W8TEE Morse tutor

Jack W8TEE, a keen µBITx builder and co-designer of the JackAl board,  is giving a presentation at FDIM (in advance of Dayton Hamvention) this year on his new Morse Tutor project.  He will no doubt publish his arduino code and schematic after the talk on 16th May 2019.

He has, however, given us his Bill of Materials so that those wanted to get a jump on ordering parts could do so.

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Battery power for your uBITx

Pop VU2POP has added a LiPo battery inside his µBITx case as illustrated above.  He says “I installed a homebrew 3S2P li-ion battery pack into my ubitx cabinet.  I had planned my cabinet for the right space & fit.  Now I can carry my ubitx for outdoor  action!”.

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TSW introduces adapter to protect DC input

Jim W0EB, TSW Project Coordinator,  has announced he has just got the boards and all the kit parts for this little adapter that allows the DC input for your µBITx (or any other kit or homebrew rig) to be protected.

The board allows connections for optional Reverse Polarity (series Schottky diode), a switch on the volume control (or separate power switch) and the switched DC output to whatever item is being powered.  This is achieved t through a small PC board using MOLEX or MOLEX Style male/female connectors. Everything can be plugged in and unplugged for ease of troubleshooting without having to solder or unsolder wires from the rig’s terminals.

TSW is making either the bare board or a full kit of parts available.  The picture shows everything that’s included in the kit.

Full details are on the TSW website

The manual for the SwitchedPowerAdapter is available in PDF form so you can see what it’s all about.

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10w linear amp from QRP-Labs now available to purchase

Hans G0UPL who operates QRP-Labs has released his 10W HF Linear Power Amplifier.  This kit comfortably produces 10W from a 12V supply.  It is a compact design with huge heatsink included, which will not overheat even on continuous 100% duty-cycle operation.   The amp provides 26dB gain with +/- 1dB gain flatness from 2 to 30MHz.

This 10W HF Linear Power Amplifier kit has no Surface Mount Components (SMD) to solder. There are a number of small transformers to be wound, and assembly requires care and patience.

The push-pull driver stage uses two BS170 transistors in the amplifier design used in the SoftRock transmitter stage. The final uses two IRF510 transistors in push-pull. Yes, this humble low-cost MOSFET really is capable of excellent performance all the way up to 10m band and beyond! Short lead-lengths and PCB layout are extremely important, they are the key to success.

Features:

  • 10W output from 2 to 30MHz, using 12V Supply
  • Generously-sized heatsink, will not overheat even on continuous 100% duty-cycle modes
  • 2-stage amplifier provides 26dB of gain
  • Push-pull driver and push-pull finals, for high linearity and low harmonic content
  • +/- 1dB gain flatness from 2 to 30MHz
  • 4dB down at 6m (50MHz) and 8dB down on 4m (70MHz)
  • Standard 50-ohm input and output
  • Through-hole plated PCB, all through-hole components (no Surface Mount Devices)
  • Standard inexpensive components throughout
  • Tested for 1 hour at full-power 10W, 100% continuous duty-cycle with no forced air cooling
  • Tested for 15 minutes at 20W, 100% continuous duty-cycle with no forced air cooling
  • Tested at 20V supply
  • Tested into open load, shorted load and various mismatches without instability (oscillation)

As Hans advises on the BITX20 I/O Groups list:

I am not suggesting that this amplifier will solve all problems and without wishing to be offensive, the “garbage in, garbage out” rule always applies – in particular, if you feed it a signal containing spurs, harmonics, or other problems… then you will get the same thing at the other end, just amplified 26dB. It also still applies that all stages leading up to the final amplifier must have flat gain. If the pre-drivers cannot provide a big enough signal then you won’t get full power output.

But, it could be useful or interesting, in the BITX context, to look at the details of this amplifier kit and see the short lead lengths, symmetric PCB and extensively “stitched” groundplanes.

For further information see the product on Hans website.

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Outboard filter unit for uBITx

Tom WB6B  wanted to build a new filter for use with the uBITX (to overcome harmonics on his output). However,  he didn’t want to build a filter that would be strictly tied to the uBITX.

So he built a standalone Low Pass Filter box that works as an add on filter for the uBITX as well as becoming a general purpose piece of Ham equipment he can use over and over for other needs.

It uses an arduino to measure the frequency you’re transmitting on and select any individual or combination of filters you like. The proposed design uses a set of filters and a relay switch board; such as to ones by QRP Labs. But, the Sketch code should be easy enough to modify for whatever you like.

The controller can show the selected filter with LEDs.  Alternatively  it can be configured to use an LCD display, which will display the transmit frequency as well.

Tom’s unit is still under construction, but he has built and tested a prototype with a signal generator.

He is releasing the preliminary design now because it is complete enough for people to try out on their own filter designs. It makes using outboard filters really easy, and he thinks  people will like it.

Tom welcomes feedback on improvements people make while building their own “Auto Filters” with the controller.

