is this CB worth fixing? Cobra classic

Yeah Leon, I've told these guys before that some of what they are told to believe is only an issue at VHF/UHF/Microwave frequencies, not at the hf band but they would rather beleive a hack tech with his videos.

 

The laws of physics begin at zero megahertz. We can't selectively choose when to apply those laws.

 

isn't that better than believing a hack technician who hides behind a screen name in a truckers forum who drives a truck for a living and refuses to make any videos or provide services to the public lest his skills might be compared to someone with a more precise test bench?
The proof is in the performance. I don't need to watch videos to know how well my system performs and by your own admission you have never had a mobile to mobile contact at 45 miles in northeast Pennsylvania on the 11 meter band.
(Let alone a 70 mile contact)

 

Are you implying something there rabbi?

You do know I an a fleet owner and retired from driving thanks to my injuries?

What do I have to prove?

I do this as a hobby, I don't sell anything to anyone so I can be critical on the BS I've heard for the last 35 or 40 years.

 

Point duly noted. If you ever feel like putting your skills to the test as an RF engineer you have a radio in your possession identical to one that I have and if you ever feel like working your magic on it I'll be more than happy to compare its performance to the one that I have in my possession.

 

OK, but it doesn't remove the issue of precision on the bench for 27mhz devices.

I question a lot of this super tech stuff, I am not saying this without knowledge of the players as you may think but rather looking at the past and what you are claiming, and think that there isn't just one person on earth that can do what he does to a cb.

The same goes for this idea of a precision bench, I've got the equipment here and if you compare it to super tech, I may out preform his a bit. I posted some of it in the past, but that's meaningless. However when I walk into a tech's shop (and I have just recently), I don't just look for the scope and the SA but look for the calibration sticker on it to see when it was last calibrated by an accredited company, chances are one or two techs have bought stuff that was but they won't go to the trouble of actually sending it off and having it done right which isn't cheap.

IN all honesty, I don't think many know how to properly use a scope, many of them will put a waveform up on it but big deal. I would post a story about one tech who rigged it up to have the same waveform appear on the scope every time he key'd a radio up, but that's not providing anything to anyone other than trashing a shop which I don't comment on.

The same goes for your comment about harmonics, I don't use a scope to see harmonics, that's reserved for an SA.

My 1963 RM565 textronix works well enough to do CB work, I don't need a 400mhz scope for that work - I made a mistake, the plugin has a bandwidth of 50mhz, not 40. If I needed something to do some precise work, I use the MO3000 for that work.

 

You seem to think the author of Bird 43 manual doesn't understand frequency effects on waveforms. If you want a more precise measurement you wouldn't use a Bird. The same goes for the present discussion. BTW how is your cables suspended?

I agree about applying the laws.

leon
kc0iv

 

Precise measurements can only occur at 50 ohms. The point of showing that page in the owner's manual is that impedance only repeats itself every hundred and eighty degrees and unless the measurement is taken at that point the waveform on the oscilloscope will be different.
Reactance varies with frequency Due to capacitance and inductance.
Capacitance and inductance cause a phase shift which slightly alters what you see on an oscilloscope.
If we understand that then it makes perfect sense that any adjustment made based upon false information displayed on the oscilloscope will be an incorrect adjustment. When David Bupp looks at one of Mark's radios he simply Sees a waveform that closely resembles something that he would have done. But when Mark looks at one of David Bupp's radios this is what happens.


This partially explains why David bupps radios have a difficult time reaching my receiver from 8 Miles Away although they do sound clear and Mark's radios have an easy time reaching my receiver from distances greater than 30 miles mobile-to-mobile consistently as demonstrated here. If you listen carefully you can hear one of David Bupp's radios struggling to make the trip to my receiver from 8 Miles Away with a clear line of sight.

 

Is that 8920 calibrated?

 

Yes It is and it cost an extra $1,500 for that certificate.
they don't normally come calibrated below 30 Megahertz