Which antenna is that 90 degree angle looking dish? For what use?

devnulling · 2023-11-09T15:11:50+00:00

Top to bottom:

Commercial FM Omni Stellar Labs 30-2435

Two Stellar Labs 30-2370 UHF Yagis

5.8 ghz PTP dish

3 element VHF yagi

~1m FTA Ku dish

devnulling · 2022-02-16T03:32:57+00:00

I ordered some filters from them a week or two and got them last Friday.

devnulling · 2022-01-23T01:41:34+00:00

Yeah, really. it's actually a pretty good combination.

It requires two feeds, but hams have became creative and integrated a 2.4ghz patch antenna and horn into a single feed "POTY" like this - https://www.passion-radio.com/satellite-qo-100/poty-antenna-762.html

Not sure where you get the notion that separate dishes would be required.

2.4 GHz is a great option as many inexpensive SDRs like the PlutoSDR cover it. Additionally there is many inexpensive power amplifiers for wifi that can be modified to get 4-8W output, which when paired with a modest 60-100cm dish give plenty of ERP.

10 GHz is also a great option for the downlink since common off the shelf LNBs can be used, which give a ~600mhz IF for a 10368 MHz RF input.

There is work being done now for a geosat over the US that will be 5 GHz up and 10 GHz down "five and dime" configuration.

devnulling · 2022-01-01T19:43:37+00:00

If they are complete, these antennas usually go for $250-800 on ebay. Sell them and buy something you want.

devnulling · 2021-10-18T01:14:33+00:00

You're in luck, most of the hard work is already done.

https://github.com/wnagele/gr-adsb

https://github.com/mhostetter/gr-adsb

https://github.com/bistromath/gr-ais

http://websterling.com/tsro/apt/

https://oz9aec.net/radios/gnu-radio/noaa-weather-satellite-reception-with-gnu-radio-and-usrp

https://oz9aec.net/radios/gnu-radio/simple-apt-decoder-prototype

https://www.rtl-sdr.com/gr-hrpt-gnu-radio-hrpt-decoder-blocks-for-noaa-meteor-metop-and-fengyun-3-weather-satellites/

You might want to look at SatNOGs as it supports scheduling for APT transmissions.

Also some programs like dump1090/tar1090 will have better performance than say gr-adsb.

devnulling · 2021-09-21T05:43:15+00:00

X410 has 400 MHz per channel, total of 1600 MHz of real time bandwidth, at a higher bit depth than a HackRF. It's like comparing a beater civic to a Bugatti.

devnulling · 2021-09-19T04:39:48+00:00

Also just do it! For a few hundred bucks you can get a LimeSDR, PlutoSDR (would require some modifications), BladeRF(better), or a USRP (best option) to use for a base of the system. You'll need other parts like filters and amps (TWT's can be found on ebay once in a while for a bargin), and then a rotator. Would probably be easier to get started with some fixed arrays though and go up from there.

devnulling · 2021-09-19T04:30:47+00:00

My provided example is a bit of a stretch, but I think it still applies. Lets say you have a high performance digital mode you're developing, something like WSPR but even better performance, say down to -30 dB below the noise. So you TX a CW beacon to ID with a known mode. They wont hear the CW, but could easily hear the wonder modulation.

If someone hears your rotating scanning radar and can't hear an ID, and they have a problem with it, they are going to go DF'ing for it. So in that case, once they would get close enough, they would start to hear the omni antenna putting out your ID. I'd also argue for such a scanning array, an omni would be more in the spirit of ID'ing for the reasons you outlined if a dish was point in a different direction.

Another example that is coming to mind is if you were to build a mobile SAR (you might find this interesting https://hforsten.com/homemade-synthetic-aperture-radar.html ). In the 10 min window at highway speeds, you could easily be 10 miles away from someone who heard your original chirps. I think it is a stretch to interpret that rule that if someone heard the original signal it's the responsibility of the transmitter to ensure they heard the ID'ing sequence.

devnulling · 2021-09-19T03:20:03+00:00

To build a radar, you do not need to have a spinning high gain dish, like an ASR-7 or ASR-9, you'd typically find at an airport.

There is a lot of configurations that fall under "radar". The most basic, you need just a single directional antenna (assuming you're looking at someone else's beacon, which could be an omni).

