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antenna matching units
- Thread starter largo71
- Start date
- Status
One Band
I agree. The only time you use a tuner is for multiple ham or military bands. Just tune the antenna for a 1:1 on Channel 19 or 20.
I agree. The only time you use a tuner is for multiple ham or military bands. Just tune the antenna for a 1:1 on Channel 19 or 20.
Rather than rehash facts, myths and outright misinformation about coax, antenna resonance and grounding, check out these websites: The Ultimate Guide to 11 Meter CB Antennas
KØBG.COM
73's
KØBG.COM
73's
jhooten
Member
BUT, BUT, BUT this fancy 102" stainless steel whip ain't got no way to adjust it!
Sure it does, it's just not all that well known. It's easy to shorten a 102" whip, but difficult to make one longer. You can shorten it by removing the ferrule on the bottom (unsolder it), cut off what has to be cut off, then re-soldering the ferrule back on. That means you don't loose any 'whippiness' from cutting the top end, or that 'ball'. Adding to the length is harder, you have to use some kind of 'extender'. It's easier to make that extender too long and then cut off the whip than to use several lengths of extenders (or at least for me).
If you can't adjust an antenna for whatever reason, then using a 'tuner' is certainly one way around it. All they do is act like an impedance transformer, they don't really change anything except how your transmitter 'sees' the impedance. Same as using a transformer to change 120 vac to 12 vac to be rectified to 12 vdc. The best place for a tuner is at the input of the antenna (eg: gamma, delta, 'hair-pin'). That eliminates the feed line from the 'tuning'. Of course, that also means very long arms to do any tuning, right? Oh well, you never get something for nothing...
- 'Doc
If you can't adjust an antenna for whatever reason, then using a 'tuner' is certainly one way around it. All they do is act like an impedance transformer, they don't really change anything except how your transmitter 'sees' the impedance. Same as using a transformer to change 120 vac to 12 vac to be rectified to 12 vdc. The best place for a tuner is at the input of the antenna (eg: gamma, delta, 'hair-pin'). That eliminates the feed line from the 'tuning'. Of course, that also means very long arms to do any tuning, right? Oh well, you never get something for nothing...
- 'Doc
Lt Doc has the right idea - to some extent - but what he is saying is not 100% correct.
If my uncle was to log on - he could be of more help - but he charges for his advice.
High SWR cannot be changed by cutting something off the antenna.
10 meters radio requires you to remove about 4 inches off the top or bottom of the antenna.
The difference between 10 meters and 11 meters ( Chicken Band ) is 1 mhz.
As the wavelength gets longer - the antenna has to get longer.
Hence a 20 meter antenna - 14 Mhz would be twice the size of a 10 meter antenna (29 mhz or 29 MC to be more exact)
What is happening is that you have a poor ground plane.
Mobile antenna's are a lot like base antenna's and repeaters.
You do not spend $10,000 to build a repeater and then build the tower next to your house because that is where it is most convenient. You build the tower on top of the highest hill or mountain you can find and as far away from people as possible - to limit the amount of exposure to the RF side of things.
At the same time - your whip antenna that you are talking about is not always the best choice.
In order for you to fit that antenna on your vehicle - you have to hang it off something - like the side of the vehicle or the bumper in order to get adequate clearance while you are driving down the road.
Great for making your vehicle look cool - but poor for the over all dynamic's of the system.
In order for your antenna to work properly - you need to establish some sort of ground plane.
When CB was first permitted - 1958 - the vehicles were made entirely out of STEEL and the roof was as much as 5' wide and 8' long.
That was a excellent ground plane for a mag mount type antenna.
Unfortunately - I don't think there was any manufacturers of mag mount antenna's back then.
Even so - a person could drill or hack a hole in the quarter panel and mount the antenna to the side of the vehicle.
This presented some problems - because it made the signal lop sided and the antenna performed better in one direction then in the others.
The best place for the antenna was either in the middle of the roof or the hood or the front edge of the trunk lid - right next to the rear window.
Now you have to remember - the trunk lid on a 1964 Pontiac - Wide Body - was about 6 feet wide by 5 feet long - or more.
Your little itty bitty car or pick up truck - is half plastic and a poor ground plane.
