LOL LOOK AT THE SCOPE. Especially when he says it looks good

[543_Dallas]

I dont know 'chop. I can appreciate good test equipment but your splitting unnecessary hairs. As long as the negative peaks aren't hitting the baseline let the positive peaks fall where they may...within reason. I shoot for somewhere around 125% for good punch and not too much distortion in the average operator's receiver.

If I understood the video correctly the difference between the 20 mhz setting and 100 mhz setting at 150% modulation was about 5% modulation. Thats within 3 to 4 percent. The tolerance Bird 43 is only 5% at full scale and 8% with pep kit. Accuracy diminishes as you go down the scale.

Bird is considered top of the line in the amateur radio and cb world. If you want to split hairs this fine Mark needs a better watt meter to go with his scope.

 

[loosecannon]

Did he say RG58 is limited to 30mhz? OooooKayyy! We have been using "High-Quality RG58" at much higher freq. for many years and it certainly is more than cool to use for bench equipment at low frequencies and on the bench 1 to 6-foot runs have virtually no loss that would cause issues for what he is doing LMR 195 Is usable to 1.5 ghz and beyond is there loss at those freq. you bet but even 1.5ghz at a 100ft it's only 14.5db. The real problem is always going to be the quality of the coax and there is some real junk out there that will give you issues at any frequency.

OT03,
This tech also believes that you have to use tuned coax lengths between pieces of test equipment in order to get accurate readings.
LC

 

[rabbiporkchop]

OT03,
This tech also believes that you have to use tuned coax lengths between pieces of test equipment in order to get accurate readings.
LC

And the readings can clearly be seen to be different. What's your point? Only one measurement can be correct.

 

[Handy Andy]

So I know...

Are you looking for the reactive types of measurements, or the ones into resistive loads for measurements?

One is - again, reactive, unknown, while another is resistive and known

 

[Tallman]

You can only make accurate readings into a resistive load. Reactive loads will change the phase relationship of Voltage and Current which will skew your readings.
Remember ELI the ICE man? And if you are really in to accuracy you need to calibrate your test load as well. 50 Ohms at what temperature? As the load heats up where does the resistance go from the initial reading?

 

[Handy Andy]

It's kinda' what I figured, but for the record, it would help us all if we knew which sandbox we'd be playing in...



I'm back in the bushes, readin' this mail.

:+> Andy <+:

 

[rabbiporkchop]

So I know...

Are you looking for the reactive types of measurements, or the ones into resistive loads for measurements?

One is - again, reactive, unknown, while another is resistive and known

Always reactance involved.

 

[loosecannon]

And the readings can clearly be seen to be different. What's your point? Only one measurement can be correct.

my point is that if he is that concerned about the accuracy of his readings at 27mhz then he would be using a network analyzer and wouldn't have to worry about feedline lengths.
LC

 

[rabbiporkchop]

my point is that if he is that concerned about the accuracy of his readings at 27mhz then he would be using a network analyzer and wouldn't have to worry about feedline lengths.
LC

How can a network analyzer help troubleshoot a radio?

 

[Tallman]

To be completely honest Oscilloscopes are not used in taking life or death readings as there are too many little switches that can be flipped and affect your readings.
I ran the Test and Quality Control area for a company that was under two watch dog agencies. FAA and the FCC were always so far up the company's A$$ about one thing or another until I came on board. Since I understood both sides of the situation It was a lot easier for the Watch Dogs to deal with me instead of "The Old Timers" in charge.
The Old Timers did not understand the intricacies of electronics and the reach the law had on the continued operation of the company.
My first day on the job I had to meet with the FAA inspector and his superior from the Dallas/Fort Worth office and they had chains and padlocks ready to go on the doors. They were going to lock the doors and put a bunch of people out of work until certain conditions were met. I was fortunate in that they were willing to talk to the new guy.
One of the big issues was calibration of test equipment. The usual O'scopes, volt meters, freq. counters, resistive load banks, and distortion analyzers. Calibration stickers expired on almost every piece of test gear.
I managed to to keep the doors open and provided the FAA a plan to correct all of the deficiencies and personally would take charge. The FCC was consulted with this plan and they agreed.
Oscilloscopes were removed from the calibration schedule all together with the proviso that the scopes were to be labeled "For Observation Only, Calibration Not Required."
This was possible since we explained that Spectrum analyzers, Frequency Counters, Volt meters, and Distortion Analyzers verified all of the critical operational points of function.
One of my technicians told me there was no way the FCC would sign off on this.
He was wrong and I made him our local calibration technician. He hated his promotion.
The point being in this situation scopes were not that important. Too many variables affected accuracy.

 

[Handy Andy]

Always reactance involved.

Not to be rude, but can I get a little clarity on what you are looking for - in measurement?

I guess an example would help.

:+> Andy <+:

 

[rabbiporkchop]

Not to be rude, but can I get a little clarity on what you are looking for - in measurement?

I guess an example would help.

:+> Andy <+:

How about stability of an amplifier across a wide impedance range without going into self oscillation. It would be difficult to do that sort of testing with a 50 ohm dummy load. It wouldn't be too intelligent to ship off multiple stages of amplification to a customer without doing that sort of testing first. Shipping back and forth gets kind of expensive.

 

[Handy Andy]

Oh, then this isn't really about asymmetry, but more like an assembly and design issue?

 

[rabbiporkchop]

Oh, then this isn't really about asymmetry, but more like an assembly and design issue?

It's about having a test bench capable of replicating real world conditions at the flip of a switch while maintaining some form of accuracy..
It's all explained quite thoroughly in the bird 43 manual in case you haven't read it.


It's a pretty good starting point for setting up a test bench.

 

[Handy Andy]

I didn't know if you caught this reference....



Because you said ...

Always reactance involved.

In the graphic above, the "Reactive" has been converted to Resistive.

It is what I was asking ...

Because if admittance isn't correct, there's the asymmetry problem - but is it a problem or a symptom?

Is it a...

Symptom of a much bigger problem - which can be interpreted as a bad design or poorly assembled work

OR

Our effort to make RESONANCE versus IMPEDANCE - solving for one typical issue develops another as a symptom - Again; Bad design or poorly assembled work...

- either way, you still have a problem.

Assist me in understanding or I'll leave this thread in haste...

It's about having a test bench capable of replicating real world conditions at the flip of a switch while maintaining some form of accuracy..
It's all explained quite thoroughly in the bird 43 manual in case you haven't read it.

That's fine, no need to get testy, I'm on your side...

:+> Andy <+: