When I took delivery of my Land Rover Discovery, I thought I looked at every "radio hobbyist" related important thing to help in antenna, power cable and radio placement. One thing I overlooked was that this vehicle had an aluminum roof.
If I ever wanted to use magnet mount antenna this would not be good. I was also not planning to drill holes in the roof. After experimenting with hood and lip NMO mounts for VHF/UHF communications it was clear that performance from all locations was not as good as had wanted, so I needed to try something different on this vehicle since I like omni directional patterns as much as possible.
Normally I always try to run low power transmit and let the antenna do the heavy lifting. On past vehicles I had steel roofs or better mount points which this vehicle lacked.
After changing out the OEM roof rails for aftermarket ones plus getting some higher cross pieces with T slot centers, this opened up more antenna options after a tip from a local ham about using carriage bolts instead of over price T-slot posts. Thanks Jim!
Before I get to the Kraken, the rear most cross bar antenna mount I fabricated from 1 1/2 steel stock drilled out to accept 2 NMO mounts plus one 3/8 24 thread mount for different antenna needs. This mount was then elevated using 1/2 inch spacers to give clearance for the underside of the mount. This should be visible towards the rear of the Kraken array.
The antenna shown is a 17 inch dial band NMO whip that is the perfect height for garage parking. The high take off angle works well in the Hudson Valley known for its geographic features which make for challenging communications at times.
When I go on longer trips I add on a much taller tri band 144/220/440 whip and then run the 17 inch whip for an auxiliary radio. Parked, I can screw on a ham stick for HF operation or use a 70 inch whip with a tie down while mobile for HF via an antenna tuner and balun. This antenna mount bar was a quick project and has proven to work well.
Currently my daily driver radio is the Yaesu FTM-300 for VHF/UHF plus Civ/Mil air band monitoring while in motion. For HF, I sometimes use the Icom IC-705 or Xeigu G90. Perhaps a Yaesu FT-891 may find a home in the car eventually, we shall see.
Now to the Kraken!
When it came time to figure out how to use the Kraken in this vehicle on a "when needed basis" , I used the same steal stock from my antenna mount for the five Kraken antenna arms and I came up with the perfect temporary mount for it in the process.
One 3/4 inch flange mount has a pair of 1/4 inch spacers which some carriage bolts pass through along with two washers. One wing nut on each bolts allows me to tighten the mount to the roof quickly and easy via the T-slot. It is easy to unlock my cross bar, loosen the wing nuts and slide the mount in or out.
The spacers were needed so I could pass the five coaxial cables through a 3/4 inch diameter coupling which connect the two flange mounts together. This allows the coax to pass through the bottom and up to the top to each antenna arm easily.
Driving around with just this center mount with no antenna arms for about a week whistled a little so a velcro wrap is put around the two spacers to deflect the wind. This cleaned up the whistle between the roof rail and the antenna hub mount and its near silent.
Each of the antenna arms made from 40 inches each of 1 1/2 steel was needed to space the antennae out in a pentagram for frequencies as low as 120 MHz. Some velcro wire ties are used to keep the cables from flopping around in the wind.
Each antenna is magnetic and easily stays attached on the arms at highway speeds. No whistling is heard so the aerodynamics must be pretty good. Each end of the antenna arms were rounded off and both edges sanded down prior to painting in flat black paint to create better aesthetics.
Antenna arm zero faces directly ahead with element one being to its approximate 2 O'clock position and the opposite side at about 10 O'clock is element four. These three elements are each held in place with a pair of machine bolts secured with nylon insert lock nuts. This makes for quick disassembly or maintenance as needed.
The rear two most elements roughly at the 4 O'clock and 7 O'clock positions are cold welded together along with a short cross piece of steal stock that has a single carriage bolt and nut to hold it down with some precision against the other antenna arms. Removing this single bolt allows for smaller storage space when the system is not on place and the front three elements stay in place.
Each of the coax lines have thoughtful cable markers on them to make it easy to known which coax goes to which receiver port on the Kraken.
I added some marker points on each antenna arm at key frequency ranges to aid in changing use cases such as for 2m Fox Hunts and other RDF related interests across the VHF and UHF spectrum.
