Hi Robin

The 27MHz correction threshold parameter only applies during GPS correction. Only when you have a GPS 1pps connected.

73 Hans G0UPL 

http://qrp-labs.com 

On Mon, Jul 8, 2019, 03:06 Robin Midgett <K4IDC@...> wrote:

Hi Hans,

Thank you very much for the tips.

I was able today to get my old oscilloscope dialed in enough to measure the pulse width of the 1 PPS output of the Trimble Resolution T GPS board...it's a 1mS pulse width. Further, and perhaps the better news, you're correct...it's only making about 3 volts above ground, so that might be the sole issue with the GPS discipline problem. I'll try a level converter & see how it goes.

Yes, I'm aware of the frequency bank switching scheme, but I hadn't realized one could take advantage of that for on/off keying..I'll give that a try & follow up with my findings. That seems rather clever to me.

Question on your point 5: Is that 27MHz. correction threshold only valid for GPS discipline mode,or does it apply for both GPS/non GPS mode? The way your point is stated makes it seem to me that perhaps the threshold is only effective while under GPS discipline...but maybe I'm mistaken.

Thanks,
Robin Midgett K4IDC

On Fri, Jul 5, 2019 at 6:42 AM Hans Summers <hans.summers@...> wrote:

Hi Robin

Several comments:

1. ProgRock was developed in conjunction with the QRP Labs QLG1 GPS http://qrp-labs.com/qlg1 which has 100ms (0.1ms) positive-going pulse. Though if your pulse-length is 1ms I would not expect there to be problems... but couldn't know for sure without testing it. I know something very short like a microsecond would be an issue. But a millisecond is relatively ages...

2. Watch out for voltage level problems. Most GPS chips operate at 2.8V supply, the ProgRock operates with 5V supply. The logic level threshold for a "1" is 3V if I recall correctly. Therefore with many GPS module models you need a level converter. A pull-up resistor to +5V can do the job often but you need the right resistor value. And even then, the noise immunity suffers compared to a "real" level converter. The QLG1 kit has a proper logic level converter so with its 5V logic outputs you never have an issue. 

3. A heatsink on the crystal helps with thermal stability. So does putting the project in an enclosure to avoid drafts etc. 

4. ON/OFF keying... are you aware of the frequency bank feature of ProgRock? There are three logic inputs, the permutations of high/low control signals in these allow you to choose one of three banks of output frequencies. If any frequencies are zero the output is just disabled. So it is often quite convenient to uses these logic level inputs to on/off key the output frequency you want.

5. Read the manual section about the GPS correction threshold register. For finest precision you want this to be 0Hz. The default is 5Hz which means the correction is only applied when the error if the 27MHz value exceeds 5Hz.

When all is well you should be well within 0.05ppm.

73 Hans G0UPL 

http://qrp-labs.com 

On Fri, Jul 5, 2019, 03:49 Robin Midgett <K4IDC@...> wrote:

Hi Jim,

Not a MASTR Exec, but a low band MASTR II mobile for use as a 6m beacon. I'm working on using the ProgRock in place of the crystal in the channel element. Once I get the low band beacon going in good order, I plan to expand to 2m, 1.25cm & 70 cm. I started this project over a year ago, set it aside for several months, and just today returned to it.

I plan to inject the RF from the ProgRock directly into the channel element connections on the exciter board, and key it on/off with a small memory keyer. It works just fine using a simple relay to key, but I want a solid state switch instead of a mechanical relay, so I've been working toward that.

I tried inserting the on/off keying in the bias & tripler circuits downstream of the channel element, but that didn't work well at all; the resulting RF was dirty & splattered across the narrow beacon sub-band. The original mic PTT simply turned the power to the oscillator in the channel element on/off, so that seems to be a good starting point.

Presently I have good stability using the ProgRock stand-alone (no GPS PPS discipline); it's running less than 10 Hertz off my desired frequency. I expected much better performance with GPS 1PPS discipline, but after trying 3 different GPS modules, I've not had better success than without. I'm beginning to question the 1PPS I've been giving the ProgRock relative to the ProgRock 1PPS requirement; perhaps the ProgRock needs a wider pulse width than 1mS, so I'm considering trying a pulse stretcher stage; perhaps 10mS will do the trick.

I did find a significant increase in stability by thermally bonding the 27MHz. crystal on the Si5351A Synth module to the heat sink of the 5V regulator AND the aluminum Bud box enclosure, so if you don't want to deal with the GPS discipline, by all means make the effort to thermally stabilize the 27MHz. crystal & then thermally isolate the ProgRock enclosure from the environment. By the way, it's an inverse relationship...warmer crystal shifts the frequency down. Simply holding my finger on the crystal is enough to move the oscillator. 

QRPLabs offers a OCXO module to replace the crystal on the Si5351A Synth module; you might consider using it. There's info in the archives of this email list on the various issues that may entail. I haven't tried that module so I can say anything about it's performance. 

I'm happy to share anything I learn along the way; feel free to contact me.

Thanks,
Robin Midgett K4IDC

On Tue, Jul 2, 2019 at 5:40 AM Jim via Groups.Io <gl1000gold=yahoo.com@groups.io> wrote:

anyone ever tried a prog rock as a crystal replacement in a ge mastr exec and how was it wired?