Discone Reception Questions

[KI5IRE]

I’ve had an attic mounted discone for about 6 months now and I’ve been fairly happy with it for monitoring anywhere from analog or digital frequencies in the 100 bands to 800 bands. I was wondering what some things to do to improve my reception might be. I understand these antennas are low-zero gain but not sure if I could use an amplifier to possibly pick up some frequencies on a system I would really like to hear? Would an amp work with P25 systems? I also know about better cable possibly helping my reception as well, however I’m using the cable that came with my antenna (Comet DS150S 25-1500 MHz Discone).

Basically I am trying to hear a P25 system (those of you in DFW, the Denton County P25 System and the Grand Prairie and Irving sites of FWRRS) that others I know within 5-10 miles of me are able to receive, but not me. I’m going to try raising my antenna up higher in my attic about the 5-6 in. I have left with the top element on and see if I can get some more line of sight reception and possibly hear the system these next few days. But if I take the top element off to get more room to get the antenna and the rods higher, would this effect my reception at all? Will taking the top element rod off effect me unless I am transmitting? I have heard the top element rod is only for transmission purposes.

I am able to hear the Parker County P25 System just fine which is about equal or more distance from me, but it is on a lower frequency band than Denton so maybe that’s why?

Thanks for any help y’all have for me.

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[paulears]

The problem with preamps is that they are not magic. They are great at taking what the antenna can hear, boosting this and then any cable losses don't matter - but the truth is simple. They can only amplify what is present, and cannot invent something that's not there. If something is above the noise floor, then a low noise preamp can stop this getting lost in the cable. If there is nothing there at all, that's impossible to amplify. Probably the real solution would be to improve your antenna system first. Decent preamps can be easily two hundred pounds or more, and wide band ones are troubled badly by local strong signals that swamp the devices. The better ones are single band, and often limited to just that band with advanced filtering.

Moving the discone outside gives a benefit, but if it has to remain in the loft, then dedicated antennas for the bands of interest are the only way, with possibly combining networks , but again, these damn things have losses. If the discone cannot hear it, then I doubt any 0dB gain antenna will.

 

[cmdrwill]

" frequencies in the 100 bands to 800 bands "

For the VHF UHF and 800 you do not need the top element rod with the black loading coil. Try removing the 'rod' and moving the antenna up a bit.

Most find the discone type antennas like yours do not work well above 400 MHz.

 

[KI5IRE]

" frequencies in the 100 bands to 800 bands "

For the VHF UHF and 800 you do not need the top element rod with the black loading coil. Try removing the 'rod' and moving the antenna up a bit.

Most find the discone type antennas like yours do not work well above 400 MHz.

They don’t work well even if they’re rated for that range?


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[nd5y]

A discone like that designed for a low end of ~100 MHz might have low SWR at 400 or 800 MHz
but the radiation pattern angle increases with frequency and at 400 or 800 MHz is mostly pointed up at a 45 degree or higher angle.
They have no gain to begin with at the low end frequencies and the radiation pattern makes for
even less gain in useful directions at the high end frequencies.

 

[prcguy]

Yse on everything from nd5y, cmdrwill and paulears. A Discone design covers about an 8:1 frequency range with most scanner types having a bottom end around 100Mhz and the top end around 800MHz but as mentioned about half way through their frequency range the radiation pattern skews upward, reducing reception at the horizon.

Removing the top whip and black coil is the best thing to do if you don't need reception below 100MHz. Height is important and if you raise the Discone another 2ft after removing the whip it will work better, question is will it be enough for you to notice.

Coax supplied with a Discone is typically RG-58 and if you have any length of that like 50ft you will really benefit by upgrading to something like LMR400. If its a very short run like 20ft or less there will be a much smaller improvement.

You probably have very little loss through your roofing material in the VHF/UHF range with a little more attenuation at 800MHz. Putting the Discone outside and above your neighbors roofs would be a big improvement if you can get away with it.

If you need help installing outside I'll be in the Richardson area in a couple of months and would be happy to help.
prcguy

A discone like that designed for a low end of ~100 MHz might have low SWR at 400 or 800 MHz
but the radiation pattern angle increases with frequency and at 400 or 800 MHz is mostly pointed up at a 45 degree or higher angle.
They have no gain to begin with at the low end frequencies and the radiation pattern makes for
even less gain in useful directions at the high end frequencies.

 

[jim202]

I noticed that there are some metal weather heads in the roof on each side of your antenna. I would try to move the antenna away from those metal objects. Sometimes just moving the antenna a couple of feet makes a big difference with an 800 or 700 trunking system reception.

