Can I just ask about a PA from Bisonelectronics.

  • Just throwing a question out there, I guess the answer will be no, but does anyone have a circuit diagram for these amps I would love to follow the bias circuit. My eyes are definitely not good enough to follow the components and tracks on the board to figure it out. There seems to be some checking that the peak amp (classC) is powered before it allows bias to the class AB? device and have noticed a track that runs around the bottom of the board for this, wondering about using this track for bias of the normally class C device but would need to work out the switching part first.


    Or does anyone know where/what the boards came out of, i.e. equipment model number etc, and I would try and give some company a message request.


    Adrian

  • So I have been straining over a magnifying glass and doing searches on the internet for SMD markings. If anyone with the same amp would like to verify my findings, I would appreciate it.


    I have drawn out a bias circuit, sorry it is not in Ki-cad or similar as I do not yet know how to use circuit programs.

    V104, V107 and V201 are marked 1PN which I believe to be a NPN transistor similar to FMMT2222.

    V108 is marked as W2F 2d. Which I believe is similar to PMBT2907A and a PNP transistor.

    V105 is marked R1E and appears to be a 1.2 Volt fixed shunt regulator as in a LM4041.

    Lastly V106 marked RAC again a LM4041 type device this time adjustable shunt regulator.


    The Green circles are my idea of ground points, resistor values in purple and what voltages I measured in Blue.

    The Analog Device AD5259 I have reduced to a variable resistor in the diagram between 1.2 Volts and GND.



    Not sure what is going on with V107 as it seems to be just using a diode junction.


    Anyway the point for me is understanding the biasing of the power devices, with the left hand one being at a measure 1.9 Volts and the right hand side one at 0.57 Volts.


    Adrian

  • I have made a video that shows my PA driven with 800 mW and producing 19W output. The power supply is 28 V DC and current abt 2.5 A



    The mods are bypassing the input isolator and the output circulator.


    I also have driven the PA with 2 W from a SG-Labs transverter and the output is 22 W with 3.6 A current @ 28V DC.


    Best 73

    Best 73 de Toni, EA4LE / KC2HAX


    A veteran of AO-10, AO-13 and AO-40 8)

  • How nice from you to make the video. I am just in the process of mounting the modules down on the cooling part and wire it up.


    Looking forward to improve my uplink signals.


    Vy 73 es tnx

    Thanks so much Stef, glad you liked it :)

    Best 73 de Toni, EA4LE / KC2HAX


    A veteran of AO-10, AO-13 and AO-40 8)

  • I have modified the two amp's I have, I have removed the input circulator and the input 2.2Ghz filter but left the output circulator in place, I am glad I did as I burnt out the cheap Ebay 50 watt dummy load at some point and did not realise. So the circulator would have been taking all the load in effect.


    Going off my circuit above I have done a few mods in changing the 1K1 resistor to a 1K0, removing the 250 Ohm to ground and adding another 4K7 to ground all on the right hand side of the board. I have also cut the track feeding the emitter follower and fed in to another point. The end effect is that both devices now have the same bias voltage.



    You may just notice where I cut the track under the end of the white wire!

    Is it the best way of doing it, probably not, it is probably better individually biasing each device for a set standing current that way you know each device is taking the same current. Out put powers have been in excess of 80 watts. The other mods have been snow-flaking, cutting tracks and removing an input cap as per some posted mods. Do be careful, the more you push these the more prone they can be to self destruct.

  • Hi Adrian, what is the rationale for the mod that results in having the same bias power in the two devices? does this mod make a great difference in performance? I am really impressed with the output power you get from your units! what is the input power you are using to get 80W out?

    Best 73 de Toni, EA4LE / KC2HAX


    A veteran of AO-10, AO-13 and AO-40 8)

  • Hello Toni;

    I will try to answer the best I can in my own words on why I think it is better, I can not prove it or disprove it. The modification information from SP8XXN and SP5XMU mention the board is a Doherty amplifier. In reading up on these amps (wiki style) one device is switched on in class AB and the other is basically class C and off, needing a high peak level to switch it on, as it is used for the high peak to average transmissions of UMTS.


