Category Archives: D-Star

Walliston Tower Configuration

Hello all,

Attached is a concept for the very important antenna installation on the Walliston tower. There may be another concept idea but I have not seen such as of yet. So to kick things off please have a read and comment.

Will
VK6UU

Walliston RF concept

 

Will VK6UU

The antenna layout on the Walliston tower can be designed in several different ways, each with its own pros and cons.

The concept presented here relies on separate antennas for each band and split antennas, i.e. separate antennas for receive and transmit, except for the 70cm digital repeater and the simplex 23cm high data rate gateway.

This design is expensive in that it uses more antennas (8) and more coax (8) and hence takes up more mast space, but most important offers several important advantages.

Antenna failure.

Antenna failure, replacement and testing only takes out one repeater. If a triband or dualband antenna fails for example it affects 3 repeater systems. Antennas can be easily isolated tested and replaced.

Desense isolation

Easier to achieve desense isolation with less reliance on duplexer performance. Good duplexer performance is difficult to achieve particularly on 2M. 70cm duplexers are cheap and don?t require as much isolation as 2M duplexers. 23cm duplexers are difficult to source. The antenna layout highlights this with only the 70cm repeater using a duplexer into a single antenna.

Below is a concept diagram of the Walliston site. It shows the antenna mast, which is 75? (23M) high along with the layout of the antennas. Yes there are a lot of antennas and yes there is more than one way to put together the antenna layout. The number of antennas could be reduced. This design uses split antennas on all systems except the 70CM digital repeater and the 23CM high-speed digital simplex system.

Split Antennas

Split antennas means one for receive and one for transmit for each duplex repeater, rather than a duplexer feeding one antenna. This offers one major advantage, less filter isolation is required (cavity filters) and zero desensing is much easier to achieve.

What type of antenna to use?

Folded dipoles and in particular the ones you see on commercial installations are cheap, broadband, DC earthed for lightning protection, low SWR (1.2 or better), robust, come in a wide frequency range, can be custom made if required (e.g. 23cm) and can be stacked (more than one) to produce increased gain. And these antennas are designed to work side mounted on a tower, which is the type of installation we are looking at. Side mounting also produces 3dB gain, which is ideal, as the Walliston site should direct most of the signals to the West.

VHF Folded Dipole

Variations

Due to the number of antennas and the number of coaxes required in this design there are some options to reduce this. For example the 2M receiving dipoles (2 of) could be phased together (3dB gain) connected to one coax and then split via a low gain RF amp at the bottom of the tower, giving two antenna feeds. Or only one dipole could be used (to save antenna space) and split as described.

The 4-dipole arrays on 23cm and 70cm could be reduced to 2 dipole arrays. It all depends on what the tower can support.

The diagram is only roughly to size but a to scale diagram can be produced to give us a better idea of the antenna space taken.

Suggested Tower Config

Walliston tower configuration

I hope this document encourages discussion and more ideas. The antenna installation is one important (if not the most important) aspect of this complex installation. If we wish to achieve the very best performance RF wise then considerable engineering excellence needs to be our number one goal.

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D-Star Progress/Update – 16 April 2008

On the subject of progress on my DStar commitments: the 400AH battery bank is OK & on charge, but difficult for me to do much more (ie: arrange support racking/battery straps & cables/DC distribution system) until we agree where & how the batteries are to be housed in relation to the equipment. Mains power supply is tested & working OK, I plan some preventive work to improve its reliability, and modify to add dry-contact alarm outputs (to signal mains failure/low voltage etc).

70cm diplexer still needs a fair bit of work, but should be straightforward. 23cm iplexer is still an unknown quantity – although I have an offer of assistance I am yet to follow up properly, but aim to do so soon.

BR & 73,
Anthony VK6AXB.

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D-Star Progress/Update – 15 April 2008

VK6RWN: Brief Status Update

  • Power on
  • Feedline installed
  • Lightning arrestors ready
  • Racks installed
  • DSL installed
  • Server awaiting final config changes
  • UPS awaiting batts
  • PSU ready
  • 2m Filters being tuned
  • 70cm Filters being tuned
  • Antennas TBA (awaiting further discussions amongst all DSTAR groups)
  • WIA license waiting

In terms of physical work required, I believe that most of it could be knocked over in a weekend with a few helping hands. Perhaps if we can have some more people volunteering for some tasks, we can speed things along. food for thought.

73’s

Heath
VK3TWO/6

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D-Star contacts in Melbourne

I was in Melbourne for a couple of days this week and was fortunate enough to loan a D-Star equipped handheld from Duncan VK6GHZ for the trip.

I configured the handheld before heading to Melbourne from the instructions on the Australian D-Star website. (Recommended) . I am usually the type that can take a radio straight from the box and start operating it, hardly having to read the user manual. I am afraid that with the D-Star radio this wasn’t possible and I had refer to the manual on more than one occasion! Once the D-Star was setup for the first time I could put the manual away, but there are certainly more functions in it than I was able to use.

I fired up the radio after checking into my accommodation in Kensington (Approx 5kms from the Melbourne CBD) and did some listening around.

