- Bitx20 Version 3 Manual Download
- Bitx20 Version 3 Manual
- Bitx20 Version 3 Manual Pdf
- Bitx20 Version 3 Manual Free
- Bitx20 Version 3 Manual Online
Bitx20 Version 3
Bitx20 and other Qrp projects. Cqbitx was started in 31st July 2000. That is 10 years now. We have contributed to the cause of Bitx and have never mentioned that Bitx has to do anything with our contribution towards the design. We have helped more then 300 members with Bitx 3 Kit as by Ashhar Farhan and Mods by VU3WJM.
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You can find Sunil's blog page with ordering links at Sunil's blog page
Bitx20 Version 3 Manual Download
Important!
There are new assembly manuals available. These are step-by-step instructions. You can obtain them from:
FullResolution Picture of completed exciter board
This is alarge format, full resolution picture of a completed board. Thefile is 2.6 meg in size. This will allow you to zoom in on sectionsto check the construction.
The old pages below are left for informational purposes. They contain some very useful waveform and construction photos.
After building a Far Circuits Bitx20 and a Hendricks's QRP Kits bitx20a kit, I decided to build another bitx after seeing this posting:
A new batch of Bitx PCB, in glass epoxy ,masked, roller tinned and with
component place-ment is in ready stock for delivery world-wide.
Also available is the pcb for Avala 01 Sdr monoband tcvr.
I am giving a very special discount on the pbc's. To know further about
the discount, kindly send me a mail at suillakhani123@ gmail.com
I sent off my email and received this back:
Dear Leonard,
The Bitx Version 3 PCB is for $10 PCB +Coils+1 No 2570 transistor.
The Avala sdr pcb is for $5.Shipping is extra $ 10.
I looked at this web page to get an idea what the Avala sdr was and decided that I couldn't pass up a deal like this.
After a trip to paypal, the boards for the bitx and the avala were ordered. Soon I received a package in the mail. In it was 3 pcb's. This was the bitx board along with some of the specialized parts. The other boards were the PA board and the Avala board,
There was enclosed, a schematic, a component layout, and a few other pages of documentation.
After examining them, I decided to make an 'exploded' layout drawing using a section-by-section approach to the assembly and testing. I will function test each section as it is assembled. This will almost insure that the board will function when everything is completed. I already had an head start on the project as this would be the 3rd Bitx I had built. I already knew what the signals should look like in each stage.
Bandpass filter section
I have been building this board from past few days and was searching for some help regarding the tuning parts of various sections. And I asked Sunil to help me with some images, notes and he updated his blogs with a couple of pictures. His blog is available here. When I looked closely, I found that those images and tutorial work was actually done by Leonard L Leeper (KC0WOX). His home page is here. The complete set of instructions he wrote is here. Great job Leonard!!.Update on 05/03/2008
I couldn't access Leonard's site most of the times for checking up information, So I am just copy pasting the information i found in leonard's page along with the images so that the visitors can see them, basically a mirror.
Bitx20 Version 3
After building a Far Circuits Bitx20 and a Hendricks's QRP Kits bitx20a kit, I decided to build another bitx after seeing this posting:
A new batch of Bitx PCB, in glass epoxy ,masked, roller tinned and with
component place-ment is in ready stock for delivery world-wide.
Also available is the pcb for Avala 01 Sdr monoband tcvr.
I am giving a very special discount on the pbc's. To know further about
the discount, kindly send me a mail at suillakhani123@ gmail.com
I sent off my email and received this back:
Dear Leonard,
The Bitx Version 3 PCB is for $10 PCB +Coils+1 No 2570 transistor.
The Avala sdr pcb is for $5.Shipping is extra $ 10.
I looked at this web page to get an idea what the Avala sdr was and decided that I couldn't pass up a deal like this.
After a trip to paypal, the boards for the bitx and the avala were ordered. Soon I received a package in the mail. In it was 3 pcb's. This was the bitx board along with some of the specialized parts. The other boards were the PA board and the Avala board,
There was enclosed, a schematic, a component layout, and a few other pages of documentation.
After examining them, I decided to make an 'exploded' layout drawing using a section-by-section approach to the assembly and testing. I will function test each section as it is assembled. This will almost insure that the board will function when everything is completed. I already had an head start on the project as this would be the 3rd Bitx I had built. I already knew what the signals should look like in each stage.
I decided to start with the antenna end and soon I had the following parts placement diagram for the bandpass filter section.
Next I assembled it and connected a sweep generator to the input and my oscilloscope to the output.
After a little tweaking, this was the final result. The scope is displaying from 10mhz to 20 mhz. Each division is equal to 1mhz.
Rf Driver Section
Following my plan to work from the antenna back, the next section was the RF driver stage. It was the next logical section of the board to populate also.
With the drawing done, the next step is assembly, then add a little power, no smoke, that's good, and a signal input.
Then on to test with the scope. 100mv 14.2mhz in, 1.5 volts out. That was open circuit and we probably won't get that when we hook to the PA, but for now, thats a gain of 15. On to the next stage!
