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SWR indicators should be used as a
tune up tool. The reflection indicated can be easily tuned using a
"trans match". There is no reason to believe SWR is any indication
of a poor radiating antenna any more than it should be used to
indicate feed line losses.
The answers...29 of them are
TRUE, only one of the questions is
FALSE. Do you know which one?
There you have it. The
explanations, all the references and editors notes (tips). You can
follow along with each question and maybe learn something about SWR
that you never realized. You will also understand why the ANTENNA
TUNER is a more important device today than it was 50 years ago.
There is a million ways to use SWR information. But above all don't
consider it the "end to all" when you build that antenna. MATH is
still the single most important tool you have in your radio room.
The second will be your tape line.
Explanation and references:
(1) From an SWR reading, reflected power
does not represent lost
power beyond cable attenuation.
True: The SWR indicator, no
matter how simple or extravagant, reads the FORWARD power to the
antenna and the REFLECTED power returning from the load. It does not
read the currents, simply the voltage. There are RF type current
meters, but the SWR bridge is not such a device.
In a loss-less feed line no power can be lost due to REFLECTION. In coax,
attenuation is the power loss factor. There are devices that can
read power loss along a specific length of coax, but at HF
frequencies and the lengths common to Ham Radio installations, these
losses are insignificant. It should be noted that at VHF and UHF,
certain feed line does have significant loss, but for HF bands
these losses, for all practical purposes, are not detectable.
In the statement "does not represent lost power" is not a trick
component. The SWR bridge simply cannot detect these attenuated
It should be understood that SWR "standing wave ratio" is very much like
a wave incident in a standing pool of water. Drop a stone in the
absolute middle and waves form toward the shore. these waves are
"reflected" back to the point of origin and return to the shore
again to be reflected. Assume water turbulence as the attenuation of
these waves. The more turbulence, the more these waves are
attenuated. Open feed line has less turbulence than coaxial line;
but our pool is big enough that this turbulence does not effect the
wave...UHF would be a much smaller pool and any turbulence at all
will effect the "re-reflected wave" as it travels back from shore to
the point of origin.
ARRL handbook, any recent edition since 1970.
(2) Reflected power does not flow back into
the transmitter or the tuning device and it does not cause damage to
the components there in.
True: Damage that is blamed on
high SWR is simply not true. There are many articles written that
make these claims. There is even "false advertising" that makes
claim regarding a product and product warranty. This damage simply
cannot happen due to HIGH SWR.
Such damage rendered to over heated final amplifier tubes, comes not from
"reflected" power but from "poor loading" techniques, mistuned
(reactive) final stages or over coupling. The trick when using a
tube type amplifier, one should tune for maximum "output" and not
just the "dip and load" sequence we have been taught. The SWR bridge
is a tuning indicator in the FORWARD meter position. In fact the
"transmitter" (tube or solid state) does not see SWR at all. It only
sees the impedance. ALL IMPEDANCES ARE MATCHABLE...this must be
understood. In one way or another we can match these impedances and
transfer 100% of the power (less the attenuation) to the radiator.
ARRL handbook, any recent edition since 1970 and the ARRL antenna
handbook since first print.
(3) Any effort to lower an SWR of 2:1, on a
coaxial line, is completely wasted from the standpoint of
significant increase in power transfer.
True: Basically, any attempt
would yield a result very similar to using no. 6 wire to transfer
energy to a flashlight lamp. The effort yields little or nothing in
respect to an increase current transfer.
Reference: Reflections, chapter 1 illustration 1.1
(4) An SWR reading of 1:1 is not proof of a good quality antenna
system or any indication that the system is radiating properly
True: On the
contrary, lower than normal SWR values exhibited over an extended
range of frequencies by a straight dipole or vertical "over ground"
is a sure sign of system problems. These undesired readings come
from lost load resistance, such as found in cold solder connections,
poor mechanical joints, bad grounds and poor physical cable
conditions (water or contamination under the jacket skin). SWR is an
indication that all is well and without it (extremely low SWR over a
wide range of frequencies) there is a problem.
A good example for questions "3" and "4" would be in the case of a
"quarter wave" vertical over ground that has 50 radials under it to
effectively create an "impedance" of 35 ohms. That termination to
the radiator will yield a 1.6:1 SWR reading when fed with 50 ohm
coax. If enough radials are removed to lower the ground resistance
of the radials to 18 ohm the SWR will be a flat 1:1 and all would be
perfect...NO, that is not true. The SWR went down but the effective
power is being divided between the 32 ohm radiator resistance and an
18 ohm ground resistance. As a result, the effective radial tuning
did not increase radiation but actually hindered it by radiating
power into the ground. This will certainly raise interest with earth
worms, but it will not render an effective radiator. Commercial
broadcast antenna systems are, by law, required to have a minimum of
90 radials under the tower system. This eliminates the "ground
warming" effect described above. The Amateur Radio system should
have at least 25 radials under the ground mounted vertical in order
to be effective.
