Posts by David G0MRF

    Hi Robert. You may want to double check the AD amplifier after the Pluto. I'm not sure it has enough gain at 2.4G to generate 500mW output from a Pluto. Also, the max output from the Pluto could be lower than +7dBm. The Lime has an even lower output.
    Another option would be to use the new version of the SG Labs amplifier which needs 40mW for 20W output.
    Better to need a small attenuator, rather than be 4 or 5dB short of signal.


    Thanks es GL


    David

    Is this right?.

    Hello Thomas,

    I cascaded the different attenuators as I started with the Pluto Output of 1dBm followed by -10dB attenuator, so -9dBm, followed by the CN0417 (+21,8 dBm) and then attenuator of -20dB. We are now at -7,2dBm. This signal goes to the EP-AB003 (+14dBm) and the final (3.) attenuator of -9dB so I measured at the end -2,2dBm.


    1dBm -10dB +21,8dBm -20dB +14dBm -9dB = -2,2dBm (red =attenuator)


    The challenge is to keep the signal in the input range of the amplifiers but below 0dBm for the RF 8000 at the end. The attenuator have only 2W so I have to be careful after the PA.


    73, Oliver

    Hi Daniel.


    Hopefully the diameter of yours is about 40mm. In the past I found that winding on a tube creates an antenna that has a fairly narrow bandwidth, whereas if the winding is self supporting or on small pillars then the bandwidth is greater.

    Here is a pic of a tube mounted helix using a PCB as a ground plane. (not mine) Note it has a sharp peak in return loss, the same as yours.


    73 David


     

    Hi Karen


    There are some spectrum analyser shots by Ole OZ2OE for the Lime mini in this thread


    "Filtered driver amplifier for SDRs"


    Both SDRs have much better IMD products when run below maximum output.
    FYI The Pluto can produce a maximum of +3dBm at 2.4G while the Lime is around 0dBm.


    Also, I believe the Lime transmits a short pulse at 100% output while it is booting up.


    Given the difference in price, possibly the Pluto has a small advantage?


    73 David

    I was thinking about a waterproof enclosure for the patch, Then it occurred to me that if I make the enclosure the correct length, a director could simply be added onto the outside or inside of the enclosure. - Think end cap over tube with disc or loop bonded on.
    Shame we don't have those antenna test ranges we've organised in the past at University of Surrey in the AO-40 days.

    I have a K3TZ patch feed for 2.4GHz,

    Does anyone know a way to reduce the beamwidth / increase the gain so it illuminates a 0.6FD offset fed dish with better efficiency?


    I was thinking to add a single director in front of the patch. A loop ? or a disc? or a traditional pair of halfwave (x0.9) long directors as used in a crossed Yagi.


    Thanks David

    Hello Chris.
    There are now a couple of good choices for 3 - 5W PAs. My 5W in the photo above was also short of gain but still produced 5W with a fraction under 200mW drive. I think most of them are better than that with an input requirement nearer 160mW.
    The filtered driver amplifier uses a "quarter Watt linear amplifier" and it can produce 250mW, but not with a linearity that would be acceptable on the transponder. However, as a driver for the amplifiers that need <200mW it is very good.
    I'm in the middle of producing an article for AMSAT-UK and as soon as the Gali5 amplifiers arrive I'll send off a batch of kits to the AMSAT-UK shop.
    Looking at the DJ0ABR board, I wondered if I could mount the driver amp on the PA PCB. (?) The input stripline looks to be just coupling the SMA socket to the input matching. Given the loss in FR4, it may even recover some of the gain.

    Thanks for the info on the MHL21336. Always good to hear other people's experiences. With the EP-AB003, I was considering bypassing the 2 TX/RX switching ICs, That would probably improve performace a little.


    73


    David

    Now the part I'm not so keen on. Mechanical assembly.

    2 Members of my local radio club want a low cost way to get onto QO-100. Seen here are the modules for a 70cm to 2.4GHz upconverter.

    Top row: e-bay ADF4351 oscillator board. (1967.5MHz)
    Upconverter PCB with RMS30 mixer and PIC12F629 controller,
    Filtered Amplifier board
    EP-AB003 Wi-Fi Amplifier


    Bottom row is the same except for the PA which is the kit version of the 5W DJ0ABR design

    I've probably been a bit optimistic thinking that Wi-Fi amplifier is going to fit in the Hammond box :(


    73 David



    New driver ampliifer PCB arrived. Only minor changes on this version to allow ERA or a Gali device for the first stage. The silk screen has the correct component designations and now makes sense. When a Gali 5 is used the overall gain of the board with a Murata bandpass filter is 25dB. An ERA2 gives around 2dB less. Testing is still ongoing, but Mike G0MJW reports good SSB into QO-100 using just this driver amp. - Of course a nice 2.4m dish helps. Thanks Mike. Should be good to go between a Pluto / Lime SDR and a 5W PA.


    Final update: To avoid the frequency 'jumping' observed in the cheaper Fox and ECS TCXOs, I swapped the reference crystal in the local oscillator module to a TCXO by Murata. This 3 x 5mm unit is very much better working well on CW and FT8.
    It is a reasonable cost from Digikey.
    10MHz 280 ppb. Order Number 490-18053-1-ND cost £7.99 + tax

    PCB has now been changed to allow MAR or Gali style devices to be fitted in the first stage.
    Boards and components have been shipped......Now I just have to wait for the postman. At least I will not miss the deliveries. - I'm not going anywhere :(

    While I'm waiting, I've just changed the 10MHz TCXO in my upconverter. The ECS and Fox products both had noticable jumps as they corrected for temperature change.
    This device from Murata, £7.99 from Digikey, is 280ppb and seems very much better.
    490-18053-1-ND


    73 David

    Measuring linearity with questionable power metering ability has not been conclusive, So the board has been posted out for testing. ( Tnx Mike). Meanwhile I have ordered a batch of components and have begun making a few changes to the PCB. The major change is to the pad layout for the first amplifier. I want the layout to allow different devices to be fitted to the same board. Hopefully, it will accept either ERA or Gali devices from Mini-Circuits. This should allow any one of Qorvo PAs to be used. TQP7M9101 (250mW) TQP7M9102 (500mW) or the TQP7M9103 ( 1W ). All are available from Mouser. :)

    Thanks Ole, that gives a very good picture of the performance of the Lime mini SDR. Not running it at 100% seems essential if you want good IMD performance.
    Meanwhile, tests on the 2 stage amplifier have left some questions about which of the 2 stages are the limiting factor in the P1dB (linearity) performance. I decided that the only way to answer this was to build and test the PA stage alone and measure it's performance. Then I can select the most appropriate amplifier for the first stage.
    Pictured below is the Qorvo TQP7M9101amplifier alone. It gives me the chance to swap the matching components while looking at gain and output power. I expected some loss of performance due to the 0.8mm FR4 PCB material, but it's not as bad as it could be.



    The PA device output is internally matched to 50 ohms. However, the data sheet recommends matching on the input. Qorvo have suggested circuits for 2110-2170 and 2500 - 2700 built on microwave laminate, but nothing specific for 2.4G or the much cheaper FR4 PCB material and so a little bit of exerimentation is needed. Initial results for gain look OK at 15.2dB using 'standard' capacitors rather than any expensive RF products. Also the 15.2dB does not account for the small amount of loss in the 5 cm length of UT-086. Qorvo measued a gain of 16.5dB at 2.5G, so I'm about 1.3dB low. Actually, given the FR4 and best guess matching, that's not too bad.

    Now to look at P1dB which needs work to calibrate out all the losses in patch leads between sig gen and power meter.