If you have a portable receiver, try moving around in the attic to see if you can find a better hot spot where you can hear the system better. Just remember to not put your body between the system and the radio while trying this. Try looking in the direction of the trunking system while holding the portable.

As others have mentioned, RG-58 is not what is a very good type of coax to use for 800 MHz signals. It's loss is way up there. Some RG-8, RG-8X, RG-214, 8913, or maybe some LMR-400 would be much better.

Just make sure you have connectors that will work on the cable your getting. If your going to use crimp connectors, make sure you have the correct sized crimper.

 

[Ubbe]

As mentioned, do not use RG58 coax. Go for RG6 that wont empty your wallet and have excellent performance. If there is a specific system you're trying to receive it probably will be in a specific frequency range, like 800-850MHz. Then you could remove that top antenna element and put a good 800MHz antenna there to boost that frequency range. Good antennas are a gain version that are at least 5/8 type that focus on signals at the horizon and preferable stacked antennas like a 1/2 over a 1/4 and more, antennas that are 2 feet or longer. That will improve performance much more than raising the discone 2 feet. That top element could interfere with frequencies at other frequency ranges like 400MHz but could also be the opposite.

Amplifiers work wonders, almost a must when trying to receive UHF high frequencies, but must always be used in pair with a variable attenuator. If the amplifier have a noise figure that are lower than your scanners, and most are, then you will actually pull in signals that cannot be heard at all on the scanner and no coax at any cost will do that.

/Ubbe

 

[Mark]

I find discones work fine for aviation etc but good old fashioned beam type
for 800 band may be the way.. Directional of course but strong gains.
an example on internet and am in no way affliliated with this company.
Just what a good beam can do.. Miss my old roof top antenna beam with rotator..was the Best!
Got to get me another one soon.
Indoor 700/800 MHz Yagi Directional Antenna with Desktop Stand | Scanner Master

 

[JamesO]

Personally I would abandon the discone and go for some other omni antenna and consider a good LNA.

Suggest you read this thread - https://forums.radioreference.com/s...60107-vhf-770mhz-antenna-recommendations.html

 

[bobsav21]

Dont give up on the discone yet.
I recently put a diamond D-130J in my attic and am able to receive 800 MHz trunk system from 32 miles away. ( Portland ME PD and FD ). Try moving it around the attic a little, I moved mine from approx the middle of the attic to the end gable wall and it improved reception quite a bit.
I used 50'RG8U coax. Many people here say discones are no good for general scanning but mine exceeded my expectations. I never thought I'd be able to get the Portland system from this location.
Bob

And yes the other poster is correct, you don't need the vertical whip on top for what your doing. Remove it and you'll gain some space that will help you move it around.

 

[JamesO]

Dont give up on the discone yet.
I recently put a diamond D-130J in my attic and am able to receive 800 MHz trunk system from 32 miles away. ( Portland ME PD and FD ). Try moving it around the attic a little, I moved mine from approx the middle of the attic to the end gable wall and it improved reception quite a bit.
I used 50'RG8U coax. Many people here say discones are no good for general scanning but mine exceeded my expectations. I never thought I'd be able to get the Portland system from this location.
Bob

And yes the other poster is correct, you don't need the vertical whip on top for what your doing. Remove it and you'll gain some space that will help you move it around.

But you had no antenna in the attic before, so you have no other antenna to compare against.

You are going to spend between $50-$100+ for a discone, I think there are many other better suited antennas on the market in this price range. And forget Yagi antennas because they will limit what you can receive. There are plenty of better options for omni directional reception that can still do a good job on fringe signals.

I am still not sure what the overall interest is in discones is, if you have multiple antenna for many activities, then a discone might be one antenna that is available for use, but if I could only have a single antenna, I would not consider a discone.

 

[pro92b]

Discones are intermod magnets. They are more efficient in the FM broadcast band than any other scanner antenna. The chances of FM broadcast overloading a scanner are quite high with a discone, especially if the scanner is a GRE design. There are certainly better options.

 

[bb911]

Discones are intermod magnets. They are more efficient in the FM broadcast band than any other scanner antenna. The chances of FM broadcast overloading a scanner are quite high with a discone, especially if the scanner is a GRE design. There are certainly better options.

I agree -- intermod magnets. Also, if you use RG 6 coax as was mentioned, I'd suggest using the quad shield variety. Good stuff.

 

[KI5IRE]

Thank you all for your input and suggestions so far everyone has posted. I really do appreciate it.

