No PTT input from a Knwd TS-850

ka9ees · June 22

My new 8400 had to back to the mothership because of no RF out. I am trying to use an older Kenwood with the TGXL. I have manually tuned it with no trouble, but it won't pass PTT to my MercuryIIIs amplifier. Every time I key the rig the tuner displays "No PTT Input". Mind you this old Kenwood has no BCD or other CAT connection.

Something strange is going on with the amp. When it is offline, it pass 100w + from the 850. When it is online, it only shows 1.5w or less on my LP100-A.

Any suggestions on what I should do next?

Gord-VA7GP · June 23

I own a TS-850 and it is my recollection that the TX delay is a fixed 10ms.

I think this was designed to allow the (Panasonic) TX - RX relay to close before shooting RF through it.

ka9ees · June 23

@Gord-VA7GP Tnx Gord, thay's nice to know. Apparently it's not enough.

David Decoons, wo2x · June 23

hi Ed

Can you confirm Amp keying line from radio goes to the TG XL PTT In then TG PTT Out to Mercury?

The other thing may be the TS850 does not have enough TX Delay.

73 Dave wo2x

ka9ees · June 23

@David Decoons, wo2x Hi Dave! Hope you are well. I have. I don't know if I can even change the TX delay. My solution has been to order an ICOM 7300 as a backup rig. Hopefully it will be here tomorrow.

Gord-VA7GP · June 24

For completeness in this thread, I'm attaching the timing information for the TS-850, from p.23 of the Service Manual (this is the only place I can find it written down). The delay is indeed "hard-coded" in an R-C time constant; the QST test from 1991 remarks that CW keying is exemplary.

Slightly asymmetrical, 10ms is a good working estimate of the (fixed, non-adjustable) delay:

TS850_Service_timing.pdf

(but even so: when the signal to Transmit is produced, and RF out is delayed by 10ms, so also is the Amplifier TX relay-closure! It is delayed by "normal" mechanical movement. Some Amps in addtion have yet another relay to switch the amp from bypass to "active", and maybe also turn on bias, etc. Thus, the Amplifier and other stuff quite possibly will be hot-switched. Perhaps use a sequencer, or PTT into tuner → amp → radio. Or, buy an Icom 7300 🤣)

ka9ees · June 26

OK I am no longer using the 850. I am using an ICOM 7300. It's my 4th… This morning it had no error. So I borrowed a friends LUX, and now I get "No PTT In" error. Nothing wrong with the amp. I by-passed the tuner and get PTT with no trouble. I have set the TX timing in the 7300 to 30ms. The CAT works fine the tuner knows what frequency it's on. Anybody have any idea what I am doing wrong?

No PTT input from a Knwd TS-850

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