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uSDX QRP Transceiver - First Impressions

This is the first of a series of articles and videos as I move to exploring HF radio. 

1- Getting a HF QRPradio the μSDX 10/15/17/20/30/40/60/80m 8 Band SDR All Mode HF SSB QRP Transceiver by N7DDC

2- Building a basic HF ATU - the Manual-Days-Antenna-Tuner

3- Building an automatic HF ATU - The ATU-100 (ATU-10) designed by N7DDC

I have just had the uSDX radio for a few hours and wanted to write down my first impressions, so here they are -

  • It is smaller than you think! 8cm w, 12cm d, 5cm h
  • The display and controls are excellent
  • The finish and internal construction are excellent.
  • On the digital encoder anti-clockwise is up and clockwise down, you soon get used to it.
  • It is VERY sensitive!
  • It doesn't lose settings when not powered
  • Mine came without an internal battery but it can be added for about 12 GBP. 


Okay, now for using it, the antenna connection is BNC so be sure to have an adaptor or rewire your antenna for best results, 5w doesn't go far.

The internal speaker is just ok, turning the volume above 10 can result in instability. I solved this by plugging an amplified external speaker into the front 3.5 mm headphone socket. Plugging stereo headphones or speakers in result in sound from the left channel only. Do not plug speakers in the back, it doesn't like it and buzzes and may damage it. I have more info on this later, it will accept a Kenwood /Boafeng style Mic/Speaker and indeed comes with a tiny one that is surprisingly good.

Tuning below 3.5Mhz results in a horrible noise, so forget it!

Using it without an ATU is not advised and can blow the PA stage. I have heard they the ATU-10 works okay with it but it costs around 80 GBP. I have plans to build a manual tuner elsewhere on this blog.

For SSB tuning work it is advisable to set the smallest frequency step to 1Khz, that doesn't mean you have to use it all the time.

Out of the box the audio filter is set to 'Full' setting it to 2400Hz gives much better SSB and when on CW mode try 500Hz.

Ensure that the two attenuators are set to 0 to start with unless you have strong local signals, ATT is the course one in dB, ATT2 is the fine adjustment from 0-16. 0 is strongest on both.

You can select S-meter, S-bar dBm or wpm-words per minute, I am guessing that is for CW training.

It will decode CW-Morse Code signals into text, I haven't had much luck with this so far.


1.1 Volume -1 to 13

1.2 Mode CW, LSB, USB, AM and FM (this is the only way to select AM-FM and they are not brilliant!) The mode button on the front alternates between LSB, USB and CW only.

1.3 Filter bandwidth for the mode you are in.

1.4 Band 6m/10m, doesn't appear to change anything as it won't receive anything over 40.0 Mhz.

1.5 tune rate, from 0.5kHz to 10Mhz, bit extreme! Just the same as pressing the digital encoder.

1.6 VFO Mode, A or B as shown on the left of the digital display. Works as 2 memories.

1.7 RIT allows receive and transmit frequencies to be separated, but it just says ON or OFF so not sure how to do this.

1.8 AGC Fast, Slow, Off. Fast seems optimum.

1.9 NR, Noise Reduction, each step is pretty extreme and reduces the overall volume, but it is useful.

1.10 ATT coarse attenuator 0 to -73dB

1.11 ATT2 fine attenuator 0 to 16

1.12 S-Meter setting, S, S-Bar, dBm, wpm (words per minute for morse)

2.1 CW Decoder on/off. Only works in CW mode so you can leave it on unless it gets annoying.

2.2 CW Tone - 600 or 700, I assume this is for Morse Code practice

2.4 Semi QSK - unsure about this, let me know

2.5 Keyer speed, 1 to 60 for Morse Code practice?

2.6 Keyer mode, straight, Iambic A, Iambic B. Morse guys will know this.

2.7 Keyer swap on or off. 

2.8 Practice on or off, for Morse Code practice.

2.9 Tone vol. Volume of practice tones. 16 to 0

3.1 VOX is voice operated TX

3.2-Noise gate sets the level of VOX activation.

3.3 TX Drive - 0 to 9 , default 4

3.4 TX Delay 0-255, yeah but what units?

4.1 CQ Interval 0 to 60, default 5. No idea!

4.2 CQ Message. Yeah but what for?

8.1 PA Bias min, 0 to 139 default 0

8.2 PA Bias Max, 0 to 244 default 140

8.3 Reference frequency 27000000. 

8.4 IQ Phase 0 to 180 default 90

10.1 Backlight ON or OFF, default ON

Okay let's receive stuff!

So having attached an antenna with BNC connector we are ready to receive. I am using and end fed long wire of around 15m (non-resonant) with a 49:1  balun

I will be making videos very soon!


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