Discone / Yagi

[RISC777]

I know this may be a dumb question, but I don't know the answer. So I'll fall back on "the only dumb question is the one you don't ask." And... it may have already been covered, but I haven't had the time to do a search (and I'm on a dial-up connection), so please bear with me.

Comparing a yagi to a discone, how much, if any, will a yagi receive as far as distance goes? (That wasn't worded very well, was it.)

Okay, say a discone is up and it's receiving signal(s) up to 50 miles away at the most. Now say a yagi is put up, will it receive signal from greater distances? *If* yes, how much farther will a yagi "reach out?"

 

[Randall]

think of it this way, the discone has a pattern like a flood light and the yagi is like a search light.the distance depends on many conditions, not just the antenna type.

 

[RISC777]

I'm cognizant of the omni directional radial reception versus the aimed reception, I'm just looking for info on generalized distance a yagi will receive.

 

[nd5y]

There is no generalized distance a yagi will receive. How far you can receive depends on the
path loss between the two stations, and each station's system gain and noise level.
Path loss can vary greatly no matter what antenna you use. A discone has less than
0 dBd gain and a yagi can have anywhere from about 5 to 15 dBd depending on the
number of elements and boom length.

 

[Al42]

At the frequencies we're usually discussing for these types of antennas, 450-900 MHz, you can receive just about any signal you can see the transmitting antenna of (except low-powered transmitters, like hand-helds), so the distance is determined by the distance to the horizon, which is approximately 1.17 times the square root of the height in feet. If the antenna has enough gain to overcome the loss of receiving a signal through the ground (many db/mile), a high gain antenna may increase the range a bit past the horizon - but we're talking something with higher gain than any practical Yagi, even at 900 MHz.

Bottom line is that changing from a discone to a Yagi will allow you to receive weaker signals, but not signals over the horizon, while a good discone will allow you to receive decent strength signals to the horizon (which is surprisingly close for, say, an antenna mounted on the roof of a single story house - on the order of 4.5 miles [plus the distance to its horizon of the transmitting antenna]).

 

[RISC777]

...while a good discone will allow you to receive decent strength signals to the horizon...

But a discone it not limited to just point-to-point/the horizon, correct? Otherwise there are transmissions I can receive that are going through one or more repeaters (correct?).

 

[VintageJon]

Now repeaters come into question, and a good question it is... You gotta know where the repeaters are to really tell.

Al42- interesting post, "so the distance is determined by the distance to the horizon, which is approximately 1.17 times the square root of the height in feet. "
Is this to say that if I have a 1/4 wave ground plane, cut for 800MHZ, at 7' then the horizon is
3.3 miles, (based on the square root of 7 being apoximately 2.65...)

If I have your theory right I guess height is a good thing! (Silly me, you can't argue with height, it was always thus).

73's,
Jon

 

[RISC777]

Now repeaters come into question, and a good question it is... You gotta know where the repeaters are to really tell.

Jon

Repeaters I can locate because most, if not all, in this state are already mapped out and located. But my quandary is I can input a frequency which a close tower is using, but I cannot to date "hop repeaters" to the desired originating source.
I can be in the automobile, have a CC that's good/correct and listen to all I want (even though the freq.s showing on the display change as the various TGs come up), but in similar fashion from a farther distance I cannot achieve the same result. In that, the same result (desired result) is having a CC that a "local" tower utilizes and have it connect/find/bring in the more distant originating transmission(s).

 

[Al42]

But a discone it not limited to just point-to-point/the horizon, correct? Otherwise there are transmissions I can receive that are going through one or more repeaters (correct?).

If the repeater's antenna is above your antenna's horizon, you can probably receive signals from it. If it's not (appreciably, not just an inch short of showing, but a few miles or more too far to be above the horizon), a discone can receive the signals if they're being bent or reflected by something, or if the transmitted power is high enough. "High enough", in this case, is much higher than anything legally permissable in the public service frequencies, since the attenuation is so high.

For instance, if the transmitting antenna was 5 miles too far to be above your horizon, the signals from it to you would be going through 5 miles of dirt. That's probably (depending on moisture content, mineral content, building foundations, etc.) thousands of db of loss, which the transmitter power would have to make up for. Over-the-horizon RADAR (the so-called "woodpeckers") could do this - by (in part) transmitting tens of thousands of kilowatts ERP. PS transmitters are usually no more than hundreds of watts, so anything above 400 MHz is limited to line of sight. At 200 MHz and below there are atmospheric effects that extend the range.

But the range is always from you to the transmitter you're receiving, so if you're looking to receive a repeater that's 100 miles closer to you than the dispatch point, the repeater antenna, not the dispatch point, has to be above your antenna's horizon. You calculate your antenna's horizon and the other antenna's horizon and add the mileage - if it's less than the distance between you, whether you can receive it depends on the path loss and the antenna gains. If the gains are high enough, and the loss (this includes cable on both ends) is low enough, you can receive the signal.

