Update from 2020-01-28
The following changes have been made:
– Added power injector for power through the feeder. SWR (TX mode) not worse than 1.1 for 2m and 1.2 for 70cm;
– Added the function of switching the LNA input from the antenna to a load of 50 Ohm. Useful for checking the ratio of antenna noise to load noise. Switching is carried out by applying increased power to 16 V (briefly, for the duration of the measurement). The operating voltage of the LNA is 12 V. To prevent overheating of the LNA, do not leave 16 V for a long time!
– LNA 70cm QRO with SAW filter now, compensation inductances and power injector.
This project is allow to organize the LNA’s «bypass» in TX mode with help of small relays. The key difference from our low-bypass project is following: the relays can handle RF Power up to 1500 Watts (2m band) and up to 1000 Watts (70cm band).
This product lineup is based on same active element, as our low-bypass project – PGA-103+ Mini-Circuits Monolithic Amplifier with high dynamic range. Simulation results are similar.
LNA 2m design features
LNA 2m QRO with bypass relays (up to 1500 Watts) contains four RF relays, two G2RL1E12DC with I = 16 A, two signal IM03GR for additional decoupling, the input matching circuit, PGA-103 active element, integrated 6V L7806 type voltage regulator, 3dB attenuator and 3-link band-pass filter (Fig. 1). Without the power supply LNA works in «bypass» mode – RF power of the transmitter goes to antenna through the LNA.
Values of the input matching circuit elements and bandpass filter depends of operating frequency range. Possible frequency ranges are from 6m to 70cm bands. Power supply specs are: VDC = 12 – 13.8 V, IDC = 230 mA.
This LNAs are suitable when operational conditions requires huge RF power bypass. They are quite simple in installation – just connect the unit into the feeder.
Please, notice, that unlike our low-bypass solutions this lineup doesn’t contain RF VOX and they can be powered only through the pass capacitor on LNA’s body from DC power source. For RX/TX switching you should use the sequencer, for example this one.
This LNAs can’t be supplied through the feeder.
Never put RF Power on LNA Output with DC Power ON.
LNA-QRO PCBs are assembled on FAF4 board material, 1.5mm substrate material with plated via holes and soldering mask, SMD components, 50 Ohms microstrip lines, dimensions are 45х75 mm. VSWR < 1.1, isolation on the LNA’s input -62dB (for 2m band).
LNA 2m QRO schematics and layout.
LNA 2m QRO AFC graph is shown on Fig. 3.1. BW(-3dB) < 15MHz. Supression of the broadcast FM band is not worse than -50 dB.
NF measurements results Fig. 3.3 Fig. 3.4 (provided by RU3T)
QRO series LNAs are allow to use PAs with high RF power without additional RF relays. Considering the fact that NF < 0.6dB is usually enought (for 2m band), LNA-2m-QRO is pretty universal solution. For 70cm NF < 0.8dB is OK for Tropo and Contest QSO. For 70cm EME QSO we still highly recommend to use our EME solutions for this band (based on SAV-541+ or ATF-531P8) with additional RF relays.
We had more than 30 working QRO units for 2m and 70cm bands when this article was created. However you should consider some protective measures – reducing the transmitter’s RF Power while this LNAs are used with antennas that have a bad VSWR (greater than 1.5).
Working with antennas, that have a bad SWR (> 1.5) may lead to failure of the RF relays.
List of changes:
– instead of PGA103, ATF53189 used;
– LNA 70cm QRO switched to SAW filter design.
LNA 2m QRO N-female
|Pmax TX bypass||1000 Watt|
|Gain||> 24 dB|
|NF||< 0.4 dB at 144 MHz|
|Filter BW (-3 dB)||< 15 MHz|
|P input (max)||24 dBm|
|Supply operation||12 V & 300 mA|
LNA 70cm QRO SAW filter N-female
|Pmax TX bypass||800 Watt|
|Gain||> 20 dB|
|NF||< 0.4 dB at 432 MHz|
|Filter BW (-3 dB)||< 20 MHz|
|P input (max)||24 dBm|
|Supply operation||13.8 V & 300 mA|
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