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Bitx40 review (video)

 

There's not much in it that most people here won't already know, but a video review I've just uploaded could still be of interest.?

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Another nice video Peter.? Thanks.?? In your comment on the pot in the RF amp stage, I think you made the same mistake that I did: assuming that that pot was for setting the IRF-510 bias (as was the case in all earlier BITX circuits).?? But take a look at the schematic:? The bias is set by a regulator chip (smart move Farhan!) and that pot just sets the RF level going to the driver (thus allowing VK3YE to go QRPpppppppppppp from the beach!). 73? Bill


On Saturday, December 17, 2016 1:59 AM, "parkerp@... [BITX20]" wrote:


?
There's not much in it that most people here won't already know, but a video review I've just uploaded could still be of interest.?

?
 

The blue RV1 is the bias set for the IRF. The drive is set by the preset R136 before the driver transistor.

At 17/12/2016, you wrote:

?

Another nice video Peter.? Thanks.?? In your comment on the pot in the RF amp stage, I think you made the same mistake that I did: assuming that that pot was for setting the IRF-510 bias (as was the case in all earlier BITX circuits).?? But take a look at the schematic:? The bias is set by a regulator chip (smart move Farhan!) and that pot just sets the RF level going to the driver (thus allowing VK3YE to go QRPpppppppppppp from the beach!). 73? Bill


On Saturday, December 17, 2016 1:59 AM, "parkerp@... [BITX20]" wrote:


?
There's not much in it that most people here won't already know, but a video review I've just uploaded could still be of interest.



 

Ah yes, I see it now.? Thanks.


On Saturday, December 17, 2016 7:33 AM, "Raj vu2zap@... [BITX20]" wrote:


?
The blue RV1 is the bias set for the IRF. The drive is set by the preset R136 before the driver transistor.

At 17/12/2016, you wrote:

?

Another nice video Peter.? Thanks.?? In your comment on the pot in the RF amp stage, I think you made the same mistake that I did: assuming that that pot was for setting the IRF-510 bias (as was the case in all earlier BITX circuits).?? But take a look at the schematic:? The bias is set by a regulator chip (smart move Farhan!) and that pot just sets the RF level going to the driver (thus allowing VK3YE to go QRPpppppppppppp from the beach!). 73? Bill


On Saturday, December 17, 2016 1:59 AM, "parkerp@... [BITX20]" wrote:


?
There's not much in it that most people here won't already know, but a video review I've just uploaded could still be of interest.





 

Peter, in the video you mention removing a cap in addition to the toroid from the VFO circuit when converting to a DDS VFO. Which cap did you decide to remove (I assume it would be C91)???
73, AL - VE3RRD
 

Yes - C91 has to go.
 

Adding a DDS isn't all plain sailing. ?

I got a horrible whine that was coupled into the BitX via the power supply rail. ?I needed to add some caps and big RF choke to provide isolation. That removed about 95% of it so it's hardly noticeable unless the antenna is removed. ?Another choke should fix it completely.?

Also I sometimes hear a lot of carriers from SW broadcast signals when tuning 7 MHz that weren't there when using the free running VFO. My theory is that it's a harmonic of the DDS VFO but I haven't tracked it down yet.?
 

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Peter,

I didn't need to remove C91 on my BitX40 board, only L4 and it works perfect with a Si5351 and a Arduino, however i too was getting harmonics from the Si5351, so I added a LPF between it and the BitX board and now it works great with a much lower noise floor.

Joel KB6QVI

On Dec 17, 2016, at 12:43 PM, parkerp@... [BITX20] <BITX20@...> wrote:

?

Adding a DDS isn't all plain sailing. ?

I got a horrible whine that was coupled into the BitX via the power supply rail. ?I needed to add some caps and big RF choke to provide isolation. That removed about 95% of it so it's hardly noticeable unless the antenna is removed. ?Another choke should fix it completely.?

Also I sometimes hear a lot of carriers from SW broadcast signals when tuning 7 MHz that weren't there when using the free running VFO. My theory is that it's a harmonic of the DDS VFO but I haven't tracked it down yet.?
 

Haven't tried this but it should be possible to use L4 (taking off a few turns?) as the inductor in the LPF, so not wasting any parts. ?It could even possibly be done on the board, with a capacitor across R93 and more capacitance across C94/C95. The DDS1 socket connection would need to be changed over to the right side of the LPF inductor.?
 

I too had to get rid of C91 when adding an external VFO.? Details here, in the last couple of paragraphs:
?




On Saturday, December 17, 2016 3:57 PM, "Joel Caulkins caulktel@... [BITX20]" wrote:


?
Peter,

I didn't need to remove C91 on my BitX40 board, only L4 and it works perfect with a Si5351 and a Arduino, however i too was getting harmonics from the Si5351, so I added a LPF between it and the BitX board and now it works great with a much lower noise floor.

Joel KB6QVI

On Dec 17, 2016, at 12:43 PM, parkerp@... [BITX20] <BITX20@...> wrote:

?
Adding a DDS isn't all plain sailing. ?

I got a horrible whine that was coupled into the BitX via the power supply rail. ?I needed to add some caps and big RF choke to provide isolation. That removed about 95% of it so it's hardly noticeable unless the antenna is removed. ?Another choke should fix it completely.?

Also I sometimes hear a lot of carriers from SW broadcast signals when tuning 7 MHz that weren't there when using the free running VFO. My theory is that it's a harmonic of the DDS VFO but I haven't tracked it down yet.?
 

Those who have used an Si5351 to supply both the VFO signal and the BFO signal; I am wondering where you would inject the DDS BFO signal into the BITX40 board. The existing BFO osc could be easily disabled by cutting the jumper at L5 on the PCB. If C104 were removed, could the DDS BFO signal be injected into the base of Q10 and use Q10/Q11 to amplify it? or is there a better way???
73, AL - VE3RRD
 

Thanks Peter for that review on Yotube. As a long time subscriber to your channel, I watch all your videos and so I watched that one too. Did not know the Bitx40 before but that cought my interest and so I ordered the kit as soon as the new one was available. Now waiting for the kit to arrive here in Austria and looking forward to build it.
 

Sorry, just discovered that my stupid nickname, that I have chosen years ago, is still showing up although I wrote my real name and callsign into my profile.
Name here is Helmut and call is OE4HDS.
Can anyone tell me, how to change that to show my name I antered in the "my membership idntity" section to be shown?

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