Designs for factory made PCBs for
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These RF couplers are designed to have abt. -30dB @ 145 MHz output in respect to the main 50 Ohms thru-line.
The coupling loss rises +6dB / octave towards lower frequencies, and vice versa.
They are usable between 28 MHz and 435 MHz.
At 145 MHz, theoretically abt. 900W input generates 1W heath in the 50 Ohms 1% terminating resistors.
On 435 MHz, the coupling loss lowers 3 times (abt. 10 DB) to abt. -20dB, and the coupling lines start to influence the signal line.
On 29 MHz the coupling loss rises 5 times (14 dB) to -44dB.
For frequencies below 72 MHz, the coupling lines should be made longer to decrease coupling loss to abt. 30dB at the frequency of interest. Resulting in long lines (20cm @ 14 MHz), a long PCB and long enclosure.
For frequencies higher than 435 MHz the coupling space between the lines should be enlarged to increase coupling loss to abt. 30dB..
At the DC output versions, loaded with
1Mohm or higher value, the output of the forward port at 145 MHz is abt :
at 1 W RF input abt. 0.1 Vdc output.
at 800 W RF input abt. 9 Vdc output.
When the ports are loaded with lower resistance, low values RF power will give lower readings, due to the diode characteristics and the voltage drop over R2/102.
Here are six designs presented.
Four especially shaped PCBs will fit with 0.5mm free space inside RF-tight TEKO 371 and 372 1mm steel enclosures. Connections are four short length BNC busses (for max wall thickness 3.5 mm) with PTFE (Teflon (R)) insulation, nut mount, and each two long ground lugs. Installation in plastic enclosures is possible, if a little RF radiation is no problem.
The two PCBs without BNC busses are designed to be installed inside equipment, with coaxes soldered to the PCB. It is wise to wind a few windings of each coax through a hi-Mu ferrite core to damp mantle currents.
The bottom copper of the PCBs is full mass plane. The mass planes are only connected to the mass of the BNC busses via two ground lugs at each BNC bus. A number of carefully placed wide-hole-vias ensure good RF inter connections between top and bottom ground surfaces. If the current capacity of input tracks need to be improved, these tracks can be filled with a thicker layer of solder tin. They intentionally are kept partly free from solder mask.
Each terminating resistor is one resistor 50 Ohms 1% 1W size 2010, or are two 100 Ohm 1W size 2010 SMD resistors in parallel, soldered on top of each other (totally 50 Ohms 2W).
The diode is a Skottky UHF type, with very low
threshold voltage, if loaded with 100 kOhms or higher.
If available, use a BAT62 (single diode, white stripe = k). A double diode version of it BAT62-03W can be used (with only one diode connected). The PCB shows where the wide leg (anode) should be located. See picture ==> .
The BNC busses are short types (max. 3.5mm wall thickness), with nut, lock ring, PTFE (Teflon (R)) insulation an two long grounding lugs. Their rim could be soldered to the outside of the box, for mechanical and electrical stability.
The enclosures are TEKO type 371 of type 372.
R1/101 is 50 Ohms 1% 1W or two 100 Ohms
soldered on top of each other (parallel) size 2010.
DC output types (see schematic an parts table ==>).
D1 is a single diode BAT62, or (one half of) a double diode version BAT62-03W.
Observe the location of the Kathode on the PCB (k is conneted to C1/101).
All other components size 1206.
Solder all components to the PCB, exept the diode.
Prevent static damage to semi conductors.
==> Connect the soldering iron and your body to a mass plane of the PCB.
Then solder the diode as last.
Before installing the BNC busses, put the PCB in the enclosure first. The PCB will be installed with the top copper surface against the underside of the BNC pins.
Before soldering a BNC bus, temporally install a BNC plug in it, to cool and center the pin.
After installing the BNC busses,
- solder the PCB traces to the UNDER side of the BNC pins.
- solder both ground lugs of each BNC bus to their grounding surfaces on the top copper of the PCB.
- if high power should be measured, fill the blank parts of the RF input and RF output tracks with extra solder to enhance their current capacity.
The RF couplers should show abt. 30 dB reflection damping at 145 MHz, when a good terminating resistor is connected to the main signal line "Out".
ordering these PCBs, ask information at : .
Please state the PCB name of interest.
All my PCBs are military quality, and contain component layout, solder masks and informative texts.
Small coupler with RF output.
Dimensions in millimeters.
Drill the BNC holes at a distance of 10mm from the bottom.