If the vertical SWR is effectively less when transmit frequency is
adjusted away from the calculated resonant point, chances are
you do not have enough radials under the antenna. Moving the
frequency away from adjusted frequency should yield an SWR increase.
If tuning higher or lower yields a LOWER SWR you have conclusive
proof that the radial system is not effective.
(5) Any antenna RADIATING element
need not be self-resonant for full "resonant" current flow, and the
feed line need not be a particular length, and termination point of
radiator and feed line needs not a "perfect match"
A substantial mismatch at the feed point of the feed line does not
prevent the radiator from absorbing all the power available at that
W1DF, "The Why's of Transmission Lines", QST Jan. Feb. Mar. 1965
(three part lecture).
(6) If a suitable "matching network"
(tuner) cancels all reactance rendered in a non-resonant radiator,
fed by a random length feed-line that is mismatched to said
radiator, the antenna system resonant.
The "tuner" ("T" network. "Pi" network or "L" network) effectively
cancels the mis-match by tuning out the reactance in the antenna
system. Therefore maximum current flows into the radiator and all
power available at the radiator is absorbed.
The "matching device" (ATU) removes the mismatch (reactance) that
effectively lowers the output of modern solid state radios. The
Hybrid radios of the 70's that are still in use today, effectively
tune out the antenna reactance within the "Pi Network" of the output
tank circuit. The SWR is not important because the reflected waves
returning from the antenna system are simply re-reflected back to
the radiator. In a low-loss feed line system, less power is lost due
to attenuation, not SWR. (NOTE:
Again at HF frequencies these losses are almost meaningless.)
(7) The majority of AM BROADCAST
tower radiators operating between 540 KHz and 1600 KHz are at
heights which mathematically are not resonant at the frequency used.
True: A perfect example would be
a broadcast station at 1000 KHz or 299.8 meters. The antenna would
be over 900 feet high in order to be a full wave resonant antenna.
Most Commercial Broadcast antennas are quarter wave or less. many
are not resonant at all on the broadcast frequency. Proper coupling
and "matching devices" are used to effectively couple the radiator.
These systems are based upon one single transmit frequency
and are unlike amateur use where the antenna must "compromise" for
multiple frequencies of operation, both transmit and receive.
(8) The SWR on the transmission line between the
radiator and any matching device at the feed line input, is
determined by the mismatch at the "load" and cannot be "changed" by
the matching device.
True: This is what you hear on
the air..."Why should you use a tuner(?), it does not have any
positive effect on the antenna." Yes that is true, but nothing else
you do will change the mismatch. The tuner is an aid to removing the
reactance (created by the mismatch) of the antenna system and
therefore it does have an active, positive effect on the antenna.
Most operators believe "matching devices" effectively "fool the
radio into thinking it is looking at a perfect SWR". Now that is no
further from the truth than the the previous statement is from a
lie. If a suitable "matching device" cancels reactance, then the
mismatch is absent and all the power is absorbed at the load. The
true statement should be..."Lower SWR obtained by using a matching
device indicates only the mismatch remaining between the
input impedance of the network and the impedance of the line from
To rephrase this, the SWR indicator is placed between the "matching
device" and the transmitter. The transmitter would see the lower SWR
at the input to the device, BUT ONLY after the reactance is
properly tuned out. If another SWR indicator is placed behind the
tuner it will see no change in the mismatch, no matter how perfectly
the SWR is indicated. But, because the reactance has been tuned out
the REFLECTED incidence is not a LOSS it is re-reflected back to the
load and absorbed in the radiator. (NOTE:
See question number 2)
(9) Proper adjustment of a "matching
device" for maximum line current creates a "perfect mirror" of
termination for the reflected wave incident.
True: Tuning the device creates
the "perfect mirror" terminator for the reflected wave. This causes
the the REFLECTED WAVE to be re-reflected, on arrival at the input
end of the line. The tuner provides "proper reactance" to cancel the
"equal but opposite reactance" between the source and the reflected
wave. This causes the REFLECTED wave to be added in phase
with the source wave to render the total incident, or FORWARD
POWER...which is the sum of the source and the REFLECTED
That may be hard to swallow, but like the perfect wave in the pool of
water, when it is reflected from the shore back to the point of
origin, it is again added to the source of that wave, and
re-reflected back to shore as an incident wave.
