Yesterday, I got the boards for the latest revision of the layout (2017-10-24), as now available via OSH Park. I just assembled a new prototype and can confirm it works like a charm. It works best with 2.5 - 5 W, but can be calibrated to also work with 1 W. The only downside of the simple design is that the calibration is accurate only for the same power level (or at least within a narrow power range).
As for winding the toroid, use enameled wire no thicker than 0.22 mm for the secondary winding, otherwise the 25 turns won’t fit well. Make sure you only occupy ca 270 degrees of the core, otherwise directivity might suffer.
When ordering the parts, it may make sense to add a few 100 Ohm / 2 W resistors, for they make for nice dummy loads for various SWR levels.
I hope this tiny SWR indicator will turn out useful for many of you and will save lots of final transistors.
As for the ease of assembly: The board is pretty small and tightly packed with components on both sides. It should not be your first SMD soldering project. But then again, all parts are 0805 sizes and the pads optimized for hand-soldering. Take your time and a good magnifying glass
Another (slightly customized) TinySWR is ready and works as expected - not as a SWR Meter but as a SWR and RF Indicator - excactly as promised by the circuit developer.
Many thanks again, Martin@DK3IT.
My TinySWR should especially draw my attention if there is a real problem with the home made resonant antenna (trapped/linked EFHW) used together with the Mountain Topper Transceivers. That’s why I used different colored LEDs - the red LED starts to glow at antenna loads of: infinity, short circuit, <= 20R and >= 125R (SWR of approx. 2.5). The yellow LED starts to glow at <= 33R and >= 75R (SWR of approx. 1.5).
Modifications made (all the LEDs are low current types from Knightbright):
R4: 680R
RF1, SWR1: green LED (1.9V)
SWR2: yellow LED (1.85V)
SWR3: super red LED (1.7V)
The filter housing FG1B 37x20x20 mm used is very tight …
Hi Martin,
Here is your tiny SWR meter installed in one of my MTR-5B SOTA radios. The LEDs are a little dim but bright enough. All that is needed are assurances that the radio and the antenna are working properly, and this does it!
Thanks & 73,
John K1JD
Santa Fe, NM
Hi John,
thanks for the feedback and picture! As for the brightness of the LEDs: It will be better if you operate full 5 W from 12V. You can use my switchable 6-9-12 V DC-DC boost converter with input and output filters for that purpose:
Also, I am working on a fully digital version of the SWR meter with a tiny Stockton coupler and an ATTiny in SMD. It will be only slightly bigger than the current version but actually measure the SWR independent of the power level. But this is work in progress, will likely take until 2018 to complete the firmware etc.
Dear Fred, sorry for my slow reaction: I do not have the exact types from Barry’s list at hand, but basically most 2 mA versions should work fine, and even some standard bulk 3mm LEDs will do. Really critical is the OSRAM SMD LED on the PCB, because most other SMD LEDs in red have a significantly higher forward voltage.
for the secondary winding, use ca. 30 cm of 0.2 mm enameled wire 0.2 mm. For the primary, I now recommend using simple insulated wire, because burning of the insulation from such a short piece of magnet wire with precision is a bit challenging.
Thanks… Martin… visiting the company R+D lab this week (I work from home)… so its a good time to pick up a couple of items for home electronics projects… and that’s something encouraged by the company I work for… they like us to have home electronics projects!
I couple this with an EFHW tuner built into a dental floss case. Also visible are the two posts which serve as the paddle of a built-in touch keyer. I log using a small card clipped to the back of the radio. In this way sitting down (usually not a good idea) isn’t necessary. A tethered spacepen (stores in an attached soda straw) serves as writing instrument.
The Mouser list has 3 components that are out of stock with long lead times. Could you have a look at that list and suggest replacement components if possible. I have the boards, just need the components.
at the top right of the screen.
