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Using uBITx Memory Manager with the HF Signals v4.3 Firmware

Remi F1MQJ has modified the manufacturer’s v4.3 original firmware (published on may 23 2018) to include communication with KD8CEC memory manager.  

This could be very useful for those wanting to stick with the HF Signals latest firmware, while making it easier to view or update initialisation settings, such as calibration of frequency or setting the BFO injection point, in the original firmware.

Modifications are the same as those described by Ian KD8CEC  here but are adapted to the HF Signals V4.3 original firmware.

The file removes all text after .ino in your firmware directory replacing the original ubitx_cat.ino file.   

You can access this file at the following URL:
https://groups.io/g/BITX20/files/ubitx_cat.ino_modified_KD8CEC_F1MQJ.txt

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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.

Reference
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Further details on Nextion Display and second arduino

Ian KD8CEC, in his third article on using a second arduino with the µBITx, demonstrates the signal scope feature made possible with having a dedicated ardunio nano connected to the main Raduino control processor via i2c lines.

The signal scope shows a section of the band surrounding the currently tuned frequency IN REAL TIME.    The nano and the serial connections to the Nextion doesn’t have the agility to provide a full blown waterfall display, but a real time display of signals around where you are currently tuned is still pretty impressive.

The other feature that is present in the Nextion display version of this arduino add-on, is a CW decode function.

Bring on the release of v1.097 of CEC firmware!

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VU3SUA case documentation

The µBITx case from Sunil Lakhani VU3SUA  is popular with constructors based on its value for money.  However, many find it difficult to find wiring guides for this case.    It is documented at various places by VU3SUA.  Sunil Sankaranarayanan VU2MTM has downloaded all of the photos and these are collected together.

[wpdm_category id=”vu3sua-case-construction-help”]

[wpdm_package category=’vu3sua-case-construction-help’]

Reference

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Crystal filter experimentation

Rahul VU3WJM has been scratch building a µBitx and experimenting with the 12 MHz QER filter.  He notes the following:

1) With the set of xtals that I have with 100pF caps and 200Z I/O filter the bandwidth is around 1.85Khz for HC49S crystals and 3.3Khz for HC49U crystals.

2) With a filter based on HC49U crystals, a lower bandwidth is achieved using 150pF caps but impedance drops down to 150-160 ohms. Lowering the
bandwidth also degrades the shape factor to around 1:2. This can be well understood considering that HC49U crystals have a lower motional inductance Lm.

3) As suggested by Allison KB1GMX, 82pF is working just fine in the filter and achieves a bandwidth of around 2.2Khz. Capacitor value is bit touchy between 82 to 100pf.

4) The Q of capacitors used has a major impact on the filter response. Parallelling up two values to arrive at a desired overall capacitance value results in a better response.

To see sweeps of a few different filter configurations select the reference on the list.   Rahul would love to hear from others of their experiences on the 12MHz crystal filter.

Reference

 

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Reducing CW click on your uBITx

Bob N1KW found that by simply increasing C1 to 2.2 uF (just parallel the existing 0.1 uF cap) the keying shape is greatly improved with about 3 ms attack and 6 ms decay. That is much better than the key click machine it was originally with about 0.5 ms attack and decay times.

Reference
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Fan mod with temperature control

Rob AG5OV picked up a cheap temp fan relay from Amazon.

These are also available on Aliexpress for less than US$2.00.

Rob  superglued the probe to one of the heatsinks on the finals and then played with ON temp and hysteresis temp.  He settled on 50deg for turning ON the fan and 35deg for turning it OFF.   Rob says it works great.

Reference
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Glitch on CW keying on uBITx

Bob N1KW has identified the cause of the brief glitch on going into TX on CW with the µBITx.   While analysing the circuit Bob realised that the large capacitor C52, which is charged during receive, would feed back through R52 and R18 keeping the receive path (Q10, 11, and 12) after the balanced modulator “hot” for a brief period. When the transmit path is activated, the receive side of the circuit is going to remain on for some period of time due to the time constants of C52 and its loads. It is understandable that if both directions of the circuit are on, it could oscillate during that time!

To resolve the issue he simply added a diode in series with R52 (cathode toward C52) so that C52 can no longer back feed power to Q10, 11, and 12 upon initiation of transmit state. Now the transmitter output looks perfectly clean on the spectrum analyzer at beginning of TX. Shorting the diode causes the problem to show as before.

The same issue could apply to C64 when transitioning from TX to RX but at least there will not be spurious emissions going out over the air.  He plans to add a diode in series with R66 in the same manner just for fun.

Note that in KD8CEC firmware you can add a keying delay to fix this issue in firmware.

Reference
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Nextion display and a second arduino

Ian KD8CEC has now given us part 2 of his description of the latest firmware update (v1.097).   If you have a Nextion display, and add a second arduino you can have a higher quality s-meter and multi-band signal monitor on your µBITx.

For more details go to Ian’s website at hamskey.com

The wire up diagram follows:

The second arduino echos information in one direction from the main raduino via the i2c serial channel which is faster than via serial port.  It uses a dedicated serial port to output the signal again, potentially making the sampling faster for taking signal strength readings.  It will be interesting to see what effect this has in practice.