Can I just ask about a PA from Bisonelectronics.

  • they are called P-SMP...but there is one cable included with 2 P-smp connectors.. so you can cut it in the middle and then you make two cables P-SMP to SMA and you can use it for connecting input and output..:)


  • Instead of milling recesses in the heatsink for the transistors and isolator, I am going to use a spacer plate made of thin brass sheet which has rectangular holes for the transistor heat sinks to pass through. These holes can be cut by hand, so no milling machine is needed. So the transistor heatsinks will be bolted directly to the main heat sink.

    In my case I found that the spacer plate needs a thickness of about 0.5 mm and brass sheet of this thickness is found in model shops (in the UK) . It is branded K&S # 252 and a sheet 0.016" x 4" x 10" (enough for two PA boards) costs about £6.

    73 Barry G8AGN

  • I was working on a dxf file with all the drill points and pockets for the PA transistors and the circulator yesterday. I measured the PA drop to be 0.7mm and the Circulator drop at 1.59mm. If you are going to remove the circulator then I think the brass shim will work OK the difference is only around 7 or 8 thou. I am lucky in that I have a milling machine with home brew CNC. Before I use it in earnest I intend to try it on some mdf to make sure the holes are correct as measured. I am thinking of 4mm screws for the cover and possibly 2.5mm screws for the board as I could not get a 3mm drill shank through the board holes.


    Once I find it is all OK, I will post the dxf on here just in case it helps others.


    Adrian

  • Mine arrived yesterday too. There are actually two PAs and the cover looks easy to bisect. I will find a copper heat spreader, or ask for one to be made. Are there any existing suppliers out there ? Here is a scan of what we are talking about.

  • Watch out these boards are fragile and bend easy around the circulator hole. ;( Do not drop one!


    I have done my MDF modelling and got it to a stage where I think I can mill the base plate.


    I have been surprised at the cost of aluminium, planning on mounting them to a 6.35 mm thick aluminium plate and then bolting that down to a heat sink rather than drill and tap into a heat-sink and hit fins. The holes in the cover piece are not symmetrical and that threw me for a while.


    Going for two mounted at the same time, not to have both powered up but one as a back-up and have a larger heat-sink area. Also should be able to have fan cooling. This will be a longish project I should think.


    Adrian

  • P SMP connectors to fit the PA boards can be found at Digi-Key


    Right Angle Jack (Jack Female Socket 50 ohms) Digi-Key part no 1868-1052-ND (Rosenberger 119K207-272N5)


    Straight Jack (Jack Female Socket 50 ohms) Digi-Key part no 1868-1045-ND (Rosenberger 119K101-272N5)


    These are available as 1 offs at about £9 each +VAT + postage.

    Both connectors are solder type for UT-141 cable


    73 Barry

  • Adrian


    Yes, my PA boards came with short leads with a crimped P SMP plug at each end - the coax is flexible not UT141 semi-rigid. The Digi-Key plugs are meant for 141 semi-rigid.


    Re your milling of the heat sink, note that the 28v power connectors on the PA pcb each have two plastic (locating ?) bumps which protrude on the ground side. I just snipped mine flush with some side-cutters.


    Barry

  • Have have completed most of the mechanical mounting, done mine side by side as per the cover.

    Dry run up to now no heat-sink compound. I still have to modify the boards, sort out cables, get a 26 Volt power supply, and find an overall enclosure. So still a fair time off completion yet. I plan to drive one of the units with my small MHL 21336 amp, not sure if it will be enough so will just have to wait and see.