Bit of background first, i am running a pi with a home made colinier antena which has improved my coverage which i am happy with. Thanks to those of you for putting up the build links and tips. I live in central west queensland australia and have a small country airport with light plane and RPT traffic with very small number of movements per day. There is also overhead traffic for within australia and overseas flights. My rane is up to 200nm with the collinier but i would lime to extend the range on the specific airways/tracks across my sky as there is little other adsb coverage.
Can i run two directional antenna (for example one pointing north, other pointing south) and joint them to one receiving pi as an additonal data recieving source? I am thinking the directional antenna will give better range along the tracks that the aircraft always take.
I will continue the original pi collecting traffic from the collinier as well.
it should be posible.
But the biggest problem is to find a antenna combiner with less as posible copling loss for hooking up multiple antenna’s
in that case you could even hook up 4 directional antennas (be aware it shall not be 100% 360 degrees after coupling.)
i dont know how diseq switches works and how they look under the hood,
but if measure from pin to pin only 1 antenna is pass true.
making a bridge to use both antenna in’s for that frequency is a pain ,specialy if you want low loss.
a alternative is using a low nois LNA for satelite, i have good experiance with them ,ok, mine was cheap but the amp has lesser noise as my old amp and the gain in visible planes was beter.
if there are commercial bridges i dont know, but build is normaly not that hard, but the isue is the high frequency, perhaps a 23cm ham signal combiner for multiple antenna can work, 23 cm is 1250 mhz or so.
I’d experiment - shove a 1/4 wave whip at the focal point of a satellite dish (just strip the shielding off the last 68mm of a length of co-ax) - the local point is about 40mm in front of the ring that mounts the LNB.
Now remember if it’s an offset disk - the dish face will be sort of vertical when it’s receiving a satellite that’s 30+ degrees above the horizon - so to get planes on the horizon the dish will have to lean forwards a good way (it will look like it’s looking at the ground)
Also check what is possible. Go to heywhatsthat.com/, do a new panorama from your exact position specify your antenna height correctly
the select “in the air” and put in an altitude of 38000 and zoom out
You will get a ring that shows when planes at 38000 feet will appear above the horizon to your antenna (assuming no trees, buildings etc, in the way). You might see planes a little beyond that - but not much.
A “Really directional antenna” at these frequencies is possible using a corner reflector but wow will it affect your backside reflection. I worked IFF (M2,M3,M3A,MC, and Mode 4 crypto) on F4’s in Vietnam and Okinawa. At Kadena AFB our tacan shop (basically a UHF VOR system) could pick up the local station (3 Miles) but not the NAHA DME signal so I put a blade antenna that was used on the airplane and a corner reflector basically a V snap copper reflector to pick up the NAHA VOR DME 32 miles away. This worked really good but now my local Tacan DME didn’t work. Kinda pissed off the boss, back up to the roof take down the corner reflector put back the plane blade antenna. Lifers had very little sense of humor or technical inventiveness for the most part.
The construction is very easy and very directional but kiss omni signals good bye. Not a bad idea if you want to point at a busy airport.
Maybe a corner reflector and and omni antenna with a combiner (transformer) to get the best of both worlds, never tried that configuration.
I think this is the way to go. The focal point of the parabolic (satellite) antenna would be more similar to a rifle shot with great reception in a very small area as compared to the wide reception (more like a shotgun shot) needed to cover a wider area. I’ve used a corner reflector made from aluminum foil to pump up router wi- fi reception at home and it worked great.
Yes on the corner reflector – plenty of writeups on them for use with WiFi. Major variations are flat reflector, corner, and parabolic. You can easily get 10-12 dB of gain and a really good front/back ratio. Also look at the biquads discussed around here, but I like the dipole/corner combo as it’s more flexible.
I’ve been doing some preliminary playing around with a dipole/corner reflector configuration, changing the corner angle to tune the coverage. That configuration picks up more birds in its sector than my high gain omnis, giving me some confirmation that in a target-rich environment, collisions (the signal kind) are an issue. This also reinforces the use of separate RF chains - receivers for each sector.
