abcd567,
I have a 4 leg spider antenna with a 25 foot run of RG6QS to my Perfect Vision amp (located indoors), then onto the Pi. If you had to guess, how much attenuation would you estimate (in terms of percentage loss of flights or positions) having the amp closer to the Pi versus at the antenna base? I know the optimal amp position is at the antenna, just trying to justify (or avoid) a trip into the scary attic!
Thx, Brian
The cable loss from a 25 foot run of RG-6 is around 2.5dB. What that translates into for message rate and range is hard to say, but you can look at it like this: If the majority of aircraft you receive are fairly close and have a strong signal, then you most likely won’t see a big drop in message rate. ADS-B is a digital mode, so as long as the signal strength is sufficient for the receiver to discriminate the data, then it will still receive. Where you will lose out is on signals that are of marginal strength. The attenuation can make the difference between a discernible signal and it being lost in the noise. As the weaker signals are those at long range, those are the ones that you will lose - if the majority of aircraft you see are near the edge of your reception range, then it will have a correspondingly bigger effect.
It’s worth moving the amp, as the difference is not just loss due to the cable, you will also see an improvement in signal to noise ratio. When the amplifier is right next to the antenna, it gets the strongest possible signal to boost and send down the cable. If it’s at the receiver end, it’s making a worse signal louder. An analogy is the difference between someone using a megaphone to shout at you from across the road, and you holding the megaphone up to your ear and using it to listen to him shout. It should be clear which one will be more effective.
So, learning more and more after reading these post.
Antenna: Beer Can, Coaxial Cable, or Spider
Attach an AMP to the antenna and then connect as short as possible coaxial to the Dongle and your as good as you can get.
Sound about right?
What type of AMP is best/worst?
What type of Coaxial cable is best to make the antenna with and also which Coaxial cable is best to run the signal to the Dongle?
Does the diameter of the copper wire affect anything on the Spider? What about the diameter of the Copper wire on the Beer Can 69mm rod?
Best is probably the HAB amp from Nevis ava.upuaut.net/store/index.php?r … duct_id=85 because it also has a filter to remove other signals, but it’s not cheap.
Many use an amplifier that’s intended to go on a satellite dish downfeed (search on ebay for “dish amplifier”) since these cost a few dollars.
The amplifier is best positioned close to the antenna, and is powered by putting DC voltage onto the center core of the co-ax … this needs a power injector - they are simple but harder to find.
LMR400 (expensive), but most use good quality satellite downfeed like RG6 since it’s very affordable and fitting connectors is easy
Do some experiments - probably about 1 - 1.5 mm, most just use what they have available.
It is hard to say how much difference in reception it will make if amplifier is moved from receiver to antenna. It depends on how much noisy is the location.
In hypothetical case of zero noise, there is no difference between amplifier at antenna and at receiver. On the other hand, in very noisy locations, placing amplifier near receiver can have detrimental effect on reception. For moderate to low noise locations, the difference will be marginal.
To summarize, the only practical way is to move the amplifier to antenna and observe how much difference it made. If it is hard to move amplifier, leave it near Pi. Normally residences don’t have high EM noise, and both options of amp location work good. Also you are using Quad Shield Coax (RG6QS), which provides better shielding from noise compared to normal double shield coax.
But the amplifier is going to cause some noise itself. If the signal has already lost some strength (say 3db = 15m of RG6 = 50%) in the down lead then the amplifier noise will be twice as significant … and we’re dealing with weak signals to start with. If RG58 cable has been used that loss will be 10Db (only 13% gets down) - so even more important to amplify early.
All that said, I’d try to find a way to get the antenna outside somehow - but stay safe.
Bought a bunch of Directv power inserters.
Work great - in a nice package - and the price is right <$10 US.
I just thought I’d add something I (unsurprisingly) found out yesterday.
Coax cable quality matters, a lot.
I was mounting my 8 leg spider outside and used a long (10m I think) length of premade satellite coax with moulded ends and the performance was awful. No better than inside (using different cables). The coax in question had a centre core that didn’t look much thicker than a hair!
Unfortunately I hadn’t tested this before I had everything in place so I was pretty disappointed to find out after it was mounted that it was rubbish. Took it all down and I’ll try again this weekend with better coax. I did a quick test after all this with better coax and the improvement was huge, but it was getting dark so I gave up.
I then mounted the antenna in the attic using the existing Aerial cables because I have a wall point in the room with the RPi. Better signal than downstairs but nothing to write home about. The attic is fully insulated and there is now a longer length of cable between antenna and RPi so that’s probably not much of a surprise either.
I think I’ll first of all test this weekend with the RPi in the attic and a much shorter cable length, if I’m not too happy with that I’ll attempt an outside mount again with better cable.
