Icom IC-2200H Adjustment Mode Jig

In order to adjust the power output of the IC-2200H transceiver it must come to "Adjustment Mode" and we need also the adjustment jig. The jig itself is made of 22K resistor connected to Pin7 and Pin2 of the RJ45 connector. When the jig is inserted to the microphone jack, "Adjustment Mode" can be initialized by holding the keys "SET" and "MONI" simultaneously while pressing "POWER ON"

The transceiver screen should look like this;

Adjustment items are displayed in the lower right corner of the LCD and these can be toggled by pressing the "BLANK OPT" or the "V/MHZ" keys. When the transceiver is on "Adjustment Mode" you can now remove the jig and reconnect the microphone. Please refer to the IC-2200H service manual for more details on the adjustment parameters. Note that the power output of the IC-2200H can be adjusted to 85W max by setting the PO parameter in the "Adjustment Mode". When done please perform a "Master Reset" to take effect the changes made on the transceiver.   ---73 de du1vss

Attachment: 2200H.pdf

Turnstile Antenna for FM Broadcast

Above photo is the hand drawn illustration of my own version of Turnstile antenna used for my fm broadcast test station. It is basically two dipoles feed using a 75 ohms phasing harness but intentionally one of the dipole is 90 degrees delayed from the other dipole in order to have a circular polarization. You may find my design differs from the usual turnstile antenna posted in the internet anyway, in my project the two open dipoles is known to have an input impedance of 75 ohms. Feeding the these dipoles using a 75 ohms phasing harness will not transform the impedance therefore two 75 ohms phasing line in parallel will yield 37.5 ohms. You may find the 37.5 ohms a little mismatch with our 50 ohms transmission line but this will just raise the standing wave ratio to 1.3 : 1 which i think not too bad for the transmitter. For those who would like a perfect match, you can include a matching transformer out of coaxial cable but be reminded for the additional loss it would create. To avoid feedline radiation, pawsey stub was installed to each dipole using a #16 stranded wire cut to a quarter wave length of the operating frequency. When computing the phasing harness, include the velocity factor for the coaxial cable used. The signal polarization of this antenna is circular and purposely chosen to minimize the multipath fading. The theoretical gain is only -3dBd reference to a vertical dipole therefore multiple stacking is recommended.   ---73 de hevir

Homebrew 30W FM Broadcast Amplifier

The original diagram was taken from the data sheet of Mitsubishi 2SC1946A designed to operate at 175MHz. Both input and output tuning network was modified to work between 88 to 108MHz very well intended for our main purpose. Large heat sink is required since the 2SC1946A must operate at 100% duty cycle. Forced air cooling aids in dissipating the heat produced by the rf transistor. The use of high voltage trimmer capacitor is a must and the use of ground plane technique is best suited for this project. RF input of 1 to 2 watts coming out from the exciter is enough to drive this amplifier to produce 20 to 25 watts of rf output assuming that the DC supply is at 12 volts. Take note that this rf amplifier is operated in class C therefore, the need for low pass filter in the output must be installed to avoid interference caused by the harmonics generated by this amplifier. --- 73 de hevir

Collinear antenna for FM transmitter

This collinear antenna works perfectly after the installation. The antenna is basically two dipoles excited in-phase and theoritically exhibits 3 dB of gain when compared to a dipole. 3/8" aluminum tubing was used here but i suggest 1/2" will do the job even better. The quarterwave stub is made of #12awg stranded wire and is grounded at the center(null). When properly tune, this antenna should have SWR value of 1:1.1  to 1:1.2.   73 de hevir