Even worse is these truckers who hangs their antenna off the side of the mirror - there is no ground plane on a fiberglass door or on a mirror mount.
So what you need to do is to move the antenna to a more favorable position.
Using a antenna tuner ( transmatch ) only tricks the radio into thinking that there is a good match between the radio and the antenna. It keeps the reflected portion of the signal away from the finals / front end of the radio. At the same time - it reduces the amount of signal present in the wire to the radio on the receive side. ( there is no free meals when it comes to broadcasting)...
My advice is for you to buy a better 1/4 wave antenna - such as a Larsen and have someone professionally install it and tune it for your vehicle.
One thing to note is - there is going to be some drilling and some paint removal involved in installing the antenna properly.
On the other hand, one thing you have not looked at is using a better coax.
RG 58 - normal coax for a mobile install - throws away a forth the signal in the wire in 18'..
Using a longer wire - does not help - because if you have to coil it up, it becomes a simple choke.
You can use a Smith Chart to check impedance's and resistance in wire, but my advice still stands that unlike changing your own spark plugs or motor oil - radios should be left to the professionals - if you want a professional job done.
If my uncle was to log on - he could be of more help - but he charges for his advice.
High SWR cannot be changed by cutting something off the antenna.
10 meters radio requires you to remove about 4 inches off the top or bottom of the antenna.
The difference between 10 meters and 11 meters ( Chicken Band ) is 1 mhz.
As the wavelength gets longer - the antenna has to get longer.
Hence a 20 meter antenna - 14 Mhz would be twice the size of a 10 meter antenna (29 mhz or 29 MC to be more exact)
What is happening is that you have a poor ground plane.
Mobile antenna's are a lot like base antenna's and repeaters.
You do not spend $10,000 to build a repeater and then build the tower next to your house because that is where it is most convenient. You build the tower on top of the highest hill or mountain you can find and as far away from people as possible - to limit the amount of exposure to the RF side of things.
At the same time - your whip antenna that you are talking about is not always the best choice.
In order for you to fit that antenna on your vehicle - you have to hang it off something - like the side of the vehicle or the bumper in order to get adequate clearance while you are driving down the road.
Great for making your vehicle look cool - but poor for the over all dynamic's of the system.
In order for your antenna to work properly - you need to establish some sort of ground plane.
When CB was first permitted - 1958 - the vehicles were made entirely out of STEEL and the roof was as much as 5' wide and 8' long.
That was a excellent ground plane for a mag mount type antenna.
Unfortunately - I don't think there was any manufacturers of mag mount antenna's back then.
Even so - a person could drill or hack a hole in the quarter panel and mount the antenna to the side of the vehicle.
This presented some problems - because it made the signal lop sided and the antenna performed better in one direction then in the others.
The best place for the antenna was either in the middle of the roof or the hood or the front edge of the trunk lid - right next to the rear window.
Now you have to remember - the trunk lid on a 1964 Pontiac - Wide Body - was about 6 feet wide by 5 feet long - or more.
Your little itty bitty car or pick up truck - is half plastic and a poor ground plane.
Even worse is these truckers who hangs their antenna off the side of the mirror - there is no ground plane on a fiberglass door or on a mirror mount.
So what you need to do is to move the antenna to a more favorable position.
Using a antenna tuner ( transmatch ) only tricks the radio into thinking that there is a good match between the radio and the antenna. It keeps the reflected portion of the signal away from the finals / front end of the radio. At the same time - it reduces the amount of signal present in the wire to the radio on the receive side. ( there is no free meals when it comes to broadcasting)...
My advice is for you to buy a better 1/4 wave antenna - such as a Larsen and have someone professionally install it and tune it for your vehicle.
One thing to note is - there is going to be some drilling and some paint removal involved in installing the antenna properly.
On the other hand, one thing you have not looked at is using a better coax.
RG 58 - normal coax for a mobile install - throws away a forth the signal in the wire in 18'..
Using a longer wire - does not help - because if you have to coil it up, it becomes a simple choke.
You can use a Smith Chart to check impedance's and resistance in wire, but my advice still stands that unlike changing your own spark plugs or motor oil - radios should be left to the professionals - if you want a professional job done.
Daniel Boone, some of your info is not correct. You DO NOT lose a fourth of the signal in 18' of RG-58 at 27 MHz, the loss is 2.5 dB at 30 MHz per 100 feet, slightly less at 27 MHz Coaxial Cable Attenuation Chart
Attenuation at18 feet is only 0.45 dB which is so insignificant that I challenge anyone to actually measure it on an S-Meter, it's miniscule. And besides, coax length DOES NOT MATTER to a resonant antenna (unless you are co-phasing antennas). This nonsense of needing 18' or 9 of coax' (or whatever length) that has been quoted over and over is yet another example of pure bull crap repeated as gospel, and it's flat out wrong.
Did you look at either of the websites I posted? I say again, read up and become informed by people who know. KØBG.COM
The Ultimate Guide to 11 Meter CB Antennas
As for trimming antennas for resonance, if you trim from top of the antenna, replace the corona ball which is a good idea anyway because most are too small,especially if you are running any power. K0BG's static webpage talks about this at length Controlling Static
73's
Attenuation at18 feet is only 0.45 dB which is so insignificant that I challenge anyone to actually measure it on an S-Meter, it's miniscule. And besides, coax length DOES NOT MATTER to a resonant antenna (unless you are co-phasing antennas). This nonsense of needing 18' or 9 of coax' (or whatever length) that has been quoted over and over is yet another example of pure bull crap repeated as gospel, and it's flat out wrong.
Did you look at either of the websites I posted? I say again, read up and become informed by people who know. KØBG.COM
The Ultimate Guide to 11 Meter CB Antennas
As for trimming antennas for resonance, if you trim from top of the antenna, replace the corona ball which is a good idea anyway because most are too small,especially if you are running any power. K0BG's static webpage talks about this at length Controlling Static
73's
LOL, that's funny.
Token
Member
As a matter of fact high SWR most certainly can be adjusted by changing the length of an antenna the majority of the time.
Specifically if you have high VSWR at the higher frequency end of the band, and lower SWR at the low end, this means the antenna is longer than desirable, and then trimming the length is exactly the right answer.
Or don’t use the 6” spring at the bottom of the antenna.
But didn’t you just say above that you do not change the SWR by cutting anything off the antenna?
A little more than 1 MHz, closer to 2 MHz. However, lets go with that 1 MHz number for a bit. If it is really only 1 MHz than there is no reason why a single antenna cannot work for both 11 and 10 M. 1 MHz is only about 3.5% of bandwidth for a 10M frequency. A good antenna can often do 3.5% bandwidth or more, depending on the exact design.
Now, the problem is the higher the Q of the antenna the lower the bandwidth. And one way (among many) to increase Q is to use loading coils or to physically shorten the antenna while maintaining the same electrical length.
This means a loaded antenna might, or might not, do both CB and 10M, depending on the exact antenna, but a 102” whip (minus spring) can indeed do both bands with less than 2:1 SWR. In fact, the one on my truck will do a 4.9 MHz 2:1 bandwidth centered on 28 MHz when 2” was removed from the antenna. With stock length it also did a 4.9 MHz 2:1 bandwidth but the center was more around 27.7 MHz. There was really no need to remove the 2”, because the antenna exhibited acceptable SWR from 25.0 MHz to 29.8 MHz, but trimming the antenna changed it from “acceptable” to “good”, and more centered on my desired frequencies. In fact, the 1.5:1 bandwidth now includes all of the ham 10M band and the CB band, roughly 2.8 MHz of bandwidth (26.965 MHz to 29.700 MHz). And this is close to a 10% bandwidth.
If a person wanted to use the spring at the base of the whip you would have to remove a few inches (about 6 or 8) to achieve the same results. Remember, always remove less than you think you need to, it is easy to trim some more, hard to add it back.
Well, a 14 MHz antenna would be twice the size of a 28 MHz antenna.
By the way, the “H” in MHz is always capitalized, it is a mans name, after all. And the “M” in MHz is also capitalized, otherwise your are not saying “mega”, but rather “milli”. And 29 milli-Hz is a lot different from 29 mega-Hz.
