These modules have been around for a while, but they fascinate me. For only US $12,88 you get a fully functional 1 Watt transceiver working on either VHF or UHF. The last letter in the model number tells you which version it is. The modules are available on eBay from seller Dorjigroup (link).
Hamshop.cz sells PCBs including the DRA818 series:
In combination with an Arduino you can build a full-featured transceiver.
Schematics below (courtesy kh-gps.de)
It’s time to order these and do some soldering- and programming work. Maybe I go for a dual-band transceiver…
Links to documentation (PDF): DRA818U, DRA818V
For more information on finished projects go to http://www.kh-gps.de/dra.htm, where you can find schematics and example Arduino code.
Hans dit is echt heel leuk! Bedankt voor de tip. PD0FDX
Raspberry Pi 2 yesterday, now this today? I think Christmas came early this year!
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I need councilling I can’t keep up!
Lets us know if you do some testing with this board. I’m looking for a remote control PMR for ages…a redio that I could control by software in all his functions, installed on a PC that I would remote control….
Hi Rui, try this one, it could be helpful: http://www.transkommunikation.ch/dateien/schaltungen/diverse_tbs_schaltungen/Alarmzusatz%20fuer%20PMR-LPD-Funkgeraete.pdf
Avond, lijkt op deze module maar is toch weer anders.
Leuke ontwikkelingen 🙂
Leuke dingen, maar wel een heel goed LP filter achter zetten. Meet maar eens met een spec. , en schrik hoe sterk de harmonischen zijn. Vooral van de VHF versie.
3r/5r/B5/B6 are based on RDA1846
those DRA818 modules are single band probably due to lack of space to fit switching and dual filters
btw KK6BWA(elazary) tore down B5 and seem to have found an answer to better selectivity:
“they have added more circuit isolations between circuit blocks”
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Nice for Diy experiments!!
Btway, German magazine funkamateur webshop sells them also> http://www.box73.de/product_info.php?products_id=3245 uhf
http://www.box73.de/product_info.php?products_id=3221 vhf version,
If anyone could mess this up, it would be me!
I find parts of the documentation somewhat cryptic, such as the squelch settings (What will the values 0 or 1 to 8 actually do?) and also recommended mounting/soldering (Should the three pads be connected to or isolated from ground? Does the larger pad require cooling?)
The modules I ordered on eBay arrived in less than two weeks, and I plan on playing with them when I get the time.
Brilliant!!! Looks great for making some cool projects (I’m currently thinking of making a mobile phone app which can control a TRX over bluetooth). Thanks for the tip Hans!
I just wish they’d have modules like these with the RDA1847 instead, that one has I/Q SDR input/output. That way we could even build all-mode TRXes with digital modes and SSB.
But the RDA1847 seems very hard to get, I’ve been looking to buy some for years, but the only ones I can find are sold by the 1000’s 🙂
PS Does anyone know where you can still get them? The ebay seller has no ads up anymore and the Czech hamshop is also sold out of everything 😦
Personally I would have preferred them to have used a standard 2.54 mm distance between pins/connectors. It would make it much easier to solder it to a standard protoboard.
When I check the (international) eBay site the item is still available. The seller is away until February 21 (Chinese new year), so it might take a few days longer to get what you order. If you can wait another 3 days I think you will be able to place your order. (On the other hand it took less than two weeks for the modules I ordered to arrive to me here in Sweden.)
Dorji eBay store: http://stores.ebay.com/embeddedsolution?_trksid=p2047675.l2563
VHF module: http://r.ebay.com/7XEIzQ
Personally I have no plans on trying to use these for any SDR project, I would be quite happy to make a decent APRS tracker having it connected to a Teensy 3.1.
And indeed there is no point in even trying with these, the RDA1845/1846 is only an SDR internally: It does not expose the raw data outside. That will only ever work with a module based on the RDA1847.
By the way, I read on the site Hans mentioned (http://www.kh-gps.de/dra.htm) that you need to use at least 1 second TXDelay with APRS (1.2s is what they advise) which is very long. So it doesn’t sound too great for APRS either unfortunately, it probably takes a while for the transmitter to come up, which is not handy on a packet switched protocol.
Ok never mind, the box73 shop linked above still has them 😀 Thanks Ron!
GekkePrutser: The TXdelay should not be a problem, I think.
With APRS I expect to send a few times an hour and spend the rest of the time receiving, it’s not a high speed two way data link. Let’s say I want to send some information every 15 minutes, that’s once every 900 seconds. If I spend one second waiting for the radio module to stabilize I loose about 0.1 % of possible reception time.
I plan to use the squelch output from the module to determine whether to transmit or not.
73 de SA0CLI
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I want to make a VHF receiver for Australian Narrow band radios to listen those stations. I did the construction with Arduino but the quality of the audio is very bad. I tried all the filter compinations (de-emphasis/Low/High) but the problem is still there. An other problem is that the squelch still cutting out the audio even it is set to “0”. Have you any ideas?