PilotAware
British Forum => General Discussion => Topic started by: PaulSS on April 05, 2017, 10:59:35 am
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Hello everyone,
I'm in the absolutely rubbish position of not owning any sort of PAW system, nor even an aircraft. However, I plan to remedy that situation and have been spending far too much time looking at goodies for my potential craft and asking far too many questions of long-suffering but patient people, such as the excellent support at MGL (sorry Paul). My plan would be to install a permanent PAW system and I have read all the the documents on the main site regarding that AND antenna location, so I'm not just going for the easy 'answer my questions' without having done some homework :)
My potential steed will be fabric covered (Stitts Polyfibre) and I'd really like to know if mounting one of the tuned low profile antennas in the tail would be a decent set up. Clearly it wouldn't have too much metal around it apart from the tube fuselage and I understand it would not be a good idea to actually mount the antenna to one of those (vertical) tubes. I THINK it would be acceptable for the ADSB antenna because of the incoming signal strength but it would be good to know about the P3I reception from back there. I suppose I am in the enviable stage of being able to think about 'extras' before the order is even in and may be able to plan ahead for a couple of ground plates to be mounted in the tail before it gets covered but, if possible, I'd rather keep things nice and protected inside the fabric......and fewer bits sticking out. So, has anyone done this in a fabric covered aircraft yet and can report on their findings?
The second absolutely trivial thing I was thinking about was reducing the number of GPS antennas I would (potentially) have. At the moment my plan is to run two MGL iEFIS units and both will have separate GPS antennas. If I permanent-mount the PAW then could I use a GPS output from one of those EFIS units instead of having a third antenna on top of the glareshield? I'll be using EFIS GPS position for input to the transponder for ADSB but even if I only run one GPS 'out' from each unit then the PAW can be fed the data. As I said, trivia and only a means to have two matchboxes instead of three on the glare shield.
I'll leave my meanderings there for now as I have so many thoughts about power supplies and filters for MGL EFIS that I would bore everyone to death and that's before I've even got a toy to play with.
Thank you for your thoughts and any information on these vital questions ;D
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Paul,
Immediate thought is that mounting the P3i antenna in the tail would probably mean a long co-ax run, which isn't a great idea when you are only playing with 500mW out and correspondingly weak received signals. Depends of course on where you will be putting your main PAW unit, but again, you don't want this too far away from your display tablet as the connection is via WiFi. Also with the 1090MHz antenna - although the transmitted signals are much stronger, you still don't want to hide the antenna behind metalwork if you can avoid doing so.
If planning from a 'blank sheet' the best option would be to mount your antennas on a suitable ground plane where they are reasonable close to the main PAW unit and have a good view forwards (things hit you much faster from that direction). In a fabric aircraft, you could mount them internally, though you will inevitably get some screening from the metal frame structure. Personally, I'd go for externally mounted antennas sited so as to have their best view forwards e.g. on the underside of the fuselage around the wing root area.
Re your second query, I have some experience of using external GPS (from FlarmMouse) to feed PAW, but have to say it was considerably less effective than PAW's own fitted GPS - which may work fine in a fabric covered aircraft without the need to use a remote GPS Mouse. The other potential issue you would have is that PAW may not be configured to accept the GPS data in the form your MGLs provide. Sorry I can't be more specific.
Hope this helps
Regards
Peter
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I was about to type much of the same comments as Pete, so he saved me some tablet taping :)
I will add that an antenna in a presumably wooden or glass fin, would not be accessible for maintenance? Though Europas have the VHF dipole in the fin/rudder gap.
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Immediate thought is that mounting the P3i antenna in the tail would probably mean a long co-ax run, which isn't a great idea when you are only playing with 500mW out and correspondingly weak received signals.
Hi All,
We have experimented with RG8X (Keith Vinning please correct me if I am wrong)
This has very low loss, something like 4.5db/100ft.
So the benefit of getting the antenna in the clear, far outweighs the loss in the coax.
