Going to the title on the thread, “Confused about antenna design”
Part of the confusion is that we’re not just dealing with antenna design issues – we’re dealing with system issues!
That’s why you see people posting about going from a simple indoor antenna to a more complex (better?) outdoor antenna and having their numbers go down. It’s the overall system performance we’re dealing with, and seeking to optimize.
Yes, the first Achilles’ Heel of an ADS-B system is most likely the antenna.
And the second is the poor little SDR.
abcd567 has posted some wonderful, simple, reliable antenna designs, with simulations to back them up.
The Spider has existed for a long time, frequently used by amateur radio operators.
A close relative to Cantenna, the “Coaxial Dipole” has also existed for a long time, but was not so popular as the Spider. It was mainly used in rubber ducky antennas of Hand-held radios. It has a very narrow diameter sleeve, which was made of a copper tube or pipe, slightly bigger in diameter than coax. It did not have the performance as good as it’s newly discovered wide-bodied relative, the Cantenna.
The Cantenna was born only about an year ago, as a result of series of my experiments on CoCo. In June 2014, I added a decoupling sleeve, made of Pepsi can cut to 69mm length, at feed point of my CoCo. This experiment was not successful, possibly because the sleeve was too large in diameter for decoupling purposes.
Instead of discarding the sleeve (Pepsi can cut to 69mm), I decided to use it to make another type of antenna, the sleeved dipole, and it proved very successful. It’s performance was much better than “Coaxial Dipole”. This was birth of Cantenna.
After 2 months I renamed sleeved dipole to “Cantenna”.
Having scanned through this thread, I must say the simplest solution has been overlooked. The cheapo antenna shipped with the SDR isn’t bad at all, it just needs to be trimmed to length and a groundplane added.
Trim it so it stands 2.9" tall (2.7" plus a little more since the whip doesn’t extend to the bottom).
Add some groundplane, like the steel lid off a gallon pain can. The bottom of the antenna is a tiny groundplane, it will couple into a bigger one.
That’s it. You’ll get much better performance than you did before. Put everything high up in the attic, wifi to get to internet, and you’re all set. No cables to run, no lengthy construction projects.
Stock antenna connected to only center wire of coax without any connection to groundplane (aluminium cap with glued magnet) on the bottom.
Not on mine. Shield was nicely spread out, and crimped in position by the press fit aluminum cap. I’m getting excellent results now, 60,000 position reports in a day, and >1200 aircraft seen. Noticeable improvement just by clipping to proper length, and putting on paint can lid.
What compound is better/best for sealing exterior antenna terminals (weatherproofing it)
i.e non-corosive silicon, acryl baed sealant, polyuretanne based sealant, bitum based sealant
Thanks
For sealing terminals connectors (N or the SMA or F connectors) I would suggest amalgamating or “self fusing tape”. This would allow you to remove the connectors later and they seal great. Just a few layers of tape can probably seal for a decade and very easy to remove later.
Professional will use layers of different sealant for more permanent connections. IE. Self fusing tape + electronic tape + connector goop + more tape. These connectors can last a few decades and usually overkill and quite hard to remove.
For sealing other parts of the antenna (the gaps on the antenna enclosure or between antenna sections) depends also on how long you want it to last. Usually an epoxy made for outside will work best (this is what is used on the FA antenna). Anything rated for outside is good like silicon, polyuretanne, etc. Also hot glue actually works quite well too but might melt in warmer temperatures.
You have to remember that water can enter through the antenna and then into the cable. Keeping the antenna waterproof is a very good idea.
Connectors are usually self sealing between the threads. If you make connectors tight enough they are water proof.
hello david, i am not sure of the rules of this forum. are we allowed to post a link to a company that sells a nice waterproofing kit for antennas and connectors?
i use a product from DX Engineering called “weather proofing kit” the part number is DXE-WK-1. it contains both amalgamating tape and heavy duty black tape and nice instructions.
Usually just a bit of generic self-fusing tape would work fine. 3m definitely makes some of the best stuff for professional antenna installers. We can’t have cellphone towers from losing connections
There are some installs that went very low tech with 2 liter soda bottles. I always wanted a gallery for ADSB sites. There is an amazing amount of variations out there and you can see that you don’t need to use the recommended things but whatever you have local and easy to get.
hello david, i am not sure of the rules of this forum. are we allowed to post a link to a company that sells a nice waterproofing kit for antennas and connectors?
I don’t have a problem with people linking to products that are in line with the thread. Spamming products that don’t have to do with antenna sealing is bad.
This is my case. I want 360° coverage, but even the best omnidirectional antenna cannot get me that - I am surrounded by high-rise buildings, and my antenna sees aircrafts visible in the slots between buildings. What I need is an x-ray antenna which can see through the buildings.
