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  • Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    Qualifications for being a 'Ham Antenna'.

    1) The antenna is being used by a Ham
    2) Any piece of metal apparatus or wire that will effectively radiate at a given frequency used by Hams

    #1 covers #2, as they are still antennas. :)

    But I had one friend who while living in military quarters loaded up the gutters of the house for HF. :)
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    With a proper matching circuit they will ALL radiate well. The pattern might be funky.

    GREAT read - http://www.amazon.com/Reflections-T...=sr_1_2?s=books&ie=UTF8&qid=1392892266&sr=1-2
    Yup, thank you, a well recommended book and definitely on my 'To Do' list.

    I still would have to maintain that, in spite of popular opinion, tuners are not a magical, lossless fix for mismatched antennas and "radiate well" might be a bit optimistic, depending on how we define "well".

    My point is that we STILL cannot get something for nothing, and the matching circuit (tuner) will dissipate a sometimes substantial portion of our transmit energy as internal heat, never reaching the antenna.

    Rhetorical questions:

    1) If a mismatched antenna feedpoint impedance is 20 ohms, and a matching circuit is used to present 50 ohms to the amplifier, where does the other 30 ohms come from, and how do we defeat ohms law so it doesn't drop any voltage when we get current flow across this resistance/impedance?

    2) The schematics in the ATK manual linked below show the power input only lights a lamp and powers a relay to switch feedline connections, which begs the question: If the tuner doesn't draw any power supply current, and is thus passive, how does it "work" i.e: where does the energy to actually "do" anything come from?

    3) Is the tuner warm after operation? Where does that heat come from?

    4) The tuner still sees improper impedance at its output if the antenna is mismatched, while showing the amplifier a corrected load. Why don't we lose a lot of reflected energy in the feed line due to this still improper match?

    If you look at the ATK4k Manual, a popular and representative tuner, it lists insertion losses up to 16% with their selected loading of a regular antenna. I'd wager loading up a non-antenna will set up a slightly less ideal condition.

    Another good quick read: http://owenduffy.net/blog/?p=728
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    Here is a good laymans explanation on tuners..

    <snip>

    <edit copyrighted material>

    <snip>

    <edit copyrighted material>

    <snip>

    <edit copyrighted material>

    <snip>

    <edit copyrighted material>

    <snip>

    <edit copyrighted material>
    Hard to tell how much is yours and how much is the original work, but the gist of this is exactly what I am getting at.

    You STILL can't get something for nothing. :shrug:
     
    Last edited:

    chale127

    Ultimate Member
    Nov 5, 2008
    2,613
    Brooklyn, MD
    Hard to tell how much is yours and how much is the original work, but the gist of this is exactly what I am getting at.

    You STILL can't get something for nothing. :shrug:

    Precisely, the radiator (if not a band-specific antenna) will still transmit or radiate in the same pattern and with the same efficiency as it would without a tuner, the tuner just changes the reactance of the system and dissipates the mismatch as heat instead of the final section of the transmitter doing it much less efficiently and in many cases at the expense of the final amplifier section

    If anyone ever doesn't believe you...just hook up a tuner with an external SWR meter on each side of it and tune, the meter on the antenna side will show the same mismatch and the one on the transmitter side will show the proper match

    Ive opened many a mind with that little experiment
     

    ke3gk

    HAM from U.N.C.L.E.
    Aug 27, 2007
    1,383
    Glen Burnie
    All this reminds me - I have to rebuild my 10-80m folded dipole this spring - during some heavy winds - a branch or 2 took it out.
     

    K31

    "Part of that Ultra MAGA Crowd"
    MDS Supporter
    Jan 15, 2006
    35,632
    AA county
    You might want to go back and edit the post to include just the link itself.
     

    Norton

    NRA Endowment Member, Rifleman
    Staff member
    Admin
    Moderator
    May 22, 2005
    122,847
    copyrighted material removed.
     

    gamer_jim

    Podcaster
    Feb 12, 2008
    13,233
    Hanover, PA
    I have a 2008 Cobalt that came with an XM radio antenna on the roof (towards the middle back). Could I remove that and place a NMO antenna in it's place? I'm fairly certain (but not positive) that XM satellite antenna is drilled through the roof. I'm having some trouble finding information on this.

    A friend (my elmer really) lent me his HT to use but I realize I need to get one in my car soon. I'm looking for a mobile with a proper antenna. The car came with a double DIN stereo head unit which I've been thinking about replacing with a 1 DIN unit and then the 2M/70CM mobile radio in it's place.

    Does this sound sane to you? Am I missing anything?
     