Odd, and here all this time I thought those repeaters were up on hills, mountain tops, and tall buildings to push out the radio horizon and increase the coverage areas. It is a lot cheaper to put a 100 foot tower on top of a 1500 foot hill than it is to build a 1600 foot tall tower.
A nice side benefit is that you do not have to worry about people being close to it, people who might do things to cause interference as well as might be exposed to some minimal RF.
Good antennas always pay off. Get a good one, not just one you like because it looks cool. Larsen is a fine brand, and there are others. Also remember that with antennas bigger is almost always indeed better. Get the tallest antenna you can that fits your needs, if you park in parking garages often a 102” whip might not be for you.
Actually, the quality of the cable matters a lot. For example, a good quality RG-58, like Belden 8240 RG-58/U, might have less than 0.5 dB loss in 18 feet. At 0.5 dB loss a 4 Watt signal would have 3.56 Watts at the end of the cable. A poor quality cable will have more loss, possibly even as much as the one forth loss you mention, but that will be some pretty bad cable.
I do not advocate using longer cable to control SWR, but not because coiling it causes issues. However, for the very reason I said above, the loss is not that high, you need a loooonnng cable to affect SWR by enhanced loss (on the order of 3 dB or more needed, so say 50+ feet of junk cable at CB frequencies). And 3 dB of loss in the transmit path is also 3 dB of loss in the receive path. There are ways to trim the cable to specific lengths impact perceived or indicated SWR, but no need to go into that now, better to just do it right.
The very nice thing about a coiled piece of coax at HF frequencies is it can indeed become a common mode choke, lessening common mode noise. So you often find it done intentionally, with the coil as close to the antenna feed point as possible.
T!
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jhooten
Member
There in lies the problem. The whip sold locally does not have the ferrule soldered on or held on by set screws. It is friction welded to the element. If I cut it off it goes in the trash and a new rod holder is required.
It most certainly can, and if the reason for the high SWR is because the antenna is too long, then cutting some off would be the right thing to do. Many antennas actually come with a "cutting chart".
You know... about 90% of the technical advice you give to others is seriously wrong. You may want to go into learning mode before you go into teaching mode.
Odd, I don't see where I mentioned SWR at all. I did say adjusting the antenna, and that does typically mean making it resonant and matching impedances to the rest of the system.
- 'Doc
(I don't charge for this advice/information stuff. If I absolutely have to be paid for it, I'd accept beer instead of money.)
- 'Doc
(I don't charge for this advice/information stuff. If I absolutely have to be paid for it, I'd accept beer instead of money.)
LOL, Old Milwaukee?
Hello Largo71:
Yes a matcher or antenna tuner will be easier on the finials. But the finals see a good match, but the antenna still will have a bad SWR and may not radiate real well.
Yes adding coax (a lot of coax 50 Ft or more) will show a lower SWR, and broader SWR bandwidth. But again its just a band air putting loss between the radio and antenna showing a some what lower SWR. Again not a fix.
The antenna should be able to work properly and some are tunable allowing it to be tuned for min SWR. I would think you could find a good web site or the antenna manufacture to help you out. You did not show us the antenna installation or what type antenna it is.
Jay in the Mojave
Yes a matcher or antenna tuner will be easier on the finials. But the finals see a good match, but the antenna still will have a bad SWR and may not radiate real well.
Yes adding coax (a lot of coax 50 Ft or more) will show a lower SWR, and broader SWR bandwidth. But again its just a band air putting loss between the radio and antenna showing a some what lower SWR. Again not a fix.
The antenna should be able to work properly and some are tunable allowing it to be tuned for min SWR. I would think you could find a good web site or the antenna manufacture to help you out. You did not show us the antenna installation or what type antenna it is.
Jay in the Mojave
Well I can't sit here all day and type all that is on my mind.
Yes - what I inferred when I said about not building the repeater next to the house and to build it on the top of a hill or mountain is indeed because it is cheaper at times to buy real estate then tower and because it will increase your line of sight..
Radio line if sight - exceeds visual line of sight by about 15% - due to the fact that radio waves can be bent.
http://en.wikipedia.org/wiki/Non-line-of-sight_propagation
I didn't think I had to hold someones hand here on this subject.
