At 1/13/2025 06:43 PM, you wrote:

ANDing RSSI gating with SINAD gating will make for a rather tight squelch.

Re: firmware: I think I ended up using 3.05.? Later versions require an SFE (Tait's version of "entitlement key") to enable wideband, so you're stuck with 2.5 kHz deviation, & earlier versions have a bug that causes brief interruption of RX audio whenever CTCSS decode state changes.

I went through my old e-mails on the subject, & yes v3.05 is the latest version that works properly.? Apparently the audio dropout on CTCSS state change bug was introduced in v3.07 & never fixed by v3.27, which is the last version before 12.5 kHz mode became mandatory w/o SFE.? So v3.05 is the firmware to use.

Bob NO6B

ANDing RSSI gating with SINAD gating will make for a rather tight squelch.

Re: firmware: I think I ended up using 3.05.? Later versions require an SFE (Tait's version of "entitlement key") to enable wideband, so you're stuck with 2.5 kHz deviation, & earlier versions have a bug that causes brief interruption of RX audio whenever CTCSS decode state changes.? Not a problem for most but I'm using extended bypass on the TX & RX so I can use an external squelch (replica of Kevin's MS-50) so having holes punched in the output audio would be a problem.

Bob NO6B

I've found most people done really know what Epic they have, especially on eBay.? Can you post a link?

That won't work. The loop must be in the cavity. That's part of the circuit...

Recently took ownership of a TPRD1554 VHF duplexer set. After tuning the set up,
and some process of elimination, I have found that no RF is passing through the
first cavity. Pulled all jumpers and tees. All pass. Good RL, Z, etc.
Went further and pulled the loop from the cavity earlier to test further on the bench.
Simply Will not pass RF at all, as long as the loop is part of the circuit.

I read this, along with your other posts, and am confused by what you're saying.

First, RF doesn't "pass through" the cavity. In this type of coupling design, the passband RF path is through the tee. The cavity Z is shunted across the thru-line: at the pass frequency, the cavity Z is (ideally) an open circuit allowing RF to pass through the tee, and at the reject frequency it is (ideally) a short circuit resulting in reflection.

Second, you say "good RL, Z, etc." Are you talking about the tees and cables, or about all other cavities+loops other than this one in particular?

Pulling the loop and testing on the bench isn't going to be particularly helpful, other than to visually inspect it for defects. You might be able to do an A/B comparison between loops taken out of the cavities using a wide frequency sweep with the tee inline to look for a gross difference between the two but that's about it.

The first thing I would do is to swap loops between cavities to make sure the resonator itself is OK. If the cavity tunes normally with a different loop+tee installed, then you know the loop assembly is the problem.

If the cavity is the problem, which is pretty unlikely unless it has suffered some major trauma, it should be easy to see, but maybe not so easy to fix, once you have the cavity open.

If the loop assembly is the problem, start with the obvious - the tuning capacitor. Back the trimmer out completely and remove, look for any sign of deformation, arcing, etc. on both the rotor and stator plates that could result in a short. I'd say there is a very good chance that this is where the problem lies, as there isn't much else go wrong in the loop assembly save for a solder bridge or something equally obvious. You said it was the "first cavity" that was acting up, and if this was the first cavity on the transmit side, arcing caused by transmit RF into a bad load could have initiated the failure.

--- Jeff WN3A

Josh

Can you measure the C of the ceramic tuning device.
IF yes does the C vary as you turn the adjuster.
it's more than likely 10 pf.
Might it be open crt or shorted?

I'm suspect of that loop not completely clear of adjacent metal objects.

What does the Surecom tell you?
A cheap VNA might produce better results than the HT and the Surecom.

Blue VNA Android Application User’s Manual - Version 0.9.4 Jul 1, 2014:


NO I do not own or sell this tool
but the miniVNA was a neat tool

73
John VK4JKL

开云体育

开云体育

Recently took ownership of a TPRD1554 VHF duplexer set.? After tuning the set up, and some process of elimination, I have found that no RF is passing through the first cavity.? Pulled all jumpers and tees.? All pass.? Good RL, Z, etc.? Went further and pulled the loop from the cavity earlier to test further on the bench.? Simply Will not pass RF at all, as long as the loop is part of the circuit.

?

Excuse the cheap analysis gear, but it works FB to test RF passthrough.

?

Wonder if there are any thoughts on a cavity loop not passing RF.

?

73

Josh W4ZZK

Did you take a "good" loop and put it into the "first" cavity and redo your tests?? How about taking the "bad" loop and putting it into a different cavity?

Kevin W3KKC