When you put up an antenna in the the old
days, it could be a real struggle. The only way to tell if it was tuned to the
right frequency was to fire up your transmitter and check the SWR over the band
you're trying to hit. But if the antenna was not resonant in the band your
transmitter covered, about all you might be able to tell is that it is resonant
above or below the band. With an Analyst, which goes outside the ham bands, you
can tell exactly how much adjustment to make without taking the antenna up or
down or running back and forth to your ground-mounted antenna. And it can do so
much more! Read on:
As shown above, any Analyst can be used to
measure at the far end of the feedline or directly at the antenna. Of course,
any type of antenna can be measured--not just verticals. Also, the units can
measure balanced line as well as coax, since the unit is so small that it
essentially "floats" from ground.
Making SWR plots and determining resonant frequency is the main use for any
Analyst. Simply connect as shown above, vary the Analyst frequency and measure
SWR.The antenna is resonant at the frequency where SWR is lowest.
If you've never used an Analyst before, you're in for a treat. Previously,
the normal procedure for adjusting an antenna was to transmit using your main
transmitter and measure SWR. If the SWR was high, it was often difficult to tell
what correction to make, since the transmitter is limited to the ham bands.
Using an Analyst you can now tell the resonant frequency exactly
and determine exactly how much to shorten or lengthen your antenna
after only one measurement. For example, if you're shooting for a 14 Mhz
resonance, and the SWR is lowest at 14.56 MHz, this is exactly 4% higher than
desired. So you know to lengthen the antenna by exactly 4%. There's no need to
keep cutting the antenna and raising and lowering it many times.This is
explained in more detail in the instructions.
Furthermore, the frequency of lowest SWR for random length antennas well
outside Ham bands can tell you whether to add a coil or capacitor. (For example,
maybe you can "tune up" your house gutter!)
The other advantage is that you can take the Analyst outside or up a tower
since it's completely self-contained. So you can adjust the antenna on
the spot without having to go back to the main transmitter each time
you make a change.
To measure line loss, simply measure the impedance (Z) of the open or shorted line vs. frequency until you find minimum value. This minimum value reoccurs periodically in frequency. The minimum impedance yields the line loss in dB. For example, if you measure an 8 ohm minimum impedance with 50 ohm line, the loss is about 1.4 dB.( A lossless line would read zero ohms.) Loss in line other than 50 ohms, e.g. 300 ohms, can also be measured. All Analysts are accurate at low impedance with digital readout.The instructions explain this simple procedure further.
Changing the Analyst frequency until you
find the minimum impedance for the above circuit gives the resonant frequency of
the circuit.
Bonus:Not in all
Analyst Instructions. A simpler way to measure the resonant frequency
of a trap, or any tuned circuit, is to connect a piece of wire between the
Analyst output and the Analyst ground (the ground screw next to the coax
connector, or the outside of the coax connector.) The wire can be a few inches
to many feet long.(Note:You must disconnect at least one end of the trap from
any antenna to measure its resonant frequency.)
Put the Analyst in the Z mode. You will read a small Z which simply
represents the inductance of the wire. Now put the wire near the trap. As you
tune the Analyst frequency, Z will increase dramatically at the trap resonant
frequency! The frequency of peak Z is the trap resonant frequency.
If the trap has high Q and is large you can probably see the jump in Z with
the wire several inches from the coil. For a small coil, you might need to wrap
the wire into a small loop at the end and bring it near the coil. No fancy
plug-in coils are needed such as a grid-dip meter requires...just a few inches
of wire! And the Analyst's digital frequency and Z readout pinpoint the resonant
frequency exactly.
The same wire can usually be used over the entire frequency range of the
Analyst, so you can also forget about the many plug-in coils that a grid-dip
meter requires. 
If you construct a simple switch as shown
above, you can use an Analyst to tune your antenna tuner without transmitting.
Simply set the Analyst at the desired frequency and set the tuner for lowest
SWR.
The RF1 and VA1 both measure coils and
capacitors at the RF frequency of your choice. Simply connect the coil or
capacitor across the units coax connector; directly, or using clipleads
(supplied.) Both units subtract the stray output capacitance of the connector,
etc., so C is usually read directly without any correction required. The VA1 ,
which measures the sign of X, will show a negative L if a capacitor is measured.
This is often handy since this is the L value which resonates with the capacitor
at the measurement frequency. The RF1 does not measure the sign of X, but will
also show the equivalent L value.
Please note that the L and C functions of the RF1 are only for measuring pure
L and C, whereas the VA1 shows the L or C component of any load (R + jX),
including the sign.
Please note that one can buy other meters
which measure L and C, which are usually intended for TV repair people. These
meters usually operate at 1 kHz to 100 kHz and so are essentially
useless for RF measurements of coils ! . The inductance of a
coil varies considerably at high frequencies because of stray capacitance and
other factors.In addition, if the coil is wound on a ferrite core (e.g. toroid),
the core material causes the inductance to vary even more with frequency. So, an
L/C meter which operates at 1 kHz or 100 kHz will not read RF inductance
correctly. In contrast, Analysts can be set to the frequency of interest when
measuring L.
By connecting a known resistor value to
the far end of a transmission line and observing how Z varies with frequency,
the line impedance can be determined.This simple procedure is discussed further
in the instructions.
If you have a 1:1 balun, simply connect a
small 50 ohm resistor across its output, and verify that Z at the input is also
50 ohms. Similarly, if it is a 1:4 balun, connect 12.5 ohms at the output and
verify that 50 ohms is measured at the input. Or, for a 4:1 balun, connect 200
ohms at the output, etc. (Don't expect "perfect" results, and especially expect
some degredation at the low and high frequency limits of the balun specs.)
Bonus:Not in Analyst
Instructions. "Current" baluns are often used to keep current from
flowing on the outside of the cable when coaxial cable feeds a balanced antenna
such as a dipole or inverted V. Also, vertical groundplanes (verticals that
don't use an "earth" ground) should have one, especially if only one or two
groundplanes are used, as is becoming more popular. However, compact baluns are
easy to burn out at high SWR. So, if weight and size are not a problem, a "choke
balun" is often used. This can be made by coiling 4 to 10 turns of the coax
feedline in a loop (very simple and cheap), or, similarly, by slipping many
ferrite cores over the outside of the coax (not so cheap, but lighter.) See the
ARRL Antenna Book for details...sorry, we cannot supply details.
The impedance of the "choke" is easily found by measuring the Z of the coax
shield between the input and the output of the "choke." That is, connect the
Analyst ground to the coax braid on one side of the "choke," and connect the
"hot" end of the Analyst (inside of Analyst coax connector) to the coax braid on
the other side of the "choke." You can stick a hairpin through the coax
insulation to reach the braid without cutting the coax. Vary frequency, and
verify that Z is high over the frequency range of interest. You may measure Z
greater than 1000 ohms over part of the range.
The R and X components of the load are
often desired. It turns out that R and X can be calculated from SWR and Z, which
are read out by the RF1 and RF5. The equation to do this is in the instructions.
So, if you occasionally need R and X components, this is adequate. Note,
however, that this does not yield the sign of X, and the
results are not nearly as accurate as using a VA1. Also, this method does not
work above 150 to 200 MHz because of stray inductance and capacitance which can
cause large errors in Z.
I notice that your Analysts have a coax connector output. Can they also be
used to measure on balanced lines such as twinlead and ladder line?
Yes! The Analysts are so small that they essentially float from ground. So
just go ahead and hook balanced line to the coax connector. It will measure
these just fine. (We could have added two screw terminals in parallel with the
coax connector, but this is a waste of space and not necessary.)
What are those round things on the panel next to F,SWR, etc ? Are they
LED's ?
No. LED's would drain the battery. All the round things on the panel next to
F,SWR,ON/OFF, Band, etc. are pushbutton switches.
What is the reliability of your units? I've had some bad experiences with
similar units.
We consider reliability to be very important. Each unit is
thoroughly tested. If any unit, or component, seems to be in any way marginal it
is rejected or the component is replaced. The little things are important,too.
For example, 9 volt battery connectors are notoriously unreliable. We
stress-tested over 15 types before settling on the brand we used.
Does this mean nobody ever has a problem? Of course not. Some units fail "in
the mail" despite our tests.Or someone leaves a decal off a unit, or forgets to
enclose instructions. Despite having ten's of thousands of products in the field
which are beyond the one-year warranty, we average less than 2 hours a
week on all repairs, including wattmeters ! We think this is
outstanding, and want to keep it that way.
The VA1 measures R and X, including the sign of X directly and
instantly, and does everything else that the RF1 does, of course. The VA1 also
shows SWR for lines other than 50 ohms, and shows the R and X components of an
antenna in the air. If you're an advanced user, you should consider the VA1.
However, the less-expensive RF1 is also extremely accurate and adequate for most
tasks.
A few common questions:
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