Wednesday, September 9, 2015
Tuesday, September 8, 2015
Balun for my 14AVQ?
Giving some thought to Baluns,
Original article is here http://www.hamuniverse.com/balun.html
Came across this guy ...
Rather simple , take 21' coax and wind it around anything and you have it .
Why a Balun ...
A balun's purpose is to allow connecting a balanced, (e.g., a dipole or driven element) to an unbalanced line such as coax which is not balanced, thus the name, Balun. The 1:1 choke "balun" is not actually a balun. It's function is to help eliminate rf currents from flowing on the outside of coaxial cable using the principle of choke action. Another "name" for it is the air choke.
In transmitting antennas, this is accomplished by presenting a high impedance (resistance), to RF currents flowing outside the coax shield. This forces currents in each side of a driven elements to be equal. This is especially important in beam antennas because it prevents distortion of the beam's pattern caused by unequal currents in the driver(s). In a simple dipole, the balun (choke), assuresthat the dipole, and not the feed line, is doing the radiating!
When you connect center fed antennas, like dipoles, V's, triangles, yagis, rhombics, loops and so on, to coaxial cable, unless care is taken, it is not difficult to end up with feeder radiation. Not only can the loss in power be quite significant, but the radiation characteristics of the antenna system will also be seriously compromised.
In laymen's terms, it won't be what you are expecting from the pattern of your antenna.
As the feedline becomes part of the antenna, currents can flow from the line into the mains and on TV cables, metal masts and yagi booms, causing a variety of EMI problems that can be very difficult to trace. Frequently these problems are simply due to unbalance - and the solution is the humble air choke.
If an antenna system is fed at center with a parallel conductor line (provided that correct installation procedures are followed) balance will be maintained, USING A BALUN, with currents in equal and opposite phase canceling each other out.
When the connection is to a coaxial cable, WITHOUT A BALUN, this cannot occur because currents flowing inside the cable from the connection to the inner conductor are separated from those flowing on the outside from the connection to the shield, and the result is unbalance causing feeder radiation. However, if the two electrical circuit elements (antenna and coaxial cable) are coupled using a balan, balance will be maintained.
Original article is here http://www.hamuniverse.com/balun.html
Came across this guy ...
Rather simple , take 21' coax and wind it around anything and you have it .
Why a Balun ...
A balun's purpose is to allow connecting a balanced, (e.g., a dipole or driven element) to an unbalanced line such as coax which is not balanced, thus the name, Balun. The 1:1 choke "balun" is not actually a balun. It's function is to help eliminate rf currents from flowing on the outside of coaxial cable using the principle of choke action. Another "name" for it is the air choke.
In transmitting antennas, this is accomplished by presenting a high impedance (resistance), to RF currents flowing outside the coax shield. This forces currents in each side of a driven elements to be equal. This is especially important in beam antennas because it prevents distortion of the beam's pattern caused by unequal currents in the driver(s). In a simple dipole, the balun (choke), assuresthat the dipole, and not the feed line, is doing the radiating!
When you connect center fed antennas, like dipoles, V's, triangles, yagis, rhombics, loops and so on, to coaxial cable, unless care is taken, it is not difficult to end up with feeder radiation. Not only can the loss in power be quite significant, but the radiation characteristics of the antenna system will also be seriously compromised.
In laymen's terms, it won't be what you are expecting from the pattern of your antenna.
As the feedline becomes part of the antenna, currents can flow from the line into the mains and on TV cables, metal masts and yagi booms, causing a variety of EMI problems that can be very difficult to trace. Frequently these problems are simply due to unbalance - and the solution is the humble air choke.
If an antenna system is fed at center with a parallel conductor line (provided that correct installation procedures are followed) balance will be maintained, USING A BALUN, with currents in equal and opposite phase canceling each other out.
When the connection is to a coaxial cable, WITHOUT A BALUN, this cannot occur because currents flowing inside the cable from the connection to the inner conductor are separated from those flowing on the outside from the connection to the shield, and the result is unbalance causing feeder radiation. However, if the two electrical circuit elements (antenna and coaxial cable) are coupled using a balan, balance will be maintained.
30 Meter Ant #s
30 Meter Wire Antennas
This Band CW Only
Center Frequency: 10.120 Mhz 29.87 Mhz 3rd Harmonic Halfwave in space is: 48.62 feet 33.06 coax|39.87 twinlead Quarterwave in space is: 24.31 feet 16.53 coax|19.93 twinlead Quarterwave Vertical is: 23.12 feet 27.23 foot ground radials Five Eights wave Vertical is: 59.58 feet 23.12 foot ground plane Three Quarter wave Vertical: 71.74 feet 11.56 foot eighthwave Halfwave Dipole/Vertical is: 46.25 feet 23.12 one side. Halfwave Reflector is: 48.56 feet 44.16 for Director Low Mount Halfwave is: 45.26 feet 22.63 one side. Halfwave Folded Dipole is: 45.65 feet 22.83 one side. Halfwave Inverted V is: 47.92 feet 23.96 one side. Colinear Array is: 94.86 feet 47.43 one side. Extended Double Zepp is: 119.17 feet 59.58 one side. Fullwave Quad Loop is: 100.79 feet 25.20 one side. Reflector|Director: 105.83|96.25 26.46|24.06 one side. Fullwave Delta Loop is: 100.79 feet 33.60 one side. Reflector|Director: 105.83|96.25 35.28|32.08 one side. Waves 1: 94.86 |1.5: 143.48 |2: 192.09 |2.5: 240.71 |3: 289.33 |4 : 386.56 Waves 5: 483.79 |6.0: 581.03 |7: 678.26 |8.0: 775.49 |9: 872.73 |10: 969.96This is a shared band. Expect to find Commercial RTTY and FAX, especially Weather FAX transmissions on this band. Most international HAM signals will be found near 10.105, but Japanese stations frequently cluster around 10.130 Mhz.
