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Old uniden Grant PC-196aa board
- Thread starter Robalo
- Start date
You raise a good point...
Once you have all your ducks in a row, no matter how equal you try to make them be, one will always be too slow, and one will always go too fast.
You question refers to what 399 and many others touched on that makes following the "Curve" such a dangerous road to be on.
The schematic above is only representative, but it deals with what makers did back then to handle power curves - and make the next stage operate in a "Window" that optimized the previous stages Lowest-IMD products - it's a factor in any amplifier stage - the purity of output of one stage into the other - to idealize it, you have make sure both the output of the stage BEFORE that Stage, and the Stages' own OUTPUT to the next one - are making power, not adding distortion factors like IMD (Inter-Modulation Distortion) AND are in a range acceptable to the next stages INPUT window to match that which came before it.
Many call this Admittance, but to understand that, you have to understand the ability or how a Transistor accepts power and develops it into an amplified signal.
It's not as easy as it looks, as you are finding out.
You can also experience this effect you're talking about - when you TUNE for CARRIER versus Tune for SSB Linearity (PEP) one is "steady state" while another is Asymmetrical Linearity. It's why you LOSE power for PEP but obtain Carrier power.
Have you also noticed that the AM Only radios like the Cobra 29 or PC-66 only develop PEP power at one point of the tuning tanks' slug position, but they produce Maximum Carrier power in another turn or so away from that Slugs PEP position? And when you modulate, you seem to swing "Backwards"?
So what do you turn - or tune - to?
That's where your IMD factor as well as Admittance - come into play - the Maker doesn't have the time or patience to fool around with radio and make it perfectly straight in performance - it has many other things to worry about - including production cost and parts values and availability of those parts. It just wants to make the Radio acceptable to the FCC and be able to sell it to maximize the profitability of these intricate detailed things...
So when you get a Brand New radio - it works one way...
But in some circles, you can buy the same model Refurbished and it works even better...
Why?
Because someone took the time to realign and re-fit parts the OEM didn't and they reap the rewards of the quality of the workmanship - the effort they put into it - to make it work right.
When you work with your TX Strip, remember that you are COMBINING two RF signals of different frequencies together - you know this - but the circuit has to be designed to amplify the PRODUCT of the two combined into the new HIGHER frequency - not one of it's counterparts.
So the issue then becomes a matter of BANDWIDTH for this new combined signal and remove the unwanted artifacts from ABOVE the frequency and BELOW the frequency and still have something left.
But remember too in Wave metrics, the two SINE waves getting combined into one does not always INTERSECT at the proper Point of PHASE (I call this Inception) where both peaks and troughs are summed properly - it's not possible in every event, so you get a resulting effect of approximation and summation of the two intersecting at a specific energy level at any given moment - if they intersect properly you GAIN energy (In Phase) - if they don't, you lose energy (Out Of Phase) - even in specific times you may only get a partial energy summation of power - it's at a lower power level but it is at the frequency we want.
You also have to add in Audio Power onto this mess.
Welcome to the Forum!
this is us wwdxforum ,
so what i choose for AM/SSB radios dk or pep, let see for DX I go for pep for AM local dk mmm, rf circuit is complicated. on this case i think i deal with 7.8 mhz signal loose some where for ssb or audio pat like some wrong capacitor value. i do not know any thing about rf electronic is just my radios my hobby and thank you, all you mates for the help on this long jorney.
. i do not know any thing about rf electronic is just my radios my hobby and thank you, all you mates for the help on this long jorney.
Keep up the good work, it's fun seeing these older chassis and radios you get - just show up in such good condition and yet I (if not WE) wonder how you ever came across them?
You are one cool dude for sharing your learning with the rest of us.
It's awesome.
Enjoy the ride!
Robalo-
I need to correct what I said earlier about the output power settings after returning the driver final circuit to original. The 2SC1307 final is rated at 25 watts max. It can do more, but then you're getting into risky territory. If you have a reliable watt meter, after doing the transmitter alignment, Adjust the SSB ALC (CT7) for a max PEP output of 23 watts. Next, check the max swing on AM. Set the AMC (VR7) to max. Modulate the rig with a 1khz tone, and adjust AM POWER (VR8) for 23 Watts out. Then readjust the AMC for just a little over 100% modulation. Check the deadkey. It should be 4 watts or so. If you need a lower deadkey but want max swing, do Modification #18 "Adjustable Deadkey with Full Audio Swing" on the 858 site. Good Luck. 73s
- 399
I need to correct what I said earlier about the output power settings after returning the driver final circuit to original. The 2SC1307 final is rated at 25 watts max. It can do more, but then you're getting into risky territory. If you have a reliable watt meter, after doing the transmitter alignment, Adjust the SSB ALC (CT7) for a max PEP output of 23 watts. Next, check the max swing on AM. Set the AMC (VR7) to max. Modulate the rig with a 1khz tone, and adjust AM POWER (VR8) for 23 Watts out. Then readjust the AMC for just a little over 100% modulation. Check the deadkey. It should be 4 watts or so. If you need a lower deadkey but want max swing, do Modification #18 "Adjustable Deadkey with Full Audio Swing" on the 858 site. Good Luck. 73s
- 399
are you mean the collector to test point ondriver C + TP 4 AND FINAL C + TP2 OK I HAVE 0.3 ohms nice now
Yes, but also to make sure you didn't have the Diode reversed in the Bias scheme - for one way, the diode conducts, and TAKES IN CURRENT - meaning it (power) from the BIAS circuit will flow thru it, so the meter will reflect that flow as a HIGHER current.
If you had reverse the diode - reversed it's polarity - it wouldn't conduct, you'd only see the OHMIC values of the resistor - being higher - as a lower mA reading and the Transistor would conduct lower or LESS current thru the Test point (barely turns on, as in; you're reading the resistor ABSORBING the power flow across it)
If you had reverse the diode - reversed it's polarity - it wouldn't conduct, you'd only see the OHMIC values of the resistor - being higher - as a lower mA reading and the Transistor would conduct lower or LESS current thru the Test point (barely turns on, as in; you're reading the resistor ABSORBING the power flow across it)