Finally a radio technician that actually knows what he is doing!!!!!!

[4x4junkie]

So you don't believe light travels at ~186,250 miles per second then, huh? (or is it "186,000" miles/sec you're disputing? Like that even matters???).
But you go ahead and enjoy playing around with your 'scope, as all you've really proven is that you know how to hook up a tone generator to a radio and make wave patterns on it.

At least I was able to spot some behavior within some of the waveforms as you were adjusting the tone input level indicating that the radio still had it's modulation limiter intact (at least the one that is up by the radio's mic input circuit), so I'll give you props for that for not yanking out every mod limiter transistor like some techs do.

Have fun.

 

[unseenone]

:lurk:

For someone who knows that much, why would you need this technician? What does he do, that you cannot? Seeing as it appears you're on a first name basis with him, perhaps he could legitimize his business with say... a phone number or something along those lines. Otherwise, the entire exercise is a complete and total waste of time.

 

[rabbiporkchop]

So you don't believe light travels at ~186,250 miles per second then, huh? (or is it "186,000" miles/sec you're disputing? Like that even matters???).
But you go ahead and enjoy playing around with your 'scope, as all you've really proven is that you know how to hook up a tone generator to a radio and make wave patterns on it.

At least I was able to spot some behavior within some of the waveforms as you were adjusting the tone input level indicating that the radio still had it's modulation limiter intact (at least the one that is up by the radio's mic input circuit), so I'll give you props for that for not yanking out every mod limiter transistor like some techs do.

Have fun.

I'm not here to dispute the speed of light, and I'm not Mark Sherman. Here is a valuable lesson on transmission lines.
http://www.hamradio.me/antennas/measuring-quarter-wave-coax-stubs-using-mfj-analyzer.html
Coaxial cables 1/4 wave long serve a variety of useful purposes in antenna assemblies. Whether it is the phase delay line for a Turnstile Antenna like the 80 meter Turnstile Antenna or to make the feed lines for a four-square antenna, the transformer action of a 90 degree long feed line serves many purposes.
Coax Transformer

A transmission line 90 degrees in electrical length “will have a purely resistive impedance when terminated with a pure resistance.” [1]
Two methods of creating a quarter wave long transmission line come to mind: Calculation and Measurement.
Calculation of Quarter Wave Stub Length

The most straight forward method of calculating the electrical length of a piece of coax involves first calculating the free space wavelength of the target frequency and multiplying by the velocity factor of the coax.
Coax velocity factor of popular coax cable types is published in many places. Two come to mind: RG58 has a Vf of 0.66 and LMR-240 has a Vf of 0.84.
So…
If you need a 1/4 wave piece of coax for, say, 7.150 MHz start by calculating the freespace wavelength…
Wavelength(Freespace-7.150MHz) = 300m/s / 7.150 MHz = 41.95 meters
…divide this by 4 to get 1/4 wave…
41.95 meters / 4 = 10.48 meters
…and if you are an Imperialist like me I convert to inches…
10.48 meters * 100 cm/m * 1″/2.54cm = 412 inches
…or about 34.5 feet.
Now take this and multiply by the Velocity Factor of your coax.
For RG58 -> 34.5 feet * .66 = 22.71 feet.
For LMR-240 -> 34.5 feet * .84 = 28.9 feet.
Depending on what you are doing with this quarter wave piece of coax, this may be perfectly adequate accuracy. Plus if you are dealing with HF frequencies the extra length added by connectors is not a major contributor towards phase angle accuracy.
However, what if you have unidentified and/or low quality coax and are not quite sure of its Velocity Factor? Measure it… electrically…
Measuring Electrical Length of Transmission Lines

