Sigma SE-900 discone antenna - 2m / 70cm TX performance?

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Sigma SE-900 discone antenna - 2m / 70cm TX performance?

Postby aerol1 » Wed Jan 25, 2017 12:58 pm

Dear community,

I'm about to get Sigma SE-900 discone antenna to put it on roof and use with Bearcat BC355N scanner and a few handhelds.

I can see that manufacturer stated 2m / 70cm TX capability in spec.

I'm wondering how bad is that i.e. if Sigma SE-900 is any better than 1/4 wave stick antennas that come with HTs?

Please kindly share any feedback if you have any experience with TX using that antenna.
Thank you!
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Re: Sigma SE-900 discone antenna - 2m / 70cm TX performance?

Postby G4RMT » Wed Jan 25, 2017 2:26 pm

I'm a bit confused? You want to use it with the scanner, AND a few hand-helds? You want to connect a hand-held to the discone and transmit, I assume?

The discone is fine, and always a good match for a scanner that can listen to many different users - amateur, marine, civil and military air and the public and private mobile radio users who use radio for business and leisure. The transmit ability can be useful because the antenna presents a decent enough match for practically all the common transmitters.

The antenna offers no gain performance on all those bands. Band specific aerials might have some gain in some bands - so perhaps producing double or more the signal in certain bands, but performing performing less well on other bands.

The discone has the same gain as the 1/4 wave antenna fitted to some portable radios - IF, and it is a big IF, the radio has a suitable ground plane to enable the 1/4 to be efficient. A quarter wave antenna on a walkie-talkie sitting on the window sill has very little surface area to allow the 1/4 wave to perform optimally.

So the 1/4 wave antennas can be ok, and on a portable, are probably the best balance of performance and size. Moving to VHF it gets a bit worse because most VHF 1/4 waves on portable radios have to be shortened for practical reasons. A 17 or 18" whip isn't the easiest to stick in a pocket.

The Sigma up high (WITH DECENT CABLE) will out perform a portable by quite a lot. frequency specific products are better than discones on those frequencies, but a discone is much better if you need multiple band performance.
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Re: Sigma SE-900 discone antenna - 2m / 70cm TX performance?

Postby m0lsx » Wed Jan 25, 2017 2:53 pm

I have a three band 6,2 & 70 discone & it's not a great TX antenna. All it is is a small inefficient mobile whip with radials.
As a compromise antenna they are OK. But don't forget simply because your radio sees low SWR & can use it as a TX antenna, it does not mean it's a good antenna. A dummy load shows 1:1.1, but it's not a good antenna.
If you want one antenna & are not going to work simplex on the handhelds, then as long as you can access the repeater or repeaters you want to, then it's a good compromise. but don't expect a small mobile whip to work as well as a collinear.
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Re: Sigma SE-900 discone antenna - 2m / 70cm TX performance?

Postby aerol1 » Thu Jan 26, 2017 2:12 pm

Thanks a lot for your suggestions, I will certainly go for it and try at least
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