70MHz filters

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Low pass filters on 4m remove signals from e.g. the broadcast radio band beginning at 88MHz.

QRP-Labs sell a Low Pass Filter kit for 4m that may be suitable for 71MHz duty with the Portsdown TX.qrp-labs.com lpf kit Low pass filter kits from QRP-Labs built by M0YDH for Portsdown TX use. 4m on left and 2m on right

Higher power duty filters. In CQ-TV 260 Charles G4GUO published a low pass filter using ATC capacitors to go in a die cast box.

G4GUO filter built by David M0YDH Spectrum analysis trace for this filter. Ref level was -14 dBm with a 10dB PAD. So -2dBm loss.

Mini-kits sell a low pass filter kit described as a 75MHz 7th order Chebychev Low Pass filter.

Band pass filters may present a problem. The QRP-Labs 12m or 10m Band pass filter kits may be a valid point for starting on experimentation for your receiver application. The upconverter shown on this Wiki contains good filtering for receive already. Antennas-amplifiers off a bandpass filter covering 70-70.5MHz with published characteristic curves. PA3CSG has a home built band pass filter which will tune to cover 70.5 -71.5MHz. 2021 update:- Mini-Circuits make an excellent low power Bandpass filter - the RBP-75+ which passes 50-72MHz signals and is for mounting on a PCB. Very low insertion loss. About £16 each or try your luck with an application to their EZ Samples programme.