Outdoor tower (tree) antenna mounting questions for Kraken and Kerberos SDR

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Outdoor tower (tree) antenna mounting questions for Kraken and Kerberos SDR

Post by fresnoboy » Sat Apr 03, 2021 8:27 pm

Folks, given the upcoming KrakenSDR with builtin switching for calibration, as well as the retrofit switching hardware for the Kerberos SDR (https://www.tindie.com/products/lakesho ... -ohm-load/), I am thinking about mounting an array, probably a circular one high up in a redwood tree I have that is about 110 ft tall. I could mount it on my roof which would be much easier of course, but it's only 35 ft tall.

Mounting it up high gives excellent visibility and range for the system. But mounting up that high has challenges.

Is the Kraken SDR designed for outdoor mounting? the case looks sealed, but there aren't glands for the USB-C connection. I don't think you'd want to try running the USB-C cable a 100 ft - even if you can make it work electrically, it would probably emit a ton of RFI... While you can get USB-C over fiber adapters (https://www.amazon.com/Transwan-Extende ... B08JGFSJBT), they are pretty expensive. So that means the Rpi 4 probably needs to be up there with it.

What is the Kraken's power consumption? I assume it it's powered from the Rpi? If it needs to be put in a box, I am thinking about how it could be cooled passively. It does get hot here, but it would be shaded by leaves depending on how close it was to the mounting. I think it would still be smart to extend the connectivity from the Pi by Fiber to avoid RF emissions from the CAT5 cable, though maybe a shielded cable would be OK, and it could then everything could be powered by POE, which would avoid the need for running a separate power cable. Of course POE adapters also could generate RF noise.

I notice in some of the Kraken videos it appears the Rpi is in some sort of shielded case. Is that needed? IS there one that could be bought or does it have to be fabricated?

Now for the antennas, it would seem the better approach would be a circular array. I would love to be able to do direction finding from aircraft transmissions down at 121 MHz, all the way up to public safety comms at 480 Mhz. A half wave at 480 is just about a foot, but that is about 1/8 wave at 121 MHz. How does that sound as a compromise for the design?

If that works, it's about 8.5 inches radius, which should work well around the trunk of the tree at the very top where the trunk is only about 4 inches in diameter. I was thinking I could fabricate a lexan frame (it's strong and UV resistant) that could be mounted around the trunk that could mount the antennas. I notice in one of the Kraken videos the antennas are mounted on a metal frame. I thought that was a bad idea from some of the comments about causing multipath reception?

I do see this ad for arrow Kerberos antennas: http://www.arrowantennas.com/arrowii/sdr.html They mention dual and triband antennas, but I don't understand how that works without making the spacing be more than a half wavelength at the higher frequencies. How are these supposed to work?

Lastly, this would mounted about 5 ft below the base of a Diamond X300N collinear vertical antenna for 2M and 440 Mhz operation. The antenna would be sort of above the center of the array. Is that spacing enough?

One thing that might be good would be to have the RF switches always disconnect the antennas in idle state, so they don't pickup TX power from nearby antennas or static discharge etc... I don't think it's possible to put lightning protection on these antennas, so disconnecting them and possibly grounding them as the default state might be a good idea.

Am I being just plain crazy by thinking about mounting a Kraken array that high?

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Re: Outdoor tower (tree) antenna mounting questions for Kraken and Kerberos SDR

Post by ckoval7 » Sun Apr 04, 2021 12:07 pm

Unless climbing trees is one of your favorite hobbies, I'd advise against putting anything up that high. Sometimes the KSDR needs to be unplugged/plugged back in again, SD cards on the Pis will go bad, animals will find their way into whatever weather resistant enclosure you put up there. Unless you live in a valley, having it on your roof will be perfectly fine.

The dual and tri-band Arrow arrays come with multiple sets of elements for the different frequencies, with different sets of holes drilled on the arms that hold the elements. You would switch the elements out as needed. I inquired about building a stacked array, but they weren't willing to do it.

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Re: Outdoor tower (tree) antenna mounting questions for Kraken and Kerberos SDR

Post by fresnoboy » Mon Apr 05, 2021 4:31 pm

Thanks for the feedback. I think I could probably still make it work if I remoted the USB over fiber, and kept the Pi on the ground. I can easily powercycle the unit remotely, but am I correct in assuming the KrakenSDR is not weatherized and must go in a weatherproof case?

Any idea as to the power consumption of the unit?

Thanks for explaining how the arrow antennas work. Is it realistic to have a compromise antenna array that can pick up both UHF and VHF reasonably for DF'ing, or would I have to pick one or the other? I guess two separate units would work in any case, though that would get expensive.

Any idea as to when the Kraken will start to ship?

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Re: Outdoor tower (tree) antenna mounting questions for Kraken and Kerberos SDR

Post by rtlsdrblog » Wed Apr 14, 2021 11:16 am

KrakenSDR won't be designed for outdoor use, but you could enclosure it in your own waterproof box (probably needs a fan though).

Kraken will draw about 1.5A, more if you're using the bias tees.

I'm not sure how it will operate with such a long USB cable though, even if it's fibre. I'd guess that any conversion circuitry might increase the sample delay latency and make it more difficult to compensate for that.

The Arrow antennas will only work with one type of element used at a time. You just move the elements to the correct spacing for the frequency you want.

Aiming for Q3 shipping, but TBH it's a little uncertain as there are currently major semiconductor shortages affecting all supply chains right now. We have most of the components already however.

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