Cantenna

[JayM]

After almost a month or ordering parts, tools and accessories, waiting for deliveries, plus trips to several hardware stores I was finally able to build and deploy my "cantenna" 1/4 wave ground plane yesterday afternoon. So far it's working very well, considering. My maximum range has increased from around 80nm with the magnetic mount antenna that came with my NESDR SMArt bundle to around 130nm. That maximum range is SE by S, near Cagayan de Oro in northern Mindanao. That's like someone in Leicester seeing a few flights just north of London, so not too bad. I'm also seeing twice as many aircraft within my range which for the most part is limited to around 60nm average.

I fabricated a mount for it out of 1 inch PVC pipe that places it near the edge of the eaves of my 2 storey house and about 20cm from the gutter. I added a 3 turn choke balun to the coax, good-quality RG6, to mitigate the effects of being near the metal gutter. I have yet to build my planned 1/2 wave vertical dipole for VHF air band but it will be placed near the cantenna. I also have yet to check the VSWR as I'm having trouble getting a NanoVNA. The first one I got was defective and I had to return it for a refund, the second one I ordered was cancelled by the seller who'd run out of stock, and the third one is stuck somewhere in transit between China and the Philippines where I live.

For the amount of money I've spent on parts and tools to build the cantenna I could have just bought a FlightAware antenna! I had to keep reminding myself how much fun it was to build my own. Later I may try my hand at making a coaxial colinear antenna but I want to get my money's worth out of the cantenna first. FYI I did it right and used a beer can, not a sugary drink can, and of course I needed a few spares in case I made a mistake during construction, and the beer had to be consumed before the cans could be used. Oh, the sacrifices we make for our hobby!


I guess I'm hooked already. I just ordered a FlightAware Pro Plus dongle with inbuilt LNA and filter which will leave my current dongle for general-purpose reception use such as shortwave radio, and possibly air band voice traffic if I ever getting around to building the dipole. I guess I'll need another coaxial cable if I want to be able to listen to airplane comms at the same time as tracking them in VirtualRadarServer and Dump1090. I never suspected that tracking airplanes on my computer could be so much fun.

[Anmer]

Thanks for the interesting project report.  Next time the beer can go on the vegetable patch.

My maximum range is 260nm, helped by not having anything but sea to the south,  It's buildings, hills and trees that can be a problem.  Getting the antenna as high as possible helps, subject to coax run limitations.

[rikgale]

Great write up. I hope it was good quality beer?

Depending on where you are and how close you are to mobile phone masts you may also want to get a FA Filter to go in front of the FlightAware Pro Plus dongle. In the FA Pro+ I believe the LNA is sequenced before the filter and can overload the filter at times.  I discovered this the hard way with my 3rd feeder location. 200M direct LOS to a mobile mast. Started off with the FA Pro+ and cheap dipole stuck to office window. I was getting a/c out to about 100nm, but message rate was low, noise floor was higher than I would have liked. Put in the FA Filter, range out to 160-180nm and message rate increased by 80-90% and noise floor dropped to better levels.

[JayM]

Yes, the problem here is buildings and a few big trees. The Philippines is an island archipelago so land is dear, lots are small, people tend to build upward, so there are many three-storey houses. I can't have an antenna installed on top of the (hip) roof because it isn't my house, and I don't think putting one in the loft would work out because the roofing is galvanized iron sheets, so I got it as high as I could, in a location with the fewest obstructions to the horizon.

I got one of these PCB microstrip ADS-B filters several days ago and was using it with the Nooelec antenna , and it seemed to improve message count and planes seen, and there were fewer one-message bogeys. Unfortunately, while changing over to the new cantenna one of the SMA female sockets that was soldered to the PC board snapped off. There's a slight possibility that I may be able to repair it, otherwise I'll have to get another (and this time re-enforce it with epoxy and gorilla tape before use.)

I won't be getting the FlightAware dongle after all. The seller  notified me yesterday evening, asking me to cancel my order as he/she had run out of stock, and no one else on Lazada Philippines has one for sale. I can't shop at eBay or Amazon because my bank won't let me use my Philippine peso debit card for foreign currency transactions, so I can only shop where the prices are in pesos. I'm going to look into changing banks later this year when I'm able to as I know that other banks we've used in the past didn't have this restriction. I only chose this one because the branch where I opened my account is open on Sundays which I thought would be handy in case of emergencies.

While upstairs feeding cats yesterday evening I realized that I had put two choke baluns in the coax, not just one: one in the length of cable between the antenna and what would have been the filter if it hadn't broken, and one in the other length that leads downstairs and through a window to my computer. I undid the second one and see some improvement. I'll continue to monitor

By the way, I had one small stroke of luck while building the cantenna. I had purchased a 20cm jumper made of RG174 with male F connectors on each end, then decided I actually needed two. The first one arrived in a box but the second one was in a paper envelope, and when cutting the end off of the envelope with scissors I accidentally severed the coax. One of the pieces was exactly 69mm long so all I had to do was strip off the outer insulation and remove the braid. It screwed nicely onto the female-female "gender bender" that I installed on the bottom of the can after drilling a suitable hole, so no soldering or anything was required. I cut the bottom off of an empty plastic 1 liter Datu Puti vinegar bottle and taped it to the bottom of the can to protect the antenna from the wind as the dielectric and center conductor of the RG174 isn't very stiff and also prevent rain from pooling on the top of the can. It looks odd but it works OK.

[JayM]

I redid the PVC pipe antenna support contraption (which resembles something from Rube Goldberg) yesterday, welding most of the bits together with PVC cement rather than having them just pushed together, and adding a second support that rests on the windowsill to the load-bearing horizontal pipe. I also replaced the vertical section that supports the actual antenna by one around 34cm higher. This was enough to net me an additional 25nm on my maximum range, which is now slightly over 150nm.

I was thinking about it last night, took some measurements, and I think I can lengthen both supports, the one on the stand just inside the window and the one on the windowsill, by another 20cm and still be able to lift everything off of the stand without the horizontal pipe hitting the top of the open window. It's not much but "many a mickle makes a muckle", right? I need to be able to bring the entire assembly inside the house so I can close the window tightly if there's a storm or typhoon. I can't raise the horizontal pipe with the antenna on it any more due to weight concerns, plus it's all getting rather unwieldy anyway. I almost couldn't navigate the turns on the stairs as it is. It reminded me of people who build boats in their cellars then can't get them out. I may raise it higher tomorrow or this weekend, or I may wait awhile as I have some other changes planned in a bit over a week (such as finally building my VHF airband dipole and attaching it to the antenna support. I'm waiting for more parts to arrive.) Then I can do everything at once. I also need to check my VSWR when my NanoVNA finally arrives (assuming that it works) and possibly add a few snap-on ferrite chokes on the coax near the antenna if need be.