Temperature induced WSPR frequency drift in QRP-lab QCX

My QRP-Labs QCX works well in WSPR beacon mode with the external GPS receiver unit. However, it has consistently generated a frequency drift reported by receivers. There has been some discussion on the QRP-Labs forum about this, and the FETs do get warm when the unit is transmitting.

Today I tried a simple experiment: during one transmit window try blowing on the unit to keep it cool, during the next, try fanning it. Results are below. Time windows 06:14 and 06:26 are "normal" with no external fanning. Time window 06:38 has me blowing on it moderately strongly. Time window 06:50 has me fanning it fairly strongly with a piece of cardboard. Time window 07:02 is back to no fan.

This seems pretty clear evidence of temperature induced drift. Why the drift goes in the other direction when I strongly fan it I have no idea... The unit does seem to reset itself after each window (by re-reading the time from the GPS), so perhaps it is over-correcting for a previous reading?


2020-11-01 07:02 VK6WR 14.097091 -16 -4 OF77wx 5 VK4NE QG62nj 3609 92 2
2020-11-01 07:02 VK6WR 14.097119 -4 -4 OF77wx 5 VK3LRE QF12vk 2612 111 2
2020-11-01 07:02 VK6WR 14.097106 -9 -4 OF77wx 5 VK5MR PF94gw 2123 105 2
2020-11-01 07:02 VK6WR 14.097077 -29 -4 OF77wx 5 VK6BMT OF78ve 24 341 2
2020-11-01 07:02 VK6WR 14.097097 -15 -4 OF77wx 5 VK6HIL OF78ve 24 341 2
2020-11-01 07:02 VK6WR 14.097102 -28 -4 OF77wx 5 VK3TPM QF22mf 2724 112 2
2020-11-01 07:02 VK6WR 14.097064 +2 -4 OF77wx 5 VK5EI PF95gd 2122 105 2
2020-11-01 07:02 VK6WR 14.097056 -24 -4 OF77wx 5 VK2WQ QF56rn 3316 102 2
2020-11-01 07:02 VK6WR 14.097100 -10 -3 OF77wx 5 ZL2BCI RE79nd 5289 118 2
2020-11-01 07:02 VK6WR 14.097097 -15 -4 OF77wx 5 VK3ANP QF33di 2828 109 2
2020-11-01 07:02 VK6WR 14.097094 -10 -3 OF77wx 5 VK3ATQ QF21qx 2755 112 2
2020-11-01 07:02 VK6WR 14.097100 -24 -4 OF77wx 5 VK4TDI QG62lm 3598 92 2
2020-11-01 07:02 VK6WR 14.097096 -18 -4 OF77wx 5 VK3KEZ QF31gq 2860 113 2
2020-11-01 07:02 VK6WR 14.097093 -15 -4 OF77wx 5 OE9GHV JN47wk 13707 309 2
2020-11-01 06:50 VK6WR 14.097114 -8 3 OF77wx 5 VK3ANP QF33di 2828 109 2
2020-11-01 06:50 VK6WR 14.097119 -20 4 OF77wx 5 VK3TPM QF22mf 2724 112 2
2020-11-01 06:50 VK6WR 14.097074 -20 4 OF77wx 5 VK2WQ QF56rn 3316 102 2
2020-11-01 06:50 VK6WR 14.097118 -23 4 OF77wx 5 VK4TDI QG62lm 3598 92 2
