly assumed that the CB and 10M pseudo NFM would work without any hardware changes, but that obviously is not the case.
Sorry for my misunderstanding. I assume for NFM an up-converter is required to use the FM tuner section?
73, Dave

[Binns]

I assume for NFM an up-converter is required to use the FM tuner section?

Yes it is. The completion scheme is presented on this forum viewtopic.php?t=11&start=22

[G8PTN]

Hi,
Thanks for the reply.
Yes, I initially thought that the hardware was only required for the VHF bands down conversion, but this will be for AM and SSB/CW modes.
For NFM which will be using the FM tuner, I also see that frequency conversion will be required.
Again I had assumed a patch had been generated for the SI4732 DSP to do NFM, so no conversion would be required for CB/10M.
73, Dave

[Binns]

G8PTN, tell me, how did you manage to turn on the FM in the receiver? Without a mixer, it's blocked.