DV-RPTR YouTube Video

Following on from my previous blog post... here is a short YouTube video featuring the DV-RPTR board.


DV-RPTR Board has arrived from Germany

My new D-Star toy has arrived!!


I first blogged about this board back in August 2011 and got quite excited when I started to read about it's features. Some may say that it's just another D-Star modem board... but this amazing board is quite different.

Designed by a group of amateur radio operators in Germany, instead of using a CMX589 GMSK modem chip like the other boards out there, this one uses an advanced software DSP modem instead of a hardware modem.  Initial tests shows that it works just as well (and possibly a little better on receive) as a CMX589 based modem board.  It's built around an open source hardware, software and firmware philosophy and it's ready to be enhanced with alternative firmware to handle virtually any digital mode... APRS, P25, PSK31, etc.

I put together an adapter cable from 6-pin mini DIN to a male 9-pin D-sub. This made it easy for me to plug this new board into my existing Hot Spot radios.  I have been using a Tait T2000 UHF radio with this board. Instead of having to use trimpots to adjust input and output audio levels, TX level control is done with a software slider adjustment, as it the transmit delay setting. There is no receive audio level adjustment, I'm not sure what input level range the software needs to accuratly decode, the output from my Tait T2000 is quite low.  The red/green TX/RX SMT LED can be seen through a small hole between the mini-USB socket and mini DIN socket.  I've been thinking of some way to fit a small "light pipe" to better direct the light from the LED. 

This board can also be powered through an on-board 2.1mm coaxial DC connector but precautions must be made so you DON'T connect both external DC and the USB cable at the same time.  There is a solder bridge on the underside of the board that enables powering the board via USB. When this is done there is a danger of damage to the board if you plug in the USB cable at the same time as external DC.  The onboard polyswitch fuse can be removed if you never plan on using externel DC.

The custom enclosure is very nice too, the accuracy of the cut-outs for the sockets is incredible. The non-slip buffers on the ends of the enclosure is a special touch and really finishes the final product off nicely.

The on-board processor is an Atmel AT32UC3B0256.  As is the case with all of these hardware projects, it's in the software & firmware that the real magic happens.  I am a hardware person, I have great admiration of those who create the code that makes devices like this possible.

The DV-RPTR Control Center software has become quite mature in recent weeks and provides virtually all the connectivity features you might want in a D-Star Hot Spot setup.





DV recording and playback.






The Dutch*Star WinDV software will support the DV-RPTR board in the future and there is already a version of the G4KLX Repeater software that supports it.  Hopefully in coming weeks I will be able to try the DV-RPTR board out with alternative software.


You can see some more pictures of my DV-RPTR board in the photo gallery section.

Check out the projects web page here :-


Check out the DV-RPTR Yahoo Group page here :-



A quick update...

It's been some time since my last post.  Not much has changed, the VK5REX 70cm D-Star repeater is still operating perfectly.  The 2m module is out of action while I wait for a duplexer.  I have been talking to some of the guys at AREG about the possibility of them building me a duplexer... hopefully they can help me out.

I have changed the 70cm duplexer arrangement slightly. Instead of using four cavity filters (two on TX and two on RX) after the notch duplexer, I have removed two and am using one on TX and one on RX.

This has improved the performance slightly and has not impacted on interaction between the receiver and transmitter.

I did some simple de-sense tests a few weeks ago and found that there was no noticeable de-sense when the transmitter keys up.

The VK5REX D-Star site is now home to IRLP node 6510 using a 1 Watt 70cm link to the VK5RAC 2m FM repeater.  The 5.8 GHz Mikrotik wireless link has plenty of bandwidth for the extra IP traffic.



Real world distance test of the VK5REX B 70cm D-Star repeater

On Thursday 13th October 2011, I was able to really test out the performance of the modified 70cm duplexer recently installed at the VK5REX B D-Star repeater. The blog post previous to this one details what I did to the duplexer.

The family and I were on a road trip, travelling from Port Lincoln to Adelaide the capital city of South Australia. We were heading off on a much needed break from work and to catch up with family. This rather long drive necessitates driving North East following the East Coast of Eyre Peninsula, rounding Spencer Gulf at Port Augusta and then heading South toward Adelaide.

