SSM2167 board – improving compression control

Brad N8YG has been reading over posts concerning the ssm2167 compression pre-amplifier with quite a bit of interest. So he finally integrated the board into his ubitx v5.

He put a trimmer on the output of the board, and potentiometers on the compression, and noise gates. The problem that he ran into was that on the air, rotating the 100K compression potentiometer had little to no effect.  However he was getting compression that was clearly audible on the air.

He re-read the data sheet for the ssm2167 more thoroughly and found that the input voltage need to be quite low at -20 to -30 dBV.  A quick check on the electret microphone output using the oscilloscope, showed a much higher output from his microphone.

This led to him adding another pot to trim the input voltage.  He still needed the 5V to get to the electret so he wanted the trimmer after the 0.1 uF surface mount capacitor on the board.

Brad modded the board by removingthe 0.1 uf capacitor, and he made connections for the trimmer after the 0.1 uF capacitor.

The net result is a board with three additional potentiometers and one trimmer.  The trimmer adjusts the output voltage, and potentiometers control the input voltage to the board, compression and noise gate.

On the air.. with the compression potentiometer turned down the rig sounds like it has no compression… while turning up the potentiometer makes a profound difference in on the air sound.  The rig now has a LOT of punch and the power meter goes way up.   

Brad believes that what was happening was that the input level was too high forcing the chip into the limiting portion of the transfer curve.  Now that the chip is operating back in the linear portion, all is well!  

Reference

Official release of VU2ESE’s Antuino

Antuino

Ashhar Farhan VU2ESE, the designer of the BITx range of kit transceivers marketed through HF Signals has launched his next design: the Antuino.

The website states that:

“Antuino is an accurate instrument that can be used in the field to measure SWR, field strength, modulation, etc. In the lab, it can be used to sweep filters, measure gain, distortion, frequency response, etc. It works upto 150 Mhz. On the third harmonic, it is usable on 435 Mhz band as well (with reduced sensitivity).

“The Antuino, unlike simpler instruments is based a superhet architecture that measures the response of the antenna or circuit at exactly the tuned frequency. It is based on Analog Devices’ Lograthmic Amplifier, the AD8307 to provide accuracy of 1db in your measurements. It is tuned with a crystal locked PLL based on Si5351 oscillator chip.”

Ashhar has confirmed that this is not a kit, but rather is a fully tested unit in an all metal case. It has an internal battery case to hold 6 AA cells. It comes with two SMA connectors.
Steve G1KQH has opened a support group for the Antuino:   https://groups.io/g/Antuino
Reference

Nextion Bezels for a variety of display sizes

Ian from Computer Freaks Anonymous found the uBITx.net website and let us know about his Nextion bezels.

He has been producing these on his CNC machine for some time now.  They are manufactured from acrylic, have tapped holes to secure the display with plastic screws (supplied).

The bezel allows you to cut a rectangular hole, glue the bezel in place and secure using the screws. It provides a nice glossy finish and they can be produced in many colours. From the front view there are NO screw heads visible, adding a more professional finish to your project.

He ships worldwide, to US, Canada, UK, Austria, Germany, etc.

More info here:

https://www.compfranon.uk/product-category/products/screen-bezels/nextion/

Temperature measurements on the fan shroud

Mark AJ6CU released a fan shroud for the “tall” Sunil case a short while back. See https://www.thingiverse.com/thing:3790450

He was curious to check out its effectiveness, against  just using the supplied heat sinks or using the heat sinks with a fan.  So here are the results….

Test Setup

  • ubitx v4 with stock PA transistors and the new larger heat sinks being shipped with the case
  • Noctua 1800RPM 80mm 12V fan (Blowing in)
  • Little Volt/Temp gauge that was mounted on the front panel (measurements in Fahrenheit)

Search for: ” DROK Car Voltage Temperature Display” on amazon if you want one!

Unfortunately Mark took the “shroud measurements” on a different day than the”no shroud measurements”.  So focus on the temperature gain over “ambient temperature, for a true comparison.

The first set of tests were for 5 minutes on 40m into a dummy load.
The second set was on FT8 CQ into a dummy load, until the FT8 watchdog timer terminated transmissions.

The Results

No Shroud            Ambient               After 5 Min Xmit       Temp Gain
Fan Off                   81F                          128F                               +47
Fan On                   76F                           94F                                +18

With Shroud       Ambient                After 5 Min Xmit       Temp Gain
Fan Off                   83F                          128F                               +45
Fan On                   81F                           98F                                +17

Operating for 5 minutes into a dummy load suggest that a fan is probably as good as a fan and a shroud.

