## Designing L and T antenna tuners for HF on the Smith chart

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.

## Why you should choose a lowpass configuration on your L antenna tuner

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.
http://k6jca.blogspot.no/2015/04/notes-on-antenna-tuners-t-network-part-1.html

## Repeaterlist for Oslo area, Norway (repeaterliste Oslo området)

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.

repeaterliste_eksport_XLS_XLS_sortert

## How to do export and import of Excel files with CSV firmat in Chirp

• Program a couple of memory channels in your radio (in my case Icom Ic-2725) from the RADIO menus
• Connect chirp to the radio
• Export from Chirp to a CSV file
• Study this CSV file and use it as a template
• Copy paste frequency and ctcss and offset info ++ from ANOTHER XLS file to the CSV file you made above!
• Save as CSV from Excel (this is now your frequency list to import to the radio)
• Check with Notepad ++ that there is COMMA (not semicolon) separation saved when you save as CSV from Excel. If this is not the case, go to regional settings / additional and set list separator as , (as opposed to ;). Start and stop Exel and a reboot wont hurt to make the settings take effect
• Now you import this CSV list into Chirp
• If you get error message that Chirp cant convert floating point in the tone settings, make sure to format EVERYTHING in your Excel sheet as GENERAL (not text, not number)

## MD-390 DMR UHF radio. Modified firmware.

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

## Norwegian repeaterlist / Norsk repeaterliste (unofficial / uoffisiell)

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

## Tytera TYT-390 GPS setup

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.

## CAT / RS232 / CW interface (FTDI, MAX232, 5V controllable FETs)

I made a CAT and CW interface from readily available components. Of course it is possible to buy a microham interface or simular. However, I wanted no USB soundcard functionality and Xp, Win 10, Linux compatibility without having to install drivers. A native FTDI chip from SF will do the job nicely. The FTDI chip has 5V TTL out and the true RS232 has +-1 12V signal levels. Therefore I pressed a MAX232 board that I designed approx 10 years ago and was laying in the junkobox into service. 5V TTL into and out from the MAX232 chip into the FTDI chip.
I used some “5V TTL FETs” for switching the CW signal. The RTS / CTS signals from the FTDI interface can drive these fets directly. I needed to invert the signal so that the CW keying is off by default. So since I had two of the 5V TTL FETs laying in the junkbox, I used one to invert and one to drive the CW key output. On the picture to the left the fets can be seen.
Here the quick and dirty prototype can be seen. The old RS232 converter board to the left, the switching FETs to the right and the FTDI board below.

## New front end for use of the Red Pitaya in SDR applications

The Red Pitaya SDR board is based on the Xilinx Zync SOC and has 14 bit external A/D converters. However, for SDR usage on the HF bands from 0.1-30 MHz (and for that matter up to 50 MHz) the Red Pitaya is a bit “deaf” in the stock configuration. I have made a broadband amplifier that has a fairly high gain and very good IIP3 properties. Below I have posed some pictures of the prototype amplifier.

This is the prototype amplifier. I inserted a ferrite ring on the input lead to roll off the VHF / UHF sensitivity to reduce problems with nearby broadcasters etc. There is a also a PI network attenuator on the ouput and I have inserted a couple of beads in that as well to roll of the outpu response when frequency increases. The other components in the lower part is a input pi attenuator I used when I did some VNA frequency response measurements. This as well as the RCA plus is not used (RCA plugs are surprisingly good for low level RF signal routing in the HF bands and nice to use in the lab).  I used a more professional attenuator with a large attenuation range and flat response to determine the proper attenuation level after the preamp into the Red Pitaya. Reducing gain after the first amplifier has very little effect on the noise figure. Reducing it before the first amplifier directly adds to the noise figure. I added some protection diodes over the input to reduce the risk of strong RF signals or static voltage build up damaging the input. Below I am measuring the response of the attenuator with the DG8SAQ VNA. It was flat from 0-1,3 GHz.