Small discone antenna used on a handheld scanner

I've been researching some ways to get better reception in less-than-idea monitoring stations. For example, I typically will set up my scanner when I travel in hotels to search out trunked systems in the area as well as business-band users. 99% of the time, this means that I'm concentrating on 450-470 MHz. I have a high-gain beam antenna mounted on a tripod for home use, however it's much to large and bulky to travel with. I'm looking for something I can fold down or unscrew and put in a small case, then set up on location in a minute or two and have decent reception to my handheld scanner or in some cases an RTL-SDR. I did some testing with a number of handheld antennas yesterday and found that out of all of them, the little telescoping antenna that comes with the RTL-SDR outperformed pretty much all of the others, some of which I paid $20-30 for. I suspect this is because it must create some kind of a ground plane on its small mount, but I was certainly surprised at the results.

I know that Maxrad makes an 800 MHz discone that was designed to be mounted on handheld scanners. I would like to try something similar for business-band UHF. I've found two antennas for sale commercially that I think could do the trick. Obviously I would have to convert from SMA to PL-259 to connect to the antenna. My question is that if I were to remove only the hardware that connects these antennas to a mast, and instead mount them directly to the top of my BCD436HP, for example, how much difference can I realistically expect as opposed to a regular 6" UHF antenna cut specifically for 450-470 MHz?

Here are the two antennas that I'm looking at, one of which is obviously a lot more expensive than the other:

MP Antenna 08-ANT-0891 from The Antenna Farm ($109.95)
UHF 1/4 Wave Ground Plane Base Antenna from Centerfire Antenna ($29.95)

Though I've never gone the discone route, I have attached small yagis and a home made 1/4 wave ground plane (SO239 bulkhead mount and solid copper wire) and both did fairly well. Each performed better that the duckie that came with the scanner in my particular scenario - scanner, 6 ft of coax and antenna on a tripod about 5ft off the ground.

No really, get a coconut.

The idea of a discone is that every element is resonant to a different frequency and as a result of having MANY different elements, the antenna is broadband. That piece of malarkey has three upper elements, you could just as easily make a "fan dipole" with three wires and some matching counterpoises. Tape it to a piece of cardboard of PVC pipe and you'd have the same result for $10 instead of $110.

The big hint that it is junk is the "UNITY GAIN" rating on it, i.e., it has NO gain.
And if you're aiming at 460+-10Mhz, you shouldn't notice any difference between three tuned segments and simply using one, tuned at 460Mhz. Especially if you used a 1" pipe instead of a wire, since the pipe (being fatter) would have a lower SWR over a wider frequency range.

Buy an ARRL antenna book, skip the complicated parts, you'll still come out ahead. And not waste time and money on malarkey and magic antennas.

You want gain for UHF? In an omnidirectional antenna? OK, then you look at how to make an coaxial collinear antenna, which is essentially multiple 1/4 wave antennas vertically connected and stacked. Not something you'll find in the store, but easily made, and as cheap and effective as you can get.

Rred said:

No really, get a coconut.

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But which variety is best?

Dwarf yellow coconut
Dwarf orange coconut
Golden Malay coconut
Dwarf green coconut
Fiji Dwarf (Niu Leka)
Green Malay coconut
King coconut
Makapuno coconut
Maypan coconut
Nawassi coconut
Yellow Malay coconut

antenna

by Rred

"The idea of a discone is that every element is resonant to a different frequency and as a result of having MANY different elements, the antenna is broadband. That piece of malarkey has three upper elements, you could just as easily make a "fan dipole" with three wires and some matching counterpoises. Tape it to a piece of cardboard of PVC pipe and you'd have the same result for $10 instead of $110."

Not quite accurate..... First time I've seen that "technical" description of a Discone.


As bharvey2 stated, just experiment with various UHF designs. 1/4 wave ground plane can be made to fold flat and travel well. Think BNC chassis connector, screw mount for the radials, bent to 45 degrees. self supporting with a short length of RG174 coax to the scanner.

$.02

Rred said:

No really, get a coconut.

Click to expand...

So obviously you don't think that would be a worthwhile effort, and I certainly appreciate your input as that's the reason I asked in the first place; so that people more knowledgeable about antennas could provide the necessary insight.

A while back, I purchased a Laird Technologies BB4505CNS which has about 5db gain for my vehicle. On my car, it is incredible. It works extremely well and really pulls in the signals. Having attempted to use it by itself without a proper ground plane in the past, it doesn't do well. Perhaps you could offer a suggestion as to how I could use something like this (NMO-style mobile whip) and make a ground plane that could be easily transported in luggage, etc... It obviously has the gain and seems like it would be worthwhile to try to use it, especially since it is omnidirectional. I'm not great at building things and so the idea of trying to purchase something commercially is definitely appealing.

Gilligan - If you already have that antenna and wish to place it into portable service, you might consider a mag mount NMO base for it. You'll still need a ground plane and a steel (magnetic) cookie sheet would be suitable a start. Not as good as an auto roof mind you. To be honest though, the home made 1/4 wave dipole that I mentioned isn't too tough to make. The hardest part is soldering the main/vertical element to the SO239 connector. The rest is just bending wire with pliers and assembling screws and nuts.

