MORE ADSB Antenna Stuff

[Ian Melville]

Paul, you can get some darn long USB leads. I use 20 and 20 metre leads in my job.

End fed dipole clamped to farme with no ground plane should be OK, provided the clamp holds it half wavelength,  give or take  a bit, away from any metal tubes.

OGN-R stations use a long(10m) USB lead. With the ADSB dongle mounted on the mast. Just a short coax clear to the antenna. This is for Weak FLARM  and P3i signals. They are attenuated in the coax, but once digitalised, within reason can be set down any length of USB cable without loss. For ADSB I would prefer to make sure the dongle is accessible, but need not be directly connected to the PAW.

[PaulSS]

Well, that's very interesting, so thank you Ian.

I was actually going to attach the clamp to one of the metal tubes of the fuselage, so that kind of scuppers the idea of an end-fed dipole. Back to Plan A with the fancy ADSB antenna and a ground plane I suppose.

I think it is very interesting to know about the difference in attenuation between the two cables and it certainly seems to favour the long USB cable. I can understand the need to have access to the ADSB dongle but it sounds from what you have written that having the signal digitised close to the antenna (by the dongle) and then using a high speed USB 3.0 cable would lead to a stronger signal into the PAW than if it travelled by coax and was then digitised closer to the PAW. One of the things that attracts me to this idea is the shielding on the USB appears to be less susceptible to interference from electric cables etc than coax. I will be trying my very best to ensure any coax cables (radio, transponder, P3I and PAW's ADSB) stay as far away from electrics as I can but this seems to be a neat way of managing the ADSB better.

[Keithvinning]

And then I read of a USB extension cable being used betwixt the PAW and an ADSB dongle and I thunk a bit more    I have a Flight Aware ADSB dongle. At one end is the USB connector for the PAW and at the other is an SMA connector to the antenna. Does anyone know how a USB extension cable and a coax cable compare, since I thought of a couple of scenarios? In one scenario the ADSB dongle would plug into the PAW and the coax cable would then lead to the back of the aircraft and the antenna. In the second scenario, imagine a very short coax from the antenna to the ADSB dongle, which is now mounted close-by the antenna. From the dongle, instead of a coax running to the PAW (which is behind the panel), a long USB cable would be used.....I really should see if such a beast exists before I postulate further...... In my imagined scenarios, let's compare a 3m USB cable with a 3m coax cable, of the sort available in the PAW shop (which I just so happen to have). What have I got wrong this time 

Paul

Yes this can be done. This is in fact how we do some of the OGN installations when we have a long run and don't have thick CoAx. Using a short length of CoAx minimises attenuation and once the signal is digitised it can be regenerated. We use 10 Metres of USB extension cable to good effect.

However does the distance on your Eurofox justify this? Why not go the whole way and put the Pi in the back as well then you will can have 1 foot of CoAx and no attenuation problems. The 1090 MHz transmissions are very high and will basically be picked up by the proverbial piece of wet string (50ohms of course)

[PaulSS]

Why not go the whole way and put the Pi in the back as well then you will can have 1 foot of CoAx and no attenuation problems

HMMmmm, now you've got me thinking    This is why I shouldn't read this forum or engage in correspondence; every timeI think I've got stuff sorted out in my head, someone comes up with another good idea.

[Ian Melville]

How are you going to ensure you have 5.0-5.1v at the Pi?

KISS

[PaulSS]

I was thinking of something like the cable below from my Charge4 unit. I am definitely a KISS believer but just examining the different options. If there's a good reason, such as the charge cables being no good due the length, then I'm more than happy to bin an idea.

https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B

[JCurtis]

I was thinking of something like the cable below from my Charge4 unit. I am definitely a KISS believer but just examining the different options. If there's a good reason, such as the charge cables being no good due the length, then I'm more than happy to bin an idea.

https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B

You don't really want to go over 1m of cable for the power to the PAW, even with a 20AWG cable.  At 10 feet in theory the voltage would be down to 4.8 excluding connector losses (which are more than you would think).  Charge2 & Charge4 are set to provide a nominal 5.25v, regardless of load, so it would be a bit touch and go IMHO. 

That said I have made up some cables with much larger power conductors for testing - so there is potential to make something suitable if all else fails....

[PaulSS]

You don't really want to go over 1m of cable for the power to the PAW, even with a 20AWG cable.

Thank you very much, that has put that idea to bed    As I said; I'm more than happy to take the advice of those in the know and I'm not even going to think about questioning your credentials.

Plan 267: PAW is back behind the panel, with WIFI dongle. Charge4 is also under the panel and probably no more than 30cm from the PAW (maybe less). GPS mousey thing is on top of the coaming. Fancy ADSB antenna is on its ground plane in the boot. P3I antenna sticks out under the aircraft on its own ground plane and almost certainly the ADSB dongle will be behind the panel and plugged directly into the PAW....... but the long USB lead and the ADSB dongle near the fancy antenna does still intrigue me 

Okay, enough, I'll shut up now........but for how long

[JCurtis]

I'd just run a long coax to the ADSB dongle, the loss will not be a problem given the power of the transmissions.  That keeps all the active stuff in one place, if needed you could use a short USB extension lead for ADSB dongle and strap it to something for better cooling and separation from the WiFi dongle etc.  That may actually help and make the cable routing easier, you can strap the coax, dongle, and usb to something as a unit to prevent issues with any minimum bend radius of the coax etc. and give better strain relief on the connections too.

Its the PAW coax you should try and keep short with good strain relief and ensuring it isn't kinked or bent below it's minimum radius (during or after install), they are the lowest power transmissions so the most care is needed there.

[PaulSS]

Good advice and thanks for the short USB cable idea for the ADSB dongle. I agree that would be an elegant way of keeping the temperatures a bit lower around the PAW and making it more flexible in its location (plus less susceptible to wriggling out of the USB slot). All ideas are in the idea box 

[Paul_Sengupta]

You could screw one of these:



Directly onto one of these:



Use the USB extension, then use some sort of clamp to mount the SDR thing in the right place, leaving the antenna free above it.

Just a thought.

[PaulSS]

STOP IT!!!  Now you've got me thinking again 

Edited as it did get me wondering:

Ian advised before:

End fed dipole clamped to farme with no ground plane should be OK, provided the clamp holds it half wavelength,  give or take  a bit, away from any metal tubes.

If one of the end fed dipoles above was attached directly to the ADSB dongle, would it still need to be kept half a wavelength (14cm ish) from any metal tubes? I think it would but I'd just like confirmation. I see now why people like wood frames :-)

[exfirepro]

Paul,

It would be fine if you fix (cable tie) the dongle to a horizontal tube, so that the antenna is proud of the tube and vertical.

Regards

Peter

[PaulSS]

That sounds good to me and kind of what I was thinking until I read Lee's advice. I was then thinking of having the antenna sticking out on a prong away from the frame to satisfy the separation requirements, but if I could clamp an aluminium 'L' bracket to the frame and then mount the dongle/antenna combo onto that it would be great. Obviously the antenna would be vertical.

I really do need my machine so I stop just talking about this and get on with it!