Skip to content

VHF/UHF selectable Bandpass filter and signal amplifier

License

Notifications You must be signed in to change notification settings

rfrht/SignalSurge

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

41 Commits
 
 
 
 
 
 
 
 

Repository files navigation

SignalSurge

This is an open source (check licensing here) Bandpass filter for VHF and UHF bands, with a selectable LNA and a sequencer. Projected using Eagle CAD 9.

Why?

I live in a metropolitan area and very RF-polluted. One of these days, only FFS I have added a FM bandstop filter and I found that, contrary to my belief, my reception was way better! That means:

  1. The front-end radio filtering is less than great
  2. Out of amateur band signals (and there's plenty of them) will desensitize your radio
  3. By filtering out unwanted signals, you give more dynamic range to your radio, improving your reception.
  4. See for yourself here.

That said, the objective of this project is to remove everything outside 2m and 70 cm bands (like: FM broadcasts, air band, commercial VHF & UHF, and everything else between), ensuring that the precious front-end gain by the radio built-in amplifier focus on amateur band signals only.

I could buy a 300 EUR filter, but... man, that's expensive. So why not expend EUR3,000 man hour-worth of my time to build one?

Features

  • Two selectable sharp amateur band (2m and 70 cm) bandpass filter weeds off signals, ensuring that the transceiver front-end focus its gain figures on inband signals only
  • High performance and selectable low noise 15 dB amplifier after the bandpass filter, adding some oomph to weak signals
  • The amplifier is shut down when the radio is transmitting by powering off its 5V voltage regulator (by cutting the regulator “Enable” line)
  • Specialty RF relay allowing 50W in VHF/UHF frequencies to flow to the antenna with low loss, while keeping unparalleled isolation to the downstream components (north of 60 dB)
  • Relay default state (NC) is to bypass radio directly to antenna, allowing the board to be safely powered off
  • TX Inhibit functionality to prevent the radio to transmit while the relay isn’t positioned
  • Static protection on antenna side
  • Small surge protection on antenna and radio sides
  • Co-Planar Waveguide (CPW) design on RF lines for impedance control and good RF performance

Schematic:

Schematic SignalSurge

Preliminary board layout

Rev A Signal Surge

For full board image, click here

BPF theoretical performance

Here's the calculated theoretical filter performance, for VHF and UHF bands:

VHF BPF performance UHF BPF performance

We shall see how that work out in the real world.

Amplifier performance

Here's the theoretical BFP460 gain figures as per the application notes:

Amplifier performance

Relay Logic

BPF and Relay control

Truth table (NOR)

RADIO_TX FORCE_BYPASS Signal Level Behavior
0 0 1 VIA BPF
0 1 0 BYPASS
1 0 0 BYPASS
1 1 0 BYPASS

RX/Via BPF states:

Circuit Connected to Power
Relays NO +
Isolation NO +

TX/Bypass states:

Circuit Connected to Power
Relays NC -
Isolation NC -

LNA

Truth Table (AND)

BPF_ON LNA_ON Signal Level Behavior
0 0 0 OFF
0 1 0 OFF
1 0 0 OFF
1 1 1 ON

LNA On

Circuit Connected to Power
V.REG. EN +
LNA SW NO +

LNA Off

Circuit Connected to Power
V.REG. EN -
LNA SW NC -

Maturity level

  • Reached the "minimally lovable project" stage.
  • I think that with regards to the base components and schematic, this is pretty much it.
  • Still untested, unbuilt - and yes, it is still green.

Library

Custom component library here

To Do

  • Create a BOM file
  • Assure the filter operation
  • Have someone else to give it another look

CHANGELOG

  • Rev. A: Initial release (in the making)

ACKNOWLEDGEMENTS

I'd like to thank the following contributors:

About

VHF/UHF selectable Bandpass filter and signal amplifier

Resources

License

Stars

Watchers

Forks

Releases

No releases published

Packages

No packages published