Quarter wave and half wave length piece of transmission lines have special properties. A line quarter wave in length acts like an impedance transformer. A short at one end will appear as an open at the other. Likewise an open at one end will appear as a short at the other. This will happen only at the frequency where the line is 1/4, 3/4, 5/4, etc. waves in length.
Testing a Quarter Wavelength of Transmission Line
Testing a Quarter Wavelength of Transmission Line
Transmission lines a half wave in length come full circle by mirroring the impedance on one end to the other. An open circuit at one end will appear as open at the other. A short at one end will appear as a short at the other.
Testing a Half Wavelength of Transmission Line
Testing a Half Wavelength of Transmission Line
Note in both figures above the distance a wave travels is shortened by the dielectric properties of the coaxial line. This fact is represented in transmission line characteristics as a variable called Velocity Factor… a unit-less number indicating the fractional speed of light in transmission lines with respect to the free-space speed of light.
So let's apply the above concept to this 182.5 inch piece of RG58C/U coax from Pasternack I have laying around the shack.
Let's find the frequency where this piece of coax is a quarter wavelength and a half wavelength. Since the end of the coax is terminated into nothing, it is an infinite impedance. In the quarter wave case this infinite impedance will transform to zero impedance; We should adjust the frequency for minimum impedance…
Those of you with later model MFJ meters have the advantage of seeing complex impedance. Adjust your frequency for minimum impedance and zero imaginary component.
We measure about 10.9 MHz. The accuracy of this method with this MFJ meter seems about +/- .5 MHz so this not an ultra precise way of doing this. However, it should be good enough for HF stub measurement.
If our goal is to make a 1/4 wave stub at 14 MHz we simply take out our coax cutters and snip off portions to raise the 10.9 MHz to 14 MHz. After each snip, adjust the frequency up and down to find the new zero impedance point. It's that simple. When you cut the coax, be sure pieces of the shield braid do not short to the center conductor or you will suddenly be reading a high impedance at your meter.
Let's raise the frequency of our meter to seek out the half wavelength frequency. Intuitively, this should be exactly twice the 10.9 MHz measured before.
Well, we didn't quite reach 21.7 MHz, but then again, it seems a bit more difficult to measure the center of a high impedance than low.
Continuing to raise the frequency allows us to discover another zero impedance point at 32.7 MHz. Again, accuracy is about +/- .5 MHz as it was difficult to really nail down a particular 1/10 of a MHz. This is pretty close to 1.5 times the half wave frequency of 21.7. We have found the point where the coax is 3/4 waves long.
When doing these calculations you should ensure the low impedance point is really the 1/4 wave rather than 3/4, 5/4 and so on.
Velocity Factor Calculation

Interestingly we have enough data to compute the velocity factor of this piece of coax using the measured frequency. We first take the 182.5 inches and compute the frequency of the free space wavelength…
[ 1 / (182.5 inches * (2.54cm/inch) * (meter/100cm) * (1s/300m)) ] / 4 = 16.2 MHz
We measure 10.9 MHz.
10.9 MHz / 16.2 MHz = .67
This is pretty close to the published RG58 Velocity Factor of 0.66.
References:
Gerald L. Hall et al. “Transmission Lines” ARRL Antenna Book. The ARRL, Inc. 13th ed. 1974. p 86.


Assuming the laws of physics apply to making precise measurements, I think it's safe to assume the laws of physics would apply at all other times as well

 

[rabbiporkchop]

:lurk:

For someone who knows that much, why would you need this technician? What does he do, that you cannot? Seeing as it appears you're on a first name basis with him, perhaps he could legitimize his business with say... a phone number or something along those lines. Otherwise, the entire exercise is a complete and total waste of time.

Being able to recognize a perfect waveform on a scope and having the technical expertise to tune a rig are two completely different things. I recognize my limitations and leave tuning up to experts.

 

[rabbiporkchop]

I'm kinda surprised nobody tried to dispute the validity of that 1974 ARRL article which clearly refutes 50 ohms remains constant through the entire length of a coaxial cable.

 

[4x4junkie]

I'm kinda surprised nobody tried to dispute the validity of that 1974 ARRL article which clearly refutes 50 ohms remains constant through the entire length of a coaxial cable.

********.

No, nobody wants to bother with your post anymore. It's quite obvious your lack of knowledge on this subject by your posting an article about ways to measure phasing lines for phased antenna arrays that has absolutely nothing to do with running a single piece of cable from a radio to an amp or antenna.
Until you show a little willingness to admit your error (and tell us who you really are), no one cares.