(Combining multiple antennas to one feed is very, very tricky – they’re called phased arrays.)
Yes on the corner reflector – plenty of writeups on them for use with WiFi. Major variations are flat reflector, corner, and parabolic. You can easily get 10-12 dB of gain and a really good front/back ratio. Also look at the biquads discussed around here, but I like the dipole/corner combo as it’s more flexible.
I’ve been doing some preliminary playing around with a dipole/corner reflector configuration, changing the corner angle to tune the coverage. That configuration picks up more birds in its sector than my high gain omnis, giving me some confirmation that in a target-rich environment, collisions (the signal kind) are an issue. This also reinforces the use of separate RF chains - receivers for each sector.
(Combining multiple antennas to one feed is very, very tricky – they’re called phased arrays.)
bob k6rtm
So how many reflectors with dipoles would we need to cover 360% (each with a dongle and PiB)?
This is definitely the case. There is no coordination between transmitting aircraft over when they are going to send messages (unlike something like Class A AIS), so it’s down to chance as to whether there will be a collision. Here is a graph showing the message rate per aircraft:
You can see that the messages received from each aircraft increases hugely overnight, where there is far less traffic. I live in very busy airspace and can usually see over 200 aircraft during the day, but usually less than 30 at night.
Using sectored receivers would help a great deal with the reliability with which each aircraft is received. It would also make long range reception easier, as apart from antenna gain the weaker signals from distant aircraft would not be quite so likely to be swamped by strong signals from local traffic.
Im not sure that phase from an omni and direction dipole would have that much affect. I design RF systems RX and TX on MRI machines, so phased array to me I immediately think transmit. We use it on high field systems (3.0 Tesla, 120Mhz, Lamor Freq for H) and above to reduce the amount of power delivered to the patient. At these frequencies there are problems with patient heating and the body absorption. On the receiver side we have multiple coper receiver bands pick up coils in the receiver coil that the head or body is in, we just add these up don’t much care about the phase difference on the return. We are dealing with signals (same frequency) that are right down at thermo or black radiator noise, to say the least we are starved for signal and will fight for anything we can get. So I can’t imagine although need to do some experiments with the spectrum analyzer on a corner reflect and omni stick on the L-band signal. Unless one signal is 180 out of phase and totally cancels the other, I think some small capacitance would solve any phase problem in the configuration.
We use very loss loss combiners to sum as many channels as we can together for signal so I think combiner(transformer) loss is overstated here.
Anyway, I need to drag home the big ars HP analyzer and look at the corner reflector and omni antenna signal…Will advise.
If you like constructing antennas you might try a simple yagi antenna. There is a program written by VK5DJ that can be used to design your antenna http://vk5dj.com/downloads.
The input parameters:
The output:
The product:
I used brazing rod for the elements, UV resistant PVC conduit for the boom and inserted a 75 to 300Ω transformer to match the 300Ω folded dipole to the 75 Ω RG6 coax.
According to the design the beamwidth is 41° and the gain is around 11dB.
Thanks!. I have not tested the performance out yet against one of my omni-directional Cocos. I have tested it handheld in the house at ground level but need to get it up on the roof to give it a good test. It’s definitely directional from my quick test in the house.
I’ll follow up with this info. I put the yagi up today at 22 ft. and the performance in distance in the direction the antenna is pointed is equal the 12 element Coco. The Coco is mounted at 24 ft. and has a preamp at the antenna. I tried a preamp both at the antenna and in near the receiver and the amp didn’t work with this antenna. I think is because the yagi uses a folded dipole, essentially shorted across the coax.
I have noticed that if the antenna is located in a good position the only advantage of using a preamp is an increase of position reports. I have both a four (4) element Coco and a twelve (12) element Coco with essentially same coverage footprint but the 12 element Coco has 20% more position reports than the 4 element coco. The plane count is within 10% between the 4 and 12 element Coco.
How does yours perform?
