It's all about the Software

Does anyone know of a suitable - low-cost - down convertor that could be used with the RX-888? I am specifically looking at the 88 - 108 MHz FM broadcast band.

So far I have found a mixer module on banggood for around £8.50 - £11.50. It would require an 80 MHz input to give 8-20 Mhz output. On aliexpress com there is an 80 MHz txco module at around £15 and another one with SMA output around £25. The latter appears to have 5V TTL level and is a square wave, and the cheaper one is probably square wave. It also have selectable muliplication from 10MHz-80MHz - so 60 MHzwould allow overage of the 65-74 MHz OIRT band.

There is a simple way to use ADL5801 module + nanovna to generate LO + filter，Actually I am designing one, but I have been busy recently and have not continued

Hi guys, just curious on my site... the RX-888 can receive 32 MHz to 1.8 GHz so why is there a need for a down converter? (more sensitive?)

Leon

It's to achieve the utility of the full 32 MHz of the direct sampling SDR on frequencies above 32 MHz. The coverage from 32 MHz up in the bare unit is via inbuilt "dongle" RTL style tuner chip with max 8-10 MHz bandwidth, so it cannot utilise the full 32 MHz bandwidth above a received frequency of 32 MHz. Actually I think new firmware allows main receiver now to have bandwidth up to 64 MHz, but still the VHF/UHF bandwidth above 64 MHz would be limited to 8-10 MHz by the tuner chip. The downconverter would solve this limitation.

73

Max

ahhh ok, Dave was talking about "I am specifically looking at the 88 - 108 MHz FM broadcast band.", so...

I have found reference to an old Elektor article which shows a VHF convertor stuck on the end of a Red Pitya unit. I looks like it is based on an old NE612 chip and looks really simple to implement-. Except there is no input filtering soI reckon it would let strong MW and shortwavesignals through. But at least it is a start. A minicircuits filter to let just the FM band through is avaialble with SMA connectors - priced at USD50 (eek!)

Maybe a bit pricey, but the way I'd implement a downconverter would be a Leo Bodnar GPSDO for the LO, PGA-103 preamp kit from minikits.com.au, and a Mini-Circuits mixer with +13 dBm LO drive level so the Bodnar can directly feed it. For 88-108 MHz there are several bandpass filters on eBay.

I am still looking for a good solution here as well.
We had a similar discussion a while ago on the KiwiSDR blog.
You can see that JP1ODJ had a good setup in place and shared online:
http://forum.kiwisdr.com/index.php?p=/d ... my-airband

I actually have all the parts as a result of the thread above, but I haven't put them all together.
I hope to do this over the holiday and then put the setup in front of the RX888.

I would love to see a more integrated solution, kinda like an down-converter version of the SpyVerter.

I was looking a bit further into the RX-888 or to be more accurate the BBRF103 original design by ik1xpv. On his blog (steila.com) there is a design for "Just another BBRF103 version" which uses the undersampling technique to directly receive the 88-108 MHz band. So instead of a 30MHz low pass filter in front of the ADC chip, a simple bandpass filter for the FM band is used, and a 30 MHz LPF for the HF band.
It is also interesting that this original breadboard design uses a commercially available development board board to provide the USB 3 interface.
So it would be possible to have a 16 bit ADC version of this SDR dedicated to FM-DXing if anyone has the dsire to produce it.

There is another exciting project that Oscar posted about in the NextGenSDR group.io group called the Lucy SDR.
https://so5wi.pl/2021/02/17/fx3-ltc2217-board/

From what I can tell all of these these are new designs are all built on top of Oscars original BBRF103 ideas.
These new, very wide bandwidth receivers are being developed quickly and hitting the market fast.
Great stuff!