Thinking Of Installing A Discone For My SDR Receivers

[JRBarrett]

Ahhh. . . I see. I hadn't thought of it that way. I thought the horizontal rods and the lower angled rods made up the groundplane and the whip was the main element. I understand better now. If the cone rods determine it's lower frequency is it then that the horizontal shorter rods determine its higher frequencies?

The upper and lower rods both determine the lowest frequency at which a discone will work. The lower rods should be one quarter wavelength at the lowest frequency, and the upper rods are 0.7 of a quarter wavelength.

I have a Diamond D130N discone. The upper elements are 22 inches across, and the lower elements are 32 inches long. That equates to a lower cutoff frequency of about 88 MHz. (Lower end of the FM broadcast band). I did not install the loaded whip on top as there is not a lot of low band activity around here.

Although you could cut the elements shorter to raise both the lowest and highest frequency a discone will work at, another variable is the width of the gap formed by the insulator that separates the upper disc from the lower cone. That gap is related to the lowest operating frequency, so if you simply cut the elements shorter, the antenna’s directional pattern would suffer.

If you want to do a lot of monitoring of 700-800 MHz systems, a second discone optimized for the higher frequencies would be the way to go.

 

[Merovingian]

The upper and lower rods both determine the lowest frequency at which a discone will work. The lower rods should be one quarter wavelength at the lowest frequency, and the upper rods are 0.7 of a quarter wavelength.

I have a Diamond D130N discone. The upper elements are 22 inches across, and the lower elements are 32 inches long. That equates to a lower cutoff frequency of about 88 MHz. (Lower end of the FM broadcast band). I did not install the loaded whip on top as there is not a lot of low band activity around here.

Although you could cut the elements shorter to raise both the lowest and highest frequency a discone will work at, another variable is the width of the gap formed by the insulator that separates the upper disc from the lower cone. That gap is related to the lowest operating frequency, so if you simply cut the elements shorter, the antenna’s directional pattern would suffer.

If you want to do a lot of monitoring of 700-800 MHz systems, a second discone optimized for the higher frequencies would be the way to go.

I had thought about getting two Diamond D3000 and cutting one a little shorter but now after what you said it doesn't seem so simple. I have been searching the internet for UHF discones around the 500 MHz - 1300 Mhz range but haven't found hardly any, just links to the usual Diamond or other brand 25 MHz - 1300 MHz antennas. I did come across this one: 400 MHz - 4 GHz. it is a bit higher at $350

https://aventasinc.com/product/discone-antenna-2/

iMONITOR mentioned the AOR DA6000 starting at 700 MHz but I don't need a $500 antenna.

I was hoping to find a "cheaper" Diamond like antenna for the 700 MHz - 2 GHz range or so. Does anyone know of any?

 

[prcguy]

The Sirio SD 3000U looks like a good choice for a higher freq Discone. I can't tell exactly how big it is but it should cover 300-400Mhz on up. I would remove its top whip. There are some cute little Discones floating around made by Decibel Products that are a solid sheet metal disc and cone inside a plastic radome. They are stamped 806 to 1990Mhz and I've bought them for anywhere from $5 to $20. I only have two left otherwise I would offer you one. Here are some pics of the little Decible Products Discone.

I had thought about getting two Diamond D3000 and cutting one a little shorter but now after what you said it doesn't seem so simple. I have been searching the internet for UHF discones around the 500 MHz - 1300 Mhz range but haven't found hardly any, just links to the usual Diamond or other brand 25 MHz - 1300 MHz antennas. I did come across this one: 400 MHz - 4 GHz. it is a bit higher at $350

https://aventasinc.com/product/discone-antenna-2/

iMONITOR mentioned the AOR DA6000 starting at 700 MHz but I don't need a $500 antenna.

I was hoping to find a "cheaper" Diamond like antenna for the 700 MHz - 2 GHz range or so. Does anyone know of any?

 

[Merovingian]

Thanks for the pictures! I did some searching for the Decibel Products homepage but couldn't find it, they must have gone out of business. That antenna kind of looks "home made". Hahaha

I took your advice earlier about the Sirio SD 3000U and wrote it down as a likely antenna to get, I was hoping to find something with the starting range of 500-700 MHz and up. If I don't come across anything else I will probably go with the Sirio. Amazon had it for $108 but I found it listed on their homepage for $99.

The Sirio SD 3000U looks like a good choice for a higher freq Discone. I can't tell exactly how big it is but it should cover 300-400Mhz on up. I would remove its top whip. There are some cute little Discones floating around made by Decibel Products that are a solid sheet metal disc and cone inside a plastic radome. They are stamped 806 to 1990Mhz and I've bought them for anywhere from $5 to $20. I only have two left otherwise I would offer you one. Here are some pics of the little Decible Products Discone.

View attachment 70651View attachment 70652View attachment 70653

 

[Ubbe]

I would need to know if I was doing it correctly, not cutting off too much or not cutting off enough. I would need something like this antenna analyzer:
KC901V 6.8GHz Handheld Network Analyzer RF multimeter | DEEPACE

There's no point in analyzing a discone as it will measure almost perfect on all frequencies.

I had thought about getting two Diamond D3000 and cutting one a little shorter but now after what you said it doesn't seem so simple.

All antenna types I know of can be scaled freely up and down in size to match different frequency bands, there's no magic going on with antennas, just middle shool mathematics. Simply change all measurement from a good working antenna the same percentage as the frequency you want to change. Discones are one of the more easy ones to modify as there are no spacing between elements that needs to be moved.

/Ubbe

 

[Merovingian]

There's no point in analyzing a discone as it will measure almost perfect on all frequencies.

All antenna types I know of can be scaled freely up and down in size to match different frequency bands, there's no magic going on with antennas, just middle shool mathematics. Simply change all measurement from a good working antenna the same percentage as the frequency you want to change. Discones are one of the more easy ones to modify as there are no spacing between elements that needs to be moved.

/Ubbe

I see. I was told earlier that the width of the gap formed by the insulator that separates the disc and the cone has an affect also. The gap isn't so easy to change. Either way I'd rather have something already made that I know, at least is supposed to be correct, so that it performes as it should.

https://forums.radioreference.com/t...cone-for-my-sdr-receivers.387533/post-3115967

 

[nd5y]

I did some searching for the Decibel Products homepage but couldn't find it, they must have gone out of business.

The original company no longer exists. They changed hands several times. The remaining products are now made by CommScope and dbSpectra.

 

[prcguy]

Changing the gap between the disc and cone will affect the impedance, that's about it. Ideally the bottom cone comes to a sharp point beneath the top disc and that helps with the high frequency end of the Discone. I've scaled a couple of Discones up and down in size and they worked as expected and also built one from scratch. Not much magic to it except making the hub that holds everything together.

I see. I was told earlier that the width of the gap formed by the insulator that separates the disc and the cone has an affect also. The gap isn't so easy to change. Either way I'd rather have something already made that I know, at least is supposed to be correct, so that it performes as it should.

https://forums.radioreference.com/t...cone-for-my-sdr-receivers.387533/post-3115967

 

[Merovingian]

The original company no longer exists. They changed hands several times. The remaining products are now made by CommScope and dbSpectra.

It seems some of these antennas are getting to be as scarce as the mesh style 10' satellite dishes. You either buy a pizza pan dish or huge solid commercial dish that is 3 times the cost of a light mesh dish. . . .

 

[Merovingian]

Changing the gap between the disc and cone will affect the impedance, that's about it. Ideally the bottom cone comes to a sharp point beneath the top disc and that helps with the high frequency end of the Discone. I've scaled a couple of Discones up and down in size and they worked as expected and also built one from scratch. Not much magic to it except making the hub that holds everything together.

Hummm. . . . I see. I guess I need to find some photos or drawings online to get a better idea of how the hub is designed. I know rod length varies. Does the angle of the rods as well? I need to do some research to better understand this type of antenna. I have learned a lot from everyone in the last 24 hours. This antenna is much different than what I had in my mind a day ago.

 

[krokus]

Thanks for the info. You are probably right. I'm guessing some cell phone signals are above 1GHz, then a big jump to 2.4GHz for the area WiFi signals. Everything else is probably line of sight anyway.

The cell phone bands there are digital, and probably encrypted. There is some ham activity around 1296 MHz.

There are some satellite signals, too.

Yes, everything in that frequency range is line of sight, and fairly short ranged.

Sent using Tapatalk

 

[questnz]

AOR makes a discone: DA6000 700-6000MHz for under $500 but do a little research as I don't think there is anything you can listen to much over 1.5GHz. You'll find it's almost all proprietary digital and/or encrypted from what I've been told. I don't monitor anything over 1GHz, I'm only 6'3".
View attachment 70640
AOR DA6000 UHF Scanner Antenna

Few years ago I seen exact or similar antennas mounted on Military Communication trucks parked on the field during
Air Show in Radom - Poland.
How good antenna is it for normal scanning requirements up to 1 GHz, Just like Kreco it is worth the extra money ?
Not many reviews on this gizmo, can this definitely outperform our usual Discones and Omnis.
Intimidating looking device not sure what the neighbors would think

 

[hsdtech]

Some guys seem to think the more you pay for an antenna the better it is and your receive will be top notch. Rediculous. Build quality and reputation is what matters when buying one. The Diamond discone is all you would need. If you need a specific frequency range and/or out of decent range from the source, then there are always directional antennas. A yagi antenna is of course directional and are super easy to make yourself. Spending $500 on an antenna that you could pay $50 for won't help your signal strength if they are cut to the same frequencies.
A good brand antenna (diamond, comet, hustler, etc.), GOOD coax (Beldin RG6 or LMR), and getting the antenna up as high as you can is all that you need.

