Caution for JackAl Board owners

Jack, W8TEE and Al, AC8GY produce the JackAl Board add on for the µBITx.  They are warning that two JackAl owners have reported that a voltage spike destroyed their RA8875 display.

Al has looked into this and found that there is a very narrow voltage window on the display. Buydisplay confirms that 4V on the 3.3V line can ruin the display. From what we can determine, voltage spikes were the culprit in both cases.

What the JackAl team is doing is creating a very small PCB that will clamp the supply voltage to the display. Parts for the board will cost less than $2.

They will send one of these PCB boards to JackAl owners at no charge with a request and a SASE.

Further details will be provided when the boards come in.  Jack and Al are also expanding the documentation and hope to have a new assembly manual shortly.  Announcements will be made on the BITX20 IO Groups list and this article will be updated accordingly.

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Add-on board for uBITx

Nick VK4PP is working on a nice little add-on board for the µBitx with the following mods incorporated:

  • 200hz CW Filter
  • Mic Preamp (SMM2167 Module)
  • VK3YE LED AGC
  • LPF section (Dual relay per filter)
  • POP fix for earlier v3 boards, and
  • High Pass Filter on RX for BCI option.

Nick is designing it for use with through hole components with the exception of the 100uh inductors underneath the board, which will need to be 1206 Surface Mount devices.  At this stage he is hoping to provide the board at $5 each plus post (VK-$1, DX-$3).

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Mini-microphone for your uBITx

David N8DAH suggests you can use your µBITx stock switch and microphone element with this nifty mini-microphone case from Kit Projects.  They cost US$10 plus shipping.  These are 3d printed  with all hardware included (Mic’s use the stock element and tac button that came with your bitx40 or ubitx).

Kit Projects has red and black microphones right now and grey is coming soon!

The also have 3D printed mini paddles available to purchase, that may be of interest to µBITx constructors.

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Amateur Radio Kits case construction pics

Joe KD2NFC is building his new µBITx into one of  the cases from www.amateurradiokits.in.   In this case it is for use with the 5″ Nextion screen.

Joe says, “These cases are awesome and really add to the fun and creativity of building the uBitx. I am still waiting for the 5” LCD but here are some images of my progress.”

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Quick review of the Kit-Projects AGC board

Jim W0EB, TSW Project Coordinator,  bought two of these kits for his 2 uBITX Version 5 radios. First off, the directions for installing this board are brief, but they are easily followed and the boards are easy to install.

Not wanting to drill a hole for the included switch and run a bunch of wires to it, he just wired the common pad to the “fast” pad for always on, Fast AGC.  A “Via” hole was identified in the trace between R70 and “Vol HI” and Jim ran a wire from there to the “VOL” pad on the AGC board. This worked great.

Even though the “S-meter” output of this AGC system was designed to work with the CEC software, we found it worked with TSW’s BITeensio board as well.

The BITeensio uses the A19 analog input on the Teensy 3.6 for the S-meter. This little AGC system drives the S-meter routines just fine on the BITeensio.

A 50 microvolt (-73 dBm) signal was fed into the antenna connector and Jim adjusted the software’s S-meter routine’s division ratio so the touch screen’s display read S9 as it should with a 50µV input. The rest of the S units were so close to correct that no further tweaking was deemed necessary.

He also found that adjusting the on board RF gain control for max recieved signal was the best way to adjust the level control. As you turn the control counter clockwise, the gain increases and there is a point past which saturation occurs. This is obvious when listening to a weak signal and you can hear the gain drop past this point. Simply adjust the gain to that point and turn it back to where the signal is just peaking.  It is best to just leave it there if you want your S-meter to work right.

Once adjusted, this little AGC board keeps the RF input nicely within bounds on strong signals quite well.

Jim calls out ND6T and N8DAH and says “Well done guys, well done! The kit is certainly worth the price IMO”.

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The experience of cleaning up spurs and harmonics in a V3 uBITx

v4 board at 10w on 21 MHz (overdriven)

Mike KU4QO has shared his results in trying to clean up the output of his V3 uBitx.

He thanks all the folks who spent their time on tracking down the causes and cures and shared his results with the group for others to reflect on.

His setup comprised a signal generator at 1kHz feeding the microphone input, and the radio set to SSB mode.  He applied 12.0 VDC for power. Output of the radio was fed through a 30db attenuator into a borrowed spectrum analyzer. He adjusted the signal generator’s output to vary output power in the transmitter.

Power output of the fundamental was just below the point where more microphone signal did not appreciably increase the output power:

80m  10 watts

40m    8 watts

20m    5 watts

17m    2 watts

15m    2 watts

12m    1.5 watts

10m    1 watt

As built, his V3 uBitx was marginally compliant to US FCC rules on 80, 40 and 20 meters.  Above 20m the output was messy as a result of lower frequency spurs. For example, on 15 meters there was a spur at 2.6 MHz that was down only 23dB from the fundamental.

