Adjustments for resonance

[freecell]

I have always just tried to tune for the lowest point in the SWR curve. Then I double check with another SWR meter. I have yet to spring for an antenna analyzer. I have been lucky anytime I have a vehicle checked with an analyzer then may readjust, but it may be just to make 1,6 to 1.4. I have not ever tried to tune outside CB band. And have had antenna installs with no SWR curve then I realized that something else is wrong and have to recheck my install. I have been trying to keep everything simple.
Then again I run everything barefoot. One thing I have noticed. I had witnessed a lot of professional land mobile installs for 50 or 100watt high band VHF for 155mhz. Never once have I seen a tech with a meter. They just cut the antenna for whatever the instructions say. Most were base loaded Motorola whips to NMO mounts to hood channel.

feedpoint conditions for
full size 1/4 wl. antennas.

(Rrad & Rloss are in ohms)

Rrad 34, Rloss 16 = 50 ohms
Rrad 35, Rloss 15 = 50 ohms
Rrad 36, Rloss 14 = 50 ohms
Rrad 37, Rloss 13 = 50 ohms
Rrad 38, Rloss 12 = 50 ohms
Rrad 39, Rloss 11 = 50 ohms
Rrad 40, Rloss 10 = 50 ohms.

all values above, including
all possible combinations in
between will (or should)
result in a 1.0:1 vswr. again
we can see the unimportance
of vswr in regard to any
indication of an efficient
antenna system.

all values above assume
X=0 @ the test frequency

the addition of this third "X"
element to the equation and
all the possible combinations
that would indicate a 1.0:1
vswr will not be listed.

as Rrad is increased or
Rloss is decreased, the
radiation efficiency of
the antenna is increased.

the shorter the antenna
becomes as in the case of
physically short, inductively
loaded antennas, the lower
Rrad drops, Rloss increases
and radiation efficiency
suffers.

you will NEVER see 50 ohms
Rrad with 0 ohms Rloss in
any quarter wave antenna.
if you see a 1.0:1 vswr on
the line the first thing you
should be is suspicious, not
happy.

my experience tells me that
if i DON'T see something in
the neighborhood of a 1.25 -
1.5:1 then it's time to roll
out the l/c network analyzer
and have a closer look.

 

[fourstringburn]

Looks useful in mobile.

MFJ-908 Mobile Impedance Matcher $55.
Or DIY

“Best” resonance, first, lowest SWR, second.
Per k0bg (with MFJ-259) in Antenna Matching.
(Details apply; read).

.

Far better and cheaper to make a matching device at the antenna feedpoint.

Try it someday on a 102 whip.

You just need some 14 guage enameled wire. Sand off the tips of each end with emery cloth and solder 2 terminal rings to them. 1 ring needs to be larger to attach to the hot side of the antenna stud, the other goes to a ground bolt creating a shunt.

You can use the larger size sparkplug thread or a 1/2 diameter bolt and use the threads as guide to wrap a coil 7 turns to start with.

Using an analyzer, simply spread or collapse the coil to where you get the best readings. You may have to take a turn or 2 out of the coil and check again.

 

[jkp1]

I'm so glad you guys are posting this info. I've been trying to understand antenna tuning for a while. There is so much wrong info out there. Thank you.

 

[Slowmover]

Far better and cheaper to make a matching device at the antenna feedpoint.

Try it someday on a 102 whip.

You just need some 14 guage enameled wire. Sand off the tips of each end with emery cloth and solder 2 terminal rings to them. 1 ring needs to be larger to attach to the hot side of the antenna stud, the other goes to a ground bolt creating a shunt.

You can use the larger size sparkplug thread or a 1/2 diameter bolt and use the threads as guide to wrap a coil 7 with turns to start with.

Using an analyzer, simply spread or collapse the coil to where you get the best readings. You may gave to take a turn or 2 out of the coil and check again.

That’s the detail missing until now.

In your experience, does cold/wet/hot affect the device function? What of vibration over time? As these are what lead me away instead of towards.

Thx!

.

 

[fourstringburn]

That’s the detail missing until now.

In your experience, does cold/wet/hot affect the device function? What of vibration over time? As these are what lead me away instead of towards.

Thx!

.

Wet, yes. Water adds capacitance as well as icing which can change the tuning some but return to normal when it dries out. Your mobile antennas now do this.

The 14 gauge enameled wire is fairly rigid and will stay in place just fine. These are most commonly used for HF screwdriver antennas and handle the rigors of the road just fine.

See pic

 

[freecell]

View attachment 44538

Borrowed from k0bg in Antenna Matching

"a very common belief is that the lowest
VSWR point is always the exact resonant
point." This is a myth!

Alan Applegate

"the lowest feed-line SWR occurs at the
self-resonant frequency of the radiating
element it feeds."

"any measurements which contradict this
indicate that either the measuring equipment
or the technique (or both) are in error."

