Yep, there're still some around but I don't think the telco uses them anymore. I have a couple of the cylindrical telco assemblies stashed away but might have a couple of the removed ones that I could let go of. I'd want to run them past a digital inductance meter to be sure they weren't partially unwound at some time in the past.
Wayne
WB4OGM
On Tuesday, October 1, 2024 at 08:26:13 PM MDT, Ralph Mowery <[email protected]> wrote:
While speaking of the simple TUs is there a source for the 88 millihenry coils ? The ST-5 is very simple and works very well but needs 2 of the coils.
Ralph ku4pt
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Harold Hallikainen via GreenKeys Sent: Tuesday, October 01, 2024 4:31 PM To: [email protected] Subject: Re: [GreenKeys] Simple PLL TU
On Tue, October 1, 2024 12:53 pm, Ken LoCasale wrote: > Gang, > > I found a simple two IC terminal unit for anyone that might want to try > mechanical rtty on a budget. I think I'll layout a board and give it a > try. Has anyone else seen it before and given it a try? > > I put the .pdf here. https://qrpbuilder.com/simple-pll-terminal-unit > > ken - wa4mnt
I built a demodulator like that (based on the NE565) back then. I don't think the 741 limiter gains you anything. It's pretty easy to just saturate the NE565 input as a limiter. The datasheet (which includes a very similar demodulator https://www.fabian.com.mt/viewer/44073/pdf.pdf ) says only 10 mV is required for the PLL to lock.
A nicer (obsolete) chip is the XR2211 ( https://assets.maxlinear.com/web/documents/xr2211av104.pdf ). I designed several products around this chip. It includes the PLL of the NE555 along with the data slicer (comparator typically wired as a schmitt trigger) and a lock detector (mark hold). As shown at figure 11 https://assets.maxlinear.com/web/documents/xr2211av104.pdf#page=14 , the lock detect and FSK demodulator outputs are open collector, so they can just be tied together to get mark hold.