QMX FT8 and SSTV via mobile-phone

Equipment
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I have been planning for a while to do a “multi mode challenge” during one of my summit camps…CW SSB, FM, DV, SSTV and FT8. So today i played with my QMX+ to see if i could run FT8 from an android ‘phone.

I was amazed to find that connecting a usbc cable from ‘phone to QMX, using the Android app FT8TW (available in the standard Android app store) i could easily run FT8. See picture.

FT8TW is brilliant…auto logging to qrz, mapping of contacts and an excellent spectrum display.

Using the same direct usbc connection i have also successfully sent and received SSTV using DroidSSTV.

It all looks hopeful for a multi mode activation. I just wanted to share this as I am surprised how well the QMX works when connected to a mobile phone

The picture shows the system running on a very cheap (less than GBP100) Android tablet, so i could use my phone to take the photo

My phone is an inexpensive Ulephone Armor…so nothing special

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Check out my thread The KISS Guide to SSTV (Keep It Simple Stupid).

It seems we are trying to do similar things.

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Well that didn’t go as hoped…i am writing this from inside ny tent on Seatallan G/LD-025. I have just had a session of FT8, using my android phone connected to my QMX

I made about 6 contacts and then the BS170 transistors failed in the QMX. I had an SWR of about 2 from my EFHW on 15m…so probably my fault.

Could have been worse, for a couple of mins after blowing the finals the QMX refused to power on…I’m guessing it has some sort of temperature sense.

Stocking to CW in future.

Bag of transistors already on order from CPC, and now i am making a hot chocolate to commiserate. At least i still have a couple of 2m radios with me for the rest of the night.

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One of the BS170 transistors was already dead when my kit arrived. I ordered a batch of replacements; they’re slightly larger than the originals, but they work perfectly.

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Whan replacing the BS170’s give them a good blob of heatsink compound on both sides before tightening down.

Good brands (eh ONSemi) are more robust than unbranded ones

Rick

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Sure enough, a burn mark on the area of the pcb after i snipped out a bs170 that was measuring as shorted.

Distinctive nasty smell in the radio also, most intense when sniffing the transistor i have removed, an even better method of detecting a fault.

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Not sure if heatsink compound will do much, given these are in a plastic package?

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Most devices like these tend to use the leads for heat sinking rather than the body. Helping heatsink the body wont do any harm though.

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So this is what they meant when they said FT8 is killing amateur radio…

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According to a chap in the Radcom letters page it’s because FT8 works over a landline …

Funny, I don’t have a landline but it still seems to work

Rick

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So do voice and image modes though.

Were you running full power on FT8? On most of my rigs I try to keep power below 50% of the max rating to stop overheating.

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You should see what it done to my STC Executel… :sob:

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I was running full power, but the QMX is intended for this style of operation.

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Daft question - did you have SWR protection turned off? On my QMX it is lightning fast at locking out the TX when it detects high SWR.

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Yes, SWR protection was turned on, it was set to 3…SWR was a little over 2 at the time the finals went bad, probably as high as 2.5, so it was my own fault.

I have a Z-match that I bought from Kanga, but I don’t find it to be very effective, and was not using it at the time.

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There are suggestions in the QRP Labs groups.io that the BS170 failures in the QDX are caused by voltage spikes rather than overheating. The source of the spikes is from the inductor in the power supply to the final amp. There are two suggested solutions; either a diode (IN4148) across the inductor to quench switching transients, or two 47 V Zener diodes, one across each pair of BS170s to limit the spikes. You might want to investigate if one of these ideas might help your QMX.

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It should be no problem for QMX because of envelope shaping. Because of this there are no such spikes. The QDX has no PA voltage regulation - no envelope shaping.

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Combination of full voltage (or a bit more), bad SWR and 100% carrier over a long time are dangerous.

@M0MZB: Sometimes one or more BS170 are broken the driver IC503 is affected. Please read here. (Maybe you would need an account for the QRP Labs forum.)

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You are absolutely right, i had to replace ic503 in addition to the bs170s. My QMX is now fully working again.. and i have 25 spare ic503 and over 100 apare bs170, so well prepared for future issues

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With so many spares they’ll probably never fail and need replacing ever again.

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I’ve had a bag of BS170s for a decade plus and never had to use one for a repair.

I once blew two 1A fuses in succession using my MTR-2B - it turned out to be a worn RCA socket and the antenna connection was intermittent. The MTR has been totally fine since I replaced the socket.

73, Colin

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