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U3S & 10W HF Amp Combo on 160m!

 

The penny dropped when I realized I could shuffle some QRP Labs gear around and take advantage these winter months running WSPR on 160m.
To that end...


As you can see I'm running 10W with this current set up. I have a 6dB resistive pad (I think that's the value) between the U3S and the 10W amp. The pad is on the square green perf-board in the photos. The antenna is a long end-fed random wire with 9:1 unun.

The U3S/10W HF Amp combo at the bottom is a rig I've posted details about here some time ago (pre-QDX/QMX era). I originally built it up to use it on 8 meters. I never tried getting an experimenter's permit. I've used it on 6m and most recently on 10m & 12m.

Here's some views with the lid off:
Front to back:

Back to front:

View of the 10W HF Amp's heatsink mounting.


I'm also excited to be using the LDG IT-100 tuner that's been sidelined since I got a LDG AT-200Pro II tuner to use with my "big rig." It's not an auto-tuner but seems to work well with the U3S/amp combo since they are set up as a single-band transmitter.

IMO winding a 160m LPF on blue Mix-1 cores is a much better solution than using the stock Mix-2 red ones.

I've only had it briefly on the air earlier today and looking forward to how this combo performs. 

Happy New Year!!

--Al
WD4AH
 

Neat! 
So TX only, I assume? Do you not have to worry about t/r switching the 10W amp, then? 

I've thought about getting the 10W amp and running it at 20W... but finding a convenient T/R switch setup has been more of a pain than I'd have expected. 

-Nate
N8BTR
 

On Sat, Dec 30, 2023 at 05:39 PM, <natereik@...> wrote:
Neat! 
So TX only, I assume? Do you not have to worry about t/r switching the 10W amp, then? 
Right, the U3S is Tx only and very flexible in its applications!

--Al
 

Al, coming back to thoughts of doing a 160m WSPR beacon of my own, wondering if I can learn a bit about the oddities of 160m propagation....
How do you trigger the amp on TX? RF Sensing circuit? Or is there some sort of PTT from the U3S?
 
-Nate 
N8BTR
 

The u3s can do ptt via the key pin, see the operating manual.
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.
 

On Mon, Dec 30, 2024 at 03:46 AM, M0RON wrote:
The u3s can do ptt via the key pin, see the operating manual.
Ahh, interesting, thanks! Looking at the assembly manual, it mentions that pin goes high at TX... looks like one would have to create a switching circuit to trigger a PA off of it....something to ponder.  
 
I see QRP-Builder has created a PCB for an RF Sensing T/R switch, LPF and such for the QRP-Labs 10W amp as a way to handle this too: https://qrpbuilder.com/amplifier-ant-lpf-adapter
 
-Nate
N8BTR
 

On Mon, Dec 30, 2024 at 10:48 AM, Nate Reik wrote:
I see QRP-Builder has created a PCB for an RF Sensing T/R switch, LPF and such for the QRP-Labs 10W amp as a way to handle this too
An RF-sensed switching system will ALWAYS hot-switch your system, as it does not switch until RF drive from the radio is already present.  This will present a severe mismatch (essentially open circuit at full RF power) to your radio during the switching interval.  
For me, a wired T/R system is the only way to go.  
73, Don N2VGU
 

On 30/12/2024 15:48, Nate Reik via groups.io wrote:
Looking at the assembly manual,
And the Operating manual tells all.
"
PTT Delay
050
This feature allows the “Key” output signal from the Ultimate3S kit to act as a PTT signal for keying a
Power Amplifier in advance of the commencement of the transmission. The parameter specifies, in
milliseconds, the delay between the PTT output going high (5V) and the start of the transmission. Note that
the actual timing of the start of the transmission is not delayed – it is still accurate according to the protocol
of whatever mode you are transmitting. The PTT signal becomes active in advance of the transmission.
Correspondingly at the end of the transmission the same delay is applied before deactivating the PTT
signal."

For this reason RF sensing is really not to be recommended for switching PAs.

73 Alan G4ZFQ

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