Discone Reception Questions

[scanmanmi]

I too have been researching this and have found lots of people suggest an FM trap. I just ordered one.

 

[paulears]

You can make ¼ wave stub filters so easily, maybe out of junk box stuff that they're great to do yourself. You cut them a bit long then gradually snip a bit off until you bring the frequency it cuts up. There's a nice simple calculator here.
Coaxial Stub Notch Filter Designer
Just remember they're quite wide, so if you want the aircraft band, a filter cut for 100Mz, nibbles into it, but cut it for 90MHz works pretty well.

 

[prcguy]

Stub filters also notch odd harmonics of the fundamental frequency which you may not want to get rid of. For example a stub filter cut for 90Mhz would also notch out 270Mhz, 450MHz, 630MHz, 810MHz and so on.
prcguy

You can make ¼ wave stub filters so easily, maybe out of junk box stuff that they're great to do yourself. You cut them a bit long then gradually snip a bit off until you bring the frequency it cuts up. There's a nice simple calculator here.
Coaxial Stub Notch Filter Designer
Just remember they're quite wide, so if you want the aircraft band, a filter cut for 100Mz, nibbles into it, but cut it for 90MHz works pretty well.

 

[paulears]

Yes indeed - I have one I have to use on my SDR system to remove a rather nasty data transmission, and it works pretty well. The first harmonic at 306 doesn't cause too much grief and the one at 459 (which is on the input frequency of my UHF repeater does dull down my UHF response, but the benefit of not having the SDR full of sproggies is actually better. If you have trouble with overloading, the spurious signals that appear everywhere are probably worse than losing about 8dB, which appears to be the before and after difference up in UHF. Always worth a go if you have the bits hanging around.

 

[majoco]

Discones are intermod magnets. They are more efficient in the FM broadcast band than any other scanner antenna.

Depends on how far and how much power the FM transmitter is from your antenna. I used to get bad splatter from a Pocsag transmitter that was only about 25yards from my discone - fortunately it was only a temporary setup from a Post Office Telecom site tower before it was moved back to it's old location on a new tower miles away.

 

[Cardiac69]

With all that said my go to antenna(s), which I'm using right now on my new Icom R-8600 is a a pair of Discones, one covers about 100 to 800Mhz and the other about 400 to 3,200MHz combined with a diplexer with a transition in the 600Mhz range. I rarely use a preamp and my coax is a combination of 1/2" Heliax and LMR400.
prcguy

What discone do you use for 100-800mHz?

Bob

 

[prcguy]

I have several from Kreco and Astron Wireless rated 100-800MHz, but you typical scanner type from Diamond, Radio Shack, etc covers the same range.
prcguy

What discone do you use for 100-800mHz?

Bob

 

[cmdrwill]

" Kreco and Astron Wireless " now those are REAL discone antennas.

While scanner types from Comet, Diamond, Browning, Tram, and others are not designed, built, and tested, like the commercial ones and of course, they do not 'work' as well either.

 

[prcguy]

One of my Discones is a Harris brand but made by Kreco. Kreco's usually have a porcelain insulator and Harris specified what looks like a clear Rexolite insulator and its all black powder coated. Yum! The others are standard aluminum versions from Kreco and when I mount them permanently they get many coats of paint before going up.
prcguy

" Kreco and Astron Wireless " now those are REAL discone antennas.

While scanner types from Comet, Diamond, Browning, Tram, and others are not designed, built, and tested, like the commercial ones and of course, they do not 'work' as well either.