The practical application is to erect the antenna, connect it to the scanner and see if it works. You usually don't know the transmitted power or antenna gain, and you probably can't find out what cable they're using, so you're missing half the information you need to make the calculation in advance. But the people designing the system quite often do make those calculations to find out where to put the transmitter, and where to put satellite receivers, if they're needed, how much transmitter power and antenna gain is needed - and whether the whole thing has a chance of working. Sometimes "we need this" and "physics" don't even live in the same neighborhood.

 

[Al42]

I can be in the automobile, have a CC that's good/correct and listen to all I want (even though the freq.s showing on the display change as the various TGs come up), but in similar fashion from a farther distance I cannot achieve the same result. In that, the same result (desired result) is having a CC that a "local" tower utilizes and have it connect/find/bring in the more distant originating transmission(s).

If you're talking about Motorola SmartZone, remember that not all sites transmit all talk groups at all times. The usual setup is for a site to repeat only those talk groups that have mobiles on that talk group associated with that site. So, for instance, if you're in the west end of the city, listening to the west end site, and there's a transmission on the east end talk group, you'll only hear it if a mobile on the east end talk group is in the west end of the city at the moment, associated with the west end site.

Al42- interesting post, "so the distance is determined by the distance to the horizon, which is approximately 1.17 times the square root of the height in feet. "
Is this to say that if I have a 1/4 wave ground plane, cut for 800MHZ, at 7' then the horizon is 3.3 miles, (based on the square root of 7 being apoximately 2.65...)

It works out closer to 3.1, but yes. Which is why the rule of thumb range of two hand-helds on level terrain is no more than 5.5 miles, regardless of what the ads say. It's about 2.75 miles to the horizon from the average person's head. If the world were flat, we'd have a maximum range, at any height, of the distance from one corner of the world to the opposite corner, but Aristotle (I think he was the one) had to ruin it for all of us.

 

[RISC777]

If you can receive some signal now, regardless of how noisy it is, an 11 element Yagi, which is a small antenna at 850-900 MHz (about 28" long), will probably give you a fairly noise-free signal (it's about 13db gain, or about 20 times the signal strength).

Al42, quoting you above from another thread, since I sometimes do receive and sometimes do not receive from this one particular area - in my situation it may just not be the gamble I thought it might be to invest in the right yagi to be able to receive what I want to...?

 

[Al42]

Al42, quoting you above from another thread, since I sometimes do receive and sometimes do not receive from this one particular area - in my situation it may just not be the gamble I thought it might be to invest in the right yagi to be able to receive what I want to...?

The "sometimes do-sometimes don't" sounds like atmospherics. You might be able to receive at all times by aiming the antenna at something other than the transmitting antenna - a building halfway between you and it, for example, that would reflect enough signal toward you. Or the top of a hill that gives you some "knife edge" refraction. It's a hobby, so experiment. Find the plans and dimensions for a Yagi for the frequency range and build one. A dozen wire hangers and a broom handle (and some tools) are really all you need. A U-bolt antenna mast mount (like the Radio Shack 15-826) will mount the antenna to the mast, which can be the rest of the broom handle.

 

[n8chb]

I know this may be a dumb question, but I don't know the answer. So I'll fall back on "the only dumb question is the one you don't ask." And... it may have already been covered, but I haven't had the time to do a search (and I'm on a dial-up connection), so please bear with me.

Comparing a yagi to a discone, how much, if any, will a yagi receive as far as distance goes? (That wasn't worded very well, was it.)

Okay, say a discone is up and it's receiving signal(s) up to 50 miles away at the most. Now say a yagi is put up, will it receive signal from greater distances? *If* yes, how much farther will a yagi "reach out?"

Hi,

Omnidirectional vs directional antennas.

Often many folks are confused about just how a directional antenna works and many times I have seen manufactures complicate the confusion even more.

The gain of an antenna is not the main advantage of a directional antenna. The ability of it to block out unwanted signals is it's best feature.

Example: If 10 people were having an independent conversation surrounding you in a circle it would be difficult to tune into just one of them.
That's how a vertical antenna works. Now if you were able to block out everything but one conversation it would appear that you amplified one of them but in effect you really have not increased the level of there voices. You have just removed the others in order to hear better.

73,

Roger - N8CHB

 

[n8chb]

If you're talking about Motorola SmartZone, remember that not all sites transmit all talk groups at all times. The usual setup is for a site to repeat only those talk groups that have mobiles on that talk group associated with that site. So, for instance, if you're in the west end of the city, listening to the west end site, and there's a transmission on the east end talk group, you'll only hear it if a mobile on the east end talk group is in the west end of the city at the moment, associated with the west end site.

It works out closer to 3.1, but yes. Which is why the rule of thumb range of two hand-helds on level terrain is no more than 5.5 miles, regardless of what the ads say. It's about 2.75 miles to the horizon from the average person's head. If the world were flat, we'd have a maximum range, at any height, of the distance from one corner of the world to the opposite corner, but Aristotle (I think he was the one) had to ruin it for all of us.

I know a lot of design engineers that can not conceive things dimensional and still think the world is flat.

73

Roger - N8CHB

 

[kb2vxa]

Hi Risc and all,

There they go muddying the waters again! Ask a simple question and you open a can of worms.

