8-channel RF power amplifier assembly and testing
Figure 1 - Photograph of an assembled 8-channel RFPA
General description
The parallel transmission (pTx) RF amplifier is used to separately control the amplitude and phase of eight transmission channels for pTx experiments.
System design
As a main component the broadband high power amplifier ZHL-20W-13SW+ (SN: RB81028153) was used to amplify the signals of the eight channels. The maximum input power for each channel is - 3 dBm (see also the data sheet ZHL-20W-13SW+). A wiring diagram of the PTX amplifier is displayed in Figure 2.
Figure 2 - Wiring diagram of the 8-channel amplifier. The components used can be found in Table 1.
| Item No. | Component | Function | Est. cost per Pc. [€] | Amount | Total cost [€] | Source 1 |
|---|---|---|---|---|---|---|
| 1 | SMA connector | RF input | XX | 8 | xx | xx |
| 2 | BNC connector | Input external 5V TTL signal | XX | 1 | xx | |
| 3 | Toggle switch | TTL or manual blanking | XX | 1 | xx | |
| 4 | On/off-switch | 230 V power switch | XX | 1 | xx | |
| 5 | SMA connector | Output RF signal | XX | 16 | xx | |
| 6 | Fuse | 10 A / electrical protection | XX | 1 | xx | |
| 7 | C14 connector | Main power supply connector | XX | 1 | xx | |
| 8 | 24V Power supply | RSP-1000-24 | XX | 1 | xx | |
| 9 | 5V Power supply | Auxiliary voltage for blanking | XX | 1 | xx | |
| 10-17 | RFPA module | 20W power amplifier module | XX | 8 | xx | |
| 18 | Coaxial cable | 500 mm connector | XX | 8 | xx | |
| 19 | Housing | XX | 1 | xx |
Table 1 - Components used in RFPA build.
Figure 3 - Front view of RFPA with annotated components (see Table 1)
Figure 4 - Rear view of RFPA with annotated components (see Table 1)
Figure 5 - Top view of the RFPA with the cover removed and annotated components (see Table 1)
Functionality
Before switching on the PTX amplifier, the unit must be connected to the mains voltage (230 V / 50 Hz) at the C14 socket ⑦ and an input or output signal must be connected to the eight channels ① and ⑤Then the PTX amplifier can be switched on with the rocker switch ④. The rocker switch ③ can be used to select between internal manual unblanking (rocker switch right, ON) and blanking by an external TTL signal (rocker switch left, TTL). A 5 V TTL signal can be connected to the BNC socket ②. Unblanking is necessary to unlock the amplifier modules.
Functional tests
Test of the supply current
By measuring the supply current I_SC, the general function of the individual amplifiers (High Power Amplifier ZHL-20W-13SW+) is to be tested. For this purpose, a multimeter (VOLTCRAFT MT-51, SN: 09126841) was inserted into the current path of the supply current I_SC. According to the amplifier's data sheet, the supply current I_SC is max. 2.8 A during proper operation (with fan). The values measured (Table 2) are within the tolerances.
(table 2 here)
Testing of electrical safety
The electrical safety test was carried out in accordance with DIN 0701 0702.
Power measurement
The power measurement is intended to test the general function of the PTX amplifier. For the test setup, an attenuator (inventory no.: 98041129), an oscilloscope (inventory no.: 200052853/1) and a signal generator (inventory no.: 97037910) were used as displayed in Figure 6. The attenuator has an attenuation factor of -30 dB. The measured results are displayed in Table 3.