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bitx20 problems

dries breughe
 

I have been a radio amateur since 2007.
over the years I have made many contacts worldwide  using comercile radios like ts-450 and ic-703.
because that is the easy way.
nevertheless, I always thought that was a bit of cheating, a shared honor with icom and kenwood.
there is a lot to be found on the internet concerning homemade transceivers.
on some websites you see diagrams, explanations, photos.
sometimes it all looks so simple.
like you just build the simple circuit and you're done.
But that is not my experience. sometimes I think it's a bad design or I'm just a stupid builder
in 2012 i started building the bitx20. clean with a printed circuit board that I had made.
it was many years and failed project, But now I  want to make an attempt to finish it
the receiver works, but not completely clean. I hear many mixing frequency products.
the recipient was deaf. in ssb they were only very strong stations. who came through it.
the transmitter: almost no carrier suppression
the pre hf amplifier (q14) functions as an attenuator.
i am not sure regarding the rf transformers. TV balun core is a vague description. Can it also function well with a ft37-43?
i also built the hf amplifier with  6   2n2018 transistors.
i used an hf oscilator (ne602 with a bit of external gain) to test the hf amplifier.
there was power gain, I had 250mW not the expected 5W
it is not specified which diode it must be.
I managed to get a 1N4001 in it
I hope you can give some advice in the hope of resolving technical issues.

Dexter N Muir
 

Ham since '07, building a Bitx20 in '12? OK, have you built simpler in between? That should have taught you the basics of troubleshooting and given you some basic test-gear.
A Bitx2o from scratch is NOT a beginner's project!
I'd recommend a careful perusal of SolderSmoke blog: Bill N2CQR in particular is a consummate builder, returning to the simple and re-starting just for the joy of it - and Pete N2CQW doing real advanced stuff, again for the joy of it. IIRC Bill built bitxes before Farhan's kits - merely as proof-of-concept.

73
Dex ZL2DEX

Curt
 

OM

hard to quickly resolve how many issues remain with your build.  on receive - I wonder if BFO is properly adjusted.  note this oscillator must be appropriately adjusted to mix the RF into the crystal filter to provide the correct audio. 

most everyone here is okay with buying a bitx or ubitx board from India, and wiring it up.  there are still modifications to consider.  if you must build a rig - I suggest visiting QRP-LABS.com. 

my ubitx is receiving as I type - and I confess to having a Yaesu but it has been off several days.

73 Curt

Jerry Gaffke
 

Dries,

Here's what I hope is a helpful answer to your questions about the Bitx20

Yes, you could use FT-37-43 cores on the transformers.
Just duplicate the transformers used on the Bitx40, 10 turns trifilar:
    http://www.hfsignals.com/index.php/2017/11/23/bitx40-circuit-description/

Carrier suppression on transmit mostly depends on T3 and the two nearby diodes
being wired correctly, also the nearby 100 ohm pot must be adjusted for best suppression.
The crystal filter will then improve on this somewhat, assuming the BFO is adjusted correctly.

Curt's suggestion to check the BFO placement is a good one.
Have you tried adjusting the 22pF trimmer in parallel with L3?
There's a whole paragraph about tuning in the BFO on   
    http://www.phonestack.com/farhan/bitx.html
starting with the words "On amateur bands above ..."

Here's a technique for debugging a receiver that might prove useful:
  http://bitxhacks.blogspot.com/2016/12/troubleshooting-bitx40.html
Farhan uses a short piece of wire as an antenna, perhaps 1 meter long.
It picks up houshold QRM, and he injects that into various parts of the radio,
listening to the result out of the speaker.  Perhaps this will help.

Once the receiver mostly works, you might verify the crystal filter shape.
To do this, measure the audio coming out to the speaker using a scope
while tuning through a strong carrier in one of the bands.  
Ideally, you would start hearing it around 300 hz on one side of the carrier, 
it shouldould quickly rise up to full volume and stay there till around 2500 hz,
at which point the volume should rapidly fall into oblivion again.

I am not quite sure what to say about all of the "mixing frequency products"
that you hear in the receiver.  I don't know how clean this radio was,
but they should not get in the way of casually tuning in stations across the band.
It could be just a matter of a wiring error or bad part.
Or it could depend on how the parts were placed on the board.

When building the crystal filter, it is best to choose a set of 
four 10mhz crystals that match in frequency within perhaps 100hz
when plugged into an oscillator, using a frequency counter.   
It may be necessary to do this if the above test of the filter shape looks wrong.

We can worry about Q14 and the 2n2218 JBOT power amp
after you get the receiver working properly.
 
If you get stuck, you can certainly ask questions here.
But best would be to find a local club of radio amateurs who know
about working on radios and have appropriate test equipment.
Perhaps someone there would like to help.

Best Regards,
Jerry Gaffke, KE7ER


On Sun, Aug 18, 2019 at 05:29 PM, Curt wrote:
hard to quickly resolve how many issues remain with your build.  on receive - I wonder if BFO is properly adjusted.  note this oscillator must be appropriately adjusted to mix the RF into the crystal filter to provide the correct audio. 

most everyone here is okay with buying a bitx or ubitx board from India, and wiring it up.  there are still modifications to consider.  if you must build a rig - I suggest visiting QRP-LABS.com.