QRO LNAs with built-in bypass relays for 6m, 4m, 2m, 1.25m and 70cm bands

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).

LNA simulation

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.

LNA 2m QRO schematic circuit

Fig. 1 LNA 2m QRO schematic circuit

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.

Warning!
This LNAs can’t be supplied through the feeder.

Warning!
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 PCB is shown on Fig. 2

LNA 2m QRO PCB

Fig. 2 LNA 2m QRO PCB

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.

Amplitude-frequency response of LNA 2m QRO

Fig. 3.1 Amplitude-frequency response of LNA-2m-QRO

Amplitude-frequency response of LNA 6m QRO

Fig. 3.2 Amplitude-frequency response of LNA-6m-QRO

NF measurements results Fig. 3.3 Fig. 3.4 (provided by RU3T)

LNA 2m QRO NF measurements results

Fig 3.3 LNA 2m QRO NF measurements results

LNA 70cm QRO NF measurements results

Fig 3.4 LNA 70cm QRO NF measurements results

Conclusion

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).

Warning!
Working with antennas, that have a bad VSWR (> 1.5) can lead the failure of the RF relays.

Technical specifications of the LNA-2m-QRO

  • Model: LNA-2m-QRO
  • Active element: PGA-103+
  • Pmax TX bypass: 1500 Watt (1200 Watt recommended)
  • BW(-3 dB): 15 MHz
  • Gain: 18 dB
  • Noise Figure: < 0.6 dB
  • Output IP3: 38 dBm
  • P input: 21 dBm (max)
  • VSWR bypass: < 1.1
  • DC voltage: 12 — 13.8 V
  • DC current: 230 mA
  • Impedance: 50 ohms
  • RF connectors: N-female
  • Dimensions: 86 mm x 76 mm x 26 mm (with connectors)
  • Weight: 0.25 kg

Package includes

  • 1 x LNA-2m-QRO

Technical specifications of the LNA-70cm-QRO

  • Model: LNA-70cm-QRO
  • Active element: PGA-103+
  • Pmax TX bypass: 1000 Watt
  • Gain: 16 dB
  • Noise Figure: < 0.8 dB
  • Output IP3: 38 dBm
  • P input: 21 dBm (max)
  • VSWR bypass: < 1.1
  • DC voltage: 12 — 13.8 V
  • DC current: 230 mA
  • Impedance: 50 ohms
  • RF connectors: N-female
  • Dimensions: 86 mm x 76 mm x 26 mm (with connectors)
  • Weight: 0.25 kg

Package includes

  • 1 x LNA-70cm-QRO

You can order this LNAs via e-mail: e-mail logo sales@vhfdesign.com or by filling out this form. You can check LNAs availability at stock here.

Technical support: e-mail logo us4ici@vhfdesign.com

Appearance

LNA 2m QRO

Fig. 4.1 LNA 2m QRO, built-in bypass relays, N-female

LNA 70cm QRO

Fig. 4.2 LNA 70cm QRO, built-in bypass relays, N-female

LNA 2m QRO

Fig. 4.3 ATF-531P8 based LNA 2m QRO, built-in bypass relays, N-female (experimental assembly)

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