![bias amp 2 ptt bias amp 2 ptt](http://www.repeater-builder.com/ge/mastr2/linear-pa/schematic.jpg)
The 25 ohm transmission line impedance for T2 was realized by using parallel windings of RG316 50 ohm coaxial cable. Therefore, for T2 the optimum transmission line impedance is: SQRT(12.5 x 50) = 25 ohms The optimum transmission line impedance for a Transmission Line Transformer (TLT) is given by the following equation: T2 and T3 are each wound with RG316 50 ohm coaxial cable on two Laird LFB250150-000 ferrite cores stacked together using fiberglass tape as shown below. T3 is a 1:1 balun that converts the balanced 50 ohm output of the push-pull amplifier to unbalanced 50 ohm interface at the output. T2 is a 1:4 transmission line transformer that alternately (each half RF cycle) interfaces the unbalanced or single ended outputs of Q1 and Q2 to the balanced primary winding of the final transformer T3. Therefore, a 1:4 impedance transformation is required in order for a 50 ohm load to provide this optimum 12.5 ohm load for each of the MRF101 devices. 2.42 in Experimental Methods in RF Design by Hayward, Campbell, & Larkin): This process started with determining the output resistance each MRF101 would “like to see” based on the classic equation (Eq.
![bias amp 2 ptt bias amp 2 ptt](https://i.ytimg.com/vi/Gu-bknRZwKc/maxresdefault.jpg)
One of the objectives with this build was to improve the output matching to eliminate the ferrite core heating and improve the amplifier efficiency. R4 – R7 provide a 50 ohm load across the secondary of T1. T1 consists of a 2 turn primary winding (#22 AWG) and a single bifilar turn (#24 AWG) for the secondary on a BN-43-202 binocular core. Transformer T1 transforms the unbalanced 50 ohm input to two outputs 180 degrees out of phase to drive each of the MRF101s. With the -3dB pad, 2 – 4W is required to drive the amplifier to nominal 150W output (~18dB gain). Failures that occurred during testing this amplifier were due to overdriving the MRF101 LDMOS devices. The -3dB Pad at the input provides a stable 50 ohm load for the driving transmitter and provides some measure of overdrive protection from a 10 watt transmitter. I will continue to experiment with the ferrite cores at T2 and T3 to improve the frequency response on 160 and 80M. I welcome feedback from anyone who builds the amplifier. If you would like to experiment with this design, Gerber files for the PCB are available on GitHub. I have checked 2-tone IMD on a RIGOL DSA815 and it looks reasonable. I use this amplifier exclusively with FT4/8 which are essentially single tone modes. I decided to mount the Low Pass Filters in a separate HP436A chassis for space reasons and to allow them to be used for other amplifier projects. Low Pass Filters from W6PQL housed in a separate enclosure are used with this amplifier. This amplifier requires Low Pass Filters at its output to meet FCC requirements. The MRF101 is available in an A and B version with mirrored pin outs to simplify PCB layout in push-pull configurations. 2.101 in Experimental Methods in RF Design by Hayward, Campbell, & Larkin. The MRF101 amplifier schematic is shown below and is based on Fig. With the 2020 Transceiver driving the amplifier, the following results have so far been obtained.
![bias amp 2 ptt bias amp 2 ptt](https://producerhive.b-cdn.net/wp-content/uploads/2021/02/biasamps.jpg)
![bias amp 2 ptt bias amp 2 ptt](https://ae01.alicdn.com/kf/H36206327d9bf456f86ee8e4b9fc597a7O/TAC-SKY-U94-PTT-MOBILEPHONE-VER-1Pin-Plug-Earphone-Accessories-PTT-U94-Military-Tactical-Headset-Walkie.jpg)
The objective is to provide 150W across the HF amateur bands. The MRF101 amplifier is based on the NXP MRF101 RF Power LDMOS Transistors.