Radio Mysteries

You were a lovely +08db signal on 80m FT8 today Tom at 1020z from Gun with no preamp in and IPO selected on my radio.

I’m finding the 2020 Chaser Challenge a bit of fun - and it pays to look out for those activators who aren’t afraid of the dark, who have been going out and activating on 160m and 80m this week! Last night for this leg tonight. Will anyone try it?

Sorry couldn’t work Jurg HB9BON/P this afternoon earlier on 80m CW. Heard briefly for a minute at most, I know he called me back, but no way of getting the report as he faded away on 3550 KHz CW.

73 Phil

I could just about hear Jurg HB9BIN when I was on Gun, but very quiet, and he clearly wasn’t hearing me. I heard a HB9 chaser working him loud and clear though.

Yes, the 1st Flavour of the Challenge has been fun. I would have liked to have got deeper into my efforts with 160m, but at least I did make some contacts, and there’s another opportunity in April. Neither the full half-wave dipole nor the end fed Inv-L + ATU were satisfactory, so I’ll maybe try a doublet + ATU next time, or even have another think about making a pair of loading coils!

Hoping to see a few new activators and chasers using Datamodes for next month’s flavour. My main focus for then will be to get PSK working properly again (ie without the RF feedback problems).

Hi Ed and all,
Whenever I’ve noticed that low output power start slowly rising as I kept transmitting with my FT-817, I was monitoring relative output power on the needle indicator of my MFJ-941B antenna tunner, while the SWR was being monitored on the FT-817 display, so this doesn’t seem to be a power indicator issue in the FT-817, but a real output power issue.
I’ll try to look at that carefully the bext time I activate and I’ll try to collect some output power vs time since TX started data.



Hi Guru,
Of course you may have a different problem to what Tom has, who could have a different problem to what someone else has, as regards rising power after 10 minutes on the FT-817. If all who have reported it here have the same problem, I would say there will be a lot of FT-817 users with the problem in the general amateur radio community and there should be something on the FT-817 forums (or even a recall by Yaesu to fix the problem) neither of these appear to be the case, so this is becoming even more of a mystery - a problem on FT817 rigs that only happens to SOTA activators ??? Very strange …

73 Ed.

What’s the difference between any odd 817 and a SOTA activator’s 817?

The cold temperature during the ascent and at the mountain top.

I’ve found this video of some FT817 fault finding - it may not be the problem we are talking about here but it’s a good instructional video on how to fault find in an FT817.

73 Ed.

Activator’s get used? :wink:

Actually, I don’t think I’ve ever checked the power output of my 817ND during an activation. I leave it set to display SWR - so it may or may not suffer from this problem. If I am in any way typical, then maybe the problem is more common than it appears to be.

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Regular vibration and impact shock from being carried up and down hills in a rucksack.

Ed is right, there don’t seem to reports of this issue on the interwebs and it it was common there would be lots of noise about it based on the sheer volume of 817s sold.

Yes, it’s definitely an “activating” phenomenon - my 817s have probably had as much if not more use in “base station” scenarios and I’ve never seen it in that situation.

FWIW, I have carried out activations between -10C and +40C and I have never seen any change in power level from switch on to when my 817 has warmed up. With resonant antennas I see full output from switch on on all bands. I always operate the rig inside my backpack and it is housed in a plastic box, so the rig is protected somewhat from the extremes of temperature.

My thought on the issue with Tom’s rig is that it is down to the circuit that reads the output power. Connecting an external power meter would show whether this is the case.

I left my rucksack with the SOTA-kit out in the balcony and went for a walk with our dog. The outside temperature now is 4° C.
The walk took us nearly an hour.
Once back at home, I went out to the balcony where I had left my rucksack with the SOTA-kit, I connected an antenna (the endfed wire antenna I have in other balcony of this appartment) to the rig, adjusted my antenna tuner for perfect SWR on 30m and started transmitting dashes:
This was the output reading in this meter. (Don’t pay attention to the values on the scales, as this is not a good calibrated power meter and it served only for relative measurements.)

After about a couple of minutes transmitting TESTING TESTING DE EA2IF QRP and so on, I noticed that the relative output had increased a bit as you can see in this picture:

To me, this is the confirmation that this FT-817 electronics temperature has an impact on its output power.
My FT-817 is always inside a wooden box, which I have inside an isothermal plastic bag, inside my rucksack and it wasn’t that protected when I first noticed this problem in the beginin of my SOTA activating years. This FT-817 directly exposed to cold temps without any external protection might show a bigger difference in output power between being cold and warm.