I saw some of you suggesting to relocate my antenna in my attic, but currently it’s attached to the vertical beams in my attic with an approximately 4 ft piece of horizontal 2x4 with 4 nails similar to those used to build home frames (not sure of the exact length) in a square pattern and I only have one area (where I currently have it located) where I really can put it, it’s the highest point of my attic and farthest away from obstructions and as many metal objects as possible. Not sure where else to put it without sacrificing one or more reasons why it is where it is currently.

As to relocating it outside, that was my original idea was to mount it outside on my roof, especially since I wanted it to be as high as possible since I live in a lower lying area, but unfortunately my HOA regulations don’t allow any type of antenna either mounted to roof tops, fences, towers or poles cause it’s not “uniform”.

I am open to any ideas as to mounting my antenna in my attic stand alone in my attic i.e. a paint bucket with concrete and a piece of fence pipe or spare piece of cheater pipe I have laying around, however, I don’t have anywhere to really do that either in my attic and would really like it to be at its highest point for best line of sight and best results.

I am currently monitoring analog frequencies in various bands, really anywhere from around 100 bands to 800 bands and digital p25 systems within the same range, all of these systems are from all over directions, with no really specific direction. I currently only have one scanner, a handheld BCD436, hopefully will purchase a second when I have the money. I was told by a few other radio hobbyists that a discone was a great option given my circumstances but have seen several of you saying there are better options than a discone, i would actually really like to see what other options I may have for Omni-directional coverage as long are they are not going to break the bank.

Also have seen some recommendations on upgrading my cable, I am currently running whatever cable came with my Comet discone, but not sure what it is exactly. However many feet (50 I think) it is is being used a good bit, so if I’m upgrading cable, I’d like to keep it best quality for lowest price for however many feet i need. I also have to keep it the same diameter due to the way it is ran now. If there is something out there that could improve my reception, I may be open to that.

I also still have the rubber end caps on all of the rods on my discone that came on them in the packaging, but wasn’t sure if I am supposed to remove them. Could not removing them also be causing an issue or do you think removing them isn’t going to be much change?

I noticed that there are some metal weather heads in the roof on each side of your antenna. I would try to move the antenna away from those metal objects. Sometimes just moving the antenna a couple of feet makes a big difference with an 800 or 700 trunking system reception.



If you have a portable receiver, try moving around in the attic to see if you can find a better hot spot where you can hear the system better. Just remember to not put your body between the system and the radio while trying this. Try looking in the direction of the trunking system while holding the portable.



As others have mentioned, RG-58 is not what is a very good type of coax to use for 800 MHz signals. It's loss is way up there. Some RG-8, RG-8X, RG-214, 8913, or maybe some LMR-400 would be much better.



Just make sure you have connectors that will work on the cable your getting. If your going to use crimp connectors, make sure you have the correct sized crimper.

I did what you suggested with my portable with my rubber duck on it instead of plugged into my discone. I actually was able to pick up 3 systems I want to receive but currently don’t just by holding my portable higher than the antenna currently is and pointing the antenna in the general direction. These signals were not very strong but I was still getting bars and a DAT and LNK light and some transmissions from these systems/sites. I also noticed I when I locked on a system I that only receive with when in my house connected to my antenna but not on the portable with the rubber duck to see what it’s signal looked like. When I did this, I held it at the same height as my antennas current height and only got a faint signal as opposed to having full bars when I am connected to my discone. I thought this was odd that I am getting a weaker signal with a rubber duck than with my my discone since the discone has 0 gain? Why would this be? I am hoping that the reason I didn’t get the system I am trying to hear the most with just my portable is because I didn’t have my rubber duck as high as possible or that it was too weak to show on my rubber duck but will be stronger with the antenna.

My friend who helped me install my antenna is supposed to help me move it, so hopefully once I take the top element off and move it up, I will see an improvement.

Thanks again for yalls help and suggestions so far.


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[prcguy]

The main reason you picked up signals with your scanner and rubber duck that you could not with the Discone is because of the cable supplied with the Discone. It should be a little smaller dia than a pencil, or about 1/4" and 50ft of that looses about 90% of signal at 800MHz. At VHF its looses about half and UHF about 75% loss. Upgrading to the most popular low loss cable would be going to a something a little more than 1/2" dia and not as flexible.

I personally don't like using RG-6 TV coax on a 50 ohm rated antenna but that would be a big improvement over RG-58 and its only a little bigger. In your case a modest antenna preamp might work amplifying the signals before its shoved into the coax, making up for losses. I would upgrade coax to at least RG-6 before exploring the preamp route.

On people slamming Discones as rubbish, I probably own and use far more antennas than most people on this forum. I've used and tested just about everything that exists from cheap hobby scanner types to huge commercial repeater types to Yagi's and several Log Periodics. I have patch panels and frequency dependent combiners to connect the best commercial high gain antennas for all bands into one coax to feed whatever receiver I'm playing with at the time. I also have an array of some of the best low noise super high dynamic range preamps for every band available.

With all that said my go to antenna(s), which I'm using right now on my new Icom R-8600 is a a pair of Discones, one covers about 100 to 800Mhz and the other about 400 to 3,200MHz combined with a diplexer with a transition in the 600Mhz range. I rarely use a preamp and my coax is a combination of 1/2" Heliax and LMR400.

Think about that, my roof looks like a huge mountain top repeater site with every antenna you could dream of and well over 95% of the time I use the Discones because they work great and cover a huge frequency range with the same performance across all the bands. I use the Discones most often because they are the best all around very wide band antennas I have ever used.

I do realize my larger Discone is not so great at 800 reception due to the pattern shifting upward and that's where combining a smaller one fills that need and extends my range beyond what my receiver can do. For most people who want to receive everything including 800 my first suggestion would be a similar setup using a normal Discone for 100-500Mhz and a separate 700/800 gain type omni with the same diplexer I use to combine them on the same coax.

There are scanner specific antennas that cover the public service bands around 150, 450 and 850Mhz in very narrow ranges that will work slightly better than a Discone within those ranges. However, if you want to scan VHF air band or UHF air band or some of the amater radio bands the Discone will work everywhere where the others are only peaked in their very narrow regions.

On the subject of preamps, many preamps must be terminated with a good 50ohm match across their entire range, otherwise they can have problems like oscillations. I've experienced this with two supposedly high end preamps where they turned into a power oscillator at some random frequency, using up all their dynamic range and reception was terrible. They worked ok with a Discone but on a single band antenna they went nuts and turned into oscillators. A really good preamp from Angle Linear or possibly MiniCircuits will generally not have this problem and I'm bringing this up as another pitch for the Discone, which provides a good match to a preamp or receiver over its entire operating range and then some.

So upgrade your coax and see if that allows you to receive everything you need. If not then consider a seperate 800 antenna with a diplexer or a wide band preamp, but preamps can also introduce a host of new problems so be aware of that. Sorry if my post went a little long...
prcguy

Thank you all for your input and suggestions so far everyone has posted. I really do appreciate it.

I saw some of you suggesting to relocate my antenna in my attic, but currently it’s attached to the vertical beams in my attic with an approximately 4 ft piece of horizontal 2x4 with 4 nails similar to those used to build home frames (not sure of the exact length) in a square pattern and I only have one area (where I currently have it located) where I really can put it, it’s the highest point of my attic and farthest away from obstructions and as many metal objects as possible. Not sure where else to put it without sacrificing one or more reasons why it is where it is currently.

As to relocating it outside, that was my original idea was to mount it outside on my roof, especially since I wanted it to be as high as possible since I live in a lower lying area, but unfortunately my HOA regulations don’t allow any type of antenna either mounted to roof tops, fences, towers or poles cause it’s not “uniform”.

I am open to any ideas as to mounting my antenna in my attic stand alone in my attic i.e. a paint bucket with concrete and a piece of fence pipe or spare piece of cheater pipe I have laying around, however, I don’t have anywhere to really do that either in my attic and would really like it to be at its highest point for best line of sight and best results.

I am currently monitoring analog frequencies in various bands, really anywhere from around 100 bands to 800 bands and digital p25 systems within the same range, all of these systems are from all over directions, with no really specific direction. I currently only have one scanner, a handheld BCD436, hopefully will purchase a second when I have the money. I was told by a few other radio hobbyists that a discone was a great option given my circumstances but have seen several of you saying there are better options than a discone, i would actually really like to see what other options I may have for Omni-directional coverage as long are they are not going to break the bank.

Also have seen some recommendations on upgrading my cable, I am currently running whatever cable came with my Comet discone, but not sure what it is exactly. However many feet (50 I think) it is is being used a good bit, so if I’m upgrading cable, I’d like to keep it best quality for lowest price for however many feet i need. I also have to keep it the same diameter due to the way it is ran now. If there is something out there that could improve my reception, I may be open to that.

I also still have the rubber end caps on all of the rods on my discone that came on them in the packaging, but wasn’t sure if I am supposed to remove them. Could not removing them also be causing an issue or do you think removing them isn’t going to be much change?




