BATC Forum

After a chance browse on eBay I've discovered a source of bargain Nokia Dolphin amps which are almost purpose made for DATV and driving from a Lime or Pluto after trivial mods. The vendor also has a supply of Ionica 15W PAs for 9cm and the front end with diode mixer and IF filter equally adaptable now that we can do easy LO synthesis. He works in DATV so he tells me and doesn't much fancy more of the same in the evening, but would like the gear to be used. Bargain prices too IMHO. Search eBAy for https://www.ebay.co.uk/usr/freevilthegr ... noapp=true and message him for a deal, mentioning 'Gareth suggested......'.
73
Gareth

Gareth, I see from the various modification pages on the web, that these amps are originally intended to produce about 70W of Tetra, and are biased for ultra-linear operation at well below the capabilities of the RF devices (hence the potential for modification to run - intermittently - at around about 200W for SSB).
Most of the chatter about mods, therefore, seems to be aimed at resetting the bias point to get around 200W PEP for SSB.
Would pressing them into service for DATV be more akin to their original porpoise (Tetra)? In which case would any of the mods be necessary? What sort of power do you think you could realistically get out if them with decent shoulder levels?
John
G8PEF

I'm NOT any sort of expert but I believe you are correct. Use as-is for DATV and it can be fed right at the beginning of the driver chain (i'll dig out the and post the picture later) which means straight from Lime or Pluto. Don't know how many he had, I bought one as a spare 'just in case'.
Gareth

Here's a link to the low level input page. Needs very careful checking and is on my to-do list, but perfect for our job. Dave Crump told me has had a clean 35W out of one of these but suspect a bit more could be squeezed with clean drive??
http://www.m0dts.co.uk/index.php?item=68
Gareth

Nokia amp conversion

I bought one of these from that seller and he was very helpful and I am very pleased with the amplifier.
It took me a little time to gather the information together and then see how easy it is to 'convert' these amplifiers for DATV.
Basically if you go by M0DTS's information you can't go far wrong.
The biasing is done in two places. You have to short one track to ground and connect the other to 5 volts which can be found on the board. You also can take out three voltage regulators. Remove one small capacitor and feed in the low level DATV signal. Connect 28 volts and switch the amplifier on with the 12 volts.
The biggest tip I would say is to scrape the varnish off the tracks before trying to solder.
I got 50watts out with DTX1 running at 100% output and nearly 10 amps from the 28volts. I had 4 amps with no signal.
I did no tuning so this probably could be improved.
I put some photos here:
http://g8lce.com/forum/viewtopic.php?f=11&t=18
Note that you need to feed the new wires in a way that you can cut out bits of the cover so it fits back down. I cut these out with my 8 inch angle grinder which is not as neat a job as could be done!

Martin G8LCE

Got the Nokia amp into a real aerial today at G4GPD's house. With an output of 1.5Watts it got into GB3NQ. It was easy to get 50Watts out but the shoulders were coming up. At 35Watts they were -35to-40dB down. The driver was a DTX1 with the output set to 70% ( 437MHz 2000kSR ). After a while the amplifier got hot but that was with the heatsink on the bottom with reduced airflow. ( it was just put down in the middle of a work bench where there was mains and the aerial feed ) A fan and better airflow would mean it runs cool. The £15 28volt 10Amp PSU must have been running at 7 or more amps but only got warm even though it has no fan.
Really easy to get this amp working and really pleased with the results.

Martin G8LCE

Have you got a clear diagram/picture you could share of the power and other connections for the big plug?
Thanks
Gareth

g8lce wrote: ↑

Thu Jan 23, 2020 11:21 pm

... The £15 28volt 10Amp PSU must have been running at 7 or more amps but only got warm even though it has no fan.
Really easy to get this amp working and really pleased with the results.

Martin - what PSU were you using?

John G8PEF

Pin outs

http://g8lce.com/forum/download/file.ph ... &mode=view
May work for you
It is too large for inclusion here.

Pins are in sets of 3 and all 3 are connected together.
1 and 2 28v output
3 28v driver
4,5 and 6 GND
7 and 8 12v ( I switch this to TX )
The rest you can read from photo.
You can click to zoom in.

Still check for yourself.
My amp was best output at 35-40 watts with no adjustment. Bias rebuilding may make 70Watts work but I think I'll see how I get on with it for now.
It will need a fan.


POWER SUPPLY

https://www.ebay.co.uk/itm/DC-3V-5V-9V- ... 2749.l2649

28v 10 Amp


Martin G8LCE

Thanks for the picture Martin. I found reference to where they should be "See below for photos" on the M0DTS page http://www.m0dts.co.uk/index.php?item=68 but there is just a gap labelled "photo"

Dave

g4fre