Recently, I dusted off the rig that I normally keep in the backpack for portable activities in a “ready to operate” state (and I emphasize that it is ready, not that it is used), to test a new 30 Ah LiFePo4 battery (that’s another story).
After turning it on, I connected the trusty Bird wattmeter, its dummy load and tested the various output powers across all the bands.
The power levels were all within specifications, but I noticed that on the HF frequencies from 14MHz and above, the bars only showed a couple of notches even though the radio was actually set to 100W.
The radio was actually emitting 100W, so let’s say the problem was only “cosmetic”.
So, I started investigating to understand what the heck was happening…
I entered the service menu (A+B+C + PWR ON) and went through all the options researching for any settings related to the power meter bars. There was nothing about that.
The only setting related to the bar indicator for the display is related to the S-Meter, but it is not related to what I’m looking for…
So, I started analyzing the circuit diagram to understand how the RF signal sampling circuitry was designed: essentially, there are 2 lines, one for the “FWD” the other for the “REFL” that originate from the antenna connector and, through diodes, resistors, voltage amplifiers, lead to the processor in the form of DC voltage (mV).
Using a multimeter, I measured the DC millivolt values at various points of the sampling circuit with the radio set to 14MHz and 5W. Obviously, they were consistently the same for all the HF frequencies, from 1.8MHz up to 50MHz… so at this point, I was inclined to rule out an hardware issue (I have to admit, I even disassembled the mainboard and tested various resistors along the path… all fine; well, I took the opportunity to apply some “fresh” thermal paste).
I slept on it.
In the following days, without a specific plan, I tried reviewing all the settings in the service menu and also found a small software that can backup/restore them, exporting to a specific file for safety. So, I saved the “original” values of the radio.
At this point, two possibilities were left: either something got messed up in the firmware and I’m out of luck (I’ll keep it that way) or there’s some setting in the service menu that influences (obviously not documented) how the CPU displays the PWR OUT bars on the screen.
Naturally, I pursue the second path (also because the first one would have arleady been a dead end).
By the way, did I mention that I got the radio “used” ? 🙂
Without much hope, I re-aligned the output power on the different bands (service manual handy, RF generator, wattmeter, and lots of patience…).
I glance at the display (I was at 21MHz at this point) and I realize that the bars are “magically” fixed! (???).
At first, I couldn’t explain that, mainly because the actual output powers were already fine (the wattmeter always showed them within specifications).
However, I noticed that, on a couple of bands, the menu values were very high even though the power was indeed 100W.
Let me try to explain with an example: the adjustable values in the menu for each item range from 0 to 255. For the powers, 0 represents 0 watts, and as the value increases, the power emitted by the radio also increases.
However, there is a limit on some bands where, beyond a certain point, increasing the menu value does not influence the output power: on 50MHz, the value of 160 is the one that brings the radio to 100W, but I found it set at 240 (hence unnecessarily high). Something similar happened on 28MHz.
So, probably these numerically high values compared to the full power value cause the processor’s scaling calculations “going bananas”, resulting in only 2 bars indicating the actual full power.
I would say that someone had tampered with the values in the past without really knowing what they were doing… 🙂 but fortunately, it wasn’t one of those guys who “boosted” the watts…
P.S. Is it now clear why I used quotation marks in the phrase “…original values of the radio” a few paragraphs above? 🙂
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