Messages

1

General Discussion / Re: Tuning the DVB Antenna for 1090MHz Specific reception

« on: February 19, 2018, 11:24:21 pm »

Yes Paul, that would most likely be my strip, aligned 31/ 13 and right next to the highway. There are two other strips in Powranna, one on Powranna Road but aligned more east/west and an old one on Symmons Plains property just to my north and on the other side of the highway, behind the motor racetrack. The latter is aligned 32/14, which shares my advantage of nicely suiting our prevailing north westerly winds. It is used very occasionally though, except for model aircraft that are flown there most Sunday mornings.

The local crop dusting company likes to use our strip when dropping fertiliser granules etc on the neighbouring croplands. We had a Thrush operating off the strip a month ago. Nothing like the sound of a 800shp turbo running up in your own front yard!

The only things to watch out for here are the A.C. Mains (3 phase) feedlines that run to the house from the pole across the highway on the southern approach and the what might be politely termed "close proximity" of Class D airspace for Launceston ( and for the non-Australian resident readers, we are not talking of the one in Cornwall). Luckily, the Launceston Airport isn't what you could really consider as busy.

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General Discussion / Re: Tuning the DVB Antenna for 1090MHz Specific reception

« on: February 18, 2018, 10:13:54 pm »

G'day Peter

I still monitor the Pilot Aware scene, even though I can't use it here in Oz. Speaking of which, I would not have been confused about your heading up to Perth in Scotland, rather than Perth in Western Australia. I might though have been confused in to thinking that you were maybe heading  to Perth in Tasmania, which is older settlement that that young upstart village over in the west. In that case, since it is only 11 kms up the highway from here, I would have invited you to drop in for coffee and even invited you to use my strip

That said, you would probably have written that you were heading down to Perth, given our inverse orientation.

Cheers
Bill

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General Discussion / Re: Tuning the DVB Antenna for 1090MHz Specific reception

« on: February 18, 2018, 05:22:48 am »

In theory a  half-wave antenna would be a better performer for more distant signals, given its radiation pattern, although that is more important for transmitting than receiving and given the strength of ADSB signals, the difference would probably be negligible.

Half-wave antennas also less reliant on ground, although we shouldn't go as far as to declare them to be ground independent, as some manufacturers claim.

One other significant difference though is the feedpoint impedance. The quarter wave is a relatively low impedance feedpoint device, hence our ability to fed it happily through 50 ohm coax cable. Not so the half-wave. It is a high impedance feedpoint device and should really be connected to the coax via an impedance matching circuit, such as a parallel combination of a coil and a capacitor, tuned to the frequency of operation. That tuned circuit, often called a tank, has a low impedance at the bottom of the pair but a high impedance at its top. That characteristic of a parallel tuned circuit makes it easy to connect the antenna to the top and the 50 ohm coax to the bottom.

in terms of tuning the antenna to resonance, 4mm at 1090MHz is a significant difference in length.

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Technical Support / Re: Noise from speaker

« on: December 27, 2017, 10:48:10 pm »

I have "pondered" along similar lines on and off for a few years now. A unity gain summing amplifier readily gives the ability to plug any number of inputs into such a box and allows them to be fed to the intercom. The difficult bit is adding the ability to assign priorities amongst them, including giving the comms radio the highest priority, presumably? Seems a good task for a microcontroller I suspect.

Bill

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General Discussion / Re: Antenna Location & GPS Input

« on: April 21, 2017, 12:02:01 am »

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?

6

Technical Support / Re: Constant click noise coming from PA

« on: April 05, 2017, 01:42:48 am »

or is it that you fitted the isolator and that fixed a ground loop problem? 

7

General Discussion / Re: £50 Flarm receiver????

« on: March 24, 2017, 11:51:54 pm »

Hmm, I became a little excited for a moment but on checking the frequency ranges in the data sheet for the Nordic radio transceiver OpenFLARM has selected, it seems that it too will be essentially European-centric. Still, interesting to watch progress.

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General Discussion / Re: Tuned Low Profile Antenna - Alternative

« on: March 18, 2017, 09:03:01 pm »

and just to round out the replies, the 433 MHz antenna would actually be too long, rather than being too short.

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General Discussion / Re: PAW in Australia?

« on: November 18, 2016, 09:40:37 pm »

I am bumping this thread again, as its content is still current as far as I am aware and there may be new potential users in Australia and other non-European countries contemplating purchase.

10

Technical Support / Re: Installation

« on: August 12, 2016, 12:51:53 am »

I can't recall my own research at the moment but do you have the 868 MHz ISM licence-free frequency available to you in South Africa? Most of the world outside Europe, including Australia, Canada and the USA does not. We all need a 921MHz version.

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General Discussion / Re: PAW in Australia?

« on: June 12, 2016, 12:35:31 am »

Bump - as I'm sure other Australian readers will have been attracted by the marked increase in traffic since the PAW Classic was announced.

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General Discussion / Re: PAW in Australia?

« on: May 17, 2016, 09:34:47 am »

Thanks Jeremy, that does sound encouraging.

I certainly have yet to find anything to indicate that FHSS has been made mandatory in Australia, although I can see nothing ion the prescribed performance specifications that would preclude its use, within narrow frequency limits.

Bill

13

General Discussion / Re: PAW in Australia?

« on: May 17, 2016, 12:22:22 am »

Having discovered that FLARM in Australia uses 921 MHz, can somebody tell me what frequency FLARM uses in the UK? Just trying to widen my knowledge of such things.

Thanks
Bill

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General Discussion / Re: PAW in Australia?

« on: May 16, 2016, 01:02:55 pm »

Hi Lee

Thanks for that input. FHSS on the ISM band, eh? I'll keep digging.

Bill

15

General Discussion / Re: PAW in Australia?

« on: May 16, 2016, 05:33:46 am »

Probably poor form to respond to your own posts but I'll do so here to record the findings of my search of various international ISM licence-free allocations, outside Europe.

Fortunately, it appears that most countries follow a common allocation pattern within their respective ITU region. Hence, USA and Canada have their ISM bands between 902 MHz and 928 MHz. Most of Asia follows that allocation too, which is probably not surprising since so much of the RF devices servicing the ISM market are made in Asia. While my internet searches have yet to conclusively establish this, it does appear that South Africa also has the full 902-928MHz allocation.

Australia and New Zealand, on the other hand, have smaller allocations, although again in the 900 MHz band. Australia's is 918-926 MHz, while New Zealand's allocation is from 921-929 MHz.

Charting all those allocations reveals a common segment between 921-926 MHz, suggesting that a PAW bridge within that range would potentially cover most of the world outside Europe.

Fortunately, I haven't found significant departures within the permitted device specifications for any of these allocations in terms of power output and EIRP.

Bill