A few more velcro ties secure the five cable bundle to the cross rail and then are all carefully pulled flat against each other before closing the car door so as to not pinch the thin coax.
With each of the five coax connected to the right ports, the only other connections to the Kraken are minimal. If you wish to learn more about the Kraken SDR, please use Google. This is just about my implementation and not a review.
The "Non-Antenna" Stuff.
A nice orange hard case from you know where was pressed into use to keep the Kraken safe but I am still deciding how to make it a permanent home inside.
The red colored 1 foot length USB-C cable is used for data transfer and is connected between the Raspberry Pi 4B and the Kraken. Both the Kraken and RPI4 have grey USB-C USB cables for power only and plug in to a USB power hub which offers the 2.5A amps needed per device.
The power hub also has the ability to be powered from a range of 8-20 Volts which is nice to provide the 5V and 2.5A needed to each of the devices. Two ports on the USB power hub are not used. This is the power hub used if you are interested on Amazon. https://www.amazon.com/dp/B08MCZNYZN
Finally, the USB power hub which originally came with alligator clips were removed and replaced with power pole connectors as shown. An easy and useful upgrade for USB power!!
Shown in the photo is a Westinghouse power station which supplies 12V power to the USB hub but is easily changed to other power sources such as vehicle power or some other battery if desired. I like using the power station since it can monitor current draw and wattage.
During use, the Kraken plus Raspberry Pi seem to draw an average of about 10W which is not too bad. With intermittent use for a whole day plus forgetting to turn it off overnight, the power station still was at 40% capacity.
The photo of the Raspberry Pi, Kraken and USB power hub and its minimal cables should be easy to understand. The row of blue lights on the Kraken show each receiver is in use and the five coaxial cables lead out the window topside.
So how does the Kraken work?
A few comments to share is that the Kraken is sensitive. Do not transmit near to it. For a recent Fox Hunt where we used 146.565 MHz as the target frequency, I used the Yaesu FTM-300 on low power only on a local UHF repeater. I did not see to have any issues but was still careful to not overload the Kraken while doing RDF.
The antenna elements were all extended for about five hours and driving for about two of those. Everything held up just fine.
I paired the Kraken/RPI4 to my mobile phone using the Android App, but also monitored the spectrum and DOA via the web server on an iPad Mini. This worked out well but even though the Raspberry Pi 4B is overclocked, I really need to upgrade to a Raspberry Pi 5 when it is reasonable.
Some experimentation with the ability to track more than one signal on the same frequency was interesting. I tried it with two after making the adjustment in settings. Technically up to six signals can be tracked but I was not able to try that.
After a few earlier uses of the Kraken on my past vehicle, everything worked well at the 20.7db gain setting for VHF. Using this new mount, I found overload easily and backed the gain down to below 10db.
During our fox hunt, we had three search areas each 3 by 4 miles. I started out as a hider in the lower quad listed in FN31bp. Driving up to where the "Charlie" fox was in FN31bs, the turn by turn directions after getting a fix roughly a mile away was fun. However, this fox was hidden in a cemetery and I had to use normal eyeball navigation to reach my destination. Pretty much everyone was impressed with this setup and how fast I got to the fox.
Also worth mentioning that the 17 inch VHF/UHF NMO whip did not seem to affect the Kraken array pattern which was a major added bonus!
During the hunt, I was also tracking the western fox via a different bearing the whole time which was cool to see on the map as I drove north.
I can not say enough great things about the Kraken. It is expensive, but it paid for itself well before this fox hunt via other missions where I needed to find transmission sources. My favorite test location was a local aviation VOR since it was ground level. During that test I even used a separate SDR running with SDRangel to track its bearing, but that is best left for a different article.
Hope you enjoyed this overview and no, I do not plan to share my dimensions used in my build since you can use the calculator and details found in Kraken Forum where I drew inspiration from. All I can say that the materials for my mount ended up costing around $100 in total and that does not include brainstorming and fabrication time.
If I had to build this again, I would make a few changes but nothing major as this has proven to be really nice so far for me.