Diamond D220 Discone Antenna

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iMONITOR

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I'm considering the Diamond D220 Discone Antenna.

Diamond® Antenna ~ D220

Diamond D-220 Discone VHF UHF Antenna, Diamond D220

I like it's smaller form factor, compared to a wide band discone like the Diamond D-130J. Also, my requirements are in the 108 ~ 400 MHz range, for VHF/UHF commercial & military aircraft. It would be used for receive only, no transmit.

Diamond claims it's a discone, some reviews have claimed it to be more like a ground plane. However, Diamonds specs show it does have some gain. 2.15dBi(144/904/1200 MHz), and 5.5 dBi (440 MHz).

I can't think of a better dual-band aircraft antenna on the market. Anyone else using one? I'd be interested in any feedback, both good and bad.
 
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N5TWB

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The indication of "gain" in dBi is misleading as that means gain over a mythical isotropic radiator - there is no such thing. Real gain is measured as dBd - gain over a dipole antenna. Basic RF physics preclude achieving gain in a wideband antenna. The primary benefit to a discone is its wideband receive capability.
 

ko6jw_2

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I'm assuming you intend to use it mobile as intended - so you will need an appropriate mount which will support the wind load of the antenna.

It seems to be sort of a hybrid. The UHF portion is not a discone. That's why it has better gain. The other bands are apparently covered by the discone. It's certainly going to attract attention on your vehicle.

If you're not going to use it mobile, then I'd stick with something like the D-130J. It will probably be as good or better.

The gain on 440 may be confined to the 70cm band and may not be broadband enough for UHF aircraft reception.

There are better discones for aircraft. Check out Telewave. Very expensive, but good.
 
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prcguy

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I would say the gain claims are a bit exaggerated and in my opinion it would not be a great VHF or UHF airband antenna.

A Discone skirt (or cone) is a little longer than 1/4 wavelength at the lowest design frequency and the DJ-220 appears to be a Discone from maybe 400MHz on up to a few GHz. That leaves the top whip as the main radiator for bands below 400MHz and I'll bet its sharply tuned to the ham bands and not any air band. I see it as a ground plane with a lousy ground plane.

I would classify this antenna more as a ground plane than a Discone because the Discone is probably out of the circuit for much of its useable scanner frequency range. Another problem is the top whip needs a coil right at the base to help decouple it from the Discone so the whip doesn't interact with the Discone operation at higher frequencies. I'll bet the UHF/microwave performance is skewed or affected by the top whip and the antenna doesn't perform exactly like a Discone even within its own Discone range.

For dual band VHF/UHF airband reception I don't think you can beat a common scanner Discone line a DJ-130 or RS or similar. They are very consistant in gain and pattern from the lower end of VHF air through 400MHz and any problems in pattern appear above 400MHz. The only thing I have found to be better is some actual military/civilian airport antennas made by TACO, Antenna Products and a few others.
prcguy
 

prcguy

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dBd is preferred for specifying two way radio antennas but the rest of the antenna world is specified in dBi. check most military, microwave, satellite and other types of antennas. dBi is a known and widely accepted gain standard.
prcguy

The indication of "gain" in dBi is misleading as that means gain over a mythical isotropic radiator - there is no such thing. Real gain is measured as dBd - gain over a dipole antenna. Basic RF physics preclude achieving gain in a wideband antenna. The primary benefit to a discone is its wideband receive capability.
 

ko6jw_2

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The DPD antenna is designed specifically for military air band and military VHF FM receiving. It is not a general scanner antenna. If your only interest is in that part of the spectrum then you might find it useful. It has some gain because it is basically two half wave dipoles. This is an old design and has been described in various ham radio publications.

The discone has unity gain, but its claim to fame is that it's very broadband and you can transmit through it.

You have to decide where your interests are.
 

iMONITOR

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The DPD antenna is designed specifically for military air band and military VHF FM receiving. It is not a general scanner antenna. If your only interest is in that part of the spectrum then you might find it useful. It has some gain because it is basically two half wave dipoles. This is an old design and has been described in various ham radio publications.

