Discone dilema

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Re: Discone dilema

Postby StandingWave » Tue May 07, 2019 11:43 pm

Sorry about the drift from discones. That was my original issue, but the topic of band specific DIY antennas was did come about as a result of that discussion as a possible option for me to consider. I can start another thread if required.

I got the antenna in an upstairs window, still connected by a short RG58 coax to the dongle which is plugged into the Pi, which is also in the upstairs room. I am connecting to the Pi over WiFi. I now get a radius of about 60 miles, so a bit of improvement, but perhaps not as dramatic as hoped! I think I might have measured the length of the vertical element slightly incorrectly. The length from tip of antenna to insulator is exactly 69mm, however, the insulator on my chassis mount BNC socket protrudes by a mm or so from the metal barrel. In the photo, the insulator on the SO239 looks flush with the top of the barrel. If measurement should be from the tip of the antenna to the metal rim of the barrel, then my antenna is just a tad over 70mm long in relation to the metal plane. I am imagining that at these frequencies that 1mm or so is likely to be quite critical? Will it help to file it down a bit more?

At some point I will also go ahead and make a DIY an airband antenna (possibly two). This will at least allow me to test what air traffic I can receive with an antenna located in the loft without going to the expense of purchasing a discone. If I make two, then I could use one to decode ACARS on the 131MHz band. The co-ax would have been required either way required anyway so that cost cannot be avoided, but I will add Webro WF100 coax to the possible list of options.
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Re: Discone dilema

Postby radiostationx » Wed May 08, 2019 6:28 am

The cantenna works best with a bit of amplification shoved up there.
The can antenna is very good for close in stuff due to low angle of radiation, the coaxial co-linear or coco is good for range but not so good close in.
Cocos are notoriously frustrating to get right, simple theory but cutting has to be absolutely spot on.
I got good results with a 4 element and a 3 and a half element
there is no better for range than a coco when you get it right they are great but getting there can be testing.

Cantenna is best all rounder

On the fightaware and planefinder forums we all contributed to a project that is a single sd card image for the pi/linux which includes all the data feeder software for fr24,planefinder etc there are built in station performace graphs and webserver.

There are 2 flavours, standard dump1090 mutability and dump1090-fa (piaware cersion of dump1090), you can find more info here


and the sd card images are here

https://github.com/jprochazka/adsb-rece ... tag/v2.6.3
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Re: Discone dilema

Postby StandingWave » Mon May 13, 2019 6:02 pm

Chris P wrote:I would suggest you try a home made Bowtie they are very popular with airband listeners and are fairly wide band covering both mil and civil airbands . I have lost the link for my original post on how to construct one but apart from the cost of the feeder coax can be constructed for virtually zilch. basically they are made from two 800mm lengths of copper wire ( I use stripped 2.5mm T&E mains cable )each being bent into a V shape with the open end of the V being 340mm wide . The coax feed( screen to one and centre wire to the other ) is connected to the point of the V which is then supported in the vertical plane either fixed to a sheet of insulated board or just hung from the rafters.

Chris, I built one of those today just using a bit of mains flex, a connector block as shown in your photo and fixing the wires to some cardboard. It is just hanging from the curtain rail in the upstairs window for now, but I had no problem receiving ACARS messages on the 131MHz range with it so it does seem to work!
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Re: Discone dilema

Postby Chris P » Tue May 14, 2019 11:02 am

Did read once that the bowtie design has a massive theoretical bandwidth ( several hundred Mhz )if the angle between the two elements is correctly adjusted . The one I suggested in my post certainly performs well (compared to a commercial discone ) over the 100-400Mhz range . Glad you have had some success
Regards Chris aka G8FFF nipper or tazmin88
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