6M / 50MHz Duplexer for Repeater. Do it Yourself

Ready Duplexer. Installed to Nokia Aluminium ladder.

This duplexer resonators are made from 1"5/8 helical coaxial cable.
It have 4 resonators per RX and TX direction.

It is essential to have some sweep analyzer of network analyzer.
capable to sweep 20...70MHz band.
Without analyzer tuning of resonators is quite challange.
With analyzer you can see difference of high and lo quality capacitors and coils

Circuit diagram of 6 resonator system. principle is same with 8 resonators

In theory 8 resonator system you can get deeper notch attenuation

List of materials:

Needed Frequencys: Our case 51.370MHz and 51.970MHz
8 pcs 120cm long 1"5/8 coaxial cable. Thicker cable is also OK 

10m of Aircell 7 or RG-214 double shield coaxial cable for resonator interconnections

3m of 7/8" or 1/2" foam isolated coaxial cable. This is used for make high quality capasitors 10...15pF connecting signal to top of resonator

4 pcs high quality N-male connectors for both end of resonator line

1 pcs  N-female T adapter for interconnect antenna and RX / TX line of duplexer

4 pcs high quality trimmer capasitors 4...30pF. Used for minimize pass attenuation

4 pcs high quality coils 20...100nH. Used for minimize pass attenuation. Can be find inside 450MHz NMT radio duplexer, for example

Some pieces high quality fixed capasitors to put parallel to trimmer capasitor if needed.
values 30pF 45pF 60pF 80pF for example

Example of high quality coils and capasitors

Homemade capacitor made from 7/8" inner conductor with foam isolation

Capacitor above is adjustable very accurately few picofarads from 10...15pF

Top of duplexer coils and capacitors are visible

Picture above you can see that high and lo frequency resonators are divided horizontally left and right group

 51.970MHz pass -1.52dB
 and notch -90.23dB

51.370MHz pass -1.79dB
and notch -90.43dB

Pictures above show final attenuation measurements from duplexer