We have had excellent results from this type, ensuring you get good quality connectors
and make a good job of crimping.
Thx
Lee
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Thanks, guys, for all your replies. I was just about to reply to Peter and Ian and thought I'd got it straight but now I've been thrown a tantalising morsel by Lee :)
My plan would be to mount the unit behind the panel both for ease of power supply and connecting to the EFIS units. I don't know if the PAW installed GPS would be effective from that position (glareshield above, bits of radio etc either side and the panel's metal and engine to the back and front) but that's not a huge deal; I was simply trying to get away from having another GPS antenna on top of the panel if I could. They're only tiny, so it's wouldn't affect the price of fish but it's my OCD playing up again.
The aircraft I am considering is the Eurofox (lovely looking little things) and I would imagine the antennas, if mounted inside the fabric, would be halfway down the fuselage (ish). I was quite happy to accept Peter's advice about the cable length but it would be good to find out if Lee's proposal may alleviate the problem. If not, then would the area beneath or just to the rear of the seats (below the baggage area) be the sort of place where you'd mount external antennas. I was looking at the tuned monopole whip in the shop. Would you use one of those for P3I and one for ADSB or would it just be one for P3I and the normal ADSB aerial could live inside?
If you think this level of questioning is bad, can you imagine what it will be like when I actually get an aircraft and my PAW kit :o
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Paul,
The under body mounting I suggested was based on Keith Vinning's Sportcruiser fit, which uses (I think) standard PAW 3 metre coax extensions to feed 1/4 wave monopole antennas and I know gave great results in testing (and continues to do so by all accounts). RG8X co-ax with good quality SMA connectors would be even better as it is (as per Lee's post) lower loss at PAW frequencies, though slightly heavier.
If you think this level of questioning is bad, can you imagine what it will be like when I actually get an aircraft and my PAW kit :o
No worries - if we can help we will do so. Lots of 'daft' questions answered so far - probably by equally daft answers. Just thought I'd say it before anyone else does - hopefully not so daft answers really ;) :)
Regards
Peter
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Well RG8X is about 11dB @ 800MHz / 100 feet, to get down to 4.5dB the frequency is more like 400MHz-450MHz (check the table in the link below). To get down to ~4dB / 100 feet you need something like 9913 or RG213 - all of which are really too big and a pain to terminate in a GA environment.
That said, keep the cable short and it should be OK. If you work out your cable run then you can roughly calculate the cable loss. Previously I've used nylon rope (to get a similar diameter to the cable) to physically work out an optional route - it's cheap and easier to handle. Note that you should not put really tight bends onto coax cable, for RG-8X Belden recommend a bend radius of no more than 2.5 inches (http://www.belden.com/techdatas/english/9258.pdf).
To get an approx loss based on the cable length...
((your length in feet) / 100 feet) * dbLoss per 100 feet
So if your installing 10 feet of cable, ((10/100) * 11dB) = 1.1dB which should be no problem at all with decent crimped connectors.
For coax and connectors, try and avoid cheap clone cable (read stupid cheap cable from China on eBay), you are really only going to get what you pay for.
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Thank you everyone for your help. I can see that I'll have a lot of figurin' to do once I get my craft but it'll be worth it :)
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I am not suggesting this company has the coax cable suitable for PAW use, but they do a range of coax cables and will make up coax cable assemblies at reasonable cost.
https://www.gigatronix.co.uk/cabulator/coaxial/cable-type
I used them to make up a low loss cable for my Trig TT21 transponder.
Excellent quality and quick turnaround.
Tony
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One thing about the antenna, for a 1/4 wave monopole you'll need a ground plane, but not for a dipole.
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So....just looking at the kit available in the shop: I could possibly have an 'endfeed dipole' mounted somehow (vertically) inside the fuselage using RG8X cable extension. Perhaps the 'tuned low profile antenna' mounted somehow (vertically) inside the fuselage with an RG8X cable extension or, option 3, the 'tuned monopole whip' mounted on an aluminium ground plane and poking through the fabric with the same extension cable. I thinks that's the gist of it or am I wrong, again?