2020-11-01 06:50 VK6WR 14.097124 -10 4 OF77wx 5 VK5MR PF94gw 2123 105 2
2020-11-01 06:50 VK6WR 14.097111 -26 4 OF77wx 5 ZL2005SWL RE68mx 5113 118 2
2020-11-01 06:50 VK6WR 14.097123 -19 4 OF77wx 5 ZL4KYH RE78js 5255 119 2
2020-11-01 06:50 VK6WR 14.097081 0 3 OF77wx 5 VK5EI PF95gd 2122 105 2
2020-11-01 06:50 VK6WR 14.097111 -9 4 OF77wx 5 ZL1ROT RF81cx 5439 115 2
2020-11-01 06:38 VK6WR 14.097115 -17 -1 OF77wx 5 VK3TPM QF22mf 2724 112 2
2020-11-01 06:38 VK6WR 14.097096 -24 0 OF77wx 5 IW2NKE JN63np 13353 305 2
2020-11-01 06:38 VK6WR 14.097107 -15 1 OF77wx 5 VK3KHZ QF22pe 2746 112 2
2020-11-01 06:38 VK6WR 14.097107 -24 -1 OF77wx 5 ZL2005SWL RE68mx 5113 118 2
2020-11-01 06:38 VK6WR 14.097104 -18 -3 OF77wx 5 VK4NE QG62nj 3609 92 2
2020-11-01 06:38 VK6WR 14.097113 -12 -1 OF77wx 5 ZL2BCI RE79nd 5289 118 2
2020-11-01 06:38 VK6WR 14.097077 0 -1 OF77wx 5 VK5EI PF95gd 2122 105 2
2020-11-01 06:38 VK6WR 14.097110 +2 -1 OF77wx 5 VK3ANP QF33di 2828 109 2
2020-11-01 06:38 VK6WR 14.097130 -15 -3 OF77wx 5 VK3LRE QF12vk 2612 111 2
2020-11-01 06:38 VK6WR 14.097069 -16 2 OF77wx 5 VK2WQ QF56rn 3316 102 2
2020-11-01 06:38 VK6WR 14.097107 -7 -1 OF77wx 5 VK3ATQ QF21qx 2755 112 2
2020-11-01 06:38 VK6WR 14.097110 -14 -1 OF77wx 5 VK6HIL OF78ve 24 341 2
2020-11-01 06:38 VK6WR 14.097114 -23 -1 OF77wx 5 VK4TDI QG62lm 3598 92 2
2020-11-01 06:38 VK6WR 14.097109 -18 -3 OF77wx 5 VK3KEZ QF31gq 2860 113 2
2020-11-01 06:26 VK6WR 14.097106 -13 -4 OF77wx 5 VK3KEZ QF31gq 2860 113 2
2020-11-01 06:26 VK6WR 14.097111 -25 -4 OF77wx 5 VK3TPM QF22mf 2724 112 2
2020-11-01 06:26 VK6WR 14.097073 +7 -4 OF77wx 5 VK5EI PF95gd 2122 105 2
2020-11-01 06:26 VK6WR 14.097106 -22 -4 OF77wx 5 VK6HIL OF78ve 24 341 2
2020-11-01 06:26 VK6WR 14.097066 -23 -4 OF77wx 5 VK2WQ QF56rn 3316 102 2
2020-11-01 06:26 VK6WR 14.097107 +7 -4 OF77wx 5 VK3ANP QF33di 2828 109 2
2020-11-01 06:26 VK6WR 14.097103 -3 -4 OF77wx 5 VK3ATQ QF21qx 2755 112 2
2020-11-01 06:26 VK6WR 14.097104 -14 -4 OF77wx 5 ZL1ROT RF81cx 5439 115 2
2020-11-01 06:14 VK6WR 14.097101 -7 -4 OF77wx 5 VK3KEZ QF31gq 2860 113 2
2020-11-01 06:14 VK6WR 14.097100 -6 -4 OF77wx 5 VK3KHZ QF22pe 2746 112 2
2020-11-01 06:14 VK6WR 14.097099 -10 -4 OF77wx 5 ZL1ROT RF81cx 5439 115 2
2020-11-01 06:14 VK6WR 14.097122 -13 -4 OF77wx 5 VK3LRE QF12vk 2612 111 2
2020-11-01 06:14 VK6WR 14.097097 -21 -4 OF77wx 5 VK4NE QG62nj 3609 92 2