A TX/RX RF switch using a "low cost" pcb mounting relay.
A tx/rx relay for 1.3GHz has been prototyped using a relatively low cost pcb relay. The performance of the relay has been enhanced by tuning out the reflected power with tuning tabs on the FR4 pcb. Insertion loss of the relay is about 0.3dB, isolation is better than 40dB and return loss in thru mode is around 20dB. The relay is rated to 15W power handling, to be tested.
Bottom view
Full details of performance available here (127kB)
An add-on filter using a Toko helical filter for the 23cm transverter
A simple filter using a TOKO helical filter has been developed as an "add on" to the 23cm transverter to clean up the spectrum if required by local regulations. Insertion loss is only 1.8dB, and the filter provides about 32dB and 42dB local oscillator and image rejection respectively. The resulting spectrum can be found in the 1296MHz transverter page on this site. Full details of filter performance available here (117kB).
Photo of the completed filter
Quadrature Couplers
Various quadrature couplers are being worked on, as splitters and combiners for balanced PAs. These used the branched arm configuration which theoretically produce two signals. -3.0dB down on the input signal, 90 deg apart in phase. Non ideal couplers do not have an equal amplitude split, and may not achieve 90 deg phase difference. For balanced amplifiers, an amplitude difference of 0.1 to 0.2dB is ususally tolerated, and phase inaccuracy of up to about 5 degrees from true quadrature is generally acceptable.
To date, two microstrip couplers have been developed, shown in the photo below.
The one on the left uses 1.6mm thick FR4 as the substrate material, while the one on the right uses 0.8mm thick duroid.
Performance
FR4 coupler:
S11 -35dB at 1296
S21 -3.45dB at 1296 phase = -140
S31 -3.50dB at 1296 phase = 129
S41 -35dB at 1296
S21-S31 0.05dB phase = 91 deg, dissipative loss = 0.47dB. Estimated power handling 40-50W
Duroid Coupler
This coupler covers the whole 1.25 to 1.35GHz band with excellent phase and amplitude balance. It should be an excellent candidate to combine the output of two 35W amplifiers. Loss is about 0.15dB, and power handling should be in the region of 80W. Input return loss (IRL) is better than 20dB (1.2 VSWR over the whole band and reached about 38dB at 1296. Isolation at 1296 is about 40dB.