I do have an inline satellite amplifier, I think I need to get that incorporated and build the injector.
I have one of these - amazon.co.uk/Triax-370650-Sa … B003XN3FO4 - is this suitable for the job?
It’s got knobs on!
It’ll o the job - but if it ends up outside it’ll be difficult to wrap in self amalgamating tape.
Cable quality is very important at these frequencies. If you are in the UK, then the best readily available decent coax is WF100 or PF100, which what is usually used for satellite installations now. It’s lower loss than RG-6, as it uses copper core and shield, whereas RG6 has a copper clad steel wire core and aluminium shield. It also has quite a lot lower DC resistance as a result. You can also get WF125, which is slightly lower loss than WF100, but is more expensive and not as common.
I’ll give it a go. I’ve ordered a DC injector for £4.52 and have a load of spare power supplies lying around.
I’ve got some RG6 and WF65 lying around (the WF65 only has aluminium braid unfortunately). Discovered the aerial cabling in the attic has copper braiding and looks like decent quality. Much rather it all outside though.
The DC Power inserter arrived within 24 hours of ordering. I’d definitely recommend this ebay seller - ebay.co.uk/itm/161044085914
Using a 12V 1Amp power supply, and a female 5 mm x 2.1 mm adapter
http://ks368272.kimsufi.com/fr24/dc-in-400-1.jpg http://ks368272.kimsufi.com/fr24/dc-in-400-2.jpg
Amplifier now in use and there’s a huge improvement.
I initially tested it at the receiver end to see if it was working and only got a marginal improvement - I think there’s about 10m of cable between antenna in the attic and the receiver so that’s not too much of a surprise.
Moved the amplifier to the antenna end with about 1m of cable between amplifier and antenna and the improvement was huge. Currently receiving around 2.5x more messages/second. Range has increased a bit but the density of planes inbetween is much higher.
MSG/S isn’t as high as my outdoor unamplified tests so I’ll definitely be sorting my outdoor antenna soon.
Is it much safer to use another Power Inserter as a DC block for outdoor use?
I also made (mostly) solder-free 4 Leg spider. Performance isn’t quite as good as the 8 Leg but it was much easier to make.
http://ks368272.kimsufi.com/fr24/4leg1-400-1.jpg http://ks368272.kimsufi.com/fr24/4leg1-400-2.jpg http://ks368272.kimsufi.com/fr24/4leg1-400-3.jpg
Testing the 4 Leg in the attic
Does the wire on the spider design have to be made in brass?
Looking at the old TV antenna they were all aluminum made so is or does the signal know the difference?
A DC blocker between the antenna and the amp … is only needed if the antenna forms a DC circuit between the core and shield of the coax
It is copper, but aluminium will work. Copper is known to be a better conductor though, and with it being the core of most coax and electrical cable it’s easier to get hold of.
I’ve also made a very cheap spider with a piece of coax and 4 paper clips, it works but nowhere near as good as the others.
Makes sense. I was wondering in case of an accidental short due to rain.
Two versions of Power Inserter & DC Blocker:
Image 1 - Using commercial components
Image 2 - Home Brew, using recycled TV Splitters, ceramic capacitor & axial inductor
Components for Home Brew Power Inserter & DC Blocker
From China on eBay
2-Way TV Splitter US $1.49 + free shipping
ebay.com/itm/280766417601
100 Pcs Ceramic Capacitor 470pf - US $1.28 + Free Shipping:
ebay.com/itm/110936235671
https://c1.staticflickr.com/1/317/18355608010_60214c947f_m.jpg
100 Pcs 22uH Axial Inductor - US $2.80 + US $0.35 Economy Int’l Shipping:
ebay.com/itm/390302126183
https://c1.staticflickr.com/9/8882/18357116339_4acaa626aa_m.jpg
Question. When making an antenna using the coaxial cable, the continuity between the segments alternates between them?
If you mean the coax collinear antenna, then yes the continutity goes core → braid → core → braid → core etc.
Thanks.
Well, yesterday I built: A coke Can Antenna, a 4 Legged Spider Antenna and a Coaxial Cable Antenna.
Ordered the Filter form mini circuits
Ordered an Perfect Vision inline amp
Ordered an inline power supply DIRECTV PI21R1-03 Power Inserter
Now I will be able to try all these antenna’s back to back or in different configurations.
Cost: (with shipping)
AMP: $10.69
Filter: $50.15
Power Inserter: $16.99
Purchase a few connectors for $8.00 and 100’ of RG6 + Cable for $23.00 and a 6’ piece of PVC pipe and some electrical tape.
So for $120.00 I can build and test to see what’s best, and of course I have the control as the chrome extended antenna that came with the dongle to compare things to.