M. Walter Maxwell

 

[fourstringburn]

The lowest SWR can be ideal,

BUT, it depends what it took to get that!

We all heard the phrase in one form of another on this forum,

" even a dummy load has a very low SWR".

In other words, if antenna needs a lot of loading coil or other forms of matching to tune, then it's nothing more than a RF leaking dummy load.

 

[HomerBB]

In other words, if antenna needs a lot of loading coil or other forms of matching to tune, then it's nothing more than a RF leaking dummy load.

I think the last paragraph is too broad.
There are impedance mismatches on most antennas to overcome. Matching networks are simply impedance transformers (and are not limited to antenna systems and RF). A dummy load by design is not a transformer, but a direct impedance match and ideally limits RF broadcasting. An antenna transforming network is the opposite. It adjusts impedance mismatches into alignment across the antenna system so that RF broadcast is enabled.
They are functionally polar opposites.
Accepting it as otherwise would reduce the choices of antenna to, let me see... none, as all of them must be manipulated in some way to obtain a 50 Ohms match to modern transceivers.
I think there is a forgetfulness involved in thinking that all heavily matched antennas are RF leaking dummy loads. What is forgotten is that 50 Ohms is a near arbitrarily chosen manufacturing industry standard, and that RF hasn't any preference for any one impedance over another. The manufacturers do.
It is our efforts to create RF electronically and train it like a lap dog to do our tricks that has things the way they are. We want gain, so we squeeze our thumbs over the end of the water hose to get it, and impedance (resistance) increases as we squeeze more tightly. Because we use designs that need a lot of matching, like end fed half wave antennas, suggests that the dummy part of this may be some place other than in the antenna system.
We want our RF to be shaped like this or that (because of the hypnotic effect of the word "gain"), and we have our reasons for heavy duty impedance matching. But, even so, that matching mechanism does not impede RF broadcasting, it facilitates it.
That's my story and, for now, I'm sticking to it.

Note: if you disagree draw a little stick man picture of me and scribble through it writing in big ugly letters " I DON'T LIKE YOU!!!!"

 

[fourstringburn]

I think the last paragraph is too broad.
There are impedance mismatches on most antennas to overcome. Matching networks are simply impedance transformers (and are not limited to antenna systems and RF). A dummy load by design is not a transformer, but a direct impedance match and ideally limits RF broadcasting. An antenna transforming network is the opposite. It adjusts impedance mismatches into alignment across the antenna system so that RF broadcast is enabled.
They are functionally polar opposites.
Accepting it as otherwise would reduce the choices of antenna to, let me see... none, as all of them must be manipulated in some way to obtain a 50 Ohms match to modern transceivers.
I think there is a forgetfulness involved in thinking that all heavily matched antennas are RF leaking dummy loads. What is forgotten is that 50 Ohms is a near arbitrarily chosen manufacturing industry standard, and that RF hasn't any preference for any one impedance over another. The manufacturers do.
It is our efforts to create RF electronically and train it like a lap dog to do our tricks that has things the way they are. We want gain, so we squeeze our thumbs over the end of the water hose to get it, and impedance (resistance) increases as we squeeze more tightly. Because we use designs that need a lot of matching, like end fed half wave antennas, suggests that the dummy part of this may be some place other than in the antenna system.
We want our RF to be shaped like this or that (because of the hypnotic effect of the word "gain"), and we have our reasons for heavy duty impedance matching. But, even so, that matching mechanism does not impede RF broadcasting, it facilitates it.
That's my story and, for now, I'm sticking to it.

Note: if you disagree draw a little stick man picture of me and scribble through it writing in big ugly letters " I DON'T LIKE YOU!!!!"

Interestingly put, We'll still like you anyway!

But, there are losses in the loading coils and matching devices including tuners. The more matching needed, the greater the loss. Yes, the antennas can still work and many of us work the world with antennas that have less than ideal ERP on some or even all bands!

The losses doesn't mean an antenna won't work, just the efficiency takes a dive.

A large HF screwdriver antenna can work bands as low down to 80m and even 160m. However, at these bands the ERP on 80m is barely 2 watts and 160m is in milliwatts with a 100w radio according to a published field test I've read . The losses are in that huge coil trying to tune such a long wavelength which is needed for such a short antenna on those bands so the analogy "leaking dummy load" is appropriate. But with good band propagation it's workable just like any multiband antenna which usually has some bands using a tuner. These losses are accepted because those bands can still be usable. That's the compromise that’s acceptable.

A mono band dipole cut for a specific frequency is much better in ERP than a shortened multiband dipole or vertical with traps, coils, or other matching devices on the same band as the mono band dipole.

 

[338_MtRushmore]

I thought tuner losses were essentially a myth? I can't recall who or why, but they were convincing. Is this wrong?

