Hi-Z Input Preamp
NEW!
Interested in a preamp for a small whip or low gain Rx antenna?
Here is a new Hi-Z input amplifier for HF Rx.
This unit is configured with a slight amount of gain to overcome system losses, about +10db. The gain is fairly flat from 1MHz..30MHz. The first stage is a JFET which provides the high input impedance and some gain. It is followed by an NPN emitter follower which provides a low output impedance. The circuit works well with +12VDC applied.
The standard configuration is for Power-Over-Coax. This is important for remotely mounted preamps as using unshielded cable for power acts as antenna for noise and undesired broadcast signals.
Power over Coax (PoC) or direct +12V DC input. A "bias T" is available to feed +12V up the coax.
This PCB allows a variety of configurations to fit you needs. There are 3 jumpers on the PCB to allow:
- First stage: Common source amplifier
- Second stage: Emitter follower
- Power-Over-Coax or direct +12V
Purchasing Options:
Default configuration is Power-Over-Coax.
- All SMD's assembled $15 (no case or coax connectors)
- All SMD's assembled, + 50mm case + 2x SMA female bulkhead connectors (not installed). User needs to install connector and drill the case end plates. $20
- Fully assembled with SMA output connector and completed case. SMA for input supplied but not installed. $25
- If you want another configuration, please email.
Please select an option from the menu below: Note: Bias T sold separately.
Preamp Schematic
This is a 2 stage preamp with about 10db of gain in the FET stage. The default configuration is Power-Over-Coax, which requires a Bias T (available separately).
For independent power, you need to make a cut at JP3 and verify that DC power is NOT going to the radio.
PCB
Here is a blow up of the PCB. This fits into a 50 x 25 x 25mm extruded aluminum enclosure.