Amateur radio needs more young folks.

[WRYZ926]

Ohms Law isn't all that difficult to learn. 

You will see two basic charts. One will have V over I and R while the other will have E over I and R

V or E = volts (Electromotive Force)

I = current = amps

R = Resistance = watts

If you know two then it is easy to figure out the third.

V (E) divided by I equals R  Example: a 120 volt appliance draws 10 amps which means the appliance uses 12 watt.

V (E) divided by R equals I Example: a 120 volt appliance uses 12 watts which means it draws 10 amps.

R multiplied by I equals V (E) Example: if you know a 12 watt appliance draws 10 amps then it runs on 120 volts.

You are allowed a blank sheet of paper to use for math during the test. Write down the Ohm's Law Chart right away so that you can refer to it during the test.

 

 

[UncleYoda]

Watts=resistance?  I learned watts is power and amps is current draw.  Resistance was Ohms in my backwoods schooling.  Seems like impedance is ohms too but then I never did get impedance to make sense.  I use amps, volts, and watts, not I & R.

[SteveShannon]

15 minutes ago, WRYZ926 said:

V or E = volts (Electromotive Force)

I = impedance = amps

R = Resistance = watts

I = current (amps)

R = resistance (ohms)

Power = volts times current (watts)

 

[LeoG]

7 minutes ago, UncleYoda said:

Watts=resistance?  I learned watts is power and amps is current draw.  Resistance was Ohms in my backwoods schooling.  Seems like impedance is ohms too but then I never did get impedance to make sense.  I use amps, volts, and watts, not I & R.

Impedance is for coils that are reactive to frequency.

[UncleYoda]

7 minutes ago, LeoG said:

Impedance is for coils that are reactive to frequency.

Isn't it also used for antenna/cable rating? (that's even more common for radio users not builders)  But I meant I can't form a good picture of what it is/does.

[SteveShannon]

7 minutes ago, UncleYoda said:

Isn't it also used for antenna/cable rating? (that's even more common for radio users not builders)  But I meant I can't form a good picture of what it is/does.

Impedance is any resistance to current flow. It can happen due to pure resistance or reactance due to capacitance or inductance. 

[hxpx]

45 minutes ago, WRYZ926 said:

Ohms Law isn't all that difficult to learn. 

I remember exactly two equations from high school physics:

V = I * R, or Voltage = Current * Resistance, and

Q = V * C, or Quality = Champagne Velvet. No idea what the actual equation is [1], but that's how my high school physics teacher taught it to us and then I lived in Terre Haute where they brewed Champagne Velvet during college (and drank a lot of it - see: physics grade) so it stuck with me.

 

[1] It's Charge = Capacitance * Voltage but I still remember it as Quality is Champagne Velvet.

[LeoG]

5 minutes ago, SteveShannon said:

Impedance is any resistance to current flow. It can happen due to pure resistance or reactance due to capacitance or inductance. 

Anything that has to deal with frequency usually.  Capacitors generally don't display impedance.  Possible parasitic impedance in the nano henry range might affect extremely high frequencies.  Coax has impedance and it's usually listed as 50 or 75 ohms but that's dependent on frequency.

[UncleYoda]

13 minutes ago, SteveShannon said:

reactance due to capacitance or inductance. 

Just more terms I don't understand, except a little about capacitors storing or building up a charge.  Reactance and inductance are two of many electronics things that should never be mentioned on a ham exam.

[UncleYoda]

10 minutes ago, LeoG said:

Coax has impedance and it's usually listed as 50 or 75 ohms but that's dependent on frequency.

Yes, but old folks remember 300 ohm TV antenna cable before coax came along, and it can be used as a radio antenna.

[WRYZ926]

47 minutes ago, SteveShannon said:

Impedance is any resistance to current flow. It can happen due to pure resistance or reactance due to capacitance or inductance. 

Fixed it. Thanks for pointing out my mistake.

[LeoG]

1 hour ago, UncleYoda said:

Yes, but old folks remember 300 ohm TV antenna cable before coax came along, and it can be used as a radio antenna.

True, flat cable.  Wired up many TV antennas with it.

[Lscott]

1 hour ago, SteveShannon said:

Impedance is any resistance to current flow. It can happen due to pure resistance or reactance due to capacitance or inductance. 

On a more technical note one must be a bit careful when using the term “resistance”. Most people assume if you have a pure,  non reactive impedance, i.e. resistance that implies a power loss, heat. No. Sometimes you might see this referred to as “non dissipative resistance”.

Perfect example is your “50 ohm resistive” coax. Obviously all the power output from your radio doesn’t turn into heat. What this really means in a general sense allows one to account for power entering the coax, but says NOTHING about where it goes.

The other one idea comes directly from Ohm’s law. Resistance is Voltage divided by Current. So you could also say that a 50 ohm coax the “ratio” between the voltage and current anywhere along the length of the coax is equal to 50. It just so happens that the ratio is also called “Ohms”. 

Some people get hung up, stuck, on the idea that just because the impedance is a pure resistance doesn’t always mean power loss as heat. 

This is going into the weeds a bit but it’s important to understand the distinction.

[Jaay]

Luckily, we've recently had some new techs, and and some techs upgrading to their General ! 

[SteveShannon]

7 minutes ago, Lscott said:

This is going into the weeds a bit but it’s important to understand the distinction.

True, but not at the Technician level. The test questions on the Technician test go no further than the very basic Ohm’s Law relationships or E, I, and R. You don’t really have to use them; just understand the relationship.

[SteveShannon]

2 hours ago, LeoG said:

Impedance is for coils that are reactive to frequency.

