High power amplifier for 1296
1 KW SSPA for 1.8-54 MHz
A 1.5 KW LPF for 160-6m
1.8 to 54 MHz Dual Directional Detector
1.8 to 54 MHz combiner set
Automatic Transverter Interface
1 KW 6 Meter LDMOS Amplifier
2 Meter 80W All Mode Amplifier
1 KW 2M LDMOS Amplifier
1 KW 222 MHz LDMOS Amplifier
500w 70cm Amplifier
1KW 70cm LDMOS Amplifier
A Big Power Supply for SSPAs
Low Pass Filter/Dual Directional Detector
Sampling RF Power
LED Bar Graph Meter
Amplifier Control Board
LNAs (preamps) and MMICs
LNA Sequencing and Protection
Building UHF Antennas
MIcrowave Marker
Crystal Oven Controller
Microwave L.O.
Latching Relay Driver
12 to 28v
Relay Sequencer
High Current DC Switch
L & S Band LNA
Microwave L.O. Filters
PC Board Filters
Using Inexpensive Relays
600w 23cm LDMOS Amplifier
XRF-286 Amplifiers for 23cm
150W 23CM Turn-Key Amplifier
300w 23cm Amplifier
200w 23cm Amplifier
100w 23cm "brick"
100w 23cm Transverter
60w 23 cm Amplifier
23 CM Beacon
23cm Signal Generator
23cm Double Quad
23cm filters
13cm filter
13cm Signal Generator
13cm Transverter
120w 13 cm Amplifier
600w+ 33cm Amplifier
300w 33cm Amplifier
33cm filter
33 cm Crystal Source
33cm Signal Generator
9cm Transverter
Transverter Selector
12 AND 28 volts
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Low Pass Filter/Dual Directional Detector

Update: There is a newer version of this board available now that will also cover 6 meters. You can jump to the setup table and schematic for this newer version by clicking the bookmark here:

I thought it might be nice to save some space and simplify construction of the kilowatt 70cm amplifier, so I designed this little critter. I got lucky, it also works quite well on 144 and 222MHz.

This 3-in-1 assembly filters the harmonics from the amplifier, and feeds the forward and reflected power signals to the control board and metering circuits. It can be configured for any one of the three bands mentioned by selecting the correct component values from the setup chart at the end of this description. Components for the 2m version are shown in this photo. A high resolution photo is here.

This photo shows an earlier prototype of this board (70cm), and how I mounted it into the amplifier

On 70cm, the capacitors in the filter are printed right onto the board substrate, and the inductors are made by winding #16 magnet wire to the appropriate size. This filter reduces the second harmonic by more than 40db, and the third by more than 60.

For the 2m and 222MHz filters, additional capacitance is provided by high-power metal mica capacitors. Different inductor values are also used.

The dual directional detector provides the signals for the SWR lockout, and also drives the LED forward and reverse power meter bar graph displays.

Additional details can be seen in the write up of the 70cm KW amplifier.
These next 2 photos show the component selections for the low pass filters at 70cm and 222MHz.

If you are building this assembly from a kit I supplied, disregard the positioning of the inductors as shown here. Originally, I had them placed as you see them here because the filters would not tune easily unless I did that. I later discovered this was due to inter-stage mutual coupling between adjacent inductors; I was able to neutralize this effect by winding each inductor in the opposite direction from it's neighbor, and that way was able to place them all in a straight line across the board.  Tuning the filter is best accomplished by spreading and compressing the coils for the lowest SWR reading at the input of the filter (terminate the other end with a good dummy load). I used a scalar analyzer to set mine up, but the former method mentioned will work fine. Performance data, schematics, and a setup chart are shown at the end of this page.

The components for the 2 detector areas consist of a chip resistor attenuator to set the correct signal level, a diode detector and an LC filter. The directional pickup traces can separate the forward and reflected signals by more than 30db (directivity is the commercial term for this specification). One is oriented to detect forward, the other oriented for reverse.

Reverse power should be detected 10db below the forward power level (equivalent to 2 to1 SWR). See the article on the stand-alone RF detector board for additional explanations of this technique.




And finally, here's the schematic and setup table.

The output from the detectors should be terminated with the resistances shown in the chart. If you are driving high impedance devices like the LED bar graph displays, a 5k chip resistor can be placed across the input of the FWD power display board. The swr input on the amplifier control board is already set at 5k for the reverse detector output, which is usually connected in parallel with the reverse power LED bar graph display. Because the load resistance is already at 5k in this situation, do not also place 5k at the input of the reverse LED display.

However, on 2m, the output of the reverse detector must be handled differently. The input trimmer on the control board should be changed from 5k to 20k. This will bring the signal level up, necessary for the reverse detector on this band, as the coupling is very loose (51db) at 2m.

Here is the setup table and schematic for the 4/2014 version of this board, which also covers 6 meters and 70 MHz:

Here's a look at component placement under the shield:
One last bit of info on assembled/tested boards shipped after mid-May 2024...there are two different locations provided for mounting the detector diodes depending on whether you prefer positive or negative output signals. By default, the diodes are mounted in the locations shown in this photo, and produce negative output signals.

If you will be ordering the assembled/tested version of this product and prefer the output signals to be positive, be certain to send me an email when you place your order indicating that preference.

Most of the companion components offered on the parts page such the control board and bar graph display are also configured to respond to negative voltages; if you are a kit builder and inclined to prefer positive voltage outputs, the next photo shows the proper locations for the diodes to be placed and how to configure those other boards to be compatible.


Placing the diodes in these locations will provide positive output voltages. If you will be using these signals for the control board or bar graph displays, here's how to configure those components for positive voltages:

Control board: remove resistor R59 (formerly J1 jumper) and install jumpers at J2 and J3. This will configure the "load fail in" port for positive signal voltages. With this change in place, the J3a input cannot be used (J3a is typically used only for HF amplifier systems).

Bar graph displays: install a jumper at J1 and use the "pos sig" input.