The RE-REFLECTION then becomes part of the FORWARD wave. Only loss
encountered along the way will be from liquid turbulence in the pool
(attenuation in the line). As you can easily see, mismatch is then
determined by one of two possibilities: The shore line is not a
perfect circle and all reflected waves are distorted (the antenna is
not constructed properly), or the impact of the wave generator is
located "off center" (off resonance frequency) and generates a
FORWARD wave that does not reach the shore equally (out of phase),
on all sides (the radiator is not asymmetrical). If the feed-line is
known to be in good electrical order, the feed line can in no way be
part of the mismatch issue.
From what you have learned so far...does
the radiator have to be perfect resonance in order to be the perfect
radiator? The answer is NO, but good system design where
currents are equal and do not cancel each other is certain to be
more effective than one that is not. But again, this has nothing to
do with SWR.
(10) Total "return of reflection" of any
amount of reflected power from the radiator back to the input
(caused by feed line mismatch) is the reason such reflected power is
not dissipated at the transmitter.
True: The re-reflected power is
not dissipated as heat in the transmitter or the matching device,
but instead is conserved, rather than lost. The only LOSS is in the
"attenuation" of the coaxial line. And again...this is insignificant
at HF frequencies.
(11) A good antenna system including a well
designed "matching device" feeding an "open wire line" into a 130
foot center-fed dipole at 50 feet does not radiate significantly more power
on 75 meters than does an 80 foot dipole at the same height fed with
the same power.
True: Open wire feeder has the
least amount of attenuation (loss) of any type feed line at HF
frequencies. The same can be held true at VHF frequencies as long as
the open line has little little or no turns beyond 20 to 30 degrees.
W1DF, "The Why's of Transmission Lines", W1DX "My Feedline Tunes
My Antenna"; QST March 1956, W1ICP "A Versatile Transmatch"; QST
(12) A self resonant dipole fed with
RG-8 or RG-11 cut for 3750 KHz does not, at that frequency, radiate
more than it does at 3525 or 3985 KHz.
True: Of course the opposite is
true also; however it should be noted that feed line length can make
a difference if the length is longer than 150 feet and if the feed
line is dependent on a high attenuation loss coax.
(13) A 3750 KHz dipole fed with any length
of 50 ohm coax and having an SWR of 1:1 will yield an SWR of 6:1 at 3500 KHz and close to 5:1
at 4000 Khz thereby "using" the coax as a tuned feeder, with
no significant loss across the entire band.
True: Plain and simple truth.
Again we respond that the FEED LINE has little if anything to do
with impedance mismatch or effective radiated power in the radiator.
(Note: It is possible to tune a feed line
using various lengths of coax at different values, but this does not
make the radiator any more efficient at one end of the band than the
other. Using various length 75 ohm coax in line with a 50 ohm feed
line does not effectively remove reactance from the radiator.)
(14) With the use of a "transmatch" at the line input, proper
coupling between the transmitter and the tuned-coax feeder
(of any length) can be maintained over the entire 80 meter band
True: Refer to the previous
question and note that the "transmatch" (matching device) is used to
remove reactance in the system. This cannot be done by the coax
feeder alone. A simple "L" network of an inductor and a variable
capacitor will work just as well as any of the "exotic" feed line
devices on the market today.
(15) When using a DIPOLE antenna above
ground, changing the height above ground or lowering the ends of the
DIPOLE in order to increase or decrease radiator impedance has an
insignificant effect on power absorption by the antenna.
True: This should be a no
brainer...I hope you did not miss this one.
I may be repeating myself, but
sometimes that does not hurt when trying to emphasize one's
position. Resonance is, by all basic function, a factor of math.
Real world formulas are there for a reason. There is no secret
medicine you have to take to understand "486 divided by frequency in
megahertz". The result should not be questioned; if you build your
new dipole to those specifications, the antenna should be resonant
at that frequency. If the SWR is not a perfect match, any attempt to
make it perfect will not increase efficiency at the original
(16) A 50 ohm tuned feed line at 3999
KHz can handle 700 watts of CW
power within SWR readings of 5:1. However, SSB input power at this frequency
can increase ratings to up to 2000 watts. A 100 foot feed of RG8
with a 5:1 SWR has an attenuation loss of .78DB (or .46DB due to SWR)
which is meaningless in terms of a broadcast signal level.
True: At these frequencies you
have a lot more to worry about when it comes to signal loss. The
entire 75/80 meter band can be covered very nicely if design your
antenna around 3750 KHz. and use a dependable matching device.
