Watch out for fake RD16HHF1 devices. Buying on Alibaba and Ebay is a risk some are willing to take, but there are plenty of fake devices for sale through these channels.
AE7TO experience with evening up power output
Mark Cantrell (AE7TO) has been having fun getting his uBITx to have more even power out.
All this experimentation was to allow Mark to get enough power out of his µBITx to make up for low efficiency portable antennas. He didn’t want to carry a separate power amp. He just needs to build a 24 VDC battery pack now!
His rig can be seen in the photo above. At the left hand side (with controls incorporated on the rear panel) is an Antenna Tuning Unit and in the middle is a new daughter board.
Step 1
The new daughter board implements the relay-based band output power leveling mod designed by Bill (K9HZ).
This mod helped quite a bit at 10 and 14 MHz. Here is a summary of power levels, as observed by Mark, on each band after the mod:
- 7 MHz and lower frequencies = 11 watts out (no change from before the mod
- 10 MHz = 8 watts out (twice was I was seeing before the mod)
- 14 MHz = 8 watts out (also twice what I was getting before the mod)
- 18 MHz = 6 watts out (never checked that band before the mod)
- 21-28 MHz = 3-4 watts out (didn’t test that band before the mod)
Mark didn’t bother adding a 4th relay for tuning as he usually uses an antenna analyzer and manual tuner anyway.
A 3D model file is available for the plastic bridge built to hold the daughter-card above the main uBITX circuit board. Someone else may find that file useful.
Step 2
Mark split off the PA power line and fed it 25 VDC (two small lead acid batteries in series). A buck converter was used to reduce the 25 volt main supply to 13.5 VDC for the rest of the uBITX main board.
That gave 25W at 3.5 to 7 MHz, 12W at 10 MHz, 14W at 14 MHz, 5W at 21 MHz, and 4.5W at 28 MHz.
Then he added a 33 uH inductor in series with R86, and 220 pF caps in parallel with R87 and R88, as suggested by Howard WB2VXW.
Here is a summary of power levels after the above changes (plus replacement of RV1 with the 3-relay/4-pot mod discussed below):
Freq / Power Out / Current Draw
- 3.5 MHz / 28 W / 2.3 A
- 7 MHz / 28 W / 2.2 A
- 10 MHz / 16 W / 1.4 A
- 14 MHz / 20 W / 1.5 A
- 18 MHz / 11 W / 1.1 A
- 21 MHz / 7 W / 0.7 A
- 28 MHz / 7 W / 0.7 A
These numbers are good enough that Mark no longer feels the need to fiddle any more. In particular, he is not going to change the bias settings on the finals as they seem well adjusted from the factory. Mark has turned back the power output on the low bands to give no more than 20w out to protect his finals.
VU2ESE power mod for 10m operation
Ashhar Farhan VU2ESE notes that 28 Mhz has, unusually, been open for the last week. As a result, he realised that the ubitx output was woefully low on 10m. Hence the experiment below:
Ashhar suggests the following final fix, and asks for others to try it out and see if it is replicable:
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well)
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262.
So, what happens is that removing the C261 and C262 increases the gain of the finals. They are run open. Hence greater gain at 28 mhz.
However, the gain is very high at lower frequencies. So, in order to reduce the gain at the lower frequencies, the 0.1 uf cap is replaced by the 470 pf. As the frequency of the signal drops, less and less RF flows through the 470 pf, decreasing the gain of the predriver. 470 pf is not a magical value, 220 pf works almost as well.
Step #1 Increase the predriver gain towards the higher frequencies
The predriver Q90 has a emitter degeneration capacitor C81 (0.1uf) and and R83 (10 ohms). Replace C81 with a 470 pf and R83 with 2.2 ohms. Altenatively, short R83.
With this, the emitter reactance decreases with increasing frequency, yielding higher gain beyond 14 MHz.
Step #2 Take off the feedback from the IRF510s.
a) Replace the existing R97 and R98 with a value of 47 ohms with 220 ohm resistors.
b) Remove C261, C262.
Reference #1
Reference #2
uBITx panels for EF01 Excellway case
Bought the Banggood case? Want some 3D printed drop in front and back panels so you don’t need to cut out the hole for the display and controls?
