[Ground-station] Ground-Station Digest, Vol 19, Issue 18
Leffke, Zachary
zleffke at vt.edu
Tue Oct 29 08:06:00 PDT 2019
A Quick Look on TI's RF PLL's and Synthesizers Page shows 3 parts with integrated VCOs capable of directly producing a 10 GHz signal (one of which is space rated, no price listed...). As a quick example, the LMX2594 touts 10 dBm output power at 8 GHz, 7 dBm at 15 GHz....so maybe 8 dBm or so at 10.5 GHz. Harmonics aren't great (but not 0 dBc).....filters would probably be needed.
They all consume about 340-360 mA at about 3.3V, so a little over 1 watt.....but.....duty cycling? Any chance of getting a supercap into the design (Size might be an issue there for something like Ambasat sized boards) to support something like 'wake up....tap out a callsign for a few seconds....go back to sleep for 3 minutes...recharge....rinse repeat'.
The other idea would be the harmonics trickery. The LMX2571 is 39mA at 3.3V, so about an order of magnitude better DC power, with integrated VCO. But its 10-1344 MHz output. So, something like an 1170 MHz output and a x9 multiplication would be needed to get to 10GHz band (and filters)........but I'm wondering if the losses from the multiplication (over driven amps, filters, etc.) might kill the overall efficiency. The LMX2541 goes up to 4000 MHz, so could be used for a design that only requires a x3 multiplication.....it probably already produces something at the x3....but its 120mA @ 3.3V.....and probably needs at least one final stage amp.
As a point of reference.....path loss at 10.55 GHz, for 3000km (AOS/LOS type slant ranges) is 182.4 dB. So 0 dBm into 0 dB gain antenna is -182.4 dBm at receive antenna. 4 foot (1.2m) dish with decent efficiency is ~40 dB gain (and just under 2 deg beamwidth...manageable). So -142.4 dBm out of antenna. Noise floor for a decent receiver with 2 dB NF @ 1kHz BW (for CW reception): -174 dBm + 10log(1000) + 2 dB = -142 dBm.
So in the above quick math.....0dB SNR at AOS/LOS for a CW receiver at 10 GHz with a 4 foot dish.......but as the bird rises, for a decent elevation angle pass, could see the path loss reduce as much as 10 dB or more...probably plenty for 'human ear' CW decoding, and possibly enough for computer. Analysis obviously doesn't account for a lot such as atmospheric losses, polarization, etc......but looks like things are in the realm of possibility.
Last thought/ question......what's the best way to key something like this? I'm guessing for settling times sake you don't turn the Synth on/off. Would it be more like power up the synthesizer to get the carrier...then use something like a RF switch (with 50 ohm loads, aka 'reflectionless') to key the CW? Or would it be smarter to remove the bias from a final stage amp? Or both? Or neither? What's the right way to key a beacon like this?
-Zach, KJ4QLP
--
Research Associate
Aerospace & Ocean Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305
-----Original Message-----
From: Ground-Station <ground-station-bounces at lists.openresearch.institute> On Behalf Of Mike Seguin via Ground-Station
Sent: Tuesday, October 29, 2019 8:52 AM
To: ground-station at lists.openresearch.institute
Subject: Re: [Ground-station] Ground-Station Digest, Vol 19, Issue 18
And the LNB's are _really_ easy to lock to a 10 MHz GPSDO! Typically use
25 MHz xtal.
For those that like Off The Shelf:
https://www.dxpatrol.pt/files/PLL25-LNB_-net.pdf
Mike
On 10/28/2019 6:41 PM, KENT BRITAIN via Ground-Station wrote:
> With the new syn chips from TI, and others, they don't take that much power.
>
> We could do a lot with 50 milliwatts or so, More up to whatever you are
> willing
> to provide to that last GaAs FET. There is a reason NASA chose X-Band for
> the deep space network. And the ground stations are cheap enough.
> Those xtal controlled LNB downconverters are only about $15.
>
> Kent
>
>
>
> On Monday, October 28, 2019, 5:23:01 PM CDT, Michelle Thompson via
> Ground-Station <ground-station at lists.openresearch.institute> wrote:
>
>
> What's the minimum power we need for a 10 GHz beacon?
>
> -Michelle W5NYV
>
>
>
>
> On Mon, Oct 28, 2019 at 2:59 PM Thomas Parry via Ground-Station
> <ground-station at lists.openresearch.institute> wrote:
>
> Hey,
>
> I've had a quick look at this and by my calculations you're only
> going to get 0.5 W from the solar cell at boresight. Adding the lack
> of maximum power point tracking I reckon you can only count on >250
> mW for the design.
>
> I think this really precludes anything at 10 GHz. Anything that low
> power and low footprint will be custom silicon (or III-V). Although
> I would welcome being proved wrong.
>
> I'm my opinion that really pushes you into the sub-GHz option. Which
> raises the question of antennas, anything VHF will be very
> inefficient. Ideally a high UHF frequency?
>
> Will keep mulling it over and will have a deeper look into components.
>
> Thomas
>
> On Mon, 28 Oct 2019, 16:55 ,
> <ground-station-request at lists.openresearch.institute> wrote:
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> Today's Topics:
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> 1. draft Custom Sensors Inspired by AmbaSat (Michelle Thompson)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 28 Oct 2019 08:52:26 -0700
> From: Michelle Thompson <mountain.michelle at gmail.com
> <mailto:mountain.michelle at gmail.com>>
> To: Michelle Thompson via Ground-Station
> <ground-station at lists.openresearch.institute>
> Subject: [Ground-station] draft Custom Sensors Inspired by AmbaSat
> Message-ID:
>
> <CACvjz2XT19R27vXZHeuXuFpTS10-ZR7Cc5s3pPXMMp4xbBFnZw at mail.gmail.com
> <mailto:CACvjz2XT19R27vXZHeuXuFpTS10-ZR7Cc5s3pPXMMp4xbBFnZw at mail.gmail.com>>
> Content-Type: text/plain; charset="utf-8"
>
> Here's a draft of the custom sensor document. These are ideas
> inspired by
> the AmbaSat project.
>
> Summary: beacons beacons beacons!
>
> I found *several* other AmbaSat people at AMSAT Symposium. Most
> of us have
> asked for specifications for the custom sensors and also for the
> custom
> board. Those specifications are still missing from this
> document, but I'll
> put them in when I get them.
>
> I've stepped up the Number of Asking Gently request level I am
> giving
> AmbaSat.
>
> If we can fill out the designs a bit then I can find funding to make
> prototypes. You never know who might fly something like a 10 GHz
> beacon if
> there's an easy-to-incorporate board.
>
> Take 15 minutes today and suggest some parts, additional sensor
> ideas, or
> provide feedback.
>
> -Michelle W5NYV
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--
73,
Mike, N1JEZ
"A closed mouth gathers no feet"
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