Also, the ADSB antenna can just stay as it is, inside the fuselage, with the RG8X cable extension?
And there's me having dumped all that attenuation theory etc when I'd done the ATPL exams :-[
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Well RG8X is about 11dB @ 800MHz / 100 feet, to get down to 4.5dB the frequency is more like 400MHz-450MHz (check the table in the link below). To get down to ~4dB / 100 feet you need something like 9913 or RG213 - all of which are really too big and a pain to terminate in a GA environment.
That said, keep the cable short and it should be OK. If you work out your cable run then you can roughly calculate the cable loss. Previously I've used nylon rope (to get a similar diameter to the cable) to physically work out an optional route - it's cheap and easier to handle. Note that you should not put really tight bends onto coax cable, for RG-8X Belden recommend a bend radius of no more than 2.5 inches (http://www.belden.com/techdatas/english/9258.pdf).
To get an approx loss based on the cable length...
((your length in feet) / 100 feet) * dbLoss per 100 feet
So if your installing 10 feet of cable, ((10/100) * 11dB) = 1.1dB which should be no problem at all with decent crimped connectors.
For coax and connectors, try and avoid cheap clone cable (read stupid cheap cable from China on eBay), you are really only going to get what you pay for.
Hi Jeremy
Thanks as ever for sharing your expertise its really appreciated.
I have searched for something better than RG8x to no avail. As you say there is better stuff but one also has to consider that not only must the cable be easily available (RG8x is very available overnight from Rocket Radio on eBay) but also the SMA connectors. RG8x is a funny size (7mm OD I think) and I have to get the connectors from the states.
Interestingly enough I am still using the 3 metre extension cables available from pilotawarehardware.com which are less efficient than RG8x but still give a fantastic range on the sportscruiser. I am going to change the cables over to RG8x to see how much the range is improved but as it is over 40Kms air to air at the moment I guess its academic.
Interestingly I have been playing around with ground based antennas using a standard PilotAware dipole (This must be used to meet the PilotAware ETSi submission if transmitting). We have one located about 25-30ft above the ground at Wellesbourne with 10metres of RG8x cable between it and the PilotAware unit in the tower and we can see PilotAware users of unknown installations at over 50Km. We contacted one guy to check out if he had a special installation and it was just a standard unit on the coming of his Jabiru 400. So the RG8x can't be that bad.
PaulSS
Great choice the EuroFox. I wouldn't put it on the tail. Even though this is the best theoretical place to put it access will be a problem.
Speak to Roger at Eurofox he is very helpful. My initial thoughts would be to get the guys at the factory to put (possibly rivet) a ground plane across the chromo frame on the bottom rear of the seats where you can put the antennas. They may have other ideas as they need ground planes for radios and transponders and Eurofox are a very mature company.
This will be a good position as it is a compromise between length of CoAx and antenna location. Will you build a trike or a tail dragger? The main undercarriage struts are fibreglass I think so no problem there.
Anyway let us know how you get on great project. The Eurofox is a good choice.
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Thanks for your advice, Keith. I too think the Eurofox looks a great little aircraft and I hope to be ordering one soon when we visit the UK, from Oz, in June. No, it won't be going back there but we'll be coming back to the frozen north :)
My choice will include the little wheel at the back and your thoughts on the location of the external antenna are, I am pleased to say, in line with what I was thinking. I don't think that will affect the radio, as that's atop the fuselage towards the tail but I will be careful to ensure the transponder (on the underside of course) and the PAW antenna are separated. I'm too dim to work the minimum separation distance but I assume it would need to be > 1 wavelength and I shall attempt to work out what that is when I've finished typing. Of course, if anyone wants to chime in with the answer, then please do.....just so I can check my workings you understand :o
I'm just editing this to add: you mentioned antennas mounted to ground planes under the seats. Am I to take it that the ADSB antenna should also be external and would this use the same tuned monopole antenna as the P3I? I told you I was dim but I'm just wondering if those same aerials can be used given the differing frequencies between the P3I and ADSB. Now, what would the separation on those two be....and separating from the transponder aerial? I'm confused again :'( :'( :'(
I think I'd better give Roger a bit of a rest from my questions for the time being. Between him and Paul at MGL I don't know which one will strangle me first for interrupting their peace with another 'what if'.