    K31

    "Part of that Ultra MAGA Crowd"
    MDS Supporter
    Jan 15, 2006
    35,632
    AA county
    I have a 2008 Cobalt that came with an XM radio antenna on the roof (towards the middle back). Could I remove that and place a NMO antenna in it's place? I'm fairly certain (but not positive) that XM satellite antenna is drilled through the roof. I'm having some trouble finding information on this.

    A friend (my elmer really) lent me his HT to use but I realize I need to get one in my car soon. I'm looking for a mobile with a proper antenna. The car came with a double DIN stereo head unit which I've been thinking about replacing with a 1 DIN unit and then the 2M/70CM mobile radio in it's place.

    Does this sound sane to you? Am I missing anything?

    Well, I can tell the diameter of the hole but it looks like the space below it is plenty large for a NMO mount.

    http://www.yourcobalt.com/forums/au...actory-onstar-xm-antenna-aftermarket-gps.html

    You might want to consider a through-the-glass antenna mount if you don't want to drill any new holes. They work pretty well once they are tuned.

    https://www.theantennafarm.com/cata...-band-450/glass-mount-dual-band-antennas-454/
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    Yup, thank you, a well recommended book and definitely on my 'To Do' list.

    I still would have to maintain that, in spite of popular opinion, tuners are not a magical, lossless fix for mismatched antennas and "radiate well" might be a bit optimistic, depending on how we define "well".

    My point is that we STILL cannot get something for nothing, and the matching circuit (tuner) will dissipate a sometimes substantial portion of our transmit energy as internal heat, never reaching the antenna.

    Rhetorical questions:

    1) If a mismatched antenna feedpoint impedance is 20 ohms, and a matching circuit is used to present 50 ohms to the amplifier, where does the other 30 ohms come from, and how do we defeat ohms law so it doesn't drop any voltage when we get current flow across this resistance/impedance?

    2) The schematics in the ATK manual linked below show the power input only lights a lamp and powers a relay to switch feedline connections, which begs the question: If the tuner doesn't draw any power supply current, and is thus passive, how does it "work" i.e: where does the energy to actually "do" anything come from?

    3) Is the tuner warm after operation? Where does that heat come from?

    4) The tuner still sees improper impedance at its output if the antenna is mismatched, while showing the amplifier a corrected load. Why don't we lose a lot of reflected energy in the feed line due to this still improper match?

    If you look at the ATK4k Manual, a popular and representative tuner, it lists insertion losses up to 16% with their selected loading of a regular antenna. I'd wager loading up a non-antenna will set up a slightly less ideal condition.

    Another good quick read: http://owenduffy.net/blog/?p=728

    Read the book.

    The tuner only protects the final stage (output stage).

    What happens is the power is reflected from the mismatched junction, back to the tuner, which reflects it back to the antenna.

    The only losses in the system are the losses due to the passes through the coax.

    So, you put in 100 watts into the tuner. Say the loss is 1% for your run of coax. 99 watts gets to the antenna. Say the mismatch reflects 20% of the power (pretty bad mismatch). So 19.8 watts is reflected, 79.2 watts is radiated.

    BUT, the 19.8 watts goes back down the coax (losing 0.198 watts) and 19.602 watts is reflected back to the antenna, now losing 0.196 watts for this pass. So 19.4 is added to the 99 watts that was the original power to the antenna. So really the antenna junction "sees) 118.4 watts, but 23.6 watts is reflected, so really 94.8 watts is radiated. And do this iteration and most of the power is actually radiated.

    Maxwell designed antennas for satellites. In the book he talks of stupid mismatches, like SWR of 5, that worked fine with a tuning circuit.

    You have to read the book. It will change your mind on matching and antenna tuning.
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    Read the book...
    I will, and I think we already agree on some of the points raised.

    I also recognize that a tuner will enable limited use (radiating less than full power) of a mismatched antenna when the amplifier would simply fold back and quit, so it does get us on the air. I would have to question its efficiency though, and where the waste occurs.
    The tuner only protects the final stage (output stage).
    Exactly. It makes the amplifier happy with its 50 ohm input impedance.

    It may be a good time to point out that the antenna is still as bad as it ever was.
    What happens is the power is reflected from the mismatched junction, back to the tuner, which reflects it back to the antenna.

    The only losses in the system are the losses due to the passes through the coax.
    (bold by me) This obviously cannot be true if the tuner warms up (or otherwise dissipates heat energy) AT ALL. The tuner DOES produce heat, so I guess we can draw at least one conclusion from that fact: That statement is NOT unequivocally true.
    So, you put in 100 watts into the tuner. Say the loss is 1% for your run of coax. 99 watts gets to the antenna. Say the mismatch reflects 20% of the power (pretty bad mismatch). So 19.8 watts is reflected, 79.2 watts is radiated.