1000' of tower is somewhere in the neighborhood of around $1 million dollars to erect.
The deal with that is that Amateur Radio is usually limited to about 200 feet of tower, unless you can prove its value to the community.
Even then it still has to be permitted to be built by the FAA and the FCC and it has to have a light on the top and a lot more regulations - hence you don't build a tower next to your house for convenience - you build it in the tallest place you can find.
Yes a choke cuts down on the noise - but noise is not always a bad thing.
Let's use a GE Mastr II repeater as a example.
GE built the Mastr II - starting in 1972 - and it was designed to be used by NASA.
If you ever heard one in it's stock form - and if you ever saw a Apollo mission on TV and heard the audio - you will hear a distinct beep - roger beep - which is emitted by the transmitter.
YouTube - ‪First Moon Landing 1969‬‏
Just for the sake of example - lets say the signals thermal noise floor was -168 DB
The GE Mastr II would still receive a signal even when the signal was -148 DB
It was also designed that it would not quit transmitting when the signal became intermittent.
The design was due to the fact that the human brain processes information much faster then the ear can hear it. If the repeater stops transmitting - your ear stops listening and the brain says - ok - they are through talking.
On the other hand - if you hear every other word or loose every third or fourth word - your brain will guess the missing word and will continue to listen as long as there is some noise to listen to.
Now when human life is involved - it is important to be able to hear as much as possible - especially when the people talking to you are hundreds of thousands of miles away and are relying on you to stay alive.
If it is real important to hear as much as you can possibly hear, then isn't it also important for a person to try to make his / her set up as good as possible - so they can hear as much as possible.
If you buy a cheap antenna, do you think that they are going to put good wire on it?
Yes the bands for CB and 10 meters goes from 26 - 29 mhz, but as long as you keep the SWR down below 2:1 - it doesn't matter how long the antenna is - as long as you have it centered around a center frequency that works for all the frequencies you wish to transmit on.
That is why I said - the only difference between the CB radio's antenna and the 10 meters is about 4 inches.
If you have a good antenna, good coax, and have it mounted in the proper place and have a low SWR - then it really doesn't matter.
But when you start putting junk into the equation - it doesn't take long to mess up a relatively good set up.
The question is - why would someone want to spend money on a transmatch for a CB radio and then use junky equipment on either end.
Its obvious that anyone that uses the smaller coax - doesn't know what the skin effect is or how it works or how the coax works in the first place.
Yes - what I inferred when I said about not building the repeater next to the house and to build it on the top of a hill or mountain is indeed because it is cheaper at times to buy real estate then tower and because it will increase your line of sight..
Radio line if sight - exceeds visual line of sight by about 15% - due to the fact that radio waves can be bent.
http://en.wikipedia.org/wiki/Non-line-of-sight_propagation
I didn't think I had to hold someones hand here on this subject.
1000' of tower is somewhere in the neighborhood of around $1 million dollars to erect.
The deal with that is that Amateur Radio is usually limited to about 200 feet of tower, unless you can prove its value to the community.
Even then it still has to be permitted to be built by the FAA and the FCC and it has to have a light on the top and a lot more regulations - hence you don't build a tower next to your house for convenience - you build it in the tallest place you can find.
Yes a choke cuts down on the noise - but noise is not always a bad thing.
Let's use a GE Mastr II repeater as a example.
GE built the Mastr II - starting in 1972 - and it was designed to be used by NASA.
If you ever heard one in it's stock form - and if you ever saw a Apollo mission on TV and heard the audio - you will hear a distinct beep - roger beep - which is emitted by the transmitter.
YouTube - ‪First Moon Landing 1969‬‏
Just for the sake of example - lets say the signals thermal noise floor was -168 DB
The GE Mastr II would still receive a signal even when the signal was -148 DB
It was also designed that it would not quit transmitting when the signal became intermittent.
The design was due to the fact that the human brain processes information much faster then the ear can hear it. If the repeater stops transmitting - your ear stops listening and the brain says - ok - they are through talking.
On the other hand - if you hear every other word or loose every third or fourth word - your brain will guess the missing word and will continue to listen as long as there is some noise to listen to.