Monday, September 7, 2015
Remote antenna sw
Its in the mail ...
I am going to run the existing 30 meter Vertical through this switcher then I am planning on adding a 30 meter dipole for comparison. Not sure if I will do 2 more different 30 meter antennas but I do know one thing for sure its going to be really cool. If this switch works out I am going to get the larger one with more inputs plus VHF/UHF capabilities for the top of the hill.
I am going to run the existing 30 meter Vertical through this switcher then I am planning on adding a 30 meter dipole for comparison. Not sure if I will do 2 more different 30 meter antennas but I do know one thing for sure its going to be really cool. If this switch works out I am going to get the larger one with more inputs plus VHF/UHF capabilities for the top of the hill.
14AVQ Troubles
The 14AVQ vertical is not working well so I was reading on the internet and someone suggested taking ti apart an cleaning the traps and what not. Its seems to work OK on 10m and 15m but the TS690s really doesn't like the antenna on 20m and 40m. The old FT101e didn't mind the old antenna bit its not the same with teh new rig. The 14AVQ VSWR on 10m is great , 1.2:1 @ 28.1 MHz ... 15m is similar but 20 and 40 nothing below 2:1 VSWR.
Thought I nailed the fault right off the first trap above the 10m section had a tab broke off the cover ...
So I came up with this fix ...
Also found something growing under the second trap ...
Cleaned everything up and put it all back together...
Unfortunately it did not make much of a difference! There is a very good possibility it may have something to do with the 500' run of LDF4 cable to the top of the hill where the antenna is located. The next step is to try the antenna closer to the house with a different IFL.
Inspite of questionable performance on 20 meters I used the TS590s to make an SSB contact on 20 meters .... an ever so brief QSO with a guy in Cuba.
Thought I nailed the fault right off the first trap above the 10m section had a tab broke off the cover ...
So I came up with this fix ...
Also found something growing under the second trap ...
Cleaned everything up and put it all back together...
Unfortunately it did not make much of a difference! There is a very good possibility it may have something to do with the 500' run of LDF4 cable to the top of the hill where the antenna is located. The next step is to try the antenna closer to the house with a different IFL.
Inspite of questionable performance on 20 meters I used the TS590s to make an SSB contact on 20 meters .... an ever so brief QSO with a guy in Cuba.
Wednesday, September 2, 2015
Attenuation due to tress at HF
I sure do know the effects of Trees / Vegetation at Microwave Frequencies but I really do not know much about the effects at UHF/VHF and HF below 30 MHz. I know that there would be some affect at VHF/UHF and that it would significantly decrease as you get down to the HF band. So I googled the topic and here is what I found......
Ora E. Smith:
There is book called "HF Communications: A Systems Approach" by Nicholas Maslin (1987, I think) that addresses the issue briefly. My interpretation of what he says is that vegetative attenuation negligible below 2 MHz, but can be a major factor at 30MHz. A curious result of his analysis is that for ground wave propagation through vegetation, the loss below 30MHz for a given frequency is essentially constant and independent of distance -not sure I follow his thinking, but that seems to be his conclusion. The only way I can make sense of that is to conclude that wave propagation extends above the tree line and that the attenuation occurs mostly in the antenna near field, but that is not his explanation. If my version of this is true, it would seem that unless you are operating in a very tall rain forest, getting the antenna a few wavelengths away from trees so none of them are in the nearfield would reduce attenuation effects markedly. Also, objects in the near field are able to distort the radiation pattern of the antenna considerably, unlike far field objects.
If you're talking about skywave attenuation, then it seems that you would want the antenna to have a clear view out to a few wavelengths, according to my theory anyway.
At 30MHz he states that the standard deviation of loss (so this must be based on either some kind of data or lots of simulation runs) is on the order of 4 db through bare trees, and 7 db through leafed trees. Loss increases exponentially with frequency, he says, and is negligible by the time you are down to 2MHz. I generally try to stay away from trees except as antenna supports, and I have found that operating portable in the woods is difficult, though it's hard to separate out all the other portable antenna shortcomings from the tree influence.
Trees have fairly minimal effect on HF propagation.
Trees touching your HF antenna will tend to ground out the antenna. The more touching points, and the wetter, the more signal you will lose. Foliage touching at high voltage points can and has caught fire! There are a number of posts here and on the other board in the last couple years, some with photos, to attest to this.