    BUT, the 19.8 watts goes back down the coax (losing 0.198 watts) and 19.602 watts is reflected back to the antenna, now losing 0.196 watts for this pass. So 19.4 is added to the 99 watts that was the original power to the antenna. So really the antenna junction "sees) 118.4 watts, but 23.6 watts is reflected, so really 94.8 watts is radiated. And do this iteration and most of the power is actually radiated.
    Although the loss numbers used above are somewhat low (100' of LMR400 into 50 ohms at 100 watts/14 kc only delivers 90 watts to the other end, so we lost 10% first pass), I do realize you are just using the numbers as examples to make a point and will not dwell here.

    But then, how about one very straightforward question, the direct answer to which will put all this to rest?

    **IF** all of this energy just bounces back and forth and eventually either propagates or is radiated as heat in the coax, why does the tuner heat up?

    Clearly stated: Exactly where did the energy to heat the inside the tuner come from?

    In the example I gave previously heat was developed within the tuner to the equivalent of emitting 40 watts of heat with a 100 watt input? Seriously... 40 watts is enough power to read a book if it was light and not heat, but I actually wanted to talk to Australia...

    I really need to know where this large amount of energy in the tuner came from if "everything" eventually propagates or is lost in the feedline.

    Seems like a fair question worthy of a direct answer. Did we indeed get something for nothing and create energy from thin air?

    I'm thinking "Probably not.", but hey, I thought that about ObamaCare at first too.

    Then, the obvious follow-on question, which maybe should have been first:

    What of basic Ohms Law, and the capacitive/inductive components we add to the circuit to fill in the missing resistance? If our antenna represents 25 ohms, where does the other 25 ohms come from to fool the amplifier?

    Of course we place additional devices in the current path to provide a conjugal match between the antenna and the tuner circuitry to the amplifier. I know about resonance theory in a "lossless circuit", but our circuits are real and thus not lossless.

    Do we get to pass current through these devices without any voltage drop? How is that possible?

    Not being deliberately obtuse, but asking these questions because I think we all know where the tuner got the energy it used to develop some 40 watts of heat. It clearly stole it from your radio - there was no other place to get it. It used about 40 watts of signal power because the antenna was not matched and the tuner components had to join the circuit. If it used 40 watts of our original 100, I'd have to surmise that we somehow do NOT radiate the entire 100/99 watts, as originally stated, or even 90 or 80 or 70 or 60.....

    If we draw a schematic of the conjugal circuit formed between the tuner and antenna, we can put inductance in series with the load and capacitance in parallel to create a compatible impedance to the amplifier. Either way we correct, there is current flow through these added components, with resultant voltage drop and wasted power dissipated as heat.
    Maxwell designed antennas for satellites. In the book he talks of stupid mismatches, like SWR of 5, that worked fine with a tuning circuit.
    Maxwell knows/knew WAY more about this than I do, and I certainly don't doubt this ability to TX through a high SWR/antenna mismatch.

    Proof of this is that there are a whole lot of guys out there using a tuner with an G5RV style end fed wire presenting an SWR of over 7:1 in many spots with fair results. However, this does not mean it is efficient or is even working well.

    As another example of just shooting in the dark when we guess how much power we really radiate, look at the QRP guys working the world on 5 watts. Just because the tuner provides the amplifier the illusion of good impedance from an antenna is a poor match and inefficient radiator doesn't mean one cannot talk at all. Many of those end fed guys seem to think they are radiating full power <grin>. If your 100 watt transceiver lets you talk around the world into a mismatched antenna, it is possible (probable, actually) that you are only radiating a fraction of your available power. With the way propagation can favor certain circumstances and defeat others, who (without a field strength measurement) could know?

    Like ANY passive circuit, component or conductor, tuner circuits represent an insertion loss. Insertion loss is simply the result of a resistance. Current flow through a resistance results in a voltage drop. Always. A voltage drop results in power dissipated. Always. There can be varying degrees of loss, but energy is used. Always. When it is used in the tuner components, ALL power is clearly not passed through to be radiated.

    The tuner loss and subsequent heating I linked above was the result of a correction of a moderate mismatch. Power left to radiate after the tuner and antenna system loss actually only came to 56 watts. Trying to match an end fed in one of its ugly spots undoubtedly results in greater tuner losses yet, and yet more heat squandered in the tuner.

    Heat is clearly generated inside the tuner, there is simply no escaping this one simple clue to where the power went, and that it did go.

