TomGeorge:
Hi,
Okay, so can you answer the questions in post #11?You need to establish these to build your repeater.
It will not involve masses of code, just a timer and MP3 player in code.
Tom...
TomGeorge:
- Is this a full duplex repeater?
- What are your Tx and Rx frequencies.
- If it is in the 2m band then the standard Tx/Rx separation is 600kHz, what are you using?
- How do you aim to prevent desensitization?
- Have you got any bandwidth filtering on the AUDIO?
Hi Tom, sorry, I missed those questions but will try to answer them here.
- Half Duplex for now - only one person may transmit at a time while others listen
- For testing purposes the Input Freq is 145.025 and the output is 145.625Mhz - locally to me there's no repeater activity there.
- 600kHz separation as per the UK 2M Repeater Band Plan
- Please see my note at the end of the list RE Desensitization
- No, I don't yet have any filtering designed or implemented on the audio side, yet. At the moment, I've only got the audio from the MP3 directly going to the MIC IN on the transmitter via a 0.1uF series capacitor for DC Blocking.
RE: De-sensitising:-
That's a very good question and at the minute, the only issue I've identified (until I do more testing at least) is that the Receive Antenna will ideally need to be at least a wave length apart from the transmit antenna. I know that my local repeater uses large cavity filters - among other things - but I have to confess, I've not got that far ahead yet.
Since this is a portable project, I wanted small portable antennas that I could mount remotely from the repeater unit and keep them a wave length apart so I opted to go with two of these since they're small and portable. But an end user can use whatever they wish really.
I must confess, I started out just wanting to build an Amateur Radio Repeater but as I progressed, I started to see improvements and other potential applications where a small portable repeater could come in handy such as disaster relief in areas where there are no mobile networks and simplex radio signals are patchy / unreliable and so my design has grown with these influences to become something quite versatile and feature packed.
Would you believe that my first design concept prototype cost nearly £100 to produce initially? And while it cost that much, it didn't do anything more than the version I am working on today? However by comparison to where I am today it was large, clumsy, expensive and power hungry.
The early version used a complete walkie talkie handset and the morse was generated by the arduino and voice announcements were in WAV format on an SD Card which the arduino had to handle and play. This ate tremendous amount of prog mem (my code took up around 80 - 90% and the compiler would warn me of instabilities etc in the Atmega) and processing power but it proved the idea.
So from that point to this, my main focus has been to optimise what I had so far. To shrink it down in size and cost and make it more efficient. So where before in standby it would draw something silly like 30mA at standby, it now draws barely 2mA. I now use cheaper tiny transmitter modules instead of large expensive hand held radios and I've added power control via MOSFETS so only the Atmega is powered up all the while in sleep mode.
I think the cost of a prototype at this stage today is around £30 to produce. Ideally I'd like the entire completed project to cost no more than £50 to produce not including the cost of the battery or antennas.
And prior to all that horrible interference I was getting with the previous transmitter modules I was using, I had just designed in a small SIM800L Module for remote control and to issue telemetry such as battery charge level via SMS back to the user in areas where there is mobile network coverage. These modules only cost £8 and only one is needed per unit. I am also toying with the idea of including some sort of on board wifi as well - or maybe allowing for it to be included as a separate expansion.
Hope this helps 
Regards,