    The article I read also said that power is lost as the input power is split two ways into each device by a 90 degree phase shift with different lengths of track, so in my mind half the input power is being diverted to a device that will not amplify any signal until it reaches it's designed peak switch on point. I have no idea at what level this is!


    So to me, to get back this wasted input drive the second device needs to be biased as the first, in a class AB mode.


    Now as it was designed for around 2100 MHz the 90 degree phase shift is not going to be 90 at 2400Mhz as the tracks are longer then required, but any phase shift change on the input is being reversed on the output or close to it.


    As to drive level, I know that my pre-driver starts to limits out at less than 2 Watts, I have also reports that others that have done the mods have achieved a very maximum of 120 plus watts for short periods and this is not something I would NOT recommend, I have taken mine to an excess of 90 watts before my nerve gave out.


    There are others doing similar mods, in fact a James Smith posted on facebook and in in IO groups

    https://groups.io/g/DATVPA/top…_amplifier_using/34475663?


    James is probably the first that brought it to my attention followed by a local radio ham Tim G4WIM

    PA für 2,4 GHz


    Each has done it a slightly different way but end up with similar results. I have been to Tims's location and know his test gear is accurate. Do try and have a look at both links.


    Do not expect to run the devices at full power and for them to last long also do not forget you need something like a peak to average difference of 6dB, but if you know that the peak output is say 80 watts that is 3dB better than saying the peak output is 40 watts and the average is 20 watts rather than 10 watts.


    I hope this explains it from my perspective, it is probably the best I am capable of giving. :)


    Adrian

  • Hi Adrian,

    thanks so much for taking the time and the effort to enlighten me. Microwaves are uncharted waters to me, esp when it comes to amplifiers like this.

    I see now the rationale and this makes sense. Thanks also for pointing to the others doing similar mods, very useful! Back to the soldering iron and the tests now!

    Yours most grateful,

    Toni, EA4LE

    Best 73 de Toni, EA4LE / KC2HAX


    A veteran of AO-10, AO-13 and AO-40 8)

  • I won't buy as I already have two unmodified bards - so leave it for someone who really needs it (very fine price by the way) but I would appreciate a high resolution photograph of the modifications required.

  • Microwaves are uncharted waters to me, esp when it comes to amplifiers like this.

    I am very new to this as well, I just spend lots of time in this stupid computer, playing catch up now I have time on my hands. If you have the mod sheet for the amplifier then the sites I read up, are mentioned in the mod pages. The first one I saw done with James Smith when he also posted on Facebook about it and G4WIM also did his before I did mine. My aim was to keep everything under the screening lid hence the reason behind my mods and going through the bias circuit. I would love to have a way to program the variable electronic potentiometer IC on the board that is doing the biasing, but I do not understand enough of that yet.


    Have fun.


    Adrian

  • I have done an update to the dxf file, I realized that the previous DXF file (in the zip) would not show the actual image I had been using.


    I have done a dxf for a single PA, watch out for the holes (points for the cover) when you buy the PA as a Single you could get either the left, or, right-hand side of the cover and the holes are very different.


    So anyway here is the single PA dxf with an image file in a zip. Un-zip into a folder and then open the dxf from that folder and I hope you will also see the image file. Please let me know if you do. If it works I will then try to amend the original file I uploaded.


    Also, I need some feedback if you use the file as to it's accuracy. I used a picture of the image to determine where the points are for drilling. I drilled 2mm holes for 2.5mm screws. The PA cover can go bigger and I drilled out and used M4 screws for that.


    If anyone has CNC facilities please mill out first on some MDF or other suitable material before you build your PA. Check the accuracy of everything. My machine is not an accurate one and I am getting small errors, not enough to cause me any issues but I do not know if the errors are in the drawing or my machine, I have normal lead-screws and not ball-screws on the mill and therefore have backlash errors I can not correct.




    Many thanks and feedback appreciated to know if it works for others.


    Adrian