!!!!!!!! Edit (2024/04/11): !!!!!!!!!
Again I will have to rewrite everything because of new information.
In December 2023 Guohetec did a youtube live video where they revealed a few facts.
Dafydd, DJ0MZ has been in direct contact with Guohetec on WeChat and since March 2024 I created a small WeChat group with Dafydd and two Guohetec engineers where we get some more answers than in the WhatsApp group.
We all know that the original microphones delivered with the Q900 and the PMR-171 have a very low signal output that causes problems with modulation. Raising the mic gain only causes more noise level (maybe not on all devices).
This is what Guohetec told us:
– They removed the mic preamp since Q900 V3.
– It is their concept to talk loud and close to the mic to avoid surrounding noise getting through.
– They recommend the settings mic gain 50, TX bass -2 and TX trebble -8.
– they agree that a dynamic or amplified mic is needed if we don’t want to speak that close to the mic.
– After repeating to them that it is not ideal for most hams, they considered offering an amplified mic in the future.
Even with the recommended settings there are still problems with the SSB modulation.
But there are also reports of users having no problem with SSB modulation, with PMR-171 Q900 V3 and V4.
There is no way to say how many devices are affected, because people with working devices might not look for answers and join the community.
Since my last public video in January, I made 3 new videos that I kept as „not listed“ on Youtube, because Guohetec started listening.
After this video, they agreed that there is a distortion problem on low power mode (L, 5W) and that they will fix it.
Q900 SSB TX audio Quality compared to Yaesu FT 710
I did post this Video in the WhatsApp group.
In the PMR-171 Facebook group they are talking about waiting for the new fix. But it will probably be only for low power mode.
Then I got my hands on a PMR-171 sent to me by Matthias for testing. This PMR is worse that my Q900. And I had the idea to input some music instead of voice.
After the Video Guohetec agreed to do some more tests. At some points in the video the mic input goes over +8dB (AUD level meter). This is the max input. recommended is max 0dB to avoid distortion.
Q900 and PMR 171 SSB TX modulation test with music
After the last video they asked me if I could do the same test while using the USB interface input instead of the mic input. Done…
And I found another PMR-171 owner in my home town (Vittorio, DO1LVS). I got the chance to test his PMR as well in this video. And his Xiegu G90 in addition.
As you will hear and see, the two PMRs are different. The PMR from Vittorio is more similar to my Q900.
Q900 and 2x PMR 171 SSB TX modulation test with music
We are still waiting for an answer from Guohetec after the last video.
After the tests with music I really want to ask everybody who is satisfied with the modulation:
Are you really sure that there is no distortion?
And if you are, then I would really appreciate a recording with a good SNR. With a high noise level and a good mic you might not realize, that there is distortion. This information would also help in the discussion with Guohetec.
The gain setting does not work in NFM mode. But it does work in WFM mode. The only way right now is to use an amplified mic.
Guohetec told us, that NFM is not located in the SDR part of the radio. WFM is. That is the reason for the gain not working in NFM mode. If they can fix this or maybe adapt the WFM mode to make a new NFM mode in the firmware, I don’t know at this point.
Once more I will keep the old content online for now:
Edit (2023/11/30): after some more testing and feedbacks from the community I will have to rewrite this topic.
For now in short:
– The Guohetec mics don’t have enough audio output for the Q900. only an apmplified mic will help getting decent audio. This is my experience with the V4. (seems the same for PMR 171)
– NFM mic gain does not work on 3.3.2 also (probably all older versions). Guohetec made NFM TX wider on 3.4.1 trying to resolve the NFM issue. But now it uses more bandwidth. On 3.3.2. With amp mic still good audio. (PMR-171 with 3.4.2 also has not working mic gain on NFM and too much used bandwidth)
– SSB has a distortion issue on full power, if it exceeds 20W (limiter in the firmware). Workaraound for the Q900 V3 is to downgrade to 3.1.1 from QR20. See my download section for now. Downgarde on V4 not possible. (The distortion issue has been reported for the PMR-171)
– SSB low power alwas seems to have distortion. no known solution for that until now. Also apllies to the new 6m band with the Q900 V4. probably because the full 20W are not possible. (It also has been reported for the PMR-171)
– on all modes there is noise transmitted with higher gain and original Guohetec mics. (seems to apply to PMR-171 as well)
– The best way to know what mic and settings have the best result is testing yourself. I transmitted in a dummy load and received the signal with an antenna in the same room connected to a SDRplay device. If you have an USB sdr device or any other receiver, try to listen to your transmition on headphones or record it, if possible.
my recommendation is to use an amplified mic with gain or output adjustment, set the mic gain on the transceiver to minimum or close to it. For SSB adjust the mic output to a level, where the power meter does not exceed 20W to avoid distortion. This level should then also be fine for NFM TX.
these are my recordec tests:
https://youtu.be/aBqKUHt7svU SSB with different microphones
https://youtu.be/w7GAvoOnFLU WFM/NMF firmware 3.3.2 and 3.4.1 (Q900 V4)
https://youtu.be/B3Ii57L5o6Y SSB tests with sine wave audio input on low and high power
https://youtu.be/698vmm-fQZc Different test with firmware 3.4.4: SSB low power with sine wave audio input, NFM/WFM comparison…
https://youtu.be/on6JUua-JIc SSB TX audio tests with the PMR-171 (Original mic, 20W and 5 W)
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I will leave the old content for now, I just removed some of it that does not apply:
Solutions:
Guohetec suggests buying their new microphone.
https://www.guohedz.com/Hand-microphone
The keys on this microphone won’t work with the Q900. It is the microphone for the PMR-171 with a TRRS plug for the Q900.
It has a better signal level but still there have been reports of not solving the problem completely
Also recommended by Guohetec: turn compression “CMP” off in AF settings
I had very good results on 2m NFM and SSB with an amplified mic.
In the US you can try to find a Procomm amplified mic. It was reported to work well in the group.
I did build my own speaker mic with an electret capsule and amplifier. Audio on FM ist very good. SSB on VHF was also very good without distortion, when I reduced the output level on my amplified mic compared to the level needed for NFM because of the not working gain setting on the Q900. SSB on HF is good with an amplified only on full power not exceeding 20 W.
I did post a circuit diagram on groups.io. There you can see what components I used.
There are reports of drilling a bigger hole in the original mic for better audio. In addition to the bigger hole replacing the microphone capsule could also improve audio a little.
Edit (2023/10/25): I did drill some holes into the original mic. It is a little better, but I clearly recommend getting another mic.
And it looks like a higher mic gain setting is needed on FM than on SSB. That was mentioned in a youtube review and in the group. I can confirm that between for WFM. But I would recommend to test it anyway.
Remember that gain setting does not have an effect on NFM.
Edit (2023/10/25): I did a QSO on SSB 40m with the original mic with extra holes. The report was ok but not great.
If you want to use another mic than the ones from Guohetec, be aware that the pins in the manual of the Q900 are not correct. The MIC jack is TRRS. In the PMR-171 manual it is like this. It is called „PHONE“ on the PMR-171 but it is also a mic jack.
