Can I cut down a old discone antenna for 1090 ?

[paulgarrett6]

Hi everyone.As the title states i was just wondering if a old discone i have in storage could be cut down to be resonant at 1090.I don’t have any test equipment and the discone cost about $200 when it was new so i don’t really want to destroy it if it’s not going to work.I need someone to advise me on this who knows if this will work.If it does work i’d be happy to do it as it isn’t used anymore,thanks in advance.

[theresjam]

yes you could cut it down to work at 1090Mhz.

I have only done a quick google but it appears discone antennas are quite broadband antennas and you may actually introduce more problems from nearby frequencies cell towers etc. but this will mainly depend on where you are and what your next to.

So up to you to try it basically. I personally would go for it. It shouldn’t be hard to find a guide somewhere that tells you how to work out the dimensions.

if you can disassemble it easily enough it may make sense to use the fittings and make a new disc and cone.

[paulgarrett6]

@theresjam

yes you could cut it down to work at 1090Mhz.

I have only done a quick google but it appears discone antennas are quite broadband antennas and you may actually introduce more problems from nearby frequencies cell towers etc. but this will mainly depend on where you are and what your next to.

So up to you to try it basically. I personally would go for it. It shouldn’t be hard to find a guide somewhere that tells you how to work out the dimensions.

if you can disassemble it easily enough it may make sense to use the fittings and make a new disc and cone.

Thanks for the reply,I think I will do as you suggest.ill start googling and will report back how it goes.

[k6rtm]

@paulgarrett6

Hi everyone.As the title states i was just wondering if a old discone i have in storage could be cut down to be resonant at 1090.I don’t have any test equipment and the discone cost about $200 when it was new so i don’t really want to destroy it if it’s not going to work.I need someone to advise me on this who knows if this will work.If it does work i’d be happy to do it as it isn’t used anymore,thanks in advance.

Discones are very wideband antennas.

If it’s a comet or diamond discone, it will work fine for ADS-B as is, covering from around 50 MHz to 1200 MHz. I use a Diamond discone for one of my ADS-B systems. You’ll need a filter between the discone and your SDR, even if (especially if) it’s the FLightAware SDR with LNA and filter; the SDR front end is still quite broadband and is easily overloaded.

If you do detailed modeling of discone performance, you’ll find that the take-off angle increases with frequency. So at 1090 MHz, the maximum “gain” of your discone is probably in a lobe at about 30 degrees above the horizon. Not a problem for ADS-B. (Old editions of the RSGB VHF Antenna book have lots of detailed information on the building, care, and feeding of discones.)

If you want to look at real world performance, site 3116 is my discone. Site 4847 is a commercial gain antenna located about 20 feet from the discone. Both antennas are at about the same height. The discone is fed by LM400, where the other antenna uses a piece of freak grade RL Gore cable with precision 3.5mm connectors (the precision cousin to SMA) on both ends.

Both sites run essentially the same hardware – FLightAware filter, FLightAware SDR, RPI 3. While the discone has lower overall numbers, it also sees more nearby aircraft for some reason.

cheers

bob k6rtm

[paulgarrett6]

@k6rtm

@paulgarrett6

Hi everyone.As the title states i was just wondering if a old discone i have in storage could be cut down to be resonant at 1090.I don’t have any test equipment and the discone cost about $200 when it was new so i don’t really want to destroy it if it’s not going to work.I need someone to advise me on this who knows if this will work.If it does work i’d be happy to do it as it isn’t used anymore,thanks in advance.

Discones are very wideband antennas.

If it’s a comet or diamond discone, it will work fine for ADS-B as is, covering from around 50 MHz to 1200 MHz. I use a Diamond discone for one of my ADS-B systems. You’ll need a filter between the discone and your SDR, even if (especially if) it’s the FLightAware SDR with LNA and filter; the SDR front end is still quite broadband and is easily overloaded.

If you do detailed modeling of discone performance, you’ll find that the take-off angle increases with frequency. So at 1090 MHz, the maximum “gain” of your discone is probably in a lobe at about 30 degrees above the horizon. Not a problem for ADS-B. (Old editions of the RSGB VHF Antenna book have lots of detailed information on the building, care, and feeding of discones.)

If you want to look at real world performance, site 3116 is my discone. Site 4847 is a commercial gain antenna located about 20 feet from the discone. Both antennas are at about the same height. The discone is fed by LM400, where the other antenna uses a piece of freak grade RL Gore cable with precision 3.5mm connectors (the precision cousin to SMA) on both ends.

Thanks for all the info,and you have a great site bob.I’ve just been approved to host a feeder so ill just use the antenna that comes with the package,it seems to be ok.Im located in a town called Ocean Shores in the north of nsw,Australia.My antenna will go on my existing mast about 40 feet above the roof,fed with a run of 1/2 inch heliax ive already got.Hope to be online soon,thanks everybody for the help.

Both sites run essentially the same hardware – FLightAware filter, FLightAware SDR, RPI 3. While the discone has lower overall numbers, it also sees more nearby aircraft for some reason.

cheers

bob k6rtm