Your Opion - Please Read

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digitalanalog

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If i take the center conductor of a coax hooked to any antenna <mobile/base>(any coax).
and connect it to a 200ohm resistor input.( i know resistors do not have input output sides to them)
Then add a 100 turn pot wiper to the same input of the resistor.

Then take the output side of that resistor and the pot low side of a pot
back to the scanner.

And using the pot for a antenna trimmer what do i or should i get?

The coax can be anything and any ohm and the 100 turn pot can
be any ohm as well.

The question is.................. what is the resulting factor of using a resistor inline
with a pot to make adjustments to a antenna.

The variation in the ohm rating of the pot and the resistor will of course
have an affect on the adjust.

Your input is welcome.

I have already tried this, and i am looking forward to your comments BEFORE posting the outcome of what i have tried.

and maybe i need to change some things for better adjustments and better results.
 

mancow

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Uh... :confused:


I actually tried to draw it out. From the description I came up with a 200 ohm resistor in parallel with a variable resistor all in series with the hot conductor of an antenna circuit.

Are you trying to make a variable attenuator?

Also, what is a 100 turn pot? Do you mean a precision potentiometer? You don't specify a value.

I can't see any advantage to any of this.
 

zz0468

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You won't be adjusting the antenna. What you will have is essentially an attenuator with varying degrees of loss - and not a good flat (impedance wise) attenuator at that. If the purpose is to reduce the signal levels going into your receiver, it'll certainly do that. What is it you hope to accomplish?
 

SAR923

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Yeah, I'm a little confused on this whole concept too. First, if you're trying to use this to match the antenna impedence to the scanner's rated antenna impedence, it's kind of a waste of time, since scanners really don't care (within limits) what the impedence of the antenna is. As several guys have said, it sounds like you're really making a variable attenuator. What possible use could this have, unless you need to adjust the attenuator higher or lower than the normal -20 db or so on most scanners?
 

kb2vxa

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Your description makes no sense; all I got out of that is a variable resistor in parallel with a 200 ohm fixed resistor, how they are connected to the antenna is unknown. Now are they in series with the coax, that is between it and the antenna or in parallel, that is from hot to ground? If in series you have what amounts to an RF choke and if parallel you have a variable short; either way you do not have an attenuator nor a tuner. Whatever it is you have lots of stray capacitance and inductance upsetting the apple cart and exposed wiring leaking signal all over the place. If it's a variable attenuator you want you'll have to learn electrical circuit design and construction especially if you want something that works properly at radio frequencies.
 

KC0QNB

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I read it twice the first question that come to mind is Why?, all you are doing is varying the resistance and making essentially a attenuator, as was stated. Lesson #1 when the term ohms are used there are two versions, straight resistance and impedance they are not the same. If you want to tune antenna you need capacitors, and inductors (coils). Typically antenna tuners aren't much use above 30 mHz, are they available? yes, are they needed?, for monitoring VHF and higher, not really. Draw a schematic and find a way to post it.
 

Don_Burke

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digitalanalog said:
Tisk, Tisk people, read the description again.
I read it four times and all I get is a non-linear attenuator.


It would appear you are going to have to spell it out for me.
digitalanalog said:
If i take the center conductor of a coax hooked to any antenna <mobile/base>(any coax). and connect it to a 200ohm resistor input.( i know resistors do not have input output sides to them)
Then add a 100 turn pot wiper to the same input of the resistor.
I get one end of a 200 ohm resistor connected to the center conductor of a coaxial cable coming from an antenna with the wiper of a potentiometer also connected to the center conductor of the coaxial cable.
digitalanalog said:
Then take the output side of that resistor and the pot low side of a pot back to the scanner.
Now it is getting fuzzy. Do both of these points get connected to the center conductor of the connection on the scanner or does one go to the shield?
digitalanalog said:
And using the pot for a antenna trimmer what do i or should i get?
That will not trim the antenna no matter how it is hooked up.
digitalanalog said:
The coax can be anything and any ohm and the 100 turn pot can be any ohm as well.
Now it is getting fuzzier.
digitalanalog said:
The question is.................. what is the resulting factor of using a resistor inline with a pot to make adjustments to a antenna.
There is one component in the circuit for each component in the description, so the factor would be one.
digitalanalog said:
The variation in the ohm rating of the pot and the resistor will of course have an affect on the adjust.
You just told us the rating on the pot did not matter.
digitalanalog said:
Your input is welcome.
see above
digitalanalog said:
I have already tried this, and i am looking forward to your comments BEFORE posting the outcome of what i have tried.
My comment is that I hope your abilty to connect things is better than your ability to describe them.
digitalanalog said:
and maybe i need to change some things for better adjustments and better results.
Now we just went to super fuzz.
 

jon_k

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First of all, people should stop being so rough on OP. OP obviously did some experimenting and we should be supportive of this even if he shows to be a poor EE. For people to start breaking his post down and being so condescending is something I expect on no other than QRZ forums. Experimentation of any caliber should be encouraged for the sake of learning for the experimenter.