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I have searched for something better than RG8x to no avail. As you say there is better stuff but one also has to consider that not only must the cable be easily available (RG8x is very available overnight from Rocket Radio on eBay) but also the SMA connectors. RG8x is a funny size (7mm OD I think) and I have to get the connectors from the states.
In that size of cable I think RG8X is pretty much as good as you are going to get. So much depends on noise in the system, receiver sensitivity, good connections, etc.
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Thanks Jeremy
Great to have a second opinion. I'll let you know how I get on.
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The calculation for wavelength is to take the speed of light and divide it by the frequency.
So 299 800 000 (m/s) / 868 000 000 (Hz) = 0.345 metres, or about 35cm.
However, it's not as simple as that as the transponder transmits at a very high power, so it would be advisable to put any antenna as far away as you can from the transponder antenna, otherwise any receiver using that antenna will be swamped by the transponder's transmission.
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Thanks, Paul, even though it has thrown another spanner in the (future) works :o
I was thinking the external antenna(s) could be mounted basically under the seats, in a suitable place for the ground plane. However, I have just managed to find out the transponder antenna is mounted about in line with the wing strut attachment and slightly offset to the right side of the aircraft. Given your thoughts above, I think that might be a bit close to the PAW antenna(s). I might have to see if they can be mounted on top of the fuselage, behind the turtledeck (because that gets removed). Unless you have a better idea of course......... :D
You'll notice that I keep writing antenna(s) and that's because I still haven't really established if I need to mount the P3I AND the ADSB antennas externally or just the P3I. I'm thinking that I might be able to get away with the P3I antenna external and the ADSB antenna that comes with the PAW kit inside the rear fuselage (fabric). Any thoughts on this?
Thank you again for your expertise and I'm pleased to say that I came up with the same sort of distances between antennas but I'd used the 1090 of the transponder so had a shorter distance. Of course I should have used the lower frequency of the separation would be too little. Can I just confirm that the minimum spacing, assuming they are just receiving, would be 1 wavelength or wouldn't it matter?
My head just exploded ???
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Paul,
Are you aware that you can cut the 1090MHz (ADSB) antenna down to about half its length without any detrimental effect? In fact at that length it is 'tuned' to 1090MHz and virtually disappears on top of the coaming, with great forward view apart from downwards, though this is not normally an issue.
Regards
Peter
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Hi Peter,
Yes, I had read that in another part of the forum but as I'm considering a permanent installation and designing that from scratch this would offer me the opportunity to not have to 'Heath Robinson' it and have things on coamings etc. That's the reasonable part of the argument, then there's my OCD which has already been seen with not really wanting even a GPS matchbox on top if it :-) My absolute ideal would be to have all antennas inside the fabric fuselage but I totally understand the reasons put forth here for not doing so and that's why I'm trying to seek the Nirvana of external antennas.....for however many I don't actually know :o
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I would have thought that using a cut down to a quarter wave with a ground plane inside the fuselage would be ok for the ADS-B antenna, but you'd have to try it. Alternatively you could buy/make a 1090 MHz dipole so you wouldn't need the ground plane. Easy enough to make.
As for the P3i antenna, well, it might be a case of wait and see where you think may be the best place by actually looking at various locations, both internal and external.
As for receive antennas and spacing, still not quite that simple, you can have them closer than 1 wavelength, but there will be a certain interaction in the radiation (reception) pattern putting any sort of antenna anywhere near anything metal, which includes another antenna.
On my PAW, I've got my two antennas separated by approximately the length of the Raspberry Pi and ADS-B dongle. Seems to work ok.
