Antenna for scanner - discone, other? Attic mount.

I am looking at getting a good antenna I can mount in my attic for my scanner. I can't put outside antennas up, so let leave that out of the discussion. I have some wire antennas for ham radio use I am going to put in there also. I haven't figured out HF yet, but I have a 6m ground plane I used at another location with good results.

As far as the scanner antenna I am thinking along the lines of a discone. Are there any good inexpensive ones out there? I'd like to have an antenna that works best for about 145-170mhz and 440-450mhz, but decent performance on the 800-900mhz bands would be good too. I want an antenna that will help me listen to the 2m and 70cm ham bands and VHF marine band mostly. Right now I use a small dual band mag mount antenna. I figure if I get a better antenna and put it in the attic (4th story) I will have better luck.

The Radio Shack Discone will work well for your application as it will be protected from the weather and not be so prone to breakdown. I used one externally for very similar purposes and outside of having to check it and reattach the radials from time to time, it worked just fine. I replaced it with another discone -style antenna (MP Antenna Super-M Classic Base Antenna 08ANT0863) and gave mine to another ham in my local club.

I use two RS 25-1.3 grnd planes in the attic with 35' LMR400, they hear the IL-Digital Starcom great....Mounted on piece of PVC stuck in the insulation, I even hook them up to my FT50 ham H/H with good results...There $25 antennas in some RS stores on closeouts for $5.....

Keep in mind that Discone antennas have no "gain". The big benefit to them is their wide bandwidth. If you really only need to listen in on 145-170, 440-450 and 800-900, you'll very likely see better performance by going with a dual band (VHF-UHF) vertical antenna. You should be able to get a few dB of gain compared to a discone. It might cost a bit more (maybe) but it will certainly outperform a discone.

I have a Diamond discone at home that I use with a VHF transceiver. Works fine, but isn't an outstanding performer. I also have a Telwave commercial discone (listed for $2000) at work, and again, works well as a very wide band antenna, but not an impressive performer when compared to a good vertical.

Unless you really need the broad banded nature of a discone, there are better antennas out there.

The main limitation on any antenna's performance it location. The higher the better, and height pretty well trumps everything else, at least on the receive end. A discone in the attic will likely work as well as anything else put there for receive.

"Gain" is over hyped - most receivers these days have enough gain on the front end to pull in just about anything on just about any antenna. Signal to noise ratio is what really determines how well you will hear what your radio pulls in. Anywhere in the house is bad for that, but the attic is probably the best for inside, and beggars can't be choosers.

The "gain" antennas referred to only have real "gain" over quite a narrow band since they are designed to be resonant antennas and off resonance the SWR goes high and the "gain" disappears.

If you want to significantly improve on a discone in the attic you need to get the antenna outdoors and high up in the air. Not always possible, of course. A two foot hunk of wire 50 feet off the ground will probably easily outperform anything in the attic.

Ed_Seedhouse said:

The main limitation on any antenna's performance it location....
"Gain" is over hyped ...

Anywhere in the house is bad for that, but the attic is probably the best for inside, and beggars can't be choosers...

If you want to significantly improve on a discone in the attic you need to get the antenna outdoors and high up in the air. Not always possible, of course. A two foot hunk of wire 50 feet off the ground will probably easily outperform anything in the attic.

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I respect your info. I have been a ham for 14 years, an Extra for 8 of those, and I also worked with 450mhz systems professionally for a few years - I know all about antenna placement. We put antennas up to about 225'. I did site surveys prior to putting systems in and performance analysis after. If I had a tower here an antenna wouldn't be an issue. I am in a townhouse complex for now so I have no ability to get outside antennas up. I have also never worked with scanners until now so I figured I would check in with the forum and see what works for others. Attic antennas are like clipped wings for a radio enthusiast, but I can't change that for the near future. I'd just like to make the best of what I have.

On a side note - I remember putting in a transmitter station about 2.5-3 hours away from the area I used to live. We had a repeater at a college campus on 440. When I put the antenna up, around 175-200', I hooked up to it with an HT and was talking back to town to the repeater. That was cool.

Ed_Seedhouse said:

...
A two foot hunk of wire 50 feet off the ground will probably easily outperform anything in the attic.

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Wouldn't 18 inches be better for scanners? It's about 1/4 wave at 153MHz, about 3/4 at 460 and about 6/4 at 860.

KC8QVO said:

I respect your info. I have been a ham for 14 years, an Extra for 8 of those, and I also worked with 450mhz systems professionally for a few years - I know all about antenna placement. We put antennas up to about 225'. I did site surveys prior to putting systems in and performance analysis after. If I had a tower here an antenna wouldn't be an issue. I am in a townhouse complex for now so I have no ability to get outside antennas up. I have also never worked with scanners until now so I figured I would check in with the forum and see what works for others. Attic antennas are like clipped wings for a radio enthusiast, but I can't change that for the near future. I'd just like to make the best of what I have.

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What I said applies to receiving only. If you want to transmit you need an antenna that resonates in the band you are transmitting on for sure. Transmitters need a proper impedance match.

Receivers are a different kettle of fish. Yes, the same physical laws apply, but modern receivers are so sensitive that a good impedance match isn't essential. Signal to noise is the most important parameter for receive assuming you have a modern sensitive receiving system.

I use a cheap discone on the second floor of my flat for scanning. For my transceivers I have, of course, resonant antennas in the back yard and at a decent height (fortunately I live on a hill anyway).

A resonant antenna will put more signal into your transceiver near it's resonant frequency of course, but the receiver will usually pull in the signal even if the receive antenna is a long way from resonance. And if you have a strong local transmission near the resonance of your antenna you are likely to get front end overload which really will kill your reception.

Extremely sensitive receivers are cheap and easy to make. Receivers that can deal with strong local signals and still receive weak distant ones, while remaining extremely sensitive, are much harder to make and more expensive. For receive only, it's signal to noise ratio that makes the most difference.

DickH said:

Wouldn't 18 inches be better for scanners? It's about 1/4 wave at 153MHz, about 3/4 at 460 and about 6/4 at 860.

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It would likely make very little difference. Sure, at resonance an antenna pulls in more signal, but it also pulls in more noise. And it's the difference between the signal and the noise that matters. If your local noise is at S8 an S9 signal will be very hard to hear anyway.

Modern receivers, even low cost ones, are extremely sensitive. The stronger overall signal you get a resonance might only overload your front end, and mess up all your reception. A receiver that is very sensitive AND also very robust and resistant to front overload is a good deal more expensive.

What matters most for reception is not how strong the signal is, but how much stronger the signal is than the noise. So you will get more bang for the buck by lowering the noise level than by raising the sensitivity.