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In some configurations, the 817 can be set up with too much RF drive for the power level required, or not enough. As there is a different set of TX gain and Output power limit for each power level on each set of bands (low HF, high HF, 6m, 2m, 70cm) it is quite possible that the power setting Tom was using was one of the lower levels (0.5, 1. 2.5 w). In that case, drift in sensing components (probably resistors) or in stage gains of several active devices, could mean that the output power will vary.

It could be a case of increasing the tx gain, which would create a power spike at the start of every transmission, or using a different power level setting.
I would test to see whether the “power creep” effect occurs on one, two or all power levels. If it does occur on all power levels, it points to common component such as an amplifier stage or a resistor in the ALC loop being unduly sensitive to heat. That could be an IF chip or just a resistor (or a dry joint) in a gain control/bias circuit. It may well fail eventually. That would at least allow the problem to be fixed.

If the problem only occurs on the 5w default power level, it suggests tx gain could be increased to compensate. Ie. if no power creep occurs on the 2.5w power level, you know it’s not the stage gain changing, but a problem in the power sensing circuitry. One single SMD resistor might be the culprit. I think the 817 has a smart chip working out the SWR, if that goes kaput all bets are off.

Tom, if you do opt to alter any of those settings in the extended menu, make sure you have noted the current setting values for every parameter. That makes it feasible to return settings to normal, which are different for every radio due to component variability.

73 Andrew VK1DA/VK2UH

Hi all,
After yesterday test, I decided to leave the rucksack with the FT-817ND outside in the balcony all night. I left the isothermal plastic bag open and the wooden box lid removed, so the front of the rig was fully uncovered and in contact with the cold air. Temp 3 to 4ºC.
Let me show you, on 2 independent power meters, the difference between output power at the very begining and later after about 1 or 2 minutes transmitting, once the internal circuitry and electronics had warmed up a bit.
Since none of the meters were well calibrated, don’t pay attention to the values except for comparing the initial reading and the after warm-up reading. After warm-up, the output power was more than doubled, nearly tripled.

To me, there’s a clear impact of the electronics temperature on the output power, but it took it so little time to warm up and see the output power more than doubled, nearly tripled that I honestly don’t feel this is a real problem for us to be worried about.



Thanks Guru, I agree with your conclusion.

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Its physics ! Not unique to any radio what so ever !!!

Kt / q therefor the current increases through the drain / collector = more power out as things get hotter

The IF power cal is there to correct for it (sort of)

Its such a basic toy of a radio inside, there is no closed loop feedback correction for it, so you will see the effect.

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I don’t think thats quite correct.

If that was so, how would it produce 5w on a 13v supply and the same 5w on a 9.6v supply? There is a loop in the ALC circuit. Thats what the output power setting is for. The four output power settings for each band group (low hf, high hf, 6m 2m, 70 cm) are set in soft settings rather than in hardware like a single common trimpot which is what you would see in a basic toy of a radio.

There are things I dislike about these radios but generally they were very cleverly designed more than 20 years ago.

In this case it certainly is physics in action. But in which component or solder joint, in which part of the circuit? Hence my suggestion of assessing whether the power setting affects the behaviour. Neither of my 817s does this.

73 Andrew VK1DA/VK2UH

The silicon thingies

Boltzmann’s constant doesn’t apply here

Linear extrapolation compensation, doesn’t need CL. ALC is a Limiting Control (peak) NOT slope compensation

Hmm… It’s very basic the FT817. Dual gate FETs :roll_eyes: FT101 tech !

Let’s not go off on a discussion about ideal technology they might have used in 1995 when dreaming it up. There might have been a glut of dual gate mosfets In the Yaesu store and they had to use them up!

Identifying whether the power drift occurs on all power levels would assist in identifying where the fault lies. Checking whether an external power meter confirms what the internal metering says, would indicate whether it is a fault in the power metering. Increasing the tx gain so that the output power is closer to spec even when cold would ensure the output power is closer to rating, but would result in power spikes on start of tx once it has warmed up due to the slow response time of the ALC gain control loop. When used barefoot that’s not a problem but it could be a problem when driving an external amplifier or a transverter.
Andrew VK1DA/VK2UH

Do new FT818s do this? My understanding from Tom is that he has only noticed this recently (?). Maybe FT8 highlights it more than SSB or CW might.