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Thank you for all the replies and advice. I think I'm probably getting too far ahead of myself and will have to wait, see and experiment, as suggested by Paul. Having said all that, the posts on here have been invaluable in increasing my knowledge of the radio wave theory and what can and probably can't be done, so no time wasted :)
Sounds like an external P3I tuned monopole on a ground plane and maybe a cut down ADSB antenna in the fuselage might, possibly, maybe the way to go.
Cheers ;D
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For the P3i I would always go for a dipole where possible. A monopole is not able to see much behind the ground-plane. A belly-mounted monopole on a ground-plane will less able, or not able to see traffic that is above the host aircraft. Locations for dipoles are tricky as well due to the aircraft structure. I would locate it so that it gets the best view of where you threats are coming from. End fed dipole(as supplied with Classic PAW) below the aircraft would be a good starting point.
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Good stuff, Ian :) So option 316 could be an end-fed dipole mounted in the fuselage or externally and the ADSB antenna cut down and inside the fuselage (fabric). With coax as short as possible of course and dipole away from aircraft structure.
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Here's some photos of my PAW installation that I've recently completed in my Flexwing Microlight (Pegasus Quantum).
There's not a massive amount of spare space inside the cockpit and I didn't really want to start making holes in the pod unless I absolutely had to, so I started off with installing PAW underneath the base tube, and to my great surprise it works absolutely fine.
I was a bit worried that the GPS would need to be in the front of the pod to get a clear view of the sky, but where it is it sees 7 satellites quite happily and works fine.
I did move around which was plugged into which USB socket, but that was only so I could see the GPS light when sitting in the pod, and also had access to plug a USB stick in for upgrades.
The ADSB small antennae cable was shortened by prising the bottom off the antennae and stripping back the cable length. I soldered the outer braid to the bottom tab of the antennae base (previously it was just resting on the base), and reduced the antennae height as advised on this forum. Finally Velcro'd the ADSB antennae to the top of the base tube, again works fine, picking up planes from 50+ km away.
For the P3I I decided to cable tie it vertically to the lower section of the front strut. Although this is therefore behind the fibreglass of the pod I figured this was least worst option and is clear of engine, me, etc.
Only thing I have had any difficulty with is the power supply. Originally tried a car USB plug but loads of noise through the headset. Then tried an Anker twin USB converter and that worked fine but when I connected PAW audio into my Microavionics unit I was getting feedback that varied with engine power. No audio and it was fine but I wanted the audio.
So today I tried my son's Power Bank (model #B30224) and this works perfect. No feedback and I can hear PAW audio all the time.
Geoffrey
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Geoffrey,
Great Pics and thanks for posting. This is very similar to the installation I did on our CFI's trike, except that I put it on top of the base tube where the battery used to be (long story). The main unit is velcroed and cable tied in place with the P3i antenna mounted upright in its normal place (no coax loss) and the shortened 1090MHz antenna with significantly shortened coax (same as you did) sitting on top of the PAW on a piece of double sided tape. Seems to work great, with no problems so far. This is very similar to what I do as a 'demo' kit which can be slipped down inside the windshield and run off a small battery pack to let people try PAW out for themselves.
Remarkable how well it works with a bit of ingenuity.
p.s. Re your interference through the audio lead when connected to aircraft power, it would be worth trying a ground loop isolator such as: -
https://www.amazon.co.uk/gp/product/B01LYYRT7M/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1 ,or
https://www.amazon.co.uk/gp/product/B01IETQQQK/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
...in line with the audio lead. Several PAW users have used one of these (or similar) successfully to cure this problem.
Regards
Peter
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You've got the P3i antenna right up against a metal pole. You really want it out on its own away from any metal.
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You've got the P3i antenna right up against a metal pole. You really want it out on its own away from any metal.
Haha, I spotted that, so I'm learning. It's not true what they say about old dogs.
Another thing I thought of; is it possible to use one of those splitter boxes and share the transponder aerial, on an aircraft equipped with one, for the ADSB input to PAW? I believe the frequencies are the same so was wondering about doing away with duplication of antennas.
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You've got the P3i antenna right up against a metal pole. You really want it out on its own away from any metal.
Hi Paul
Yes I did think about this. Following the advice that the P3I should be vertical, the alternative would have been to Velcro/sticky pad it to the inside of the pod, but that would have been less secure and I thought I'd first see whether it worked first on the front strut, which it did.
My fuse box is on the top of the base bar otherwise I'd have probably gone for something like Peter did. I pass on my experience as being one implementation that is working OK for me, ultimately there's going to be some compromises in fitting the antenna as far as possible clear of metal, engine, pilot and any other obstructions.
Cheers, Geoffrey
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You've got the P3i antenna right up against a metal pole. You really want it out on its own away from any metal.
Another thing I thought of; is it possible to use one of those splitter boxes and share the transponder aerial, on an aircraft equipped with one, for the ADSB input to PAW? I believe the frequencies are the same so was wondering about doing away with duplication of antennas.
PaulSS,
DEFINITELY NOT I'm afraid. Splitters are OK in certain circumstances - such as for 'stacking' antenna arrays to achieve higher directional gain (I've used them for this in other fields), but in this case, even with a well designed splitter, you would run the very high risk of squirting the high power output from your transponder straight into your PAW with disastrous consequences - probably to both!! You need to do exactly the opposite - i.e. provide as much separation as is reasonably practical to prevent the high power transponder/ADSB signal from effectively shouting in PAW's ear and deafening it.
Regards
Peter
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You've got the P3i antenna right up against a metal pole. You really want it out on its own away from any metal.
Hi Paul
Yes I did think about this. Following the advice that the P3I should be vertical, the alternative would have been to Velcro/sticky pad it to the inside of the pod, but that would have been less secure and I thought I'd first see whether it worked first on the front strut, which it did.
My fuse box is on the top of the base bar otherwise I'd have probably gone for something like Peter did. I pass on my experience as being one implementation that is working OK for me, ultimately there's going to be some compromises in fitting the antenna as far as possible clear of metal, engine, pilot and any other obstructions.
Cheers, Geoffrey
Geoffrey,
Try 'hanging' the antenna 'upside down' by attaching it to the plastic pitot pipe to the left of its present location with a cable tie (doesn't need to be pulled too tight). That will move it far enough away from the front strut to be effectively 'out in the clear' and will give much less screening to the right. The antenna will work fine upside down and that location should not cause any problems this far forward in the pod.
Regards
Peter
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Try 'hanging' the antenna 'upside down' by attaching it to the plastic pitot pipe to the left of its present location with a cable tie (doesn't need to be pulled too tight). That will move it far enough away from the front strut to be effectively 'out in the clear' and will give much less screening to the right. The antenna will work fine upside down and that location should not cause any problems this far forward in the pod.
Thanks for the idea Peter, I will try that.
I'm having to move the Aware slightly further backward as I've spent today fitting a Trig transponder to my flexwing and ended up with the Trig control box mounted under the base tube exactly where the Aware was. Unfortunately the lead on the ADSB antenna that I shortened may now be too short and I'll have to buy a new one - grr.
Geoffrey
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http://www.ebay.co.uk/itm/5dBi-5-dbi-Digital-Freeview-DVB-T-TV-HDTV-Booster-Portable-Digital-Antenna-Aeria/272109699956 (http://www.ebay.co.uk/itm/5dBi-5-dbi-Digital-Freeview-DVB-T-TV-HDTV-Booster-Portable-Digital-Antenna-Aeria/272109699956)
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Try 'hanging' the antenna 'upside down' by attaching it to the plastic pitot pipe to the left of its present location with a cable tie (doesn't need to be pulled too tight). That will move it far enough away from the front strut to be effectively 'out in the clear' and will give much less screening to the right. The antenna will work fine upside down and that location should not cause any problems this far forward in the pod.
