BATC Forum

Does anyone have a circuit for these? I am trying to figure out how to drive
the BLF521 and supply it. The mods page at http://g4fev.atspace.com/dolphinpa.htm
only shows mods for driving at the BLF554. I suspect the BLF521 needs a separate 12v supply.

- Charles G4GUO

Hi Charles,

This may help:
http://www.m0dts.co.uk/files/70cm%20Driver.jpg

Be careful not to short out any gates when connecting you own RF in, the devices are hard to some by unless you find another amp!
There is another device under the board before the BLF521 which i have indicated the input to but you will likely want to use just the BLF521 and BLF544.

Rob
M0DTS

Thanks Rob,

Do I need to do anything extra to provide supply / bias to the BLF521?

- Charles GUO

Just a 12v supply to the header as we did with the 28v.. not sure which pins but it was fairly easy to find if i remember correctly.

Rob

Thanks again Rob,

I have it producing about 40 watts of nice clean DATV now.
Can't see any harmonics either.

- Charles G4GUO

Excellent!

The harmonic is fairly well down due to the design anyway.. i run mine at 60W (on a standard power meter) at 2Ms with a fair amount of regrowth, Peak power is probably just over 100W.

Rob

O.K I admit it. I should have asked here before hacking the amplifier!
I made an irreversible modification to the PCB which means I have to
feed it at the 20-50 mW level now.

Yes I have tried it at both 2M/s and 1M/s both on DVB-S and DVB-S2.
Now If I can only find someone local to me that can receive
1M/s H.264 DVB-S2 on 437 MHz I could do some bleeding edge tests.
I am tired of looking at myself.

The gain of the amp seems to peak about 430 MHz. I tried moving
the capacitors and it didn't seem to make much difference.

- Charles G4GUO

Are they Nokia amps or some other make?

I have one going properly now.

The spectral regrowth was awful on 2390-2400 but ok on 2320. Nice staircase on the analyser of regrowth. The transistor phasing lines aren't working on 2400 as one of the drain tracks are too long and the transistors are fighting each other's phasing.

The driver is clean to 50dB has 38dB gain and produces 3watts drive when driven with DATV express at full output.

After removing lots of capacitors and a hairpin track by bypassing it and it works great now, enough to warm up LMR 400 after 15minutes. Heatsink nice and cool.

I have a picture with the mods on I have done in Photoshop - enjoy


The Bias on the output transistor is running all the time, so turn off the 28/32volts otherwise it gets warm without the fans running.

Mike G8LES

Is this amplifier still available on eBay? I blew mine.

PE5PVB wrote: ↑

Thu Aug 31, 2023 8:43 am

Is this amplifier still available on eBay? I blew mine.

Hi
Which amp did you mean …the dolphin amp for 70cms or the 2.3ghz one G8LES mentioned