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Another QCX almost working #t1 #qcx #lpf #alignment

Richard G4TGJ
 

I've been building my 30m QCX  over the last few days. Unfortunately I put a 33k resistor in one of the 47k positions. I discovered that removing components from double sided boards is quite tricky. In removing it I destroyed it. Annoyingly I didn't have any 33k resistors in my collection but a pack arrived from RS yesterday so I was able to finish it last night.

Alignment went well up to the IQ balance stage. But the Phase Low and Phase High adjustments don't give a proper minimum - the pots just adjust right to the end of their range. But it does receive and I couldn't find the unsuppressed sideband so it is at least usable. 30m seemed surprisingly busy last night.

The output power is lower than I would expect. With 12V I am getting about 1.5W instead of the expected 3W. Transmitting at 8MHz into a dummy load gave higher output so it looks like the LPF needs tweaking. I did put it on the air and although I didn't have any QSOs my signals were picked up by a few RBN stations so it looks very promising.

I won't get chance to look at it again until the weekend and it seems I need to revisit all the coils. But at least my soldering appears to be OK and I haven't fried any components!

Mvs Sarma <mvssarma@...>
 

Richard,
 Yes , Double sided PCBs have their own Cons .
 But we should , once decided to remove a component, especially multi legged, I prefer to butcher the part  but NOT MY board. eg, resistance
 i prefer to cut body close itself and remove two independent leads , rather than resistor as a component.

After all for one or two damages we need not bother . we can always find means to salvage and use it.
all the best
regards
sarma
 vu3zmv

Regards
MVS Sarma
 

On Tue, Jul 24, 2018 at 1:15 PM, Richard G4TGJ <rpt@...> wrote:
I've been building my 30m QCX  over the last few days. Unfortunately I put a 33k resistor in one of the 47k positions. I discovered that removing components from double sided boards is quite tricky. In removing it I destroyed it. Annoyingly I didn't have any 33k resistors in my collection but a pack arrived from RS yesterday so I was able to finish it last night.

Alignment went well up to the IQ balance stage. But the Phase Low and Phase High adjustments don't give a proper minimum - the pots just adjust right to the end of their range. But it does receive and I couldn't find the unsuppressed sideband so it is at least usable. 30m seemed surprisingly busy last night.

The output power is lower than I would expect. With 12V I am getting about 1.5W instead of the expected 3W. Transmitting at 8MHz into a dummy load gave higher output so it looks like the LPF needs tweaking. I did put it on the air and although I didn't have any QSOs my signals were picked up by a few RBN stations so it looks very promising.

I won't get chance to look at it again until the weekend and it seems I need to revisit all the coils. But at least my soldering appears to be OK and I haven't fried any components!


Richard G4TGJ
 

I finally got it working and aligned. And I've just had my first QSO with it. Conditions seem to be pretty bad but I got a 599 from Belgium.

So my problems were:
1. Enamel not fully burned off on one of the connections to T1, despite holding the iron on for at least 10s.
2. Not aligning with a dummy load connected. The instructions (as far as I can see) only say not to have an antenna connected.
3. The LPF capacitors. There seems to be a common problem with C25 and C26 in the 20m and 30m kits. As I didn't have any 560pF NP0 capacitors I've actually used the more recent W3NQN design as documented in many GQRP club publications and on their website. I left C27 and C28 on the board as their 290pF is almost right (the design needs 296pF or in practice 2x150pF) but L1-L3 need slightly different turns and C25 and C26 become 470pF. There is also a 68pF cap across L2. I now get 4W with 15V, so some more tweaking may be necessary.

I set the frequency by listening to the 27MHz clock on my FT450D. I've also confirmed with the Russian time station RWM on 9996kHz.