Now when human life is involved - it is important to be able to hear as much as possible - especially when the people talking to you are hundreds of thousands of miles away and are relying on you to stay alive.
If it is real important to hear as much as you can possibly hear, then isn't it also important for a person to try to make his / her set up as good as possible - so they can hear as much as possible.
If you buy a cheap antenna, do you think that they are going to put good wire on it?
Yes the bands for CB and 10 meters goes from 26 - 29 mhz, but as long as you keep the SWR down below 2:1 - it doesn't matter how long the antenna is - as long as you have it centered around a center frequency that works for all the frequencies you wish to transmit on.
That is why I said - the only difference between the CB radio's antenna and the 10 meters is about 4 inches.
If you have a good antenna, good coax, and have it mounted in the proper place and have a low SWR - then it really doesn't matter.
But when you start putting junk into the equation - it doesn't take long to mess up a relatively good set up.
The question is - why would someone want to spend money on a transmatch for a CB radio and then use junky equipment on either end.
Its obvious that anyone that uses the smaller coax - doesn't know what the skin effect is or how it works or how the coax works in the first place.
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Token
Member
For the OP, largo71, trying to get back on subject here, don’t let all this minutia run you off m8. Using a “matcher” (antenna tuner, or transmatch) is fine for your finals, when the tuner is properly adjusted. That is the goal of the tuner, to make your radio “happy” even when the antenna itself is not properly tuned to the frequency you are using. Using a tuner is a far more correct answer than adding coax length.
The best answer, naturally, is to tune the antenna so that the SWR is correct without the need for any external pieces / parts. If you can do this the antenna will probably most efficiently radiate the energy that gets to it and more energy will get to the antenna, a plus all the way around.
There are lots of opinions and wives tales about SWR and antenna tuning out there, but it is actually pretty straightforward and simple, as long as you stay away from the math of what is behind it.
To the OP, feel free to ignore everything below this point.
You inferred nothing. What you said was “You build the tower on top of the highest hill or mountain you can find and as far away from people as possible - to limit the amount of exposure to the RF side of things.” That is a direct quote with no paraphrasing or editing.
You may, or may not, have meant to say you build it on a hill to increase coverage, but if that was your meaning that is not what you said.
A choke from coils of coax, a very small part of what was being discussed in the thread, can cut down on common mode noise. Please tell me when common mode noise is anything but a bad thing.
How does a specific signal have a thermal noise floor? How is the “signals thermal noise floor” different from the thermal noise floor of another signal on the same frequency? I understand that a signal can be below, at or above the thermal noise for a specific frequency, but how do you calculate or measure the thermal noise floor of a specific signal?
And, I am not familiar with this unit of absolute measurement DB. Do you have a conversion formula that might help convert this absolute value to something more common, say dBm, or dBuV, or maybe microvolts? If you meant it as “-168 dB” but typoed the d as upper case (twice) what is the reference? Is this 168 dB down from 1 Watt (dBW)? 1 MegaWatt (dBMW)? 1 dollar (dB$)?
And how does this apply to the discussion? Are you saying common mode noise is good for keeping the receiver squelch open during signal fading?
Ouch, that is a pretty broad brush there. In one sentence with a couple of buzz words you have just inferred that smaller coax simply cannot be used for anything and clearly implied that anyone who does use it knows nothing about RF propagation in a feedline. Of course, you have left out a definition of what, exactly, “smaller coax” is. I mean, I guess one should just use LMR400 for everything, ah? Oh, no, wait, that is smaller than LMR1200, so maybe 1200 is the answer for all 4 Watt 27 MHz mobile installations. You have also left out how, for low power HF application and short runs as found in mobile installations, “it” is bad?
I avoid small diameter coax like RG-58/U much of the time myself. At home I have none run at all. But, for lower RF frequency applications (like 27 MHz CB), lower power applications (like legal 27 MHz CB power levels), and short runs (as found in most mobile applications) small coax like RG-58/U is ideal. And running LMR400, or RG-213, or Belden 9913, or similar cable in and out of a mobile can be daunting, at best.
