Posts by David G0MRF

    The AMSAT-UK International Space Colloquium will be held as an online Zoom Webinar on Sunday 24th October 2021

    The Colloquium will run from 10.45 BST (11.30CET) to approximately 16.00 BST. (17.00 CET) A full programme of the event is detailed below.
    You don’t have to be a member of AMSAT-UK to attend, and the event is free of charge.

    This year’s colloquium will be in the form of a Zoom Webinar. It’s easy to use, simply register at the address below, and follow the instructions which will arrive by email.

    Please register before the 24th , or join live at

    The 2021 colloquium will also be streamed via YouTube.

    The event will be hosted by members of AMSAT-UK and formally opened by our Chairman, Martin Sweeting, G3YJO.

    Each presentation will be followed by a 5 minute Q+A session, which will allow those viewing via Zoom, to pose questions to the speakers.

    All times are BST which is CET - 1hr.

    10.30 BST (11.30CET) Webinar web site opens.

    10.45 - 11.00 Official opening by Martin Sweeting, G3YJO.

    11.00 - 11.30 IARU Amateur Satellite co-ordination Hans Blondeel Timmerman PB2T

    11.30 - 12.00 AMSAT-DL Peter Guelzow DB2OS

    12.00 - 13.00 Lunch break

    13.00 - 13.30 Robert Bankston KE4AL President AMSAT North America

    13.30 - 14.00 STAR-XL: AMSAT-UK Payload – An updated OBDH for Nanosats
    Phil Bladen, Sam Lane, Chris Bridges

    14.00 – 14.30 STAR-XL: X-Band Upconverter & Dual Band L/X Patch Antenna for Space
    Patrick Hope, Marcel Friesch, Chris Bridges

    14.30 - 15.00 Iain Young G7III - QO-100 using a SkyQ Dish

    15.00 - 15.30 David Johnson B2Space Presentation

    15.30 - 16.00 Satellite Operating from 57 Degrees North. Peter Goodhall 2M0SQL

    16.00 - 16.05 Announcement of G3AAJ Trophy – G3YJO.

    16.05 End of Colloquium

    16.05 - 16.35 AMSAT-UK AGM

    17.30 Onwards. Informal session. Q/A and audience participation

    SITAEL and the ESA Education Office are excited to announce that you have been selected for attending the second “lessons learned” workshop on ESEO, the spacecraft mission developed in collaboration with student teams from across Europe, which is scheduled to take place
    19-21 October 2021.

    (Plenty of material for 3 days) Should be a good educational experience.

    Hi Joseph.

    Tracking the moon should not be too problematic. It moves very slowly and there are many EME tracking programs that will do this automatically.
    Even with manual controls it should be possible to gently, nudge the rotators and watch the signal levels.

    Not so different from the old Oscar 40 with the 2.4GHz downlink where you needed to make very small adjustments every 10 minutes or so. - Will be good if it happens and much easier than 10GHz from LEO.



    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)



    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


    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