I was able to follow my D-Star transmissions via APRS. When I keyed up on D-Star, I was able to see my position pop up on APRS via my dash mounted HamHUD II display. I had VK5REX B connected to REF001 C, this ensured a lot of RF traffic and no shortage of people to talk to.

My mobile radio is an Icom IC-2820H radio and I had two antennas connected and diversity mode enabled. I kept the radio on low power for as long as I could, and only switched to higher power settings when my transmissions degraded info R2D2.

This is a screen capture from the website showing my trip as recorded via the APRS network. At highway speeds, my HamHUD beacons at 90 second intervals.


Below is my track via D-Star.  The track up the coast of Eyre Peninsula shows the coverage of the VK5REX 70cm D-Star repeater.  The last two-way QSO via VK5REX B was around 182km away from the repeater and the last GPS "ping" transmission received by VK5REX B was 202km away at Moonabie Hill.  The terrain from then on did not permit any further contact with VK5REX B. However, this is not the end of the story...

Pleae note that the D-Star GPS track/positions that appear near Port Wakefield and head South are via the Adelaide VK5RWN C D-Star repeater.



 One final surprise was being able to hear VK5REX B for a short time after we left Port Augusta and were heading South.  I had a very quick QSO with John N3SBP as we drove past Port Germein. This was most unexpected and was around 270km away from the repeater!! I was able to hear VK5REX B until we were near Crystal Brook and then a range of hills to the West prevented any further reception.  Below is a "close up" screen capture of where the QSO took place.


I uploaded a short YouTube video that was recorded 274km away from VK5REX B.  We were crossing the main railway line as the camera was "rolling" and this was just prior to my QSO with John N3SBP.




New TX/RX duplexer arrangement at VK5REX

About a month and a half ago I took the plunge and bought a "cheap" Chinese notch-style mobile duplexer via eBay.  I had heard how other D-Star repeater owners had used them to augment their existing cavity duplexer to improve the TX-RX isolation. The price on eBay was low enough that if this "experiment" didn't work... I wasn't out of pocket too much.  My eBay experience was good, the vendor looked after me and also tuned the duplexer to my nominated frequencies before shipping.

Prior to installing this notch duplexer I had split the exiting cavity duplexer and was running with two identical folded dipole antennas vertically separated... I had no luck getting the cavity duplexer to work satisfactorily on a single antenna, even with the addition of the 1MHz wide DCI bandpass filter. If you look back through my YouTube channel you can find a video showing how I tested for receive desensing.  The main remaining issue was due to low-level broadband noise emanating from the D-Star transmitter affecting the receiver. Without notching the receive frequency in the transmit path... I was still experiencing ongoing trouble with weak signals.

The combination/hybrid notch/cavity duplexer gives me the best of both worlds. Each side of the notch duplexer has a very nice narrow but deep notch tuned to the "opposite" side frequency, but it does not really stop out of band transmissions from reaching the repeater receiver socket.  By itself, the cavity filter duplexer didn't give enough isolation between the TX and RX frequencies for the Icom equipment to be "happy". The cavities do keep other on-site RF crud away from the receiver input and also help me be a good RF neighbour.  Combining the the notch duplexer and the cavity filters works very well.  The 1 MHz wide DCI filter in the receiver leg is added insurance and the AAR preamp helps claw back some of the losses from all this filtering.

I still have to do proper "scientific" measurements and tests but initial real-world testing seems to indicate improved performance, even better than the two antenna arrangement.  When I was using two antennas, I had the folded dipole at the top of the tower receiving and the one on top of the building transmitting.   Now I am using the single antenna at the top of the tower (~45m) as the TX/TX antenna.

Since the addition of the notch duplexer, I find that I can access VK5REX B in more places that I ever could before. I use my IC-91AD for everyday D-Star operation and was unable to reliably access VK5REX B from inside the building at work (~6km away) even on high power... now I can wander around inside with the radio on low power and talk to my hearts content. 

I have been able to access VK5REX B with the same handheld radio on low power connected to an 8 element commercial UHF Yagi antenna from over 35km away with no line of sight between the two locations.

One word to describe the increase in performance?? "Outstanding!"