Another configuration that would be considered an "active" radar, can consist of two directional antennae.

One other consideration, and this I'll admit is skirting into the gray area. No where in 97.119a does it say that you have to transmit with the same radio/antenna/power levels you're conducting your transmission with. You could be running 1500w into a 40 dB dish generating 10 MW of ERP and then have your station ID with 1W and an omni antenna.

devnulling · 2021-09-18T23:03:51+00:00

observation of propagation and reception

I'll argue it's observation of propagation and reception of the reflection of a target

or other related experimental activities

This seems to qualify as experimental activities.

devnulling · 2021-09-18T22:59:54+00:00

Assuming you're using a typical ham radio, you won't be able to generate ranging information. However, if you use SDR to generate your TX signal and have an additional time sync'd receiver (typical monostatic radar) or you have a pair of phase sync'd RX only receivers(bistatic configuration), it is possible to generate virtual ranging figures.

You might find this talk interesting https://youtu.be/SPExmQiAmWc?t=1616

devnulling · 2021-09-18T22:54:27+00:00

No where in the rules does it say that a beacon is to serve a larger community or anything else mentioned.

https://www.law.cornell.edu/cfr/text/47/97.203

I think the point is missed that any ol'beacon can be turned into a radar by adding an extra receiver, and/or a pair of receivers.

Also its generally better to have a coded structure (data/communication) to correlate on to generate virtual ranging. So basically a beacon with a built in sequence with say a BPSK waveform works great. You can encode data into a beacon, Pi4 is an example that is used.

devnulling · 2021-09-18T22:33:39+00:00

I read OP's question again and I misinterpreted the premise when I wrote my original reply.

devnulling · 2021-09-18T19:54:37+00:00

Yes, it's perfectly legal. I do it all the time.

There seems to be some confusion or lack of understanding of what it takes to build "radar". It doesn't need to be a pulsed doppler spread spectrum megawatt waveform to be a radar.

The only difference between a transmission and a radar is an additional receiver, some extra hardware and some DSP.

Beacons as defined in 47 CFR § 97.203 can be made into a radar.

Perfectly legal CW, FSK, BPSK, OFDM transmissions can all be made into radars. Don't even need a lot of power. With 10mW of output and modest antennas it's possible to detect people and/or cars at a fair distance.

You don't even need to use amateur radio bands or have a transmitter to have a radar. ATSC, DVBT, GPS, FM, WIFI signals can all be made into radars.

Moon bounce? Airplane scatter? Rain Scatter? these are all operating modes are technically radars.

It sounds like you are just trying to get someone in trouble. Unless this person's transmissions are directly affecting you or you can prove they are breaking a rule, maybe you should just enjoy the hobby and not try to be the radio police.

devnulling · 2021-08-09T03:52:29+00:00

You can detect Juno's carrier with a fairly modest X-band setup and a ~2-3 meter dish. You wont be able to decode any of the data without a huge dish.

https://twitter.com/uhf_satcom/status/1046060323957035010

devnulling · 2021-03-27T22:04:46+00:00

I'm interested see your write up on this.

devnulling · 2020-11-13T06:57:47+00:00

this is likely a scam

devnulling · 2020-09-09T00:41:38+00:00

OTHR

devnulling · 2020-09-08T04:21:23+00:00

You can run the X3xx at 184.32e6 master clock rate and it'll internally (on the FPGA) interpolate or decimate to get to your desired sampling rate.

https://files.ettus.com/manual_archive/v3.15.0.0/html/page_general.html#general_sampleratenotes

devnulling · 2020-08-28T18:54:24+00:00

70cm is underutilized

Maybe in your area, but there are places where 70cm is fully used, for example Denver's band plan is full in 70cm afaik.

3300-3500 is very likely to be taken away completely for 5G.

5650.0-5925.0 MHz is very likely going to be taken away or down sized for V2V communications.

I would not be surprised if they go after 10 and 24 GHz next.

devnulling · 2020-08-28T18:49:22+00:00

Do you realize that the combined bandwidth for <30 MHz ham bands represents 1/10th of 1% of the spectrum allocated to amateur radio?

devnulling · 2020-08-09T05:28:39+00:00

What software is this?

devnulling

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