The Smith chart is a tool used a lot by professional RF engineers for solving transmission line stub matching problems and all sorts of quick calculations.
The Smith chart can also be used for quick back of the envelope L and T antenna tuner engineering calculations.
I have on the picture above plotted a T configuration antenna tuner with the first capacitor set to a so big value that it is shorted as seen by the RF voltage (large C – low |Z|). Then the configuration becomes a L tuner in practice with a shunt L followed by a series C when seen from the load in towards the generator.
I measured the Z in the shack end of the ladder line feeding my doublet antenna to be Z = (24.1 – j35) ohms at 14.200 MHz by a Vector Network analyzer. That can be plotted as a point in the lower part of the Smith chart (capacitive Z).
(1) Since we have now first an inductor (in the tuner to ground) as observed from the load towards the generator, we can use this inductance to move along a constant Conductance curve in the Y plane (upwards in the Z plane). The conductance is constant but the Susceptance varies. (We remember from the RF engineering classes at engineering school that Y = 1/Z – of course).
(2) Then we use a series capacitor to move down inside the 1.25:1 SWR circle. We dont have to hit the center because anything inside the inner 1.25:1 circle is good enough. (We move while the R part of R + jX is constant, while the X part is changing to become more negative. This means we move on a constant resistance circle in the Z plane).
Determination of component values can be done easily by hand in a tool like this while still retaining an intuitive understanding of what is going on.
Black magic! Especially with a digital smith Chart tool.
K6JCA has analyzed the needed components values for matching a load while moving on a constant reflection coefficient circle. The plot below shows that in case you select the high-pass configuration for your tuner, certain angles of the reflection coefficient will give you skyrocketing component values.
Component values for the highpass and lowpass configurations
Above you can see that the LsCp &CpLs configuration keeps the max component values quite flat. LsCp and CpLS are therefore the best engineering choices based on cost and realistic component values.
European Grid Locator map (western Europe). Credit to PA2HJS for making the map.
I have made a repeaterlist for the Oslo area in Norway. This list can be saved as CSV from Excel and is then after saving as CSV compatible with Chirp.
Make sure to check that the CSV files uses commas (,) as separators and NOT semicolon (;). This can be set in the meny you see below. Goto Start menu and type locale. Click the change date, time, number format.
Thanks to Alf LA2NTA for the data I used in this list. See another posting for the direct link to Alf’s list that is located in the cloud. My list here will not be frequently updated, but per April 2017 it should give a good starting point.
I updated my MD-390 with the modified firmware. This fw. gives among others, these new functions:
- Promiscuous mode. Listen to all voice groups on one timeslot. Even if you havent programmed the VG in a channel.
- See last heard on the display on all VGs on the time slot you have assigned to the channel regardless if you have enabled that VG
- VU meter for TX audio
- Updated contact list database
- Display dimming timer and intensity adjustable
- Lower beep audio on transmit not allowed etc
- List of last heard
- Channel info on display: tx freq, rx freq, timeslot, TG, sender ID, repeater ID etc
Alf LA2NTA has made an excellent repeaterlist covering norwegian repeater that are updated quite frequently.
Alf edits the document straight at Google Drive. You can check out the most updated version on this link: https://docs.google.com/spreadsheets/d/1tPHd2HDnkHOPJrQkDUpCRH00zhCIOoMiAMqaustzqsk/edit#gid=1
To set up GPS on the TYT-390, make an own contact with name GPS and call ID 5057
Then set up Destination ID: GPS under GPS settings. Set the interval to 60s or more. (Not too often as GPS packets take repeater capacity)
Now select “GPS system 1” under the channels you want GPS enabled on. I have made a set of channels with GPS on and a set of channels with GPS off.
In Brandmeister dashboard, go to Services/Self Care and select chinese radio. Check that your call and your name looks OK (you need an account at Brandmeister).
Then program your radio with the codeplug with the radio settings above.
Set your radio outside for several minutes to achieve GPS lock (can take quite some time).
You should see a globe symbol show up without the red ring (red ring means no GPS lock).
Then you can check aprs.fi for your callsign.