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Forum Index : Microcontroller and PC projects : Silicon Chip GPS Synced Freq. Reference

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Merv
Newbie

Joined: 01/04/2019
Location: Australia
Posts: 4
Posted: 05:10am 01 Apr 2019
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I built the kit described in the Sep/Oct 2018 magazines and have had a lot of trouble getting stable/accurate frequencies. Anybody else who has built this kit and who has an accurate frequency counter to check the outputs can perhaps enlighten me as to if I am alone with this problem.
Have been making PCB's via China and populating my boards for the past 15 years so rightly or wrongly I'm assuming my problems are probably not hardware related and to try to prove this I've received 2 spare boards from S/C and once all the parts arrive from Digikey I'll do a new board using solder paste and reflow techniques and if this solves my problems then I am happy to accept that the existing problems are not software related and were possibly component and or hand soldering ones.
At least the project has kept me "off the streets" for a number of months!!

Merv
 
palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006
Posted: 07:01am 01 Apr 2019
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Welcome to the forum Merv. I did not build the project but have built a lot of SC projects and they are extremely helpful if you contact them and outline your problem.
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
Merv
Newbie

Joined: 01/04/2019
Location: Australia
Posts: 4
Posted: 03:26am 02 Apr 2019
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Hi Paical,
I have been in contact on numerous occasions with S/C including the Author of the article but after much help and co-operation from them and him they are at a loss to make any further suggestions.
I do not need the Generator as I have a good HP 5335A Counter which is GPS locked so the building of this kit was out of curiosity rather than necessity so I would like to get to the bottom of the problem and hoped other builders would share their problems, if any, and thus help me resolve mine.
My spare components arrived from Digikey yesterday so I'll have another bash at it.
Merv
 
VK2CBH
Newbie

Joined: 18/08/2014
Location: Australia
Posts: 11
Posted: 10:49am 24 Apr 2019
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Merv,

I have built the same unit and looking at the 40MHz signal on the o/p connectors I see a very unstable signal and the same is on a frequency counter.
I will power it up again and make some further observations and write them down and take screen shots too. I will try and get an accurate frequency counter from work to verify and also get a spectrum analyser to do the same.

I did have some trouble getting the GPS module (a VK16E) working. The problem was no GPS lock and GPS fix was "V" and not "A". Powered the Micromite LCD backpack up on its own with the GPS connected and all good. Problem was I had to power the GPS unit from the 5 volt line and not as i did before the 3.3 volt line. I assume the project was drawing too much current from the 3.3 volt line.

Can you let me know how your new build goes.

Cheers Brett
 
Merv
Newbie

Joined: 01/04/2019
Location: Australia
Posts: 4
Posted: 11:46am 18 May 2019
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Hi Brett,
Thanks for your comments. I made a second unit which I reflow soldered and it has major problems in that once I get the 40Mhz output reading correctly on output 4 (this is checked on my very accurate HP5335A Counter which has a 10Mhz GPS locked oscillator) and leave the unit running in a temperature controlled room it can be off frequency as much as 2 to 3 Mhz in a matter of hours. I'm not sure what the problem is as I've built it to spec and the oven covers are on and the unit is in it's box.
I tend to think it is inherently unstable and this could be a software problem but as I'm no guru on software I'm always open to any other suggestions. It will be interesting to see what your borrowed counter shows.
I have not bothered to look at the quality of the RF output on my Spectrum Analyzer yet as if it is not going to be frequency reliable then it is of no use to me. To have to spend time every time I may need to use it trying to get it on frequency is just not on.
I wonder how many other people have built it and whether they are aware the output shown on the LCD is not necessarily accurate?
Regards,
Merv VK6BMT
 
VK2CBH
Newbie

Joined: 18/08/2014
Location: Australia
Posts: 11
Posted: 07:28am 03 Jun 2019
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Hi Merv,

I have done some more checks with this unit and when the I have a GPS lock the 40MHz O/P looks distorted and is a few meg below what it should be.

I have tried a few different GPS modules same issue.

I have also noticed a lot of noise on the 5 volt line. I used a phone charger PS and a linear PS. I have a different back pack with SMD capacitors used so I will try that one out and see if the noise is reduced.

I could not get a 40MHz signal from the O/P of the VCO when I powered the main board on it own.

I had a spare VCO chip and wired it up and could not get a 40MHz signal out of it even with the the VC line (pin 1) with 1.65 volts applied to it. It was wired up correctly.

A mate of mine was considering building it but will put it on hold until I get my unit working fully.

Cheers Brett VK2CBH
 
Merv
Newbie

Joined: 01/04/2019
Location: Australia
Posts: 4
Posted: 04:36am 12 Jun 2019
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Hi Brett,

Thanks for the further comments stating the problems you are facing.

I have packed my completed unit away and filed a mental note to be extremely cautious trying any other fairly sophisticated projects from SC.

I'm convinced there are a number of basic flaws in the hardware design as well as possible glitches in the software.

I'm happy to unload my unit to somebody who wants to play around with it and would accept a reasonable offer.

Good luck with yours.

Regards,
Merv VK6BMT
 
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