Many thanks to Pedro (PP2PB), who shares the following article about his portable field radio kit, which will be featured on our Field Kit Gallery page.
Pedro’s (tr)uSDX Compact and Affordable Field Kit
by Pedro (PP2PB)
Here’s my new kit.
This kit weighs just under 1,2kg and has phone and CW operations in mind. I might add some cables for digital modes, but I haven’t tested this rig with digital modes, just yet.
The (tr)uSDX was bought assembled with the LO bands RF board, and I assembled the HI RF board myself. I got Adam’s alternative case printed out for easy band switching and did a minor mod to the RF boards soldering a Zener diode reverse polarized as a high SWR protection.
I also added a USB port to the battery pack because the (tr)uSDX can operate with around 0,5W directly from USB and that’s a great way to test for SWR and fine tune the antenna without stressing the finals.
The manual antenna coupler is also my creation and even though it doesn’t appear on the exploded view it does fit in there no problem (it was added after I took the pictures).
Gear List:
- Small Molle ag
- (tr)uSDX with both Hi and Lo bands RF boards
- Alternative case by Adam K6ARK for easy RF board switching
- RG316 2 meters
- 27MHz Telescopic antenna works on 10m –
- Small counterpoise wire
- Homemade 49:1 UNUN made with FT82-43 toroid
- 3D Printed CW Paddles for the Quansheng K5 (needs minor modification to work on regular radios)
- Male to female P2 3.5mm cable
- Homemade 6W dummy load made inside a 90º BNC male connector (2x 100ohms 3W resistors in parallel) – great cheap insurance with these simple rigs.
- Small USB Cable
- Generic Earbuds
- (tr)uSDX power cable with powerpoles
- 20m of 24AWG wire for the primary antenna with some generic red paracord for setting it up
- Charger for the battery pack with powerpoles
- Homemade battery pack using a 4S battery holder with 3x 18650 cells and a BMS board, and the extra space for a step down DC converter with USB out and the 12V powerpoles
- Homemade manual antenna coupler
72 DE PP2PB
I think this is a brilliant kit, Pedro. I love your homebrew trans-match!
I especially appreciate the focus on affordability in many of the (tr)uSDX field kits. Your kit, I imagine, is pretty accessible to everyone!
Thank you for sharing it with us!
72,
Thomas
K4SWL
I agree with a Thomas, great kit. I would appreciate more info on the antenna coupler as well as the placement of the Zener. Well done. //Al k7aoz
Hey Al, thanks for the comment.
The mod is a 47V 1 Watt Zener diode connected between BS170 PA stack Drain and Ground. Zener diode cathode is connected to BS170 drain and Anode is connected to ground. But I did it in the pins that connect the two boards, simply placing the diode on the pins “RF” and “GD” as they are labeled. If you need more info you may email me (qrz.com).
The antenna coupler is a pi match made with two am/fm variable capacitors using the 0-360pF section of each. The inductor was salvaged from an old pc power supply board (if I remember it correctly) and is about 400nH (measured with a Nano VNA), and I made a tap in the middle of it to have two inductance values selectable by a junk box mini switch (makes a sizable difference in range).
It has been tested many times with up to 100W SSB with no issues whatsoever. And digital I believe I was able to get up to 40W (maybe a bit more) before the swr went all over the place (either capacitor arching or the little ferrite bead in the inductor being overloaded). I didn’t follow any specific project, I just wanted a pi match (for the broad range) and made one as compact as I could with what I had at hand.
Again, if you want any more info or pictures feel free to email me.
72 DE PP2PB