You won't be adjusting the antenna. What you will have is essentially an attenuator with varying degrees of loss - and not a good flat (impedance wise) attenuator at that. If the purpose is to reduce the signal levels going into your receiver, it'll certainly do that. What is it you hope to accomplish?
I am in agreement with this post.

Foxhunters add resisters inline to get attenuation for signals as they get stronger to the source. They create lossy signal which means only stronger signals come through as well. Resisters resist passage of electrons, which result in the less strong signals from going to the receiver. In your case unless you want attenuated signals specifically, your current effort is misplaced.

If the OP was thinking to change antenna tuning, this will not work. Antenna tuning happens from changing electrical length of the antenna, which resisters don't do. You'll need to figure something else out for a variable tuning antenna. They do make variable tuning antennas that essentially just shorts the feed line to a different part of the antenna whip. It would probably be easier/cheaper to purchase one of these types of antennas pre-made then bother making your own.

Also to ask us to re-read your description is poor. Just tell us what you seek.
Do you want variable tuning antenna?
Do you want a 11,000% increase on ERP for your amateur gear?
Do you want attenuation?
What are you trying to do?
 
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Don_Burke

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First of all, people should stop being so rough on OP. OP obviously did some experimenting and we should be supportive of this even if he shows to be a poor EE. For people to start breaking his post down and being so condescending is something I expect on no other than QRZ forums. Experimentation of any caliber should be encouraged for the sake of learning for the experimenter.
I was doing okay until he sent this:
digitalanalog said:
Tisk, Tisk people, read the description again.
What is _your_ definition of "condescending?"
 

prcguy

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It appears the OP is confusing impedance with simple DC resistance. Impedance is AC resistance with all the wonderful contributions from inductance, capacitance and DC resistance which is way beyond explanation in a paragraph on this forum. An antenna tuner can consist of a simple variable inductor or capacitor or a combination arranged in an L, T or Pi configuration to transform impedance or make an antenna appear to resonate at a different frequency depending on where the tuner is placed. I have never seen a variable resistor as part of an antenna tuners matching components.
prcguy
 

digitalanalog

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jon_k i appreciate your comments on experimenting.

To all others slamming my testing i say to you
Thanks for your input but your slamming is not really needed.

If my description was poor i am sorry, i tested this and it did exactly what i thought it would do and Yes it worked (for what i was testing).

Due to the poor explanation and yet the even more slamming, i will not
discuse or mention what i was testing.

I will keep my thought to myself from now on unless i am able to explain
in GREAT detail for all you professional folks.

And by the way, i am an electrical engineer, specialized in DC control components
next time you go to disney world or disney land, think of me.


I will have no more comments on this thread,
 
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SAR923

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And by the way, i am an electrical engineer, specialized in DC control components next time you go to disney world or disney land, think of me.
Sweet Mother of Jesus! An EE that can't explain in simple terms what he's doing, why he's doing it, cant spell, can't use proper punctuation, and has never heard of capital letters. On top of that, he works on DC control components at DisneyWorld AND DisneyLand? How many things in either of those two parks run on DC? I sure hope he's lying because I'd hate to think of someone like him actually designing anything my safety depended on. :roll:
 

zz0468

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An EE? I never would have guessed. I've seen some pretty stupid posts here on RR, but I think this one takes the prize.

There's some pretty sharp people on this board, including several who posted in this very thread. Your "test" makes sense to no one. I'm inclined to think this was nothing more than a trolling expedition. Did you catch what you were looking for?
 

SAR923

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Don't you worry about a thing.
Thank you. I feel much better now. Maybe he played Goofy one summer while attending the Close Cover Before Striking University of Engineering. :)

Edit: His profile states he's a "DC Electrical Engineer". Maybe he missed the classes that explained the rest of the electrical spectrum.
 
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