He first completed the L5/L7 mod using surface mount 0.68uH inductors (from the Ebay seller in Poland), marked “T R68K”.  He re-ran the tests and saw no appreciable change in any of the results.

Next, he replaced the 5 relays with Axicom relays from Arrow.com. This change showed a significant change in the harmonics on the low bands. 80m, 40m and 20m went from marginally acceptable (barely -43dB from fundamental) to easily meeting FCC specs on those bands, with unwanted harmonic outputs dropping an additional 10dB or so. However (as expected), the relay change did nothing for the spurs resulting from operation on the higher bands.

Most interesting was watching the output spectrum while adjusting the microphone drive. For example, the nasty spur on 15 meters at 2.6 MHz went from 23dB down at a fundamental power of 2 watts, to below the noise at a fundamental power of 1 watt. At significantly reduced drive (power) levels, the high bands are all in compliance with FCC specs. Here are the reduced powers that provide a clean output signal:

17m   1.5 watts

15m   1 watt

12m   0.6 watts

10m   0.25 watts

Mike followed Raj’s directions for the L5/L7 mod. What should the affect of that mod have been? Should it have impacted those spurs on the high bands? He is questioning whether the inductors were actually not the correct type.

Jerry KE7ER thinks the consensus is that replacing L5,L7 should reduce coupling from the power amp back into the 45mhz IF amp where it takes another trip through the D1,D2 mixer.

Raj VU2ZAP, the originator of this mode, had a specific manufacturer in mind.  They have to be well shielded, commonly available surface mount inductors did not help at all.

Curt WB8YYY is pleased that the results show that the Axicom relay replacement provided around 10 dB improvement.   He has Gordon’s relay board installed, and he imagined his set of new relays will do at least that good.

He notes that some form of added 45 MHz filtering should help in most rigs. He first tried a xtal filter stage – but it disrupted his 40m CW output (He could restore output only by touching L5 – hence the reason for considering shielded inductors). He instead added an LC filter similar to what now appears in the stock v5 board, but he is not sure of the inductor’s Q.  He thinks it may be around 70.  According to simulation it provides more than 10 dB.  He is still waiting for verification in real life.

Curt notes that in the club’s initial measurement of many ubitx rigs, there is appreciable variation even though these are all the same board design (v4) and they were all received at the same time.

John Sutter W1JDS uploaded a spreadsheet of measurements for his µBITx for 80, 40, 30 ,20, and 10m:

1. Stock
2. Replaced L5/L7 with SMD inductors I found locally, kept C211 in circuit
3. Replaced the relays
4. Replaced the inductors with the specified Murata parts
5. Bypassed C211 per the mod

The spreadsheet can be accessed here: https://docs.google.com/spreadsheets/d/1eUFuHcprJhk_HuINxXJLhBuZ7-0DHPfaGPV-RoN8wBY/edit?usp=sharing

The mods he used are those from this website:  http://ubitx.net/spectral-purity/

Both mods helped.

To desolder the relays, he used a piece of desoldering stick,
a low temp alloy along with solder wick and a hot tip on the iron,  and this made easy work of it.  Cleanup was the worst bit.

Probably about the same as: http://www.zeph.com/lowmelt.htm

He’ll probably put the cap back in the circuit in order to be able to use 30m.

He is still needing to find a solution for 80m in order to ensure compliance.

His testing was done in CW mode with the following configuration:

  • 12V LiPo Battery pack  (link)
  • 40dB homebrew attenuator which I’ve characterized as being pretty flat
  • Agilent E4404B SA & HP 8595E SA depending on which one I could use at the time
  • 3D printed key
  • Misc cables…

    This is a v3 radio.  Right now it’s mounted in the plastic box it came in until it decides what it wants to be when it grows up 🙂   John has a JackAl board ready to go when he is happy with the harmonics.

uBITx v5 Board compatibility with JackAl

 

Jack, W8TEE and Al AC8GY have spent considerable time testing a couple of V5 µBITX boards for use with their JackAl board.  No hardware modifications are required when using their board with the v5 µBITx.

However, Jack is making some minor changes in the software because of the new IF frequency.  They expect to release a new software release for the V5 board in a few days.  They are also expanding the assembly manual with additional photos and narrative.

The JackAl boards are being sold by QRPGuys.com.

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Alison’s audio pop mod prettied up


Mark N7EKU has posted a nice clean schematic and a picture for the audio pop fix he has just completed on his uBITX V3. It works great and saves the ears a lot.

If you check the top part of the photo, you can see that I have done Allison’s fix for harmonics by re-arranging the filters a bit and moving the original relays to the bottom of the board. This worked great too and cleaned up harmonics a lot.

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