I did what you suggested with my portable with my rubber duck on it instead of plugged into my discone. I actually was able to pick up 3 systems I want to receive but currently don’t just by holding my portable higher than the antenna currently is and pointing the antenna in the general direction. These signals were not very strong but I was still getting bars and a DAT and LNK light and some transmissions from these systems/sites. I also noticed I when I locked on a system I that only receive with when in my house connected to my antenna but not on the portable with the rubber duck to see what it’s signal looked like. When I did this, I held it at the same height as my antennas current height and only got a faint signal as opposed to having full bars when I am connected to my discone. I thought this was odd that I am getting a weaker signal with a rubber duck than with my my discone since the discone has 0 gain? Why would this be? I am hoping that the reason I didn’t get the system I am trying to hear the most with just my portable is because I didn’t have my rubber duck as high as possible or that it was too weak to show on my rubber duck but will be stronger with the antenna.

My friend who helped me install my antenna is supposed to help me move it, so hopefully once I take the top element off and move it up, I will see an improvement.

Thanks again for yalls help and suggestions so far.


Sent from my iPhone using Tapatalk

 

[paulears]

Thank God for sanity. I can only confirm prcguy's observations on discones. Mine is exactly the same, and currently the discone, which is the third highest in my installation here is the solid, dependable one that I can measure the others against. The business radio UHF ones have some gain over the discone, but their performance drops markedly once you move away from the centre frequency. The ham dual bander is great in the ham bands, but drops in the marine band, only marginally better than the discone. On airband the ham antennas are worse. Swapping from antenna to antenna produces signals that go up and down like yo-yos, but the discone is the constant. I have some very high power local data signals that the discone does indeed receive, but a stub soon brings those down, and I don't see the point in having a less good antenna just because the discone hears everything. Strong signals can cause grief, but you deal with these at the radio end, I'd never choose an antenna on it's ability NOT to receive things! Given a choice of buying a commercial discone (I'm using a quite elderly J-Beam/Amphenol) or a dual bander for general scanning, there's no sensible option - discone all the way for me.

 

[bobsav21]

You said:
"I am open to any ideas as to mounting my antenna in my attic stand alone in my attic i.e. a paint bucket with concrete and a piece of fence pipe or spare piece of cheater pipe I have laying around,
"
You don't have to mount it on a pipe. You can just hang it from the rafters with some nylon or regular heavy duty string.

Take the top element off, put a screw in the top beam in your attic and just hang it there.
No need for the metal pole ...
Bob

 

[JamesO]

So here is the quickly and simpler solution, you have an antenna and a coax drop already installed and working.

Install a quality LNA right at the antenna connection, this will overcome any problems with the current coax you are running and could possibly be fed DC from a bias T inside near the radio, but it is cleaner to power the LNA directly which you should be able to do from within the attic.

If you are interested in learning more about this, PM me so I can get some more details and you can check some things so the proper recommendations can be made. There are some things to look out for, but if you can address any potential problem areas, chances are you could end up with very good end results.

 

[Ubbe]

I am currently running whatever cable came with my Comet discone, but not sure what it is exactly. However many feet (50 I think) it is is being used a good bit, so if I’m upgrading cable, I’d like to keep it best quality for lowest price for however many feet i need. I also have to keep it the same diameter due to the way it is ran now. If there is something out there that could improve my reception, I may be open to that.

RG6 has the same diameter as RG58 (which are mostly supplied with antennas) costs less than RG58 and at 50 feet and 800MHz it is a 6dB improvement in signal. If you go for the doubled thicker LMR400 it will cost you 10 times more and improve signal 7dB, not worth it. A discone antenna usually vary it's impedance between 25-200 ohms over it's frequency range so do not worry about the difference between 50 ohm coax and 75 ohm. The missmatch loss between 50 and 75 ohm are 0.17dB.

For receive the 75 coax has less loss compared to 50 ohm. See this from Belden:

You will note that 50 ohms is closer to 60 than it is to 30, and that is because voltage is the factor that will kill your cable. Just ask any transmitter engineer. They talk about VSWR, voltage standing wave ratio, all the time. If their coax blows up, it is voltage that is the culprit.

So why not 60 ohms? Just look at the power handling at 60 ohms - below 50%. It is horrible! At the compromise value of 50 ohms, the power has improved a little. So 50 ohm cables are intended to be used to carry power and voltage, like the output of a transmitter. If you have a small signal, like video, or receive antenna signals, the graph above shows that the lowest loss or attenuation is 75 ohms.

/Ubbe