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FINE TUNE CB SHOP FOR REAL?
- Thread starter Sonar
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RPC, did Mark send you those references or did you find them on your own and apply them to this discussion.
the reason i ask is that you either misunderstood them or are intentionally trying to mislead people.
first, really nice job finding just the right place to start that image of the Bird 43 manual.
for those that would like to see what it says right above where RPC chose to start, here it is:
"When a Bird 43 is used to tune a load to a transmitter and a good match is obtained, removing the unit will not change the match quality. A good 50 ohm load can terminate a 50 ohm transmission line of any length without altering conditions at the transmitter. The 43 is just an extra length of 50 ohm line in series with the measurement. When the load is not well matched (an antenna with a VSWR of 1.5 or 2.0) the line length between the load and the transmitter will transform the load impedance as seen at the transmitter."
You see folks, where RPC and possibly Mark Sherman got it wrong was in applying these rules to 50 ohm to 50 ohm connections between radios, test equipment, and dummy loads in a shop that works on CB radios which are under 30mhz.
yes, if you have a 100 ohm antenna connected to your 50 ohm radio, using odd half wavelength pieces of coax will tell you the true mismatch, where a 1/4 wavelength piece might not.
However, if you are using a 50 ohm dummy load, a 50 ohm radio, and 50 ohm test equipment, then the lengths of the coax DONT MATTER!
yes, if you get up above 200 mhz or so, where the wavelengths get small, then coax length starts to matter more with regard to lossess.
HOWEVER!
even up at 200 mhz, if all your equipment is 50 ohms, the length of the coax jumpers DOESNT MATTER!
Go ahead RPC, have your boy Mark make a youtube video where he says "pay attention!", shows a measurement, and then have him change a jumper cable to some random length and then take the measurement again.
there will not be a difference as long as everything is 50 ohms, and in a shop, everything is 50 ohms except for your 150 ohm dummy load you use to set CB SWR meters for 3:1.
once again, RPC and Mark are trying to baffle people with BS, and im sure once again, im not going to get a straight answer refuting what i posted.
yes, the laws of physics do apply to 27mhz, but you should probably leave the applications to the physicists.
LC
I am not intentionally trying to split the hair, but if you change the length of the cable and take another measurement I expect that measurement to change.
I guess yes... I am splitting the hair here.
A lot of talk in this thread is about quantifying measurements and taking precision measurements so I figured I would bring this up. It IS measurable but not with the gear most guys have in their shop.
It just depends on the length of cable added. If he went from 1 foot to 3 feet it is not perceivable. But if he went from 1 foot to 500 feet then you will very likely see it.
LC this is from bird.
5. In-Line RF Power Meter Location
The location of the directional power meter within the transmission system may have a significant effect upon the ability of the instrument to resolve antenna VSWR.
The prime consideration related to the location of the power meter is that the losses associated with the transmission line, as well as the insertion loss values of any other system components will have the effect of isolating (masking) the power meter from the measurement point.
The power meter will be further isolated if the path between the power meter and the antenna includes components such as switches, adapters, or other items because of the insertion losses of these components.
This is from Bird electronics site. The rf experts.
So coax does skew the readings ?
Anything between... like they state...
Switches, coax, etc.
All of these items have insertion losses. Some more than others.
The meter itself does as well.
Yes there is so much more to it. It depends on the situation.
Things that are unknown and we cant see.
Like CTR said on another thread its very complex and You can argue
until the cows come home. For almost a meaningless result.
The first question i would ask is, the radio itself truly 50 ohms ?
Just too many variables.
Example ; Should the swr be tuned for lowest thru the coax at the radio ?
According to bird the answer is NO it will skew the readings ?
Is it best to use matching at the antenna feedpoint ?
Or no matching is necessary ?
How about resonance is it important ?
Like Db said in another thread what difference does it make ?
Too many variables !!!
73
Things that are unknown and we cant see.
Like CTR said on another thread its very complex and You can argue
until the cows come home. For almost a meaningless result.
The first question i would ask is, the radio itself truly 50 ohms ?
Just too many variables.
Example ; Should the swr be tuned for lowest thru the coax at the radio ?
According to bird the answer is NO it will skew the readings ?
Is it best to use matching at the antenna feedpoint ?
Or no matching is necessary ?
How about resonance is it important ?
Like Db said in another thread what difference does it make ?
Too many variables !!!
73
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Hardrock, read my post again. I'm not talking about antennas or situations where the load impedance is not known.
What i am saying is that Fine Tune CB shop is trying to apply what you stated to connections between shop equipment where everything is 50 ohms and the load is a known 50 ohm resistive load.
I'm not going to type up a treatise on antenna theory just to justify my point so you'll just have to trust that i know what im talking about and would not have entered into this debate if i didn't.
Coax db losses have nothing to do with this discussion because we are talking about coax jumpers inside a shop that works on HF radios, not a 200 foot run of RG-58 to an antenna.
you and Loyal Servant seem to by trying to take me to task over the placement of a bird wattmeter connected to an antenna, while i am trying to correct RPC and Mark Sherman's misuse of antenna theory for the purposes of putting down other CB shops and gain business for FTCB.
LC
That's a negative ghost rider. Not "trying" to do anything - at least not intentionally.
I said I was splitting the hair....twice.
I actually have no intention of arguing anything about this guy Fine Tune or whoever he is. I haven't seen anything the guy has put out.
Carry on! I will refrain.
Edit: correct my nonsense !
"purposes of putting down other CB shops and gain business for FTCB.
LC"
I guess someone seems to be unaware of my purpose. My Sole Purpose has been to try to understand why the people who have the religious belief that the laws of physics do not apply at 27 megahertz are unable to duplicate the type of performance that I've gotten accustomed to. Funnier yet, when confronted with the anecdotal evidence that their two radios lost contact with each other at half the distance of the radios that were tuned with the laws of physics in mind, they still cling to the religious belief that the laws of physics do not apply at 27 megahertz. They do good work compared to butcher shops, but the performance is cut in half. Keep in mind performance is a two-way street and requires distance between two radios to be measured in the same place on the same day at the same time on the same antenna with the same microphone in order for it to be a fair comparison.
LC"
I guess someone seems to be unaware of my purpose. My Sole Purpose has been to try to understand why the people who have the religious belief that the laws of physics do not apply at 27 megahertz are unable to duplicate the type of performance that I've gotten accustomed to. Funnier yet, when confronted with the anecdotal evidence that their two radios lost contact with each other at half the distance of the radios that were tuned with the laws of physics in mind, they still cling to the religious belief that the laws of physics do not apply at 27 megahertz. They do good work compared to butcher shops, but the performance is cut in half. Keep in mind performance is a two-way street and requires distance between two radios to be measured in the same place on the same day at the same time on the same antenna with the same microphone in order for it to be a fair comparison.
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Voltage and Current are in Phase when reactance is 0.
I took what you said outa context...... sorry.
20 miles vs 40 miles with 4 identical galaxy 99's. Two done by Mark and two done by Jack Thurston. Similar results with David Bupp and Russell Clift AB7IF
( all of whom are excellent technicians by the way )
reactance can never be at zero though that's the problem.
Any wire automatically has inductance and capacitance and therefore inductive reactance and capacitive reactance and we're not even including the load in the equation.
The best we can ever hope for is for those two things to cancel each other out ( and that will only happen when that cable is resonant at a given frequency )
and even if they cancel each other out that doesn't mean they don't exist. In other words just because you don't see it with your antenna analyzer doesn't mean it's not there.
Check out this interesting article on capacitance and inductance per unit length.
http://www3.nd.edu/~wzech/CoaxialTransmissionLine.pdf
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