An insulated wire vertical could be hauled up alongside a trunk and avoid the grounding problems. Stake out some radials at the base. Very stealthy and neighbor friendly.
"Trees
As potential hazards these are usually much overrated. Horizontally polarized antennas can usually be more or less buried in trees with little or no effect"
Here is my added advice, Use INSULATED wire, do not use bare wire....
For HF, any attenuation will be essentially unmeasurable by any equipment the average ham is likely to have. Wires in the trees are common and work quite well.
As the frequency goes up past 50 mhz, the attenuation will be more and more of a factor and will be measurable. For 2m/440, higher is not only better, the antennas really need to be above the trees, unless all you are doing is hitting local repeaters. For weak-signal work height and tree clearance are everything.
Ora E. Smith:
There is book called "HF Communications: A Systems Approach" by Nicholas Maslin (1987, I think) that addresses the issue briefly. My interpretation of what he says is that vegetative attenuation negligible below 2 MHz, but can be a major factor at 30MHz. A curious result of his analysis is that for ground wave propagation through vegetation, the loss below 30MHz for a given frequency is essentially constant and independent of distance -not sure I follow his thinking, but that seems to be his conclusion. The only way I can make sense of that is to conclude that wave propagation extends above the tree line and that the attenuation occurs mostly in the antenna near field, but that is not his explanation. If my version of this is true, it would seem that unless you are operating in a very tall rain forest, getting the antenna a few wavelengths away from trees so none of them are in the nearfield would reduce attenuation effects markedly. Also, objects in the near field are able to distort the radiation pattern of the antenna considerably, unlike far field objects.
If you're talking about skywave attenuation, then it seems that you would want the antenna to have a clear view out to a few wavelengths, according to my theory anyway.
At 30MHz he states that the standard deviation of loss (so this must be based on either some kind of data or lots of simulation runs) is on the order of 4 db through bare trees, and 7 db through leafed trees. Loss increases exponentially with frequency, he says, and is negligible by the time you are down to 2MHz. I generally try to stay away from trees except as antenna supports, and I have found that operating portable in the woods is difficult, though it's hard to separate out all the other portable antenna shortcomings from the tree influence.
|
« Reply #8 on: October 21, 2003, 01:19:10 PM »
|
Yes and no!
Trees and plants do attenuate HF signals.
I found out that maïs does attenuate a lot on 10m. Just use your 10m HT or mobile setup near a maïs-field and you'll notice the attenuation of the received signals.
When you're using a 80m antenna near trees it will have (almost) none influence.
This is not a scientific study, but just the things I personally discovered.
73 de ON4MGY Nic
Trees and plants do attenuate HF signals.
I found out that maïs does attenuate a lot on 10m. Just use your 10m HT or mobile setup near a maïs-field and you'll notice the attenuation of the received signals.
When you're using a 80m antenna near trees it will have (almost) none influence.
This is not a scientific study, but just the things I personally discovered.
73 de ON4MGY Nic
Trees have fairly minimal effect on HF propagation.
Trees touching your HF antenna will tend to ground out the antenna. The more touching points, and the wetter, the more signal you will lose. Foliage touching at high voltage points can and has caught fire! There are a number of posts here and on the other board in the last couple years, some with photos, to attest to this.
An insulated wire vertical could be hauled up alongside a trunk and avoid the grounding problems. Stake out some radials at the base. Very stealthy and neighbor friendly.
"Trees
As potential hazards these are usually much overrated. Horizontally polarized antennas can usually be more or less buried in trees with little or no effect"
Here is my added advice, Use INSULATED wire, do not use bare wire....
For HF, any attenuation will be essentially unmeasurable by any equipment the average ham is likely to have. Wires in the trees are common and work quite well.
As the frequency goes up past 50 mhz, the attenuation will be more and more of a factor and will be measurable. For 2m/440, higher is not only better, the antennas really need to be above the trees, unless all you are doing is hitting local repeaters. For weak-signal work height and tree clearance are everything.
30m 1/4 GP Pictures
Base ...
Base with weather seal ... ( note N Connectors temp seal )
Vertical element - its a black wire so I added a RED Line to the left of the wire ...
There are a few outstanding things that I want to do with this antenna...
#1 - Remove Rope , add pulley and small counter weight at top to account for tree swing in the wind. Another thought I had about that was just to fix the vertical element to the tree. ( Going to try that with a future ground mounted vertical )
#2 Run through and Antenna Swicther ... when I purchase it!
#3 Weather proof the "N Connector "
#4 Lob off N connector in shack and connect to the PL259 female Patch Panel
Base with weather seal ... ( note N Connectors temp seal )
Vertical element - its a black wire so I added a RED Line to the left of the wire ...
There are a few outstanding things that I want to do with this antenna...
#1 - Remove Rope , add pulley and small counter weight at top to account for tree swing in the wind. Another thought I had about that was just to fix the vertical element to the tree. ( Going to try that with a future ground mounted vertical )
#2 Run through and Antenna Swicther ... when I purchase it!
#3 Weather proof the "N Connector "
#4 Lob off N connector in shack and connect to the PL259 female Patch Panel
Subscribe to:
Posts (Atom)