(17) If the length of feed line is critical in order to obtain the
proper match, the identical matching impedance can be obtained
using any length of feed line by simply adding a "matching network".
True: You do not need to perform
surgery on an antenna if the length of feed line you use is
critical. The matching transformer (2:1 Balun) will help "match" a
50 ohm line to a 100 impedance. You should be aware that the SWR
results shown may not reflect a perfect match at resonance. A simple
matching device can be made from any two components made up of two
inductors, capacitors or one of each.
Reference: P.H. Smith ~ Electronic
Application of the Smith Chart, R. Leo W7LR ~ An Impedance Matching
Method. QST April 1959.
(18) High SWR in a coaxial feed line caused by
severe mis-match at the load, does not produce antenna currents on
the feed line and it does not cause the feed line to radiate.
True: Nothing more to understand
the statement is true.
Reference: The ARRL Antenna Hand
Book - 10th addition 1964.
(19) High SWR in a open wire feed line at HF
frequencies, caused by load mismatch does not produce currents nor
does it cause the feed line to radiate
True: This is also true at VHF
frequencies if sharp bends are avoided. It should be noted that the
line should be balanced; equally in length one leg of the line to
the other and separators should also be equally spread apart.
Most "twin lead" made today
(450 ohm) is balanced and can be purchased as solid or stranded wire
in gauges 12 to 16 Ga.
(20) Both types of feed line may radiate, although
not significantly, caused by re-radiation of energy "coupled" into
the feed line from an asymmetrical positioning of said feed line to
True: The important factor is asymmetrical position of the
feed line to the radiator. Off center termination point to the
radiator can cause a limited amount of radiation.
Reference: J.J. Schultz W4FA ~ The
Broad Band Balun" - CQ Aug. 1968.
The use of OCF dipoles (Windom) has increased recently. These
antennas are susceptible to RF presence on the broadcast signal.
While this is only my opinion, I personally refrain from using such
antennas if at all possible.
(21) SWR indicator need not be placed at the junction of the
feed line to the radiator in order to obtain a more accurate reading.
True: In fact the SWR indicator
may be placed anywhere along the feed line. It should be noted that
if a low SWR reading is dependent on where the indicating device is
placed along the line, chances are you have feed line issues or
termination problems at the radiator. Feed line issues could be
water in the coax or a crack in the insulation. The SWR device
should be used as a "primary" tune up device and not a primary
"reflected power" device.
(22) The SWR in a feed line cannot be
changed, adjusted or controlled in any manner by varying the length
of said feed line.
True: This is a fact. Adding
different lengths of various coax to the feed point may lower the
SWR but it does not substantially increase radiation or lower
reflected power. Before going to great lengths to make these
adjustments, add a matching device ahead of the feed line and tune
out the reactance.
Reference: L.G. McCoy W1ICP ~
"Antennas and Transmatch" QST Oct. 1964.
(23) If the SWR bridge indicator reading changes significantly when
moved a few feet along the feed line it indicates "antenna current"
is on the outside of the coax or the device is unreliable, or
True: If you place an SWR device
directly behind the exciter and render one value that is incorrect
compared to one placed directly behind the amplifier, neither of the
indications are reliable. Placing the SWR indicator 1/4 wave along
the feed line should result in the same indication at the input or
at the termination point. The SWR bridge does not indicate (it
cannot) loss from feed line attenuation.
Reference: The ARRL Antenna Hand
Book - 10th addition 1964.
Note: Testing your SWR device
requires a "dummy load" of 50 OHM. You should first install the
bridge as indicated by the manufacturer. Tune for 1:1 on the device
in the REVERSE position and then simply reverse the feed line
connections to the bridge. The SWR should be the same when read in
the FORWARD position. If not, the indicator is in need of repair.
(24) Any reactance added to a resonant load (purely resistive) in
order to compensate SWR readings will only make reflected matter
worse, not better.
True: It has been taught and in
most part, understood that the lowest SWR will only occur at
radiator resonance. This can be no further from the truth. This is
because SWR is an indication of the FEED LINE and not a true reading
of the resonance of the radiator. These factors are totally
independent of each other. Any SWR indication that the antenna is at
resonance is rare and any measurements that contradict this
indicates an error on the part of that measurement device. Simple
terms...an SWR reading of 1:1 does not mean the antenna is at
(25) Of all common known types of DIPOLE
antennas, including folded, fan, trap, coaxial or a combination of
such, does not
radiate more field (pattern) than another providing each has insignificant reactance losses while fed with the same power.
True: If it looks like a DIPOLE,
tunes like a DIPOLE and radiates like a DIPOLE, it must be a DIPOLE.