Gary AG5TX says:
“I bet some find it hard to stomach buying $27 plastic panels for a $10 plastic case when debating a few bucks differences in micro-controllers.
That said, my building brother, I too get anxious on cutting holes. We don’t know what tools you have, and given the question, assume not a mill or a drill press.
“What I would do is cover the front side of the plastic panel with blue 3M painters tape. Scribe the centerline for the holes directly on the ‘inside the box’ portion of the plastic where it won’t be seen. I use center drills to start the holes (they are cheap), if you don’t have center drills, use a small drill bit. Once the initial undersized holes are cut, flip the piece over and drill from the ‘outside the box’ side so if you get a chip out it won’t be seen. Best to start small and step up to one drill bit less than size. When drilling, secure the plastic panel over a scrap piece of softwood, and make this a “pine board project.” With thin plastic and drilling with hand tools, I find that the final drill bit size is best done by hand. I have an old pcb hand nibbler tool ($10?) for cutting somewhat square holes with patience. Just slightly undercut the rectangle for the LCD with the nibbler, remove the tape and finish out with a bastard file and sand paper. If all goes wrong, you can still try 2 more cases or spend the $27. Also search this forum for good ideas on printing a full face ‘label’ which might cover up the sins of a nonperfect cut. Stain grade or paint grade? My wood working Grandfather taught me very early in life that a coat of paint covers a multitude of sins. Nothing ventured, nothing learned. Maybe someone else has some tips.”
Michael VE3WMB comments:
“I have now used three of the Excelway EF01 cases for rigs with 16 X 2 displays with good success. The ABS enclosure panels are quite easy to work with.
“Just to add a couple of comments to Gary’s suggestions. I have found that drilling corner holes and using a coping saw to cut out the “window” for the display works quite well. As Gary suggests you want to make it undersized by a couple of millimetres. With patience and a nibbler or even an exacto knife and a file you can make a decent looking opening. In all three cases I made
the “window” just large enough to friction fit the display without resorting to using screws to hold it in place and this works fine.
“One other point; I suggest that you mark the position of where you are going to drill holes and then make a small divot (a nail and hammer works fine for this) so that the drill doesn’t wander. Also starting with a small sized drill bit first helps. For larger holes (i.e. for BNC etc) I swear by a stepped drill bit to get the hole to the proper size.
“The key to getting a good result is to plan and carefully mark everything in advance on the back of the panels and then take your time. Remember if an opening is too small you can enlarge it, if it is too big there is not a lot you can do so, measure twice and cut once.”
MVS Sarma says, “For cutting rectangular windows in plastic, I resort to a lamination cutter sold in India at just fraction of a $. I keep the tool drawing across the 4 lines of the rectangle (the lcd mounting window in this case on the µBITx). After a while you can push out the small window from the plastic.
This is what a laminate cutter looks like.
Reference
Photo of mod for evening up power output
Nigel G4ZAL did Howard WB2VXW ‘s mod by adding:
- 27uH inductor in series with R86 (NB calculated value)
- Adding parallel caps of 220pF on top of R87 and R88.
The mods to the main board are shown in the photo below.
The power output changes that resulted were as follows:
- 7MHz from 12.5w to 14.5w
- 14MHz from 7w to 11.5w
- 21MHz from 4w to 8w
- 28MHz from 2w to 4w
Nigel says it is a “very worthwhile mod for just 3 components”. This mod is something that all constructors should consider.
Reference
DSP on a cheap processor
IK8YFW Giuseppe has used a cheap US$2 processor to create a DSP audio processing unit that works with any radio (including the µBITx).
The project was aimed at achieving an economic and simple DSP unit, based on the ARM Cortex STM32f103 processor module. Guiseppe implemented two narrow CW filters of about 300 and 700 hz and two SSB filters with a bandwidth of less than 2200 Hz and less than 3300 Hz. He also included a 6-level noise reduction algorithm. The project is a very cheap solution suitable for embedding in any and every QRP project. The project code can be found on Github. It is not perfect, as Guiseppe is still experimenting with the code. The project can be found here:
https://github.com/gcallipo/RadioDSP-Stm32f103
Some test here:
https://m.youtube.com/watch?v=TFcsVX59YbQ
https://m.youtube.com/watch?v=ujDCt_HhbYg
Reference
ND6T AGC design a winner – boards coming!
