[K3CAL] FW: Duplexer/Filter Status

[Dave]

I'm unable to open the attachments now but agree that the information should be shared. Thanks for the update and continuing progress and reports.

David Hardy    davehardy0101 at aol.com KB3RAN  

On Monday, July 9, 2018 David Weaver <k3cal at mailman.qth.net> wrote:
Hello all
As you can see, Chuck, Shawn and myself are progressing in correcting some of the problems with the repeater system at Mt. hope. I know this is a long time coming, but progress is here. Please take a moment and read the reports. The 1st one is about the duplexer's the 2nd one is about the filter that Shawn purchased at a ham Fest and donated to the club to use.
It looks like we will be able to install the duplexer's back at Mt. hope this coming weekend. The Motorola MSR 2000 will be in service until we can get the controller programmed for the Yaesu DR 1X . If there are any preferences for the controller. Please email me and we can take it under consideration.
73s
Dave W3PQS

-----Original Message-----
From: Chuck Shefflette [mailto:cshefflette at icloud.com] 
Sent: Sunday, July 8, 2018 9:10 AM
To: Weaver Dave; Donley Shawn
Subject: Duplexer/Filter Status

Dave and Shawn,

Things are looking up.

The duplexer is working quite nicely with its new cables. It is amazing how much more stable it is with proper length cables. It is also interesting that Celwave and Phelps Dodge both specify shorter cables for the 2M band, which make tuning it quite touchy but means it doesn’t need new cables to cover the whole band. I has happy to find that the cable lengths I calculated for the inter-cavity and cavity to tee cables were within 1mm of the actual finished lengths - I cut them long and trimmed them until I got them centered on 146.685. The duplexer is a lot less sensitive to a changing load than it was as well, the though and notch are pretty stable with and without a load on the ports, and it is well within the original specs of < 1.5dB insertion loss and > 80dB rejection at 600 KHz - I measured about 1dB insertion loss and > 85dB rejection on the TX/RX frequencies.

The filter was not so good, but I think it is better now. The picture of the sweep I sent changed almost immediately after I sent it. It turns out one of the tuning cavities was broken internally and it shifted. I ended up taking it apart and figured out how it was made to operate well outside its design frequency of 138-142 MHz. It turns out that someone had it apart and cut some dielectric material tubes and jammed it into the cavities. I also found that one of the tuning tubes was jammed in place and had actually been fractured… I adjusted it fairly close without the dielectric then slid the sleeves in place until I got close to 1dB insertion loss with the passband centered close to our operating frequencies. I trimmed the sleeves and closed it up. Depending on how the cables seat, I measured just over 1dB insertion loss with a slightly tighter passband centered on the 2M band (143-149 MHz at the 3dB points) and a bit steeper skirts, so it should work a bit better now as well.

I am short one cable at the moment - the jumper between the inter-cavity Tee and the feed line. I messed up putting on one connector - dead short between the center conductor and the shield, so I’m going to have to get another connector for that. In the meantime, I think we could install the duplexer/filter as they are and put the jumper in later if we decide it is necessary (I think it is as it will make it easier to connect the tee to the feed line.

I’ve attached screenshots from the spectrum analyzer for both the duplexer and filter as they are now for your viewing pleasure.

Since the weather looks to be OK for the next week, I would suggest we wait until next weekend to reinstall them so I can get the other cable made and ready to install everything at once.

73,
Chuck - AA3Cs

Engineer: "If it ain't broke I haven't messed with it enough yet."
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