The discone has unity gain, but its claim to fame is that it's very broadband and you can transmit through it.

You have to decide where your interests are.
The DPD MilTenna Omni is a dual band VHF/UHF, AM/FM MilAir antenna.

That's where a lot of my interest is, but I'm pretty sure it will work just fine for commercial aircraft also, as I'm doing ok right now with a Diamond RH77CA rubber duck on the back of the scanner.
 
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ridgescan

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Is the d130j that much of a turnoff for you? I understand your preference with the more "MIL" looking piece, but hey-you could get a d130j and then do it MIL green with black vertical:)
I've had mine a long time-very reliable reception within your intended target. Heard every word of comms inside the Blue Angels' planes in the 250-400meg range, as they zoomed our skies here in their show.
I regularly get Travis AFB ATIS on 135.55mHz at 49 miles which to me is impressive for an omni no-gainer.
I regularly get PD agencies in the 480-490 meg range clear down to San Jose at 42 miles.
To +1 prcguy, I say you should reconsider a d130j.
 

iMONITOR

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My concern with the D-130J is that it is a wide-band, and I don't need a wide-band antenna. As I said, my target frequencies are 108 ~ 400 MHz. Having an antenna that covers 30 ~ 1300 MHz would be larger than necessary. I'm also concerned that it would attract interference.

I'm in a development with an HOA that does not allow antennas other than for SAT TV, or HD TV. I'm thinking with a smaller antenna, I can tell them it's for HD TV, and they won't know the difference. I've even considered trying these indoors. But I don't have room for the large umbrella stance of the D-130J.
 

prcguy

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The DJ-130 and similar Discones cover from the bottom end of the VHF air band through maybe 900MHz in the Discone mode and the top whip on most is tuned to 50Mhz only. The 25 to 1300MHz claim is wishful thinking at best. If you simply take off the top whip you will have a very reasonable size antenna and smaller than a DPD MilTenna. A DJ-130 without the whip is maybe a little over 2ft tall?

You would also be using the DJ-130 or similar in its most optimum range of lower 100MHz to below 500MHz (without the whip) and it would be hard to beat for what you want receive without spending a lot more for a commercial or military version of the same thing. Why reinvent the wheel?
prcguy

My concern with the D-130J is that it is a wide-band, and I don't need a wide-band antenna. As I said, my target frequencies are 108 ~ 400 MHz. Having an antenna that covers 30 ~ 1300 MHz would be larger than necessary. I'm also concerned that it would attract interference.

I'm in a development with an HOA that does not allow antennas other than for SAT TV, or HD TV. I'm thinking with a smaller antenna, I can tell them it's for HD TV, and they won't know the difference. I've even considered trying these indoors. But I don't have room for the large umbrella stance of the D-130J.
 

iMONITOR

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Ok, that makes sense. I didn't think you could alter the geometry of a discone without upsetting the design. I know people remove the top elements all the time, but I thought doing so, would have an ill effect on the performance of the antenna, on the higher frequencies as well.

You guys know a lot more about antennas then I do, and I have all the respect in the world for your advice. I hope you weren't insulted by my questions, or comments.

I had a D-130JN back in the late 80's. I used it with my Icom R-7000. prcguy, you're right, minus that top element, it will be a much more compact design. D-130J it is!

Thanks everyone for all your help and patience! :)
 

ko6jw_2

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Confirming previous posts. The whip on top of the discone has nothing to do with the actual discone. It is a base loaded ground plane to receive VHF Low. If you don't need it, it just unscrews and you have a 100-1200Mhz discone. RS used to sell them that way. The whip tunes very sharply and in no way covers 25-50Mhz. Mine centers about 44Mhz. I need it for CHP here, but most places have very little, if any, low band use now. You can get rid of it.
 

majoco

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If you're allowed a TV antenna, why not use a TV antenna? I had a surplus antenna and cut down the VHF low band dipole to suit the airband frequencies and left the VHF Hi and UHF dipoles alone - works well.
 
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