My combination *Rxxxx*/Chinese Up Tech (tr)uSDX

[EI3HIB]

Hi all,

Just an update on my experience with the (tr)uSDX thus far - as you guys may know, I damaged my *Rxxxx* main board, then ordered a completed radio from the approved Chinese seller - and due to that working so well, I ordered the kit version from China afterwards.

When I got the Chinese kit, I just built the main board and combined it with with the *Rxxxx* RF board I had previously completed. On doing this, I was getting reasonable results: 5W on 80m and around 3W on the other bands, or more accurately, somewhere between 2.7-2.9W.

Today I followed Manuel's excellent Youtube video on tweaking the RF board, to check that the second harmonics were properly suppressed and to see if I could get a little bit more power from the *Rxxxx* board.

And I think it worked out pretty well - these measurements were made at 13.1 volts into a dummy load:

20M 4.93W - 85% Efficiency
30M 4.14W - 84% Efficiency
40M 4.39W - 73% Efficiency
60M 4.27W - 68% Efficiency
80M 5.64W - 62% Efficiency

Of note is the efficiency dropping off as the bands get lower - it seems as though the more turns around the toroid, the larger the discrepancy with the expected result becomes.

As the efficiency efficiency is higher below the 60 & 80m bands, I'm tempted to take another turn off the 60 & 80 toroids, but will first see if I can space the turns out a little bit more.

But all in all, I'm very happy with the results so far and I've learned quite a lot in the process.

The only issue with this combo (tr)uSDX is CAT control - I've updated the firmware to 2.00i and it just does not accept any CAT connection at all - the relays click and then the radio starts behaving strangely. My other (tr)uSDX is running 2.00h firmware and works reliably with fldigi and while I don't think the problem is firmware related, I'm not brave enough to test it

So, I'll probably be checking the board with a magnifying glass tomorrow to see if I can spot any possible issues.

Anyway, I've now got two radios that work pretty well - I've learned quite a lot in the process too.

Some little random things that I have found:

I generally use the radio with headphones - I find that using a small patch cable with a built in volume control dial has made the listening experience a lot nicer, it can take away some of the audio hiss and also allow for easier and more granular control of the volume.

Using higher impedance headphones (80 ohm) also tend to sound nicer to my ears than something like 20 ohm, but your mileage may vary.

I bought a cheap little Sabrent USB-C soundcard that clips into my Android phone and allows for easy sending and decoding of digital signals using Andflmsg. Vox works fine, but I'd recommend initially using another radio to monitor your outgoing signal so you know you're not overdriving the truSDX and sending out a distorted signal - after that you'll know what volume level to use.

Right angle connectors, be they BNC, 3.5mm headphone jacks, or DC leads generally seem to be kinder to radios.

Anyway, sorry for the long post - as ever, Manuel and Guido - thanks for creating this amazing little radio.

72,
Dave

[John]

I'm curious what the efficiency numbers were for each band before you tuned them.

[EI3HIB]

Hi John,

Unfortunately I didn't save all the pre-change figures, I just keyed them into a document but didn't save it.

But I did scrawl 60m & 40m down on a page, for 40m it was 67.87% with 3.2W out and after taking a turn off both of the 40m toroids this went to 73.2% and 4.39W out.

On 60m my readings were 67.86% and 3.8W out. Just checking this again this morning after some further adjustment, it looks like it's now 78.42% and 5.95W out.

20 & 30M bands both had very good efficiency (circa 80%) and I just changed the toroids responsible for the harmonic filtering, one turn off 20M and just a simple spacing adjustment on the 30M toroid. Both are now above 80% efficiency.

I only adjusted the harmonic suppression toroid on 80M and efficiency seemed to stay roughly the same, it's still low (~61%) after some tinkering this morning, so I think I might try taking a turn off the other toroid later.

I used a Nano VNA for the filter adjustments, exactly as Manuel described - if I had just taken a turn off the harmonic filters without using it, I could have introduced more problems than I solved, so it really helps to have a VNA.

Hope this helps,
Dave

[SP9TKW]

And I think it worked out pretty well - these measurements were made at 13.1 volts into a dummy load:

20M 4.93W - 85% Efficiency
30M 4.14W - 84% Efficiency
40M 4.39W - 73% Efficiency
60M 4.27W - 68% Efficiency
80M 5.64W - 62% Efficiency

Dave,

So these results are with *Rxxxx* RF board and Chineese main board from the kit. Apart from adjusting windings on LPF filter did you change any other components on *Rxxxx* RF board?

Which batch did you receive from *Rxxxx*, 1st, 2nd or maybe 3rd?

73 Marek

[DL1GKC]

A few days ago *Rxxxx* published a document on their website addressing all the issues with their kits.

As to efficiency, all trials so far for finding the cause point to the RF board. Given your findings with the hybrid sandwich, this could mean that it might worth looking at the *Rxxxx* main board.

[EI3HIB]

Dave,

So these results are with *Rxxxx* RF board and Chineese main board from the kit. Apart from adjusting windings on LPF filter did you change any other components on *Rxxxx* RF board?

Which batch did you receive from *Rxxxx*, 1st, 2nd or maybe 3rd?

73 Marek

Hi Marek,

This was the first kit - no changes on my side apart from adjusting the windings on the toroids, I'm actually getting a little bit more power on some bands with this than the pre-made Chinese version I haven't opened to adjust yet.

One thing that I have noted is that the power/efficiency reported on the (tr)uSDX when testing with my 50ohm dummy load, can be less than using a tuned antenna on the air - I guess it's something to do with how the E class amplifer works.

73,
Dave