Antenna Help

[Steveg1968]

I am looking at paying a new antenna and was thinking of getting the WBD-40 Discone Base Antenna it says it is wideband, may concern is alot of what I listen to is going to narrowband is this going to be a problem, if so can someone guide me in the right direction of what antanna I should pay that can cover both wide band and narrow band.

[popnokick]

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In this case, "wideband" refers to the very "wide" band of freqs that the antenna covers (25-1300 mHz). It has nothing to do with FCC mandated narrowbanding, and the antenna will receive wideband and narrowband transmissions equally well. You'll be fine to receive both types of transmissions with this antenna.

[Rt169Radio]

Popnokick is correct, wideband just means it covers a wide range of freqs. And in your case the WBD-40 covers 25 to 1300 MHz.

[kb2vxa]

That reminds me of the HDTV antenna hype, the antenna couldn't care less about how the RF carrier is modulated.

[Steveg1968]

Thank you very much, It is what I was thinking but just wanted to make sure. But I have one last thing to ask, can anyone help with what size cable I can use for the least amount of loss. thank you again for all your help.

[benbenrf]

Originally Posted by Steveg1968

Thank you very much, It is what I was thinking but just wanted to make sure. But I have one last thing to ask, can anyone help with what size cable I can use for the least amount of loss. thank you again for all your help.

Just tell us please -what do you anticipate the length of coax run between the antenna and your scanner/receiver to be?

[Steveg1968]

Iwould say about 50 feet

[benbenrf]

That's a fairly long run - I personally wouldn't use anything less than LMR 400 type coax, better still would be LMR 600 coax.

Using LMR 600, with connectors in place the signal strength your antenna receives will have dropped to around half the received strength by the time it reaches your scanner/receiver front-end - I wouldn't want to be loosing much more than that. With LMR 400 coax your signal strength losses over the 50' coax run are going to be in the region of around 30% more.

Look at this antennas' spec's online I see it has a Gain figure of just over 2dB. Nice to know, but what the spec's don't say is for what frequency that figure is for - it be for around 800Mhz - 900Mhz which is great if that is the region that interests you, or it may be at 300Mhz - 400Mhz, and at 800Mhz - 900Mhz the Gain may be negative |(-).

The point I'm making, is that your coax can have significant impact on overall signal strength - especially when you use a long coax run. Antenna performance may compensate, or it may add to losses. You need to keep this in mind.

As a rule, the thicker the coax is the less your losses will be over any given coax length.

[prcguy]

Most scanner Discones like the WBD-40 that have skirt lengths in the 30" range have consistent performance similar to a 1/4 wave ground plane from about 100MHz through maybe 500MHz then the radiation pattern starts to point up above the horizon. At 800MHz they are not so good due to the upward pattern.

If you don't need to listen below 100MHz then loose the top whip since it can adversely affect performance in the upper frequencies.
prcguy

[kb2vxa]

Don't let antenna dBs fool you, that 2dB figure is isotropic or dBi whis a mathematical construct for a spherical radiation pattern. There is no such thing in the real world so I much prefer dBd which is compared to a dipole which has unity gain or 0dB. That saves the trouble of subtracting 2.8 from published figures (sales hype) to get back to reality.

That having been said a discone like a ground plane has unity gain so coax loss becomes paramount concern. You will always get negative returns but the less negative the better.

[dmcgilly]

Typically "Broadband" refers to a wide range of operating frequencies. In the public safety/commercial radio industry "wideband vs narrowband" refers to either 25kc vs 12.5 kc spacing. January 1, 2013 all radios in this catagory must, by FCC Ruling, must cease using the 25kc and use the newer 12.5kc spacing!
Discone antennas are cheap, easy to find, & work well. Most don't work above 1000mhz and there is more and more activity @ 1,000mhz (1ghz). Most voice communications tops out at about 900mhz. Some new modified discones are good up to 6ghz.