    Again, I ask this question:

    Where does this heat come from if we actually did end up radiating all of our power in the antenna and coax?
    You have to read the book. It will change your mind on matching and antenna tuning.
    "Reflections" is highly regarded and I agree I do have to read it.

    I still refer to my electronics textbooks. Some of them have been around here for 35 years and I still don't 'get it' all. I worked in the production of surveillance receivers, radar maintenance and electronic controls for almost 10 years and readily admit I don't know half of it. I always look forward to learning the truth and correcting my misconceptions.

    I still just have that one question though.... :)
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    Read the book. :)

    He explains all. And no, it does not make sense until you read the book. Expect some math, but you do not need to fully follow the math to get it. You will be convinced.

    And EVERYONE that has not read the book, will not accept it. So read the book. :)
     

    garym

    Damn Right, Rebel Proud
    Sep 20, 2009
    296
    Davidsonville
    Looks like a a "Moonraker" CB antenna.

    Yeah, the feedlines look like they go to the center of the driven element, if it was a quad they would continue on to the quad wire. I think this guy was a CB'er and not a ham, although I am sure there are a lot of hams that do the same thing.

    I don't climb towers anyways, that is why I have a 61' motorized fold over tower so I can do all my antenna and tower work either on the ground or on a short step ladder. Which BTW, I have posted for sale on several ham radio forums. We will be moving to coastal NC in a year and I am not bringing the tower with me.
     

    garym

    Damn Right, Rebel Proud
    Sep 20, 2009
    296
    Davidsonville
    I have a 2008 Cobalt that came with an XM radio antenna on the roof (towards the middle back). Could I remove that and place a NMO antenna in it's place?

    The car came with a double DIN stereo head unit which I've been thinking about replacing with a 1 DIN unit and then the 2M/70CM mobile radio in it's place.

    Does this sound sane to you? Am I missing anything?

    Another option if you want to try to reuse the spot where the XM antenna was, is to use a Sti-Co antenna. Either the Euro style or SuperBand here. I have used many on LEO vehicles.

    As for the DIN mounting, I did that several years ago on a Outback I use to have. I mounted the control head of a FT-100 in the spare DIN space. There was enough room to probably mount the whole radio. I put a pix of it there in my MDS Gallery.
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    Read the book. :)

    He explains all. And no, it does not make sense until you read the book. Expect some math, but you do not need to fully follow the math to get it. You will be convinced.

    And EVERYONE that has not read the book, will not accept it. So read the book. :)
    I understand your point and I will order and read the book, surely I will. Meantime, my simple and direct question stands, and it really shouldn't need a whole book, or even a paragraph, to answer:

    Where does the energy come from to produce heat inside the tuner? :tap:

    It's there, and substantial. It positively absolutely had to come from someplace.

    As for math, I'm not very good at it, but it seems straight up:

    Amplifier Output Power - Tuner Losses (heat) = Power Delivered To Feedline/Antenna System

    Now, please understand that I agree with the premise that feedline losses mount up and increase with reflected power, but a LOT of forward power never sees the feedline.

    If that's not right, I believe I can accept a logical explanation, whether it apparently makes sense to me or not, try me. :)
     

    gamer_jim

    Podcaster
    Feb 12, 2008
    13,233
    Hanover, PA
    Another option if you want to try to reuse the spot where the XM antenna was, is to use a Sti-Co antenna. Either the Euro style or SuperBand here. I have used many on LEO vehicles.
    Thanks, I"ll check that out. I'm not terribly concerned about stealthiness or looks. I mainly travel in a pretty hilly area so I'm more concerned about performance.

    Another question I have about antennas is the angle. If I go with the NMO mount with the re-purposing of the satellite antenna hole in the roof, that part of my roof is sloped slightly. If I put that antenna there it will point 15 degrees or so off. Is that going to be a problem for me? Should I try and do something about that or not worry about it? I could either build a riser for it or just put a new hole on the flat part of the roof (which I'm not opposed to).

    As for the DIN mounting, I did that several years ago on a Outback I use to have. I mounted the control head of a FT-100 in the spare DIN space. There was enough room to probably mount the whole radio. I put a pix of it there in my MDS Gallery.
    Yes! that's what I was thinking. the stock radio is 2 DIN big so I would also need to get a basic am/fm radio that is 1 big to make room for the amateur radio. The radio I really want to get, Kenwood TM-V71A, does have the option for the remote control head. Other than the mounting the entire radio versus just the control head, are there any advantages to using remote? Would the radio function any better if it's body were in the trunk? I would imagine airflow would be better.
     

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