Quite a bit of activity was heard on 70cm repeaters and simplex frequencies. QSO’s were also heard on 2m & 6m from around Melbourne.

With a slight bit of trepidation I put a call out on the VK3RWN D-Star repeater. No CW identification, courtesy tone reset pips, unsquelched mute noise or even a reply call came back.

I called on the repeater a second time, listening to the output on my other handheld and could hear the repeater transmitting. I was also looking at the display of the D-Star handheld and watched ‘VK3RWN’ scroll across the display.

The speaker then came alive and VK3BMX responded to my CQ call. His callsign scrolled across the handheld display and we had a short contact. The audio was crisp & clear even on the handheld speaker and sounded slightly ‘nasally’.

The repeater was quite good signal strength even inside the QTH I was staying at. I did some quick experiments with the transceiver horizontal at floor level to get the signal level quite low and the digital audio not decoding cleanly (garbling) or what the locals call ‘R2-D2’.

When using the repeater, a four (4) second gap between transmissions must be left between transmissions for the system to reset (No PTT machine gunners!). This can slowdown a QSO a bit, but according the D-Star gurus this is needed to reset the system correctly after each over.

The D-Star repeater would be quite disconcerting to the local repeater ‘kerchunker’ – No CW idents, no timeout reset pips, unsquelched mute noise or your rig speaker popping open to keep the crowds entertained from this baby. Worse still for the kerchunker is that your callsign scrolls across the screen of everyone that is QRV on the repeater as well as being logged and visible on internet.

From my further observations later, I would estimate that the digital decode became garbled down around what you would expect to hear from a station with a S1-S3 signal level in the analogue FM world. As would be expected, the D-Star didn’t decode down into the noise, but a low signal sounding so clear would certainly be a welcome suprise to most FM users!

The next day I had a couple of more contacts on the VK3RWN repeater to gain an impression of the system. I also took the handheld portable around the streets of Kensington for a brief test. Mobile flutter or picket fencing becomes a thing of the past with D-Star, but garbled decodes and R2-D2 come into play. I guess that where you might lose half a word or a word on mobile flutter, I found on D-Star that it became one or two words until the decode could resume.

I also joined in on a local net one evening where a number of stations discussed D-Star and assisted each other with their D-Star experiences and helping others through problems or issues. I could also see that some operators had their name or the radio they were using in ‘My Info’, but this information is limited to 4 alphanumeric characters.

I also made a few recordings of QSO’s that took place on the repeater to listen to the action. (MP3 format)

QSO 1 (3.9mb)

QSO 2 (2.9MB)

QSO 3 (4.6MB)

QSO 4 (4.6MB)

In summary, it was quite exciting to use this new mode. The communications are exceptionally clear and all the possibilities for sending voice and data over our bands seems endless. I imagine this comes with every new innovation in amateur radio, be it SSB, FM, repeaters, satellites, packet radio, IRLP or Echolink.

The cost of new equipment seems quite reasonable and the add on D-Star capability for some older models is also good to see. Hopefully in time other manufacturers of equipment will also have D-Star equipment available in the market to spurn competition and innovation.

Australia has been very lucky to have Icom & the WIA support the provisioning of D-Star repeaters in several states. Due to the high costs of purchasing and maintaining a D-Star repeater it is unlikely and unfortunate that we will not see use spread outside of the metropolitan areas in the near future.

73’s

Rob…

VK6JRC

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D-Star -v- Analogue FM

Adrian VK6TUX has released an MP3 recording of some comparison tests he has conducted between D-Star and analogue FM on 2m/145MHz over a 40km path.

Adrian writes: “Done with VK6AWO Steve. We found DV mode to have good readability after FM analogue contact was lost. The lack of noise or interference(esp near power lines etc) is spooky & unusual for radio transmission, and is a big plus for the mode. All other files associated with the test are at files section of; http://groups.yahoo.com/group/vk-dstar/

VK6TUX D-Star -v- Analogus FM Test MP3 (1.5MB)

IC-PCR2500 screenshot showing DV text (203kB)

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D-Star Brochures

Heath (VK3TWO/6) has located several Icom brochures on the D-Star system and D-Star capable radios.

The documents are in PDF format and rather large, so please be mindful if you are on a dial-up connection or have a low monthly download quota.

D-Star System Introduction (600kB)

D-Star System Overview (2.8MB)

Icom IC-2200H (322kB)

Icom IC-2820H (636kB)

Icom IC-91AD Handheld (690kB)

Icom ID-800H (502kB)

Icom IC-V82 & IC-U82 Handheld (784kB)

Icom V-82 (Review QST 2005) (418kB)

Documents are provided for the information of WARG members. All documents are copyright by Icom & QST/ARRL and remain the property of Icom & QST/ARRL respectively.

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D-Star Working Group

The West Australian Repeater Group (WARG) have established a D-Star Working Group.

Members are:

Phil Sutherland – VK6KPS

Danny Ainsworth – VK6FZUK

Anthony Benbow – VK6AXB

Eddie Saunders – VK6ZSE (WIA TAC representitve)

Heath Walder – VK3TWO/6

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