The code for the controller is here: https://github.com/mountaintom/TX_Auto_Filter

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Distilled wisdom with respect to HF linear amplifier kits

Many constructors will have thought about adding on to their µBITx one of the cheap linear amplifier kits that can be found on eBay.com or Aliexpress.com.

A thread covering these options was started by Arvo KD9HLC.  This article attempts to succinctly cover this ground for those exploring amplifier kits in future.

Arvo asked about the kit illustrated above that costs US$36.   There is another cheaper version available and Lee N9LO says:

“I’ve read some reviews on these and it seem the big difference between the $36 100w and the $18 70w is the 100w is on 16v and the 70w is 13.8v. The heat sink for either is $8. They both need a low pass filter for the band you use it on”

Richie notes:

“The 45 watt and 70 watt amps use the IRF530, and I own both. They do work, but not for long at the advertised power. It’s very easy to push too hard on the drive and blow the FETs. The 45 watt version only takes 10 milliwatts of drive to get full power, so it can be connected directly to the BitX 40 T/R relay with a 3 to 6 dB pad (bypassing the PA). You can get about 25 watts out on 13.8 volts. The 70 watt amp needs about 1 to 3 watts of drive to work, but can produce 40 to 50 watts from 80 to 20 meters. The output falls off sharply after that. Either way, but some extra IRF530s… you will need them!”

Howard Fidel says:

“I built the 70 watt model. I changed the 2 IRF530s to 4 IRF520s. The IRF530s oscillated and failed quickly. They also run very hot. The IRF520s run much cooler (2x as many junctions) and are stable putting out 50 watts on 20 meters. The output on 15 and 10 is less, but the uBitx puts out less on those frequencies. I am working on getting it working on all bands, but for now I just use it on 20.”

David, N8DAH, says:

“Just my 2 cents. After getting two versions of the “cheapbay” amp I can say the best thing I did.  I bought a proper kit (like a WA2EBY) and built it.  The Hardrock 50 was also a great amp but the cost is pretty high. I have not used a HFpacker but know a few QRP guys that swear by them as well.

If you really want 100W look at the HLA-150. I have had much better luck with building a known kit then trying to save a few bones on the cheaper kits with next to no info on them”

Jerry KE7ER says:

“Any amateur amp should be followed by a low pass filter suitable for knocking out the second harmonic and beyond.  That means separate filters for 160m, 80m, 40m, 20m, 10m. You may piggyback some of the other non-harmonic bands into that set of filters, but that makes the filters much more difficult to design and build.  A rig with only a 30mhz LP filter is likely aimed mostly at CB’rs.

“QRP is good for experimenting.  But with a 50W+ eBay amp, you really should be testing for compliance with FCC regs.  It likely fails, and all the nasties will scale up with the output power.”

Two articles to check out

4Z1NT suggests checking out this article on how to make the 70w unit work well.

Andrew Kasurak suggests checking out this article if you want to upgrade a cheap Chinese eBay amp to a working 55w unit.

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Some great mods from PH2LB

 

Lex PH2LB  wrote to uBITx.net to tell us about a page on his website where he describes his uBitx (V3) mods.   This is a very nice build, and he has some good ideas.   Check his page out here

http://www.ph2lb.nl/blog/index.php?page=ubitx-mods

In particular Lex has developed some custom firmware that firmware geeks may be quite interested in …

“Second mod : custom firmware”

Originally based on the v2 software but merged to v4.3 and updated to code to have a lower RAM footprint (usage of F(…) macro and strcpy_P) with about 50%.

Source files can be found here : https://github.com/ph2lb/ubitx4

Over the last few months there have been a range of ideas to boost mic drive output or to add compression.  Here’s a mod designed to work with a dynamic microphone …

“Fourth mod : dynamic microphone amplifier.”

Because I like to work with dynamic microphones, I added a dynamic microphone amplifier based on the microphone preamp designed by Javier Solans Badia, EA3GCY for his ILER transceivers.

There are a whole bunch of ways to add buttons. KD8CEC does this through paralleling up buttons with different series resistor values on the encoder analogue port).   Lex has taken a different approach that will be of interest to some constructors.   He uses a PCF8574 I2C encoder (like the backpacks for a 16×2 or 20×4 LCD display) and uses the existing I2C bus…

“Fifth mod : again adding extra buttons.”

Using a PCF8574AP I2C IO Extender and hooked it up to the all-ready existing I2C bus on the Raduino for more direct menu buttons. Needs the custom firmware to direct switch between bands with a PA bandplan limitation (also has FULL option) and Step size up and down.

 

Something that a number of constructors have done is to remove the 7805  and supply 5v to the Raduio using a separate 5v supply.  Most are using buck or buck boost modules, but Lex has used a P-MOSFET.   There’s a good description of his approach on his website …

“Sixth mod : removing 7805 from Raduino and reverse power protection.”

Relocating the 7805 is a good idea, but adding a reversed voltage polarity to a uBitx is a must. I used a P-MOSFETs for that (also link to good video about using P-MOSFETS for reverse power protection).

Finally, you may be interested in Lex’s use of the Manhattan style technique for PCB layout.  It can look very professional as per this example: