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
LNA Sequencing and Protection
Building UHF Antennas
Crystal Oven Controller
Latching Relay Driver
12 to 28v
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
13cm Signal Generator
120w 13 cm Amplifier
300w 33cm Amplifier
33 cm Crystal Source
33cm Signal Generator
12 AND 28 volts
Parts and Kits I Can Supply
Comments? email to
Here's another, more compact filter that's fairly easy to
make. I designed this one to filter the output of my microwave local
oscillators, but one could also use this type of filter on the output of
preamplifiers to limit out-of-band responses in the receiver.
It's tunable from about 1000 to 1200 MHz, and by changing the
length of the resonators or tuning screws, can cover other frequency ranges as
well. Most of the L.O. frequencies required by the DEMI and DB6NT transverters
are in this range.
No connectors are needed, but one could use them if desired; I
just soldered RG-316 Teflon coax directly into the sides of the enclosure.
This 2-pole filter is a mere 1.25 x 2 x .625" high; the box is
made from inexpensive .008 tin sheet, available from most hobby stores. You'll
also need about 4 inches of .141 micro-coax, and a couple of 2-56 brass nuts and
|Here's the response with the filter tuned to 1104
MHz, the L.O. frequency required by my 3456 transverter.
The local oscillator used with this filter begins with a
184 MHz crystal oscillator.
This drives a harmonic comb generator, and
the filter picks off the 6th harmonic at 1104.
All of the other harmonics are down at least 45 db
after passing through.
This is more than enough, considering the additional
filtering that is normally part of a transverter's multiplier chain.
|Here's a closer look at the close-in response. This
is the output of a microwave crystal detector, as viewed on an
oscilloscope; the horizontal resolution is 40 MHz/div, centered on 1100
MHz. Vertical resolution is unknown, and unimportant for this
I use this test setup to adjust the
coupling between the resonators; too much coupling, and you get a
double-peak; too little, and the insertion loss is too high. The idea is
to set the coupling just beyond the point where the double-peak
The size of the shield between the resonators (shown
in later photos) is used to adjust the coupling. If you stick with the
dimensions shown below, you won't have to worry about adjusting this
|Looking inside (with the lid removed), you can see
how simple the construction really is.
- The input coupling loops are formed using the
center conductor of the RG-316 coax.
- The coupling shield is soldered to the floor and
wall of the enclosure at the resonator base wall.
- The 2-56 nuts are soldered over holes drilled in
the opposite wall.
- The 2-56 tuning screws pass through the nuts, and
thread themselves into the Teflon insulation inside the resonators.
- The resonators are soldered into the base wall,
and supported on the opposite side by the tuning screws.
|For the resonators, I used two 1.875" long pieces of
Start with a 2.25" piece, and
trim .375 off of the outer shield and insulation on one end, leaving the
center conductor exposed.
Next, secure the coax in a vice (do not crush it), and
using a pair of pliers, pull out the center conductor.
Finally, on one end, widen the hole in the Teflon
insulation using a 2-56 tap drill (#51). Drill into the Teflon about 1/2
inch. This end will receive the adjustment screw, which will self-tap
into the Teflon.
|Next, form the enclosure from a piece of tin sheet
according to the drawing and picture shown on the right.
|I form the box by hand, using nothing more than a
small vice and a couple of aluminum scraps cut to the correct length to
form a bending guide.
|Just use your fingers, and fold the sides over the
|When you have all four sides bent, it should look
|Using your fingers, bend the corner ears into place.
Solder them to the side walls. I find it helpful to use a
small pair of forceps to hold the joint closed while soldering.
This picture shows them bent into place prior to
|Next, cut a .5 x 1" piece of tin sheet for the
coupling shield, and solder it in place as shown.
|Using a #27 drill, drill holes in the base wall for
Insert the base end of the
resonators, and solder in place.
On the opposite wall, drill clearance holes for the
2-56 tuning screws. Solder the 2-56 nuts over these holes.
Screw the machine screws through the nuts and thread
them into the Teflon insulation of the resonators.
Using a #44 drill, drill the holes for the RG-316 coax
12mm up from the base wall of the box.
Strip the RG-316 as shown, pass the shield through the
hole and solder in place. Solder the center conductors to the base wall.
The center conductor (coupling loop) should be spaced
2mm away from the resonator.
|Make the top cover using the dimensions shown here.
|Form the cover using the same techniques described
for the box.
The cover is designed to fit into
(not over) the top of the filter box.
With the cover in place, test your filter.
If all is OK, solder the cover permanently into place.
|Here's some info on the tin sheet I used; I bought
this at a local ACE hardware store, and I've seen it in well-stocked
hobby stores as well.
Another material that
should work well is plain old PC board, just cut to proper dimension and
soldered together on the inside. The top cover should probably be brass,
copper or tin sheet, though.