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Kiwi for VHF/UHF
This discussion was created from comments split from:
Save money on another Kiwi or tell a friend [KiwiSDR is now available on massdrop.com $100 off MSRP]
Any chance of making a kiwi for uhf/vhf? I never have been able to figure out and find something that would upconvert from HF to UHF/VHF. I really would like to cover the air bands.
Yes, there's a chance. On my list of interesting projects is a fast-switching block converter. Essentially this would be a transverter (up/down converter) to an IF above the highest frequency of interest, perhaps 3+ GHz. This uses an LO synthesizer of reasonable performance, (e.g. Harris chip set) speed, phase noise etc paired with isolation stages to drive two mixers with BPF filtering. Picture a, say, 3.0 GHz transceiver that converts 10-32 MHz from a Kiwi or other SDR up/down.
That 3.0 GHz IF is then used with another pair of mixers and the same chipset as the fixed LO synthesizer but this time that LO is stepped in [20 MHz] steps from [3.5 - 6.5 GHz] . This is paired with another similar mixer and converts the original 3.5 GHz IF back *down* to 0-3 GHz. Because LOs are identical and use the same reference, phase noise contributions largely cancel and the result is an all-band receiver using the Kiwi as the last 'IF'/detector/demodulator moving anything the base HF KiwiSDR can do at HF to 0-3 GHz. With stitching it becomes a wide band spectrum analyzer as well.
Synthesizers that can do this are pretty inexpensive as are mixers and gain/isolation stages. Other than BPF & LPF filtering, done between planes in the PC board there isn't much to it. Since all LOs can have high PLL bandwidth, close in spurs and phase noise can be that of the base clock which is perhaps coherent with and also providing the 66.660 MHz Kiwi external clock.
A nice side effect of all this is that it can transmit at low power, as well as receive. Low noise pre-amplification and PA stages can be added as desired (or not).
I think it would make a nice open source hardware/software addition to the KiwiSDR and even Apache/Red Pitaya ... style SDR transceivers. With only 20 kHz of information bandwidth, the Kiwi might not offer every sort of mode that *could* be desired at VHF-microwave, it's not going to receive WiFi or WBFM, but it would still be good for a lot of interesting uses.
It's not a small project but a prototype could probably be running in only a few months...
Just playing with an Adalm Pluto with third party firmware.
No band filtering of course and it's sold as a learning tool rather than an SDR but still fun to start (a narrow) OpenWebRX between 70MHz and 6GHz.
The CPU is good for only about 900khz when used this way with an USB to ethernet adapter. It is clunky to have to use SSH to start and stop OpenWebRX at different frequencies but I can't help feeling it's a good device for a modular testbed and various software.
The designed bandwidth is 325 MHz to 3.8 GHz but it is simple to open up (out of spec) for experimentation. I only got this one because SDR Console was adding TX support and I thought I'd take a look.
Paging and Tetra knock it about here badly, so it works better on a lower gain antenna until I can arrange some filtering.
Sold to get people using the chips it is well priced for a RX/TX test rig (IMO).
edited April 2019
So, from reading this thread, do I understand correctly that there currently
any kind of KiwiSDR-type unit for tuning the UHF VHF bands?
I've got a downconverter on the way. I'll let you know when I get it installed
edited April 2019
"KiwiSDR-type unit" can be interpreted a number of different ways.
Kiwi + downconverter as mentioned previously.
A new version of the Kiwi with U/VHF on-board and with or without HF: I have no plans for this. U/VHF doesn't interest me.
Other U/VHF capable devices with web-style interface software. These exist but I don't know much about them.
edited April 2019
jks: Yes, "Other U/VHF capable devices with web-style interface software" is what I was asking about. I'm primarily a High Frequency user, but have recently gotten into my local amateur radio U/VHF scene. I am interested in a way to listen to/look at signals that are being transmitted on U/VHF bands near me. (I have used SDR# in the past, but don't have a spare computer to set it up on anymore).
Well I've got mine going only in the airband. Till a few kinks to work out.
Unfortunatley there really are only 2 software products that'll give you the ability to be a little more flexible with the frequencies and thats openwebrx and websdr. I really like openwebrx but I'm not a developer and I can't develop it to the level jks has with labels and all the bells and whistles. Maybe someone will as its open source and you can fork it. Kiwi was written specifically for the hardware.
A thought..... make a version of the antenna switch extension that is aimed at switching downconverter(s) bands and at the same time switch the kiwi offset
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