Posts by David G0MRF

    Thanks for the detail George.

    A good set of tests. - Particulary that a helix of only 3 turns can give good circularity.

    I'll leave the question about plate spacing or bending for either Mike, Remco or Paul, but my feeling is the circularity is primarily determined by the location of the feed point on the patch element.


    73 David

    Is this linearity test on 10GHz ?

    For the 2.4GHz patch on the POTY. Receiving a signal via a linear antenna, the RX signal should be constant as you rotate. To see -20dB you need to measure RX signals with first LHCP (optimum coupling to the LHC dish feed) then with a RHCP antenna at the same distance (max loss)


    Thanks


    David

    PA Device is discontinued, but P1dB is listed as 35dBm by Qorvo which seems quite good.
    Although this performance probably will be less on cheap FR4 PCB.


    P1dB=35dBm at 6V

    Three Stages of Gain: 37dB

    802.11g 54Mb/s Class AB Performance

    POUT=27dBm at 2.5%EVM, VCC

    6V, 878mA

    Active Bias with Adjustable Current

    On-Chip Output Power Detector

    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