 

[iMONITOR]

Few years ago I seen exact or similar antennas mounted on Military Communication trucks parked on the field during
Air Show in Radom - Poland.
How good antenna is it for normal scanning requirements up to 1 GHz, Just like Kreco it is worth the extra money ?
Not many reviews on this gizmo, can this definitely outperform our usual Discones and Omnis.
Intimidating looking device not sure what the neighbors would think

I don't have one, nor did I recomend it. I was simply telling the OP what I have found that meets his wanting a discone that covers up to 6GHz. I actually advised him to do some research before buying one.

 

[Merovingian]

I don't have one, nor did I recomend it. I was simply telling the OP what I have found that meets his wanting a discone that covers up to 6GHz. I actually advised him to do some research before buying one.

Yes, I'm Doing a lot of research. I've taken prcguy's advice regarding the discones he recommended but I'm am searching a little farther to make sure I am not missing anything. At this point I will probably go with the discones he recommended since they seem to cover what I need even though the UHF portion doesn't start quite as high as I wanted. I would like to get that $500 discone but the price is a bit too steep. I'm not that deep into the hobby yet to warrant prcguy's level of hardware.

 

[prcguy]

To a good extent, you do get what you pay for with most things in life including antennas. The original Discone design was for a solid sheet metal disc and cone. Calculations and field testing show you need at least 16 disc and cone elements to equal the performance of a solid sheet metal version. These will outperform the typical scanner Discones from Radio Shack, Diamond and others who use only six or eight elements for the disc and cone. Kreco uses 12 and so do many other commercial and military versions that cost a lot more.

Some guys seem to think the more you pay for an antenna the better it is and your receive will be top notch. Rediculous. Build quality and reputation is what matters when buying one. The Diamond discone is all you would need. If you need a specific frequency range and/or out of decent range from the source, then there are always directional antennas. A yagi antenna is of course directional and are super easy to make yourself. Spending $500 on an antenna that you could pay $50 for won't help your signal strength if they are cut to the same frequencies.
A good brand antenna (diamond, comet, hustler, etc.), GOOD coax (Beldin RG6 or LMR), and getting the antenna up as high as you can is all that you need.

 

[Ubbe]

Somewhere else in the forum we discussed discones and the optimum one uses a solid cone and a disk. You see them being designed for use at several GHz and upwards. At lower frequencies the wavelenght of the radiosignal are so long that it hardly slips between the space of rod elements.

There's a mathematical formula that says how much signal you loose at different spaces between elements and an 8 legged discone had only a few tenths of a decibel of loss. The more elements you have the higher the wind resistance will be. A solid cone are out of the question for a MHz discone and a 16 legged needs almost a sturdy military type of installation to be able to cope with storm winds, if it's not a small one only designed for 300Mhz and upwards. A 16 leg discone doesn't cost double of a 8 legged, it costs much much more as the base where all elements are attached have less material due to double the amount of holes and the needed extra strenght to cope with the added wind resistance. So the base needs to be made of highest quality metal and mechanical engineered to support the forces it's exposed to.

/Ubbe

 

[prcguy]

There is a certain minimum fraction of a wavelength needed between the ends of the Discone elements that is required to give the equivalent performance of a solid disc and cone. I don't remember what that fraction of a wavelength is but it will be proportional at all frequencies, so whatever number of disc or cone elements are needed to achieve that minimum spacing is at 10MHZ will be the same number needed at 100MHz or 1,000MHZ. So if 12 or 16 disc and cone elements are needed on a low frequency Discone to equal solid sheet metal, the same amount will be needed for any Discone at any frequency.

Its similar to how many ground radials are needed to replicate a solid sheet metal ground plane for a vertical antenna but since the radials of a Discone are bent down at a sharp angle, the spacing is closer than if they were all on a parallel plane that would spread the ends out further.

Somewhere else in the forum we discussed discones and the optimum one uses a solid cone and a disk. You see them being designed for use at several GHz and upwards. At lower frequencies the wavelenght of the radiosignal are so long that it hardly slips between the space of rod elements.

There's a mathematical formula that says how much signal you loose at different spaces between elements and an 8 legged discone had only a few tenths of a decibel of loss. The more elements you have the higher the wind resistance will be. A solid cone are out of the question for a MHz discone and a 16 legged needs almost a sturdy military type of installation to be able to cope with storm winds, if it's not a small one only designed for 300Mhz and upwards. A 16 leg discone doesn't cost double of a 8 legged, it costs much much more as the base where all elements are attached have less material due to double the amount of holes and the needed extra strenght to cope with the added wind resistance. So the base needs to be made of highest quality metal and mechanical engineered to support the forces it's exposed to.

/Ubbe

 

[nd5y]

There is a certain minimum fraction of a wavelength needed between the ends of the Discone elements that is required to give the equivalent performance of a solid disc and cone.

I want somebody to take one of those 12 or 16 element discones, remove even numbers of elements to keep it symmetrical (not changing the element length) and measure the radiation pattern and bandwidth each time you remove a pair of elements.

 

[W5lz]

I've had a 'cone that lost several "legs". I honestly couldn't hear a huge (actually any) difference in performance. Keep in mind that my "ear" measurements are not exactly "lab" quality.
Also made one using screen instead of "legs". Ugly but it worked just dandy.