Low size VHF duplexer

[e.sotillet]

Hi Folks

I need a low size, low power duplexer for VHF. The two center frequencies are separated by 10MHz, I had two SAW filter for those frequencies but I want to avoid the additional loss (-3dB) of the splitter. 


So, it is feasable to add a order 7 or 8 diplerxer before the SAW filters or sounds like a bad idea?

Best regards!!

[TheSteve]

What frequency exactly and what isolation are you looking for, and just how small?

[fourfathom]

And what power level?

[geggi1]

Have a look on Ebay.
There are some supplyers in china that sells duplexers 25w with a split of 8-10Mhz pretty cheep.
You should check a bit on the reviews because I assume variating quality.

[e.sotillet]

Hi, I proceed to answer the questions:

1.- Frequency and isolation: I was wrong in this point, the two center frequencies are separed by 20MHz. One is 140MHz (8MHz BW) and 160MHz (10MHz BW). Isolation higher than 45 dB (The actual SAW filters achieve this).

2.- Power level: 0dBm

3.- Size: As small as possible. A comercial helicoidal duplexer is to heavy and large to add in the system.


Best regards

[e.sotillet]

Hi Folks,

I builded the duplexer using the commented block diagram. It work fine, the only detail is the high part of the low band (lower center frequency filter) been attenuated by the low pass filter of the diplexer.

I designed the later using the DiplexerDesing software by Tonne Software. Is any way to transform this diplexer topology to elliptip? Im concerned only about the transitions, the rest job is done by the SAW bandpass filters

Best regards and thanks for the time!!