The pre-amps are simply inserted into the coaxial feed line. The power supply is either done over the coaxial cable or via a separate line. Most recent transceivers offer a supply voltage on their coaxial VHF/UHF connectors, so no external Bias-T (DC injector) is required. If required we offer a large selection of DC-injectors with or without sequencer, see below.
Most amplifiers can also be supplied with a separate DC cable. Please note that the cable should be protected with ferrites against high induction voltages.
The amplifiers do have a built-in HF vox, which allows automatic and reliable operation at standard power levels. For higher power levels a separate PTT keying line must be used. Thiscan be done directly from the PTT line of the transceiver, or by means of a separate sequencer. Most important for a pre-amplifier is the adequate gain at a good (high) 3. order intercept point (IP), this is necessary for a good large signal handling capability. Most amplifers have an adjustable gain level, this protects the receiver against overload while sufficiently compensating for cable losses.
With the larger models, the transmit/receive switching is done with real coaxial-relays, the 'Mini' series by SHF-Elektronik uses print relays. Most amplifiers (except Mini-2) are installed in two enclosures: on the inside a metal case shielding against RF, on the outside a weather proof UV resistant plastic box. A metal clamp for mast installation is included in shipment.
The pre-amp should be located as close to the antenna as possible to keep the cable (and the cable losses) as low as possible. The connecting cable to the antenna should be of high quality.
Model SHF MVV 144/2 supports two antenna connectors, which can be switched with an additional signal voltage. This enables the use of the pre amp for example with a horizontal yagi and a vertical omni directional antenna. For switching an additional switching signal is required, which is connected to a 4pin connector on the pre-amp. The required connector is included. The same connector could also carry the supply voltage, alternatively the supply can be done over coaxial cable.
The 2m/144MHz band is certainly the most used VHF band, regardless if used for tropo DX, EME, meteo scatter or FM. Here a good pre-amp is certainly most useful. At several occasions contest take place and the band is densely populated with very strong signals. This requires a pre-amp with good large signal handling capabilities.
Without a power supply all SHF pre-amps (MVV-xxx models) automatically switch to 'pass-through'. This prevents any damages to the amp when the power fails.
- Freq Range MHz (MHz) 144 - 146
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