On FT8 CQ (into Dummy load, until the watchdog kicked TX off):

WITH Shroud     Ambient                 After 5 Min Xmit      Temp Gain
Fan Off                   84F                          105F                               +21
Fan On                   82F                           88F                                +6

Of course the missing measurement is the FT8 CQ with just a Fan. Mark thought of this test *after* he had put everything back together. 🙁 .

Reference

ARRL review of uBITx

Thanks to Malcolm ZL2UDF for the screenshot. For the full review, see the September 2019 edition of QST.

The ARRL has published a very positive review of the µBITx transceiver completed by the ARRL Labs team in their September issue of QST.   The kit is pictured with the Amateurradiokits.in metal case, and features the stock firmware and display module.

In summarising the µBITx the ARRL review states:

The µBITx is a good choice for a low cost CW/SSB transceiver kit.  It’s open source design enables a wide selection of modifications and enhancements from the user community for your µBITx kit.

There is also a video (with some factual errors by the reporter) available on YouTube that is complementary.

Reference

Ruminations on fast TX/RX switching on uBITx

Discussion on the IO Groups BITX20 list has recently turned to how a fast TX/RX switching regime could be achieved for the µBITx.

John K0JD mused that he could probably figure out how the circuit changes to eliminate the relay, but then changing the firmware to let it happen would have to be addressed too.

Madradiomodder suggested that it was easy.  He provided us with this example of the front end of the Elecraft K3, that uses PIN diodes.

You just need to add DC to bias the diodes above the lowest AC cycle plus the diode voltage drop (0.6V in the case of the BAV99’s and the 64-04’s they use here).  The 7T and 7R (7 volts for Transmit or Receive) used for biasing the diode switches… and the PRE_ON and PRE_OFF voltages (again, 7 volts) to pass or block the  preamp Q4.

Argosy II approach to switching using PIN diodes

Jerry, KE7ER  found  a similar circuit for T/R switching (and SWR metering) in a  manual for the Argosy   (see page 51):
http://www.tentec.com/wp-content/uploads/2016/05/Argosy_II_Model_525_Manualf933.pdf

The full transmit RF waveform goes through C1, diode D4 ensures the bottom of that waveform is at DC ground, diode D3 then rectifies it to create a DC voltage across C2 that is equal to the peak-to-peak voltage of the transmitted RF.  The notes then say that this relatively high DC voltage available during transmit is used to reverse bias diodes D1 and D2 such that  no transmit signal goes through them to the RCV connector (which then goes into the receiver front end).

Note that the PIN diodes at D1,D2 are called out as 1n4007’s.
And that this transceiver works up through 30MHz.

Another thing to note, the final remains connected to the antenna during receive, shunting some of the receive energy to ground.  Some of the other T/R switches use additional PIN diodes to isolate the final
from the antenna during receive.

Cheap alternative to PIN diodes

Tom, WB6B dug up an old article by  Don Brown KD5NDB that relates to 1N4000 series diodes and their potential for use as a cheap PIN diode.

The 1n4000 series of diodes are general purpose rectifier diodes designed for low frequency use primarily 60 Hz power supplies. The construction is the same for the series except the 1n4007. The lower voltage diodes are basic PN junctions and would not work as a RF switch. The 1n4007 however has an extra intrinsic (undoped) layer forming the P-I-N junction. This is to get the 1Kv PIV rating but it also allows the 1n4007 to work as a RF switch like a true PIN diode.

The RF characteristics are not specified on this diode because it is not designed to do this type of work it just happened to work out that way and they are very cheap. True PIN diodes work better than the 1n4007 but are more expensive and not as readily available. Elecraft has designed the RF switching to work with the 1n4007 and making substations of different diodes may not work. Other 1n4000 series definitely do not have the PIN structure so they will not work.

PIN diodes are selected because they CAN’T switch at RF frequencies

Farhan VU2ESE waded in to clear up some confusion … The PIN diodes that are used for T/R are the ones that CANNOT switch at RF frequencies. That’s precisely why they are used.

