Possibility to extend the RadioBerry range to 32MHz?

[Jean-Claude Abauzit]

I am thinking to get a 2m transverter and these usually convert 144-148 MHz to 28-32 MHz.

With the RadioBerry going up to only 30 MHz only 144-146 MHz would be usable which is good for DX but bad for the repeaters I can access: they are all above 146 MHz.

The RadioBerry samples at 76.8 MHz so it is theorically possible to use the RadioBerru up to but excluding 38.4 MHz but with a big IF: the input signal must be band limited. No signal >= 38.4 MHZ is allowed to reach the ADC which is impossible with an analog filter. On the RadioBerry an anti-alisaing filter is used an cuts frequencies somewhere betwqeen 30 and 38.4 MHz, some frequenies between ?? (>30 MHz) and 38.4 MHz will be folded back and appear as aliases between ?? (>30 MHz) and 38.4 MHz.). The resulting data stream goes to the FPGA where it is possible to implement brick wall filters. The RadioBerry throws away anything above 30 MHz.

Depending on the ?? (>30MHz) frequencies mentioned above it could be that the frequencies 30-32 MHz are clean and usable with the RadioBerry.

Jean-Claude

[Jean-Claude Abauzit]

I made some error in my post and I don't know how to edit it. Here is the correct version:

On the RadioBerry an anti-alisaing filter is used to cuts frequencies somewhere between 30 and 38.4 MHz. As it is an analog filter some frequencies above 38.4 MHz will be folded back and appear as aliases between ?? (>30 MHz) and 38.4 MHz.). 

The goal of the anti-aliasing filter is to prevent the apparition of aliases below 30 MHz. As the RadioBerry will throw away anything above 30 MHz it does not matter if any alias is present above 30 MHz. Depending of the characteristics of the anti-aliasing filter these aliases may appear only above 32 MHz.

[qrp73]

>> On the RadioBerry an anti-alisaing filter is used an cuts frequencies somewhere betwqeen 30 and 38.4 MHz, some frequenies between ?? (>30 MHz) and 38.4 MHz will be folded back and appear as aliases between ?? (>30 MHz) and 38.4 MHz.).

No, the Radioberry uses a low-pass filter (LPF) as an anti-aliasing filter, which is located before the transformer.

The digital bandwidth of the Radioberry is 38.4 MHz, since the ADC clock is 76.8 MHz. Therefore, the purpose of the anti-aliasing filter is to suppress all signals above 38.4 MHz, as any such signals will alias back into the 0-38.4 MHz band and appear as unwanted images.

If the LPF cutoff is extended too close to 38.4 MHz, image rejection will degrade, because the filter roll-off will be too close to the Nyquist limit, leaving insufficient attenuation in the transition band.

Alternatively, you can use undersampling to receive signals in the second Nyquist zone (38.4-76.8 MHz). However, this approach requires to replace LPF filter with a band-pass filter (BPF) to suppress both signals below 38.4 MHz and above 76.8 MHz. Since two filter edges are needed, you must allow extra margin for both roll-offs. A practical BPF might have cutoffs at 46.8 MHz and 68.4 MHz, allowing reception in the range from 46.8 MHz to 68.4 MHz. Keep in mind, though, that sensitivity may be lower compared to the default 0–30 MHz range, and you will also need to adjust LO frequencies in software accordingly.

If that frequency range doesn’t suit your needs, or if you’d prefer to avoid dealing with frequency translation and reduced sensitivity, the simplest and most common solution is to use an external VHF-to-SW downconverter in front of the Radioberry.

[qrp73]

> Depending on the ?? (>30MHz) frequencies mentioned above it could be that the frequencies 30-32 MHz are clean and usable with the RadioBerry.

Yes, you should be able to receive signals in the 30-32 MHz range, but with some attenuation, as this region falls within the roll-off zone of the low-pass anti-aliasing filter at the input of the Radioberry.

[Ed Marciniak]

This is a case where if you don’t like the problem, change the problem to one you do like.

If using for 144-148 MHz, a 120MHz oscillator is easier to come by than a 116MHz, and in addition can be phase locked to a 10MHz reference more easily anyway.

Use 120MHz with a 24-28MHz passband requiring no filters. As a bonus, the 150MHz public safety and business band will end up falling above 30 MHz and receive additional attenuation.

Or there’s 130MHz option for 14-18 MHZ IF, or 64MHz x2 =128 for a 16-20 MHz IF which would put its 64MHz leakage at a 12.8MHz alias outside of the wanted 14-18 MHz passband with the image at 108-112 MHz nearly outside of high power FM broadcast. Sure, there are VOR/ILS, but the power is lower and that makes filtering easier.

With a good frequency plan, low insertion loss SAW filters for 140MHz might pass all of the amateur band, and if the LO happens to be synthesized, integer N mode gives both lower phase noise and the agility to switch the IF if there’s a problem like an image of a VOR/ILS nearby that falls on a weak signal calling frequency as a spurious image.

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From: radio...@googlegroups.com <radio...@googlegroups.com> on behalf of qrp73 <qrp...@gmail.com>
Sent: Tuesday, June 17, 2025 1:43:37 AM
To: Radioberry <radio...@googlegroups.com>
Subject: Re: Possibility to extend the RadioBerry range to 32MHz?

 

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