Antenna

Portable MNO mount:

take a 2.5-3 in square of copper or aluminum (.040 to .080 thick),

punch either 3/8 or 3/4 in hole in center (depends on which NMO mount you have)

Punch 4 small holes in corners (.100-.120 dia (4-40 hardware))

cut 4 lengths of # 12-14 solid copper wire (house wire) to aprox 6.5 inches

bend a small loop in one end of each

Mount NMO mount with cable to center hole

Mount the four wires to the corner holes with 4-40 hardware.

Screw on NMO antenna. Place on desk, shelf, etc at hotel, connect to radio

to travel, unscrew antenna, coil coax around base, pack items in luggage

$.02

Thank you to all who have responded to my post; I'm always interested in learning how to improve my reception

"Not quite accurate"
No, tom, it lacks the necessary detail to qualify for a PhD dissertation. If you get into impedance matching, phase matching, electric versus magnetic fields, polarization, and all the other fine points of antenna design, you mainly wind up with glazed eyes, and I don't think that would help the OP here.

It does, however, serve the purpose of a quick-and-dirty starting point.

Gilligan said:

Thank you to all who have responded to my post; I'm always interested in learning how to improve my reception

Click to expand...

Have you tried the RS/WS 800 MHz antenna? Works great on both frequencies. Another thought, just a simple quarter wave antenna on 440.
Larry

The Maxrad discone will work as well as any rubber duck antenna, it just wont get you any gain like a directional antenna will. You will do better with a directional antenna at home and a different antenna for mobile use.

I have the MP Antenna 08-Ant-0891. It's a wonderfully small discone antenna that works the 400 Mhz. band very well. I use it on the GMRS frequencies because there is an repeater on top of a mountain about 25 miles away, and people use it. I talk up there frequently. I have it about five feet above the chimney above the second floor. I live in the rolling hills near a mountainous area, and it seems to do well in this type of terrain.

I also have the bigger MP Super M Ultra, and it works well in the VHF bands.

Rred said:

The idea of a discone is that every element is resonant to a different frequency and as a result of having MANY different elements, the antenna is broadband.

Click to expand...

I don't even know where to begin but of course I will, suffice to say that's not how a discone actually works. Want to know how I can say that?

Discones have two elements primarily: the cone (the downward radials) and the disc (the plane radials). A perfect discone is literally a solid cone (of a given thickness of material, I don't mean solid like it's a top or something) and a solid disc (same idea) but that's impractical in most situations so radial elements are used to approximate the "surface area" of the theoretical design concepts. Anyway, with that in mind you're saying a discone has MANY different elements and that's obviously not true since it has just two: all the cone radials are the same length, and all the disc radials are the same length. So, it has just two elements in theory and they are technically different, but that's about where your line of thinking should have come to a close - if your idea of MANY is only two then I don't know what to tell you.

Perhaps you might consider going back to the ARRL antenna book and actually read the "complicated parts" over a few times, you'll get it at some point.

The MaxRad thing, that's not actually a discone, it's a 1/4 wave ground plane tuned in the 850 MHz band, big difference, and after looking at the other two antennas they're not really discones either - again, ground planes tuned to the given bands/ranges/frequencies. Also, some of the info about what discones posted so far is just, well, how shall I put this... incorrect.

Hell I've made a bunch of 1/4 wave ground planes, they're dirt cheap - just needs an SO-239 chassis mount and some steel coat hangers or copper wire from 10-14 gauge - and very easy to make. In fact the ones I've made don't even use solder, just spade lugs crimped on the elements and then held to the SO-239 with a screw and nut, takes minutes to make one and it'll be tuned almost on-frequency for the given band using the center frequency.

Basic fact: a 1/4 wave ground plane will almost always outperform any typical scanner whip or rubber ducky style antenna by design so, while those other antennas are nice (I guess) I wouldn't ever fork over that kind of cash for something I could make myself for a few bucks at most but that's just me. Most of the fun in this hobby is the experimentation and creating stuff for yourself, and antennas - tuned ones - are really not that difficult to make at all.

Here's my 855 MHz 1/4 wave ground plane:



The main element is 3.25 inches for just about 855 MHz tuning and the ground radials are about 3.5 inches (good practice to give the ground radials just a tad more length) - for a 450-470 MHz model you'd want to have the main element at about 6.1 inches for 460 MHz (center of the band) and the ground radials about 6.4 or 6.5 inches, so you end up with a similar antenna that's basically "twice the size" in most respects save for the SO-239 chassis mount.

Dirt cheap, simple, and incredibly effective when built and put to actual use.

Gilligan said:

So obviously you don't think that would be a worthwhile effort, and I certainly appreciate your input as that's the reason I asked in the first place; so that people more knowledgeable about antennas could provide the necessary insight.

A while back, I purchased a Laird Technologies BB4505CNS which has about 5db gain for my vehicle. On my car, it is incredible. It works extremely well and really pulls in the signals. Having attempted to use it by itself without a proper ground plane in the past, it doesn't do well. Perhaps you could offer a suggestion as to how I could use something like this (NMO-style mobile whip) and make a ground plane that could be easily transported in luggage, etc... It obviously has the gain and seems like it would be worthwhile to try to use it, especially since it is omnidirectional. I'm not great at building things and so the idea of trying to purchase something commercially is definitely appealing.

Click to expand...

You could try a mobile/base converter kit for a ground plane. I used one of these for 800 MHz. and it worked very well until simulcast became a factor and I had to resort to a yagi.