An RF charge across the diode travels through precisely because the junction cannot switch on and off so rapidly and hence it remains either on or off. A PIN diode is like that, it can handle large currents, but it cannot change the current fast enough. That’s why for switching 100 watts of RF, you don’t need a few amps of bias current, a few milliamps will do.
There are ways of switching T/R with even 1N4148s (for QRP work). W7ZOI has, as usual, been there and done that. Read this paper to understand the concept : http://w7zoi.net/tr-qrp.pdf

ElectronicAntenna Switching” by Wes Hayward

This Wes Hayward article  could be useful to those intrepid experimenters looking to use PIN diode switching”

 

W2AEW video

Jim KH6SKY drew attention to  W2AEW’s video on PIN diode switching for a good intro to the subject.  Using the simple test setup in this video you could check the suitability of the 1n4007s for this purpose.  Interesting that the turn on characteristic of the PIN diodes is so strongly affected by frequency.

https://www.youtube.com/watch?v=XpYsCM_Wf50

Reference

TX IMD measurements for a v5 uBITx

Doug K4DSP just finished measuring the two-tone TX IMD on his v5 µBITx. These are 3rd order products, and they were measured relative to either tone. Since the ARRL states their measurements relative to PEP I have included that as well, for those who sleep better at night secure in the belief that their radio is clean 🙂

This is at 10W PEP using 700 and 1900 Hz tones. Doug’s radio puts out 10W from 80 through 20 meters, and falls off to 5W on 10M:

80m -25.5 dBc (-31.5 dB PEP)
60m -22.5 dBc (-28.5 dB PEP)
40m -22.0 dBc (-28.0 dB PEP)
20m -24.5 dBc (-30.5 dB PEP)
17m -21.0 dBc (-27.0 dB PEP)
12m -25.5 dBc (-31.5 dB PEP)
10m -22.0 dBc (-28.0 dB PEP)

As Doug’s flight instructor used to say after one of his landings, “I’ve seen worse, but I’ve seen a lot better.” This is probably not atypical of IRF510s.

Reference

Powering a larger Nextion screen from the raduino

If your larger (4.3″ or greater) Nextion display is flashing, you are probably overloading your Raduino 5v power supply.  This is because the Nextion does draw quite a bit of current.

Mark AJ6CU found a 7805 with a higher rating on Amazon (maybe 1.5A?). He mounted it on a heat sink attached to the rear panel (using the rear panel as a large heat sink) with a small perf board (to mount the appropriate capacitors).  He then brought in a set of 5V wires to replace the 7805 on the one on the Raduino.  This could be a helpful idea for those of you installing Nextion display units.

MVS Sarma suggested using a 78T05 as a replacement to the 7805. This is  a 3amp TO220 device and available very cheaply .   Managing the TO3  is little dìfferent compared to the TO220 on the 7805.
Reference

Fan cowling

Mark AJ6CU has made a 3D template for a fan cowling for your µBITx. The 3D template for the fan shroud can be found on thingiverse here:

https://www.thingiverse.com/thing:3790450

It basically bolts onto the 80mm fan at the rear of the case (you might recognize the “tan” of a Noctua fan — much quieter than the one supplied). It sits on the uBitx motherboard with two slots straddling the heat sinks.

Marks notes that he has not powered on his µBITx yet, but suspects it will keep things nice and cool even in digital modes. This was designed with Fusion 360. There have been several other suggestions for adding ducts for cooling some of the hotter spots in our radios.

I was inspired in this effort by the work by another cooling shroud for the “shorter” of Sunil’s cases. See:

https://www.thingiverse.com/thing:3360539

Reference

Removing the detent in a 100PPR optical encoder

This optical encoder (widely available on eBay or Aliexpress in black or silver) has been used by some constructors as a replacement to the standard mechanical encoder supplied with the µBITx kit.   It is a 100ppr encoder (whereas the one supplied with the µBITx is 24PPR) so may not work perfectly with either the default firmware supplied by HF Signals or Ian Lee KD8CEC firmware (i.e. you may need to experiment with the code for generating the VFO).

With the detent mechanism removed to allow free turning the encoder gives a very smooth tuning action.   With the encoder able to spin freely the protruding crank handle will always come to rest in the down position so it too has to be removed.

The main complaint with these encoders is the detent feature.  To remove the detent, here are the instructions from Robert GM4CID:

Remove the knob handle, then, using a heat gun or hair dryer heat the silver knob insert to soften the adhesive and carefully pry off that silver insert to reveal retaining screws that can be removed. The mechanism will now come apart and you can remove the detent. Replace everything but not the handle.

Reference