I followed your suggestion and hung the P3I antenna off the pitot pipe. I didn't need a cable tie, just looped the cable over the pitot pipe, but found that the antenna hung down and was going to collide with the front forks. So I affixed a sticky pad to the inside of the pod and cable tied the bottom end of the antenna to that pad.
See attached photo.
I could see another PAW equipped plane 4Km away, and they could pickup my PAW signal as well, so its working in this position, but they did appear and disappear a couple of times as they flew away from me (their PAW is in a Skyranger on the dashboard) so maybe something is sub-optimal as I'd have expected more than 4Km range?
Geoffrey
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The crew in the other aircraft may well have their bodies attentuate the signal as they flew away from you, given that they or at least their upper torso and heads would then have been between the dash-mounted PAW and your receiving antenna?
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The crew in the other aircraft may well have their bodies attentuate the signal as they flew away from you, given that they or at least their upper torso and heads would then have been between the dash-mounted PAW and your receiving antenna?
Yes fair comment, that could have been a factor. I was interested in what others experience of range on the P3I is. Seem to recall it is up to 30km straight line of sight, reduced as you say by obstructions.
Geoffrey
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I have seen so few P3i in flight, so difficult to judge what is the norm with my installation. With the antenna mounted internally on the rear cockpit bulkhead of a PA17 (fabric) I have bee seeing 20km, occasionally more. Worst case would be head on, but I don't recall any contacts in that direction.
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I have a fabric aircraft question related to mounting the antennas inside the fabric skin.
What is the screening capability of such fabric(s)?
I am mainly considering how the low power of the P3I transmissions, and the miniscule signal strength of the GPS signals cope with Ceconite (and similar) fabric. Such coverings are applied and then UV protected by the application of the silver (aluminium powder mixed in the dope) coats that render the fabric completely opaque: NO light gets through properly applied Ceconite AT ALL.
I would guess that would definitely screen GPS transmissions, and could conceivably attenuate P3I transmissions.
I am sure that it has been mentioned before that certain (domestic and industrial) window coatings are metallic and quite effectively screen low power transmissions. This makes me wonder what methods the newer fabric coverings (Poly Fibre, Oratex etc) use for UV protection and how opaque to radio signals they are.
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Rob,
My only personal experience with fabric covered aircraft and PAW has been with SkyRangers and similar, where I have noticed no negative effects attributable to the fabric. I would be interested to hear from other users though. Do you know which aircraft types use Ceconite coatings?
Regards
Peter
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Do you know which aircraft types use Ceconite coatings?
AFAIK pretty well every older fabric covered type you can think of that isn't still using linen!
Evans VP1s (had one), Piper Cubs (and variants), Luscombes (where they have fabric wings), Stolp Starduster (I'm restoring one) and associated Acrodusters, Acrosports etc, Pitts Specials, Taylor Titch & Mono etc, Druine Turbulent, Steen Skybolt, Jodels, Austers, Aviat Husky...
To name very few...
Ceconite is a DuPont trade name (I think - my partner in restoration crime does the fabric work). There are other , similar heat and/or dope shrunk coverings (including linen) but pretty well all of then use an aluminium powder in dope coating as UV protection for the fabric.
Ever wondered why airships and many WW1 era aircraft were silver?
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I would suggest trying it and reporting back! :D
As for windows, yes, the Pilkington K type glass seems to shield GPS signals quite well. When we were doing some 3G trials for a mobile operator, their office windows were coated in something metallic, and we had to open all the windows to let a mobile signal in, despite the base station being sited in their grounds with antennas pointed directly towards the building! ;D
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The tests we've done recently on modern glass-fronted buildings suggest that the glass provides 30-40dB of isolation across a wide frequency band, certainly above 400MHz. 30dB means that only 0.1% of the signal gets through - 40sB means 0.01%.
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That's pretty serious attenuation Mike!
It will be interesting to get some feedback from users of PAW in fabric covered aircraft. I must admit I wasn't aware of 'Ceconite' and had assumed fabric coverings to be low to no attenuation at the frequencies we are using (excepting the screening effect of metal tubing framework of course).