There has been a bit of BITX20 IO Groups list chatter about the winner in ND6T’s AGC circuit (with RF gain control).
Ion VA3NOI has two versions of an ND6T AGC circuit board designed.
- A through-hole single-side version measuring 17X38 mm.
- An SMT board measuring 18X31 mm, with SMT components that are 0805 in size.
The . 1 uF cap is tantalum or niobium polarized.
The design was done using Eagle 7.5 freeware. The zip file in the Gerbers Folders should be uploaded to the PCB manufacturing house.
The boards are roughly 1 square inch in surface. You can place 10 boards on a 100X100 mm panel and get 10 panels for $5 plus shipping. For making into a kit, Ian recommends the SMT version as it will be more affordable and he expects it to have better performance on the upper bands.
He has ordered a through-hole version for experimenting with some values (AGC release time minimum resistor and coupling capacitors on RF line) and this is en route to Canada.
The PCBs have provision for adding a pot to adjust AGC release time and a switch to disable the AGC. Ion has posted the files (schematic, board layout and Gerbers) here:
https://app.box.com/s/qf4jubi8942dhwdc8lhivctycnue4f12
Constructors should feel free to use the files as they see fit. He is also happy for anyone wanting to put kits together.
Kees K5BCQ is looking into whether it can be sold as a kit through his website.
Reference
Simulated S-Meter and SWR meter on small OLED display
Duwayne KV4QB has been playing with an Arduino Pro Mini and a small OLED display to use as a stand alone replacement for a analog meter. The existing Raduino in the µBITx does not have sufficinet spare analog input pins to provide everything that Duwayne wanted to measure.
More information can be found on his blog at:
https://kv4qb.blogspot.com/2018/04/stand-alone-simulated-analog-meter.html
He is also working on a small board to provide forward and reflected power readings for SWR metering and power measurement.
This has created a bit of interest on the list, and represents an interesting idea that is potentially adaptable to other projects and use cases.
Reference
Poor man’s panadapter
Bruce KC1FSZ has been experimenting with a panadapter for his µBITx that is likely to be of interest to constructors, especially to anyone thinking about one of those fancy ICOM 7300s.
The goal was to build a crude panadapter into his BITX rig without resorting to external PCs, SDR dongles, etc. He used a few cheats in his scratch-build BITX that may make this a bit more tricky on a stock unit. However, Bruce is sure that someone in the group can figure out how to expand this into the mainstream.
It’s a bit like a Sweeperino. Bruce has built his firmware to quickly sweep the VFO across the band of interest (40m phone in Bruce’s case) and then to look at the AF spectrum at each point and display the result in a simplistic spectrum display. Obviously, this interrupts the receive for a brief instant when it is happening, but he has also set things up with an extra MOSFET so that the audio output can be suppressed during the sweep to hide the annoying sounds. This mod may already be in your rig if you’ve added an AGC.
The more sophisticated way to go is to do some DSP fiddling of the overlapping 3 kHz segments of the spectrum that are sampled during the sweep. At the moment Bruce sweeps in 500 Hz steps so there is overlap in the samples of the audio. This needs some more experimentation to get the optimal sweep speed, the cleanest way to stitch things together, averaging, etc. but even something basic is good enough to show the activity on the band.
Bruce also uses a cheap 128×64 OLED display, which makes these simple graphics possible. Be aware that these displays can be noisy.
The picture at the top of this news items shows what the initial display looks like. The caret at the very bottom is pointing to where the VFO is currently set. You know it’s working because you can always see the signature 7199 BITX birdie!
Bruce has produced a video with the sweep slowed and the audio on so you can hear how it works. It sounds like a strange SSTV mode, but it’s actually the entire 40m phone band being analyzed for activity.
Reference
Microphones galore
Constructors have been uploading their microphones. These are included in a single gallery called “microphones” and will be separated out into their own group with a separate link shortly.