A 50 ohm cable terminated into a 50 ohm load will show 50 ohms (1:1 SWR) no matter what length it is (and was the point of my very first post in this thread). End of story.

(Perhaps the input to that class-C CB amplifier is something very different than 50 ohms.... Did you ever bother to think about that at all?)

 

[rabbiporkchop]

********.

No, nobody wants to bother with your post anymore. It's quite obvious your lack of knowledge on this subject by your posting an article about ways to measure phasing lines for phased antenna arrays that has absolutely nothing to do with running a single piece of cable from a radio to an amp or antenna.
Until you show a little willingness to admit your error (and tell us who you really are), no one cares.

A 50 ohm cable terminated into a 50 ohm load will show 50 ohms (1:1 SWR) no matter what length it is (and was the point of my very first post in this thread). End of story.

(Perhaps the input to that class-C CB amplifier is something very different than 50 ohms.... Did you ever bother to think about that at all?)

considering that amplifier was probably made by some hillbilly in the backwoods of Kentucky I think it's safe to assume the input is not exactly 50 ohms. considering the characteristic impedance of a PL-259 connector is probably around 36 ohms, how can that Theory about impedance remaining constant through the entire length of cable even be relevant when common sense dictates (as well as the laws of physics) that impedance only repeats itself every half wavelength. Any length of cable other than a multiple of a half wavelength will act as an impedance transformer and be unable to mirror the impedance at the other end of the cable.

 

[rabbiporkchop]

characteristic impedance remains constant through the cable but you guys are completely ignoring the complex impedance due to the current and voltage being 90 degrees out of phase
Inductive and capacitive reactances combine in a complex way with resistance in a circuit to determine the overall impedance of the circuit.

I suppose in some fantasy world Inductive and capacitive reactances don't exist, but in reality they do, so they must be taken into consideration.

Complex Impedance: You may recall that impedance (Z) is defined as the opposition to the flow of current in an AC circuit. Impedance combines the effects of simple resistance with reactance due to capacitive and inductive components in the circuit. However, the relationship among resistance, capacitive reactance, and inductive reactance is more complex than simple addition of each factor. Let's consider the interactions among resistance and reactances in more detail on the way to understanding and computing the impedance of a circuit.

First, resistance in a circuit with capacitors and/or inductors will affect the phase angle between voltage and current. The “pure” cases of only capacitance or only inductance that we considered in Part 2 are only ideal models that provide a perfect 90-degree phase angle between voltage and current sine waves. All real circuits will have some resistance due to wires and components, and often will also have component resistors, all of which shift the phase angle when combined with capacitors and/or inductors. So, the phase difference between voltage and current can be angles less than 90 degrees, and the precise phase angle depends on the relative values of resistance and reactance in the AC circuit.

Resistance affects the phase angle between voltage and current in AC circuits containing capacitive and inductive components.
Second, resistance and reactance combine as vectors and not via simple addition. We will examine “vector addition” in a moment using the graphs below.

Third, inductive reactance and capacitive reactance have opposite effects on phase angle. Remember, an inductive reactance makes the voltage lead the current, while a capacitive reactance makes the current lead the voltage. When inductive and capacitive components are combined in a series circuit these opposing reactances negate one another, in part or in whole, thereby determining the resultant reactance of the series circuit and impacting the overall impedance of the circuit.

 

[rabbiporkchop]

https://youtu.be/SCCxAKWrp9Q


I couldn't have said it better myself although he waits to the very end to spill the beans.

 

[KC9RDO]

Hello there! I'd love to send my radios to that guy! How can I get in touch with him? I visit his website, but it doesn't work or something not right out there, I guess? I clicked on Hard drive and clicked on Contact Us and nothing happened. I will send him couple of my radios!

 

[rabbiporkchop]

How to contact him..

I bumped into one of his customers yesterday after work. 45 mile cobra 29..

 

[rabbiporkchop]

Here's updated contact information.
[video]https://youtu.be/P0W_Ltzeyyc[/video]
Here's a cheap export radio he tuned as heard over the air and sounds similar to his Heil PR-781 even though it's a cheap $20.00 microphone.
[video]https://youtu.be/lOFXELRFRw0[/video]