All feedback gratefully received.
Regards
Peter
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It's something I have been wondering about for a few weeks now, but uncertain of how to test scientifically. I fly a Ceconite covered rag and steel tube aircraft, but also restoring a Wooden aircraft with a lot of ply skins covered in Ceconite. I was looking to mount as many antennae in that aircraft out of sight.
I could get hold of a section of fabric that has been removed but lack a Field Strength Meter, so any test would be subjective. Could T67M run tests against a supplied fabric panel?
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Glass itself has a low attenuation, around 1dB at 10GHz, depending on thickness. Adding the IR shielding metal film makes it a lot worse!
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I am no expert, but wouldn't the tiny particles of silver (something) in the Randolph dope be non-conductive? Or, if conductive, at least not touching adjacent "silver" particles to create a an overall screening effect?
Or, to put it another way, I wouldn't have thought the Randolph silver dope would act like a thin sheet of aluminium foil under the topcoat.
Perhaps someone can try measuring the resistance of the applied silver dope?
I may be able to do this in a month or so's time when I get to that stage of my fuselage recover project. Yes, I am using the traditional Ceconite process.
Tony
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Perhaps Randolph or LAS Aerospace could advise on the paint's electrical screening properties. AIUI the silver dope is applied for its UV protection of the fabric.
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I've put ADS-B and GPS Antennae within the wing interior fixed by Velcro. It's standard pre-war wooden ribs and spar with Ceconite covering works fine.
My PAW Aerial is a PUC Type fixed above the Parasol Wing in centre and biased towards front of Aircraft.
All works well.
Gerry
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I was relating the results from a test conducted as part of a building project I'm working on. Sadly I don't have direct access to the necessary test equipment to measure an aircraft, however I too would be surprised if doped fabric presented much attenuation even with the silver.
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:-[
Seems I may have created a monster here!
I have the Starduster fuselage all covered, silvered and painted (lairy yellow - lovely) in my garage. Unfortunately getting it out is going to require removal of the undercarriage - not difficult, but not quick either - so testing the hypothesis in the open air is not really an option.
My PAW is now installed behind the dash of the RV, so extracting that is non-trivial too!
But...
I will dig out my old Garmin GPS III Pilot and use that for a bit of GPS testing, assuming I can actually get a GPS fix in the garage in the first place.
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Thanks Rob,
It will be useful to hear your results.
Regards
Peter
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I will dig out my old Garmin GPS III Pilot and use that for a bit of GPS testing, assuming I can actually get a GPS fix in the garage in the first place.
Well it appears to make little difference.
Looks like I have been wasting everyones time on this. ::)
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Noooo, not wasting time...more like getting us all guessing the outcome! Should have had a poll... ;D
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Thanks Rob,
Certainly NOT a waste of time - now we all know the answer for sure, but I have to say - definitely a relief!
We can continue to advise users with some sense of 'authority'. I must admit you did have me worried for a while. :-[ :)
Regards
Peter
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1. Can anyone tell me please, the optimum length to shorten the antenna and how to measure the length exactly?
2. Has anyone tried different antenna positions in an RV? and which positions are best?
Thanks
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Hi,
I assume you are talking about the 'thinner' 1090MHz antenna? There is a long thread about this here... http://forum.pilotaware.com/index.php/topic,438.msg5661.html#msg5661
As signals on this frequency are from strong powerful sources (compared to PAW P3i), and this antenna is 'receive only', the final length is far from critical. The length advised is about 65mm, measured from the coax attachment point inside the antenna base. For practical purposes, prise the black cap off the top of the whip then cut the whip part in half and glue the top back on. This will be close enough. It's easiest to cut it with a good pair of side cutters, but watch your eyes when the cut bit flies off. DON'T be tempted to cut it too short as this could have a detrimental effect on the Mode C/S Alerts.
Unless you are going for external antennas, the coaming is always a good location, but some of our RV users may have other suggestions.
Regards
Peter
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Thanks. That's a great help.