Engineering and application is a series of compromises. There may be one technical “best” for anything, but often it is impractical. So, you decide what is “good enough” and work from there. The fact of the matter is that for this specific application and for runs of cable that would normally be found in this application the use of the best 3” hard line you could get instead of RG-58/U would not make a detectable difference in performance, with all other things being equal.
The best answer, naturally, is to tune the antenna so that the SWR is correct without the need for any external pieces / parts. If you can do this the antenna will probably most efficiently radiate the energy that gets to it and more energy will get to the antenna, a plus all the way around.
There are lots of opinions and wives tales about SWR and antenna tuning out there, but it is actually pretty straightforward and simple, as long as you stay away from the math of what is behind it.
To the OP, feel free to ignore everything below this point.
You inferred nothing. What you said was “You build the tower on top of the highest hill or mountain you can find and as far away from people as possible - to limit the amount of exposure to the RF side of things.” That is a direct quote with no paraphrasing or editing.
You may, or may not, have meant to say you build it on a hill to increase coverage, but if that was your meaning that is not what you said.
A choke from coils of coax, a very small part of what was being discussed in the thread, can cut down on common mode noise. Please tell me when common mode noise is anything but a bad thing.
How does a specific signal have a thermal noise floor? How is the “signals thermal noise floor” different from the thermal noise floor of another signal on the same frequency? I understand that a signal can be below, at or above the thermal noise for a specific frequency, but how do you calculate or measure the thermal noise floor of a specific signal?
And, I am not familiar with this unit of absolute measurement DB. Do you have a conversion formula that might help convert this absolute value to something more common, say dBm, or dBuV, or maybe microvolts? If you meant it as “-168 dB” but typoed the d as upper case (twice) what is the reference? Is this 168 dB down from 1 Watt (dBW)? 1 MegaWatt (dBMW)? 1 dollar (dB$)?
And how does this apply to the discussion? Are you saying common mode noise is good for keeping the receiver squelch open during signal fading?
Ouch, that is a pretty broad brush there. In one sentence with a couple of buzz words you have just inferred that smaller coax simply cannot be used for anything and clearly implied that anyone who does use it knows nothing about RF propagation in a feedline. Of course, you have left out a definition of what, exactly, “smaller coax” is. I mean, I guess one should just use LMR400 for everything, ah? Oh, no, wait, that is smaller than LMR1200, so maybe 1200 is the answer for all 4 Watt 27 MHz mobile installations. You have also left out how, for low power HF application and short runs as found in mobile installations, “it” is bad?
I avoid small diameter coax like RG-58/U much of the time myself. At home I have none run at all. But, for lower RF frequency applications (like 27 MHz CB), lower power applications (like legal 27 MHz CB power levels), and short runs (as found in most mobile applications) small coax like RG-58/U is ideal. And running LMR400, or RG-213, or Belden 9913, or similar cable in and out of a mobile can be daunting, at best.
Engineering and application is a series of compromises. There may be one technical “best” for anything, but often it is impractical. So, you decide what is “good enough” and work from there. The fact of the matter is that for this specific application and for runs of cable that would normally be found in this application the use of the best 3” hard line you could get instead of RG-58/U would not make a detectable difference in performance, with all other things being equal.
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the other end
I got a problem with your problem:
If you got a bad match on a stock 11 meter 1/4 wave whip, I got a gut the issue isn't the antenna. Something else is going on here.
But I need some help here, someone help me figure this out.
I want to tell the OP to check the match on Ch. 1 and then check the match on Ch. 40.
I'm trying to think this one in my head and old-timers is kicking in bad right now:
Which scenario would he cut a 1/2 inch at a time off the TOP of the antenna to get near 1:1, if the match is better on 1, or if the match is better on 40?
I got a problem with your problem:
If you got a bad match on a stock 11 meter 1/4 wave whip, I got a gut the issue isn't the antenna. Something else is going on here.
But I need some help here, someone help me figure this out.
I want to tell the OP to check the match on Ch. 1 and then check the match on Ch. 40.
I'm trying to think this one in my head and old-timers is kicking in bad right now:
Which scenario would he cut a 1/2 inch at a time off the TOP of the antenna to get near 1:1, if the match is better on 1, or if the match is better on 40?
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