The VFO section stands on it's own and will be easy to test so I choose that as the next section. A transformer was furnished with the boards but it would have to be rewound as the VFO needed about 9uh's of inductance and the transformer maxed out around 5uh. Depending on the variable capacitor you tune with, the turns on the inductor may have to be adjusted but 50 should be plenty and then you can remove some to adjust the frequency up. My test capacitor tuned from 15-377pf and the VFO had almost a 500khz tuning range so setting the frequency shouldn't be really critical. I didn't tweak the range on mine as I will do that when I install it into a case.
Next I assembled it and connected my oscilloscope to the output. You can see the power connection for the test
I checked it out with the scope. A little over 3.5 volts. This will be less when the transformer is hooked up due to it's loading. There is some distortion of the sine wave so we know there is some harmonic content.
A quick look with the spectrum analyzer to see what the 2nd harmonic looks like.
1 Mhz/div horizontal. The left is 0hz and the right is 10mhz. Each vertical division is 10db. It looks like the 2nd harmonic is down about -25db.
Time to drink a cool one and then pick a new section to do next.
First Mixer section
This section is a little harder to understand. I've included a picture to help show the diodes placement. The colors below are the wire color connections if you use red, brown, and green wire. If you use different colors, substitute them for mine.
We need to wind the trifilar transformers. Use the small binocular cores and wind 13 turns of trifilar wire onto the cores. 1 turn is a trip through both holes ending up where you started. We need 2 transformers. I had red, green, and brown #28 wire. The cores aren't big enough to use larger wire. The original drawing called for #32 but the size doesn't make much difference as long as it will fit into the core. The different colors make keeping the windings straight easier. When pulling the wire through the holes in the cores, be careful not to scrape the insulation off. The binocular cores can have sharp edges. When you are done, it should look like this.
Now you can place them on the board as shown above. The final placement should look like this.
Notice the direction of the bands on the diodes. Make sure the leads don't short together.
Bitx20 Version 3 Manual
2nd IF Section
Before we start installing components, now is a good time to install all of the wire jumpers on the top of the board. It will make testing easier as we will connect to the rx or tx line plus the 12 volt line to power the appropriate circuit during test.
This section is almost identical to the the RF Amplifier section so it shouldn't present any difficulties.
I found a board problem on mine. On the left picture, notice there is no right hand hole for the 100 ohm resistor in the lower left corner. It's easily fixed simply by soldering the right lead of the resistor to the wire adjacent to where the hole should go.
Bitx20 Version 3 Manual Pdf
Your board should now look like this.
Lets test it!
Testing the receive side is a problem as there are many frequencies present after the mixer and when looking at them with a scope, it is confusing. Lets look at the receive side using a spectrum analyzer.
Here's some of the frequencies at the input to the crystal filter. It's a good thing that most of these will go away because they won't go through the filter. Part of the reason there are so many frequencies here is because we are overdriving the antenna input circuits with 10 millivolts input. Lets look at what happens when we reduce the input to the mixer. This is normally done by decreasing the RF gain, either with a manual control or agc on the rf amplifier.
This is a reduction of 10db of input signal. That made a big difference. The VFO harmonics are still there but a lot of the mixer products are drastically reduced. Remember, each vertical division is 10db and a reduction to 1/10th of the power. Lets reduce the input another 10db.
That almost eliminated all of the excess mixer products. This is a 20db reduction from the first picture. 20db is 1/100th of the original power or 1/10th of the original voltage so we now have 1mv input at the antenna connector. Under normal operation, that's still a big signal. Our receiver should see signals down to around .3 micro volts.
The version 3 linear amplifier board has 2 very nice additions. The first, the RF signal is switched between rx and tx by relays. This cures a problem I found with the Far Circuits board that I cured by adding relays. The other main addition is an AC power supply. It is setup to accept an AC input and has a rectifier and voltage regulator on board. This allows 13 volts to be fed to the bitx board for it's supply voltages and a higher voltage unregulated to be used on the IRF510. Above is the original board setup.
I made a few modifications to the board. The board looks like this. Power supply on the right and the IRF510 lower left on the big heat sink.
I wanted to use a 22 vac transformer that I had so I needed to use a 35 volt capacitor. I had a 6800 mfd at 35 volts in the junk box so I used it. I had to move the 2 - .1 ufd capacitors to get room for the big filter cap so I put them on the back of the board using some chip caps I had. The spacing worked out just right. Just to the right of them is the original pads for the 2 electrolytic caps.
I used 3 amp silicon diodes so I had to drill out the holes a little and then stand them up vertically. The 6800 ufd cap was hot melt glued to the board after soldering the wires for it into place.
Bitx20 Version 3 Manual Free
After hooking up the power transformer, I measured 30 vdc for the IRF510 and 13.6 volts for the bitx. The next step will be to test it after I complete the bitx. I'll be interested in the power out with the higher voltage.
Bitx20 Version 3 Manual Online
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