As long as the SWR is reasonable and reactance is at a minimum, no
matter what you call a G5RV, it remains a DIPOLE. It also radiates
like a DIPOLE, therefore it cannot radiate more energy than a
G Grammer W1DF, "The Why's of Transmission Lines", QST Jan. Feb. Mar. 1965
(three part lecture).
(26) RG8 coax used in a HF mobile installation
should have the MATCHING DEVICE located at the input to the coax in
order to improve operating bandwidth.
True: Matching devices at the
antenna (of a mobile installation) significantly decreases antenna
radiation. This type of installation also improves over all
bandwidth. This is more important today due to lack of counterpoise
in most fiberglass and composite vehicle bodies. In many cases a
"fake" ground system (a separate wire) run from the antenna mount
returned back to the matching device can increase effects of over
(27) Center loaded mobile antennas of equal size having no input
matching device at the coax input, the best efficiency is obtained
on units with the LOWEST terminal resistance, not the lowest SWR.
True: Many center loaded mobile
antennas will have a high SWR. They radiate very well with or
without a matching device located at the coax input. Antenna models
with matching devices generate the LOWEST SWR, but they are usually
wasting power in the loading coil because of a LOW "Q" in the coil
or extreme capacitance, or in some cases, both.
(28) The RESONANT FREQUENCY of an antenna cannot be determined by
probing the input of the feed line using a grid-dip meter or noise
bridge, if that device cannot properly measure reactance.
True: Devices like the modern
antenna analyzer offer a solution to the problem of antenna design
because they can measure antenna reactance. They give this result in
many forms, but the SWR indicator alone cannot do that. Use of a
grid dip oscillator or noise bridge will generate different results
with different lengths of feed line because these devices are
reading TOTAL resonance. The resonant indication will change if the
feed line is adjusted. If say they feed line is 1/2 wave at the same
frequency as the radiator, the resonant indication will be totally
different from that of either the radiator or the feed line.
(29) Placing an SWR bridge at the input to the matching device
can offer the same results when placed at the output of the matching
device if the unit is read in reverse.
False: The "matching device"
tunes reactance from the feed line and therefore it offers a more
effective load to the exciter. Any SWR indicator placed behind the
tuner should read an identical SWR when the tuner is switched to
bypass the network. The indication makes no difference which way the
bridge is installed. The tuner simply "re-reflects" the reflected
power, it does not absorb the reflection in it's network therefore
the additional SWR indicator will read the same no matter how the
tuner is matched or mismatched.
For those who say the matching
device is simply "faking" the exciter into believing it is a perfect
match are only half true. Call it what you want, but a tuner is
designed to TUNE reactance that insures full power absorption at the
radiator by simple re-reflection of the standing waves.
(30) Tuning the receiver to the highest noise floor, using a
matching device yields the same result as tuning the transmitter to
the lowest SWR reading.
True: The RF front end is a good
indicator where the transmitter should be "close" to proper tuning.
What should be noted, tune to the highest "noise floor", take an "S"
meter reading and then switch the tuner into "bypass". The "S" meter
reading should be the same. If it is not, you are most likely not
properly tuned or there is a feed line issue.
In the early days of modern receivers, there
was an "L" network attached to the first RF stage. This network was
a simple "antenna tuner" and it allowed proper tuning of the
receiver front end. Later these tuned circuits incorporated another
stage of amplification and became known as "pre-selector". It was a
simple amplified "tuner stage" that eliminated noise and cross band
Ok, I hope you got something from all of this. I am trying my best
to help you understand SWR. It is a very simple indication of
forward and reverse voltages along the transmission line. These
voltage are there for both "transmit" and "receive" The receiver
cares less what it hears, but a high SWR does not offend the
receiver...however a tuned ciscuit ahead of the receiver will indeed
improve the signal to noise ratio. Remember that an antenna that is
designed for all bands is a compromise, especially to your receiver.
That should explain why a 40 meter loop does not boost the noise
floor on 10 meters as well as a 10 meter loop. The 40 meter antenna
is much larger, but the 10 meter loop is a tuned circuit and
receives 28 MHz signals much better than one tuned for 7 MHz (this
is also true in reverse).
I welcome comments regarding this
questionnaire, but I suggest you obtain a copy of Reflections I or
II and read the book like I did...read it several times.
Thanks, The RFampGUY.
I hope to gather another quiz like this one with reference to Baluns
and feed point matching transformers. Why they are so important and
the difference between the "voltage" type and the "current" type.
This is also unknown territory for many of today's "memory made ~
multiple choice" Ham operators.
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