I like that light analogy so I'll run with it and make a slight correction. Think of the discone as a light bulb and the Yagi as a spotlight. Which can you see farther away and which illuminates a greater area? Of course the spotlight goes the distance because the energy is concentrated in one direction and the light bulb covers a greater area watt for watt all things being equal.

Hey guys, KISS! You may take that as an acronym or a sarcastic remark, I don't care. (;->)

 

[n8chb]

Hi Risc and all,

There they go muddying the waters again! Ask a simple question and you open a can of worms.

I like that light analogy so I'll run with it and make a slight correction. Think of the discone as a light bulb and the Yagi as a spotlight. Which can you see farther away and which illuminates a greater area? Of course the spotlight goes the distance because the energy is concentrated in one direction and the light bulb covers a greater area watt for watt all things being equal.

Hey guys, KISS! You may take that as an acronym or a sarcastic remark, I don't care. (;->)

Hi KB2VXA - Warren,

I not sure if I am reading correctly or you meant to say " the light bulb covers a greater area watt for watt all things being equal."

I'm sure you are aware for the past 100 years or so amateurs have commonly refered to a vertical antenna as being equally poor in all directions.

Here is a very informative article pertaining to how antennas transmit and receive RF that is carried by photons.

http://www.phys.unsw.edu.au/~jw/EMspectrum.html

73


Roger

 

[kb2vxa]

Hi CHB and all,

If a vertical radiates equally poorly in all directions why do broadcast and utility stations use them? Why when I was using a grounded vertical folded unipole on 80M was I heard in the UK 5/9 with 100W when the dipole crowd in Kilowatt Alley were screaming thier lungs out and barely being heard or not at all? I can understand why those commercial multi band verticals fail so miserably, it's called radiation eficiency, or the lack of it. Sometimes vertical takeoff angle has something to do with hitting the target zone but I might be wrong, but then again those less than quarter wave verticals may be good for moon bounce. (;->)

Then we have the vertical colinear so very popular on VHF and UHF, maybe the owners of that wonder stick the Cushman Station Master are spending too much money for too little range. OK, I'm getting silly but you're getting the point. Every antenna has a particular use, there is a vertical for every occasion and they work or we wouldn't use them.

Back to serious beans, if you calculate the signal coverage in square miles you'll find an omni covers a few thousand more than a beam of equal ERP dispite the fact a beam reaches out farther. I'm sure you did such math problems in school, calculate the area of...

Well, I hate to be the one to tell you but there's a photon torpedo headed your way, RAISE SHIELDS! (;->)

 

[n8chb]

Hi CHB and all,

If a vertical radiates equally poorly in all directions why do broadcast and utility stations use them? Why when I was using a grounded vertical folded unipole on 80M was I heard in the UK 5/9 with 100W when the dipole crowd in Kilowatt Alley were screaming thier lungs out and barely being heard or not at all? I can understand why those commercial multi band verticals fail so miserably, it's called radiation eficiency, or the lack of it. Sometimes vertical takeoff angle has something to do with hitting the target zone but I might be wrong, but then again those less than quarter wave verticals may be good for moon bounce. (;->)

Then we have the vertical colinear so very popular on VHF and UHF, maybe the owners of that wonder stick the Cushman Station Master are spending too much money for too little range. OK, I'm getting silly but you're getting the point. Every antenna has a particular use, there is a vertical for every occasion and they work or we wouldn't use them.

Back to serious beans, if you calculate the signal coverage in square miles you'll find an omni covers a few thousand more than a beam of equal ERP dispite the fact a beam reaches out farther. I'm sure you did such math problems in school, calculate the area of...

Well, I hate to be the one to tell you but there's a photon torpedo headed your way, RAISE SHIELDS! (;->)

Well fire the photon torpedoes Cap and I'm happy someone took the time to read the link even though it was not directly related to the original question.

I am not the first one to say vertical antennas are poor in all directions it's a fact. That doesn't mean they are useless or not used by TV stations, FM stations, Public safety and so on. The primary use is to serve a wide area poorly in all directions. hi hi
The prime reason many run thousands of watts also.

(many am broadcast stations use phased vertical towers as antennas and they are directional and do have gain)

A stand alone vertical has no gain because because it radiates equal in all directions. Sorry but that's the pooper scooper.

Its an interesting subject and has always caused a lot of controversy.

Anywho could be my comments caused some interest and not just to tell me how wrong I am. (that's more than I'll admit to)

keep up the gud work om


73

Roger

 

[Al42]

(many am broadcast stations use phased vertical towers as antennas and they are directional and do have gain)

Two out of three. The phased arrays are used to put notches in the pattern, not to provide gain. (Most AM stations have other stations they have to protect.)

 

[n8chb]

Two out of three. The phased arrays are used to put notches in the pattern, not to provide gain. (Most AM stations have other stations they have to protect.)

You are correct the main reason commercial broadcasting uses arrays is to not to over lap into an other station on the same frequency.

The main reason an amateur uses phased arrays is for directional gain and also not hog the same frequency in all directions.

Roger