RF Diplexer design

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RF Diplexer design

Post by opfor » Wed Nov 07, 2018 11:03 am

I've been putting together my wants and wishes for a while concerning the mobile antenna on the 'heep, and one of the bigger problems I've been having is finding a decent (read: non-shitty) quad-band antenna to run my TYT-9800 (10/6/2/70cm). The existing antenna is currently falling apart after a somewhat expected interaction with a tree.

Given that this radio offers multiple bands, but only a single RF output, and granted that I generally only talk on 2m/70cm most of the time, and the antennas for this band are quite cheap ($20?) I am failing to see many good reasons to actually maintain a single expensive and fragile quad band antenna that will remain on the top of my vehicle.

With this in mind, I decided to start looking around for a diplexer (or maybe triplexer) that would split 10/6 and 2m/70cm into different ports, using a triplexer would give me a 10, 6 and a 2m/70cm port. Most of the stuff I found out there seems to have an HF/2m, and a UHF split. For somewhat obvious reasons this is unacceptable, as this means now I'm looking for a 10/6/2 and a 70cm. Before my frustration builds too much, I chose to take the plunge into designing and manufacturing my own diplexer design to meet my needs.

I expect this thread to mostly be a log of my development efforts. I certainly appreciate any help and input anyone else has. I grok the theory of it, but RF design is still a new topic for me.

Interestingly, in doing some background I came across this which is an insanely cool design for a diplexer, unfortunately it operates many many ghz above my target band, and the science nerds over at caltech have impressed me again with a simple design that uses the capacitance of the traces to make what appears to be a rather effective band-pass filter to segment out some pretty crazy radio spectrum.

As a somewhat frustrating addendum, the lexicon on this is rather confusing most certainly to the search engines (namely google) which seems to equate diplexer and duplexer, while at the same time creating significant enough confusion that it's spilled over into the engineering community. I start to get close to what I'm looking for in a "RF Combiner" but the price starts getting out of hand.

Other info: http://jaunty-electronics.com/blog/2014 ... er-design/
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