18-11-2012, 08:40 PM
Hi Lawrence,
It's well-down. I test using my HP8656A, and at power-up, the output level defaults to -127dBm, and the step size is 10dB. I mention that so that the following numbers don't seem totally arbitrary
Connected directly to the aerial (or the aerial socket if the set has one), a good portable will be slightly noisy at -97dBm, and perfect at -87dBm. At -107dBm, good sets will be able to pick the signal out from the noise.
With this Panasonic, you need to wind the level up to -67dB or so to get clean reception. So, it's around 30dB down compared to my expectations.
Next to IF sensitivity. The Hacker Hunter - to pick an example I'm familiar with - states that the input applied to the IF amplifier should be 200uV for 50mV measured at the volume control. That's around -61dBm. The Panasonic is actually rather more sensitive here - I didn't write the number down, but it was much less - so the IF is almost certainly fine.
I'm pretty sure the oscillator is OK. I tested it at a couple of frequencies from my generator, and they appeared at the right part of the dial.
I mentioned that I could only pick up R2 - that probably didn't mean much to anyone, but basically, a good radio fed directly from that will pick up lots and lots of stations. All the national ones, several local ones too. That this set only gets R2 tells me that it's seriously unwell...
Because of the mechanical complications, I think that all I can do with this set is to try a new transistor in the front end - it's just too labour-intensive to randomly change components. I'll check the passives as best I can, but the Japanese sets were using carbon film resistors by this stage which seem to be a lot more stable and reliable than the carbon composition jobs that UK sets used into the '70s.
Right - have been putting it off all evening - here goes
It's well-down. I test using my HP8656A, and at power-up, the output level defaults to -127dBm, and the step size is 10dB. I mention that so that the following numbers don't seem totally arbitrary
Connected directly to the aerial (or the aerial socket if the set has one), a good portable will be slightly noisy at -97dBm, and perfect at -87dBm. At -107dBm, good sets will be able to pick the signal out from the noise.
With this Panasonic, you need to wind the level up to -67dB or so to get clean reception. So, it's around 30dB down compared to my expectations.
Next to IF sensitivity. The Hacker Hunter - to pick an example I'm familiar with - states that the input applied to the IF amplifier should be 200uV for 50mV measured at the volume control. That's around -61dBm. The Panasonic is actually rather more sensitive here - I didn't write the number down, but it was much less - so the IF is almost certainly fine.
I'm pretty sure the oscillator is OK. I tested it at a couple of frequencies from my generator, and they appeared at the right part of the dial.
I mentioned that I could only pick up R2 - that probably didn't mean much to anyone, but basically, a good radio fed directly from that will pick up lots and lots of stations. All the national ones, several local ones too. That this set only gets R2 tells me that it's seriously unwell...
Because of the mechanical complications, I think that all I can do with this set is to try a new transistor in the front end - it's just too labour-intensive to randomly change components. I'll check the passives as best I can, but the Japanese sets were using carbon film resistors by this stage which seem to be a lot more stable and reliable than the carbon composition jobs that UK sets used into the '70s.
Right - have been putting it off all evening - here goes