 

[HomerBB]

I'll tell you what a real loss is. Not being on the air is a real loss. That, my friend, is a 100% loss like no other.

 

[338_MtRushmore]

I haven't keyed a mic since CQWW, and that is probably a win for everyone else on the air.

 

[freecell]

I have noticed on my manual tuner that the peak forward power meter lights are usually showing greater output when the SWR indicator cross needles are not at the lowest SWR, close, but not the closest. Anything relevant.

the "peak forward power meter lights" are literally measuring forward current, a condition that occurs when at the match point between the transmitter and the feedline input provided by the matching network a complementary mismatch has been introduced at the point of the original mismatch producing a conjugate match. maximum forward current flows down the line to the load. this hardly ever occurs simultaneously with a flat swr, if the swr was flat to begin with you wouldn't need the matching network unless you're retuning after moderate-large excursions in frequency to maintain maximum forward current from the transmtter to the load and yes, maintaining the resonance of the entire link from the output of the matching device down the feedline, including the antenna, up to and including the limitations of the values of L & C available in the matching device, while simultaneously providing a feedline input impedance at the transmitter end to accommodate the fixed, 50 ohm output impedance of the transmitter. maximum forward current flows when the system is resonant. swr has nothing to do with it and none of this is possible if swr is 1:1. impedances cannot be matched if there is no mismatch present. as to L/C circuit losses, air variable capacitors exhibit little to no loss if suitably selected for the power levels and peak voltages incurred by the matching device while on the other hand by comparison, inductors exhibit more loss, that is why the matching device is always adjusted for a noticeable increase in receiver noise using the LEAST AMOUNT OF INDUCTANCE POSSIBLE and then afterwards the variable capacitor is adjusted for maximum forward current, touch up adjustments as necessary.

in a typical T matching network with variable capacitors at both input and output divided by an inductor connected between both variable capacitors to ground, the loss of a well designed inductor rarely exhibits more than .5-.6 dB. of loss. most of you are losing more than that in your feedline.

 

[Handy Andy]

Note: if you disagree draw a little stick man picture of me and scribble through it writing in big ugly letters " I DON'T LIKE YOU!!!!"

They'll have to get thru a lot of us first...
​

If it wasn't for this thread getting bumped, I would have missed that little nugget in your post...

As what your recent medical issue had uncovered...

You will be ARE missed when you're gone.

 

[freecell]

That is a very misleading quote. What he is saying is if the vswr dip indicating resonance occurs at 5:1, the antenna system will function great. No need to get to that magical 1:1, especially if it involves tuning further from the indicated resonance point.

i have no idea what you're reading because the terms "5.1," "dip," or "resonance," do not appear anywhere in that post, that is what is misleading.

here is the original post.

"The relative unimportance of low SWR
when feed-line attenuation is low is demonstrated
rather vividly in the following two examples of
spacecraft antenna applications. First, in the
TirosESSA-Itos-APT weather satellites, of which the
entire multifrequency antenna-systems design was
the work of the author, the dipole terminal
impedance at the beacon-telemetry frequency (108
MHz in early models) was 150 - j100 ohms, for a
VSWR of 4.4, reflected power 40 percent.
Matching was performed at the line input, where it
was fed by a 30 milliwatt telemetry transmitter.
(We can't afford much power loss here!) The
feedline and matching-network attenuation was 0.2 dB,
and the additional loss from SWR on the feed line
was 0.24 dB (5.4 percent), for a total loss of 0.44
dB (9.6 percent). On the prevalent but erroneous
assumption that all reflected power (40 percent) is
lost, only 18.1 milliwatts would reach the antenna,
and efficiency, determined on the same erroneous
basis, would be only 60 percent. But 27.1
milliwatts were measured; of the 2.9 milliwatts lost
in total attenuation, only 1.6 milliwatts of it was
from the 4.4:1 VSWR. So the real efficiency would
have been 95.5 percent if perfectly matched at the
load, but reduces to 90.4 percent by allowing the
4.4 VSWR to remain on the feed line. Second, in
the Navy Navigational Satellite (NAVSAT), used
for precise position indications for ships at sea, the
antenna terminal impedance at 150 MHz is 10.5 -
j48 ohms, for a VSWR of 9.8, reflected power 66
percent. Also matched at the line input, flat-line
attenuation is 0.25 dB, and the additional loss from
SWR is 0.9 dB, for a total system loss of 1.15 dB,
approximately 1/6 of an S unit. This is an
insignificant amount of loss for this situation, even
in a space environment where power is at a
premium. Why did we match at the line input?
Because critical interrelated electrical, mechanical
and thermal design problems made it impractical to
match at the load. Line-input matching provided a
simple solution by permitting the matching
elements to be moved to a noncritical location."

Another Look at Reflections Part 1
M. WALTER MAXWELL

here's your original post:
https://www.worldwidedx.com/threads/adjustments-for-resonance.257457/page-4#post-761955