Or capacitors that are also reactive to frequency or resistors which are non reactive, such as a carbon rod, tungsten wire, etc.

[Lscott]

1 minute ago, SteveShannon said:

True, but not at the Technician level. The test questions on the Technician test go no further than the very basic Ohm’s Law relationships or E, I, and R. You don’t really have to use them; just understand the relationship.

Yes. That’s true. Everything else is how you interpret what is going on. As you imply, that’s for a more advanced level. 
 

I have had some buddies with a Tech license who do think about the concept and trip over the usual interpretation. I try to explain it but it does require one to take a more abstract view. When they start to grasp the idea I feel I’ve made a difference passing along some knowledge to the next generation.

[SteveShannon]

2 hours ago, UncleYoda said:

Reactance and inductance are two of many electronics things that should never be mentioned on a ham exam

Of course they should. Reactance is crucial to understanding how antennas work as well as many other electrical components. 

[Lscott]

2 hours ago, UncleYoda said:

Reactance and inductance are two of many electronics things that should never be mentioned on a ham exam.

Yes they should. The whole point of the amateur Radio Service is experimenting and the furthering of the radio art. You can’t really do that without some basic electrical/electronics knowledge.

I run across people who use the term “Appliance Operators” for some Hams. I’ll leave it to others to figure why that term might apply to a few.

[SteveShannon]

6 hours ago, LeoG said:

Anything that has to deal with frequency usually.  Capacitors generally don't display impedance.  Possible parasitic impedance in the nano henry range might affect extremely high frequencies.  Coax has impedance and it's usually listed as 50 or 75 ohms but that's dependent on frequency.

I had to reread this to understand.  You’re using the term “impedance” where you really mean “inductance” in your second and third sentence above. 
Impedance is measured in “Ohms”. Inductance is measured in “Henries”. Both capacitors and inductors exhibit impedance depending on frequency.

Capacitance is measured in Farads. A capacitor exhibits high impedance at low frequencies. As frequency approaches DC the impedance of a capacitor approaches infinity.  At steady state DC a capacitor blocks current flow, acting like an open circuit. But as frequency increases, the impedance of a capacitor becomes lower and lower, letting more current flow. A basic capacitor is simply two metal plates placed parallel to each other with a dielectric material placed between them. 

An inductor on the other hand has inductance which is measured in Henries. Inductors operate inversely to capacitors: they exhibit high impedance at high frequencies. At steady state DC they are a short circuit. As frequency approaches infinity the impedance of an inductor also approaches infinity. A basic inductor is simply a coil of wire.

And the statement that coax has impedance of 50 or 75 ohms that’s dependent on frequency implies that there’s only one frequency where the coax has that characteristic impedance. The equation used to describe characteristic impedance includes resistance, capacitance, inductance, and conductance in a way that results in a fairly constant characteristic impedance over a wide frequency range. The amount of attenuation is frequency dependent however and I suspect that is what you mean. The higher the frequency the greater the attenuation of a signal.

 

[marcspaz]

Exactly, Steve. The signal frequency does not change a cable's intrinsic impedance. It is determined by its physical dimensions (inner and outer conductor diameters) and the dielectric material's properties. However, the effective impedance does have a small frequency dependence because the dielectric constant.

 

In real-world manufacturing, materials have slight variations in their dielectric properties with frequency, known as dielectric dispersion, which can lead to small changes in impedance, especially at higher frequencies. Manufacturing variations are not the only contributing factor, either. For example, a cable laying on the ground that gets partial collapse of material due to someone stepping on it could cause massive changes. In many of our defense applications, if someone steps on a cable, it gets replaced due to possible damage/variations in performance due to impedance variations. 

[Lscott]

This thread is evolving into a basic electronics tutorial. Nothing wrong with that. The topics do need a rather verbose explanation. Perhaps beyond the space and time constraints of a series of forum posts. 

I searched through my library of electronic books to find one suitable for newbies to read. Note the book was written when most test equipment used analog meters and no surface mount devices, SMD, but the general concepts still hold.

The book might be a bit more than one would need for a Tech Class license, but if you can understand the very basic material you'll have ZERO problems with any of the technological question on the exam I would think. Has lots of pictures to illustrate the text discussion.  I think it can answer some of the more basic questions and shed some light on a few basic concepts. Just as likely to spark even more advanced questions, good, people want to learn.

 For those that are REALLY interested I have college level electrical engineering text books. The first to master is basic circuit analysis. One needs a SOLID background in algebra, some linear algebra (matrix) theory and basic calculus up through differential equations. 

I have another whole electronic library just on Mathematics.

Basic Electronics.pdf

[Lscott]

Since questions crop up about antennas, matching and the big mystery, SWR, I have other books written just for Hams, or basically anyone who wants to understand the concepts without needing a college engineering degree. Warning some high-school level math might be required.

The Beginner's Handbook of Amateur Radio.pdf Microwave RF Connectors.pdf Another Look At Reflections - Maxwell W2DU.pdf

[WRUE951]

One of my HAM buddies that follows HAM licensing very closely told me awhile back when i was studying for my Genderal that HAM Licensing is actually increasing but the number of users is decreasing.  I guess they measure this over the use of HAM registered repeaters and LF logs.. I use both WIN and PAPA here in the desert and have noticed a big drop off in their use over the last two years..  All you hear is the same dozen people whom alway's barging in on your conversions if you don't say your call sign correctly or they just want to add their 2 cents into something..  Why do HAMs insist you use phonetic alphabet when its not requried.  

[Lscott]

9 minutes ago, WRUE951 said:

Why do HAMs insist you use phonetic alphabet when its not requried.  

The old guys are likely hard of hearing and that's the only way they can copy your call sign.