I found some more information about the app and its usage in NVIS communications:

https://nvis.club/en/hf-proxys/hfpager/android

According to an article from around 2000 I found in a periodical of the U.S. Signal Corps the Soviets were masters of HF NVIS communication due to their extensive landscape and lack of fixed radio network infrastructure. They even had specially designed NVIS antennas on military vehicles.

I'll test with my K2, first with speaker/Mike and pushing PTT. I currently don't have an interface for the K2. I'll probably design something passive, without the need of any power requirements.

Alexej RA3TLB just answered me that it is possible to use the HF Pager app using microphones and speaker but that the quality of communication can be worse in comparison to using an interface. The latter is of course something to be expected.

I had the same issue that I couldn't find the HF Pager app by searching insider the Play Store app.

In his newest video RA3TLB shows a short sequence where he uses the HF pager app with an FT-817 during a backcountry hiking trip at time frame 8:35 minutes of the video. There is a cable attached to his smartphone, but it is most likely a powerbank, as it is not connected to the headphone jack of the phone. There is a nice old full-metal soviet microphone next to FT-817 and the smartphone. So the chance is good he is simply using micro/speaker with the app and not a complicated setup with a dedicated interface:

https://www.youtube.com/watch?v=B9cjkbJ9oL8&t=13s

Too bad my kowledge of Russian is not good enough to contact him on his vKontakte group. I don't think he speaks English as he shows only QSO in Russian in his videos. I asked him in the comment section of the video about the app. I used Google Translate.  I am waiting for an answer.

Maybe we could try on 40m from F to DL (Frankfurt region). I have an Elecraft K2 with no digital connection box so far so I would have to use microphone/speaker. I can only operate HF portable in the field with end-fed antennas and 1o Watts. Though QRP from portable to portable might be challenging ond require good condx.

Videos about Syria in which Hytera handhelds can be clearly seen are in the Youtube channels of ANNA News, which has journalists embedded in Syrian army units and in R&U Videos, which produces English language captions for some of ANNA News Videos.

Of course these channels are not neutral, there are on one side of the conflict, but that is certainly not the topic of this board.

Concerning the Venezuela I haven't found those articles again as Google does not promote them, but they had a photograph of Venezuelan officers sitting in a hangar at a table with DM-1801/GD-77 in a protective pouch and the article did quote Venezuelan government sources saying use of Motorola XPR3500 by the invaders would indicate CIA connection.

A friend of mine has a Motorola DMR handheld. So is he CIA too?  ;-)

In a crisis situation I would use encryption too, but so far I haven't experimented with encryption. Would be interesting to know if the different radio brands  are still compatible with encryption.

Watching videos about global political conflicts, it seems that DMR radios are widely used by combatants, which is interesting.

In Syria the government forces uses Hytera radios, the Russian armed forces often use Baofeng RD-5R. I guess they use their own repeaters. The insurgents in Idlib province also prefer Hytera, though the government claims that NATO made encrypted communications equipment is also used.

In Venezuela the government forces use Baofeng DM-1801/GD-77, whereas the U.S. sponsored invaders recently preferred Motorola XRP3500, according to Venezuelan government sources.

So DMR radios should also be very useful in SHTF situations, especially in closed user groups with encryption (I have not used encryption so far, as it is illegal for Hams).

Best regards
Dieter

As I agree with Gil, that having to haul around a notebook, a digital mode interface, the TRX and lots of battery power is very inconvenient in a SHTF situation, I have found something that could be attractive, if it works properly:

There is an Android app made by a russian ham called "HF Pager" or "КВ пейжер" that allows short messages like text or GPS positions (with WhatsApp like functionality like Goggle Maps support) using only an HF transceiver and a smartphone. According to one YouTube video it seems to be sufficient to hold the TRX microphone to the speaker of the smartphone and the smartphone micro to the TRX speaker, as the transmit tones are in the SSB audio channel range. It should also work on FM and even C4FM. The only downside is that the price of the app is somewhat steep with 10 Euros.

Nonetheless I like to experiment with it.

Here is a video on this topic (please excuse the bad quality and the horrible music in the video, it is not my video):

https://www.youtube.com/watch?v=biAKjvsxUMU&t=780s

Here is another video in which they use a specially made TRX for this app (though it will work with any TRX):

https://www.youtube.com/watch?v=Sji85hL2tuc

The last video is by RA3TLB who BTW has an excellent Youtube channel (I use autotranslate closed captions because my russian is too bad). Apart from Gil's and OH8STN's channels it is one of my favorite Ham Radio related channels.

Best regards
Dieter