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Author Topic: Garman GPS as frequency reference?  (Read 447 times)

WA2ISE

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Garman GPS as frequency reference?
« on: February 25, 2021, 01:20:16 PM »

I've heard  :D that the GPS system uses a very accurate reference frequency, and that I might be able to tap into this frequency (or a directly related frequency) to then use as a reference to check how accurate my HF rig's receiver is.  I have a couple Garman GPSs laying around and I can receive GPS signals in my shack (I use one GPS as a shack clock, and as a small Geochron display).  It doesn't matter what the frequency is, as long as I know that it is locked to the GPS system reference frequency.  I would tap this frequency, maybe add a buffer transistor to drive a length of small coax, to feed my HF rig. 
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K6SDW

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Re: Garman GPS as frequency reference?
« Reply #1 on: February 25, 2021, 04:13:08 PM »

QRp Labs in Europe sells a GPS receiver, with built in antenna, and clock kit, very cheap that will give you GPS-accurate pulses for clocks and other devices. Not sure this is what your'e looking for. Super easy kit and works perfect and displays the time with high accuracy. Hans makes and sells a lot of ham related kits.

GL
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KX4OM

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Re: Garman GPS as frequency reference?
« Reply #2 on: February 25, 2021, 04:32:59 PM »

QRPLabs (qrp-labs.com) sells GPS kits to stabilize the frequencies of some of their rigs. They (Hans Summers, G0UPL) participate in the groups.io site  groups.io/g/QRPLabs/topics. You might get answers to some of your questions there.

Hans also has a website that has a lot of his earlier efforts and experiments www.hanssummers.com/

Ted, KX4OM
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K6AER

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Re: Garman GPS as frequency reference?
« Reply #3 on: February 25, 2021, 07:33:45 PM »

Microphone response, audio pass band adjustments, radio aging and why do you need 10 Hz accuracy? Unless your radio is a SDR unit you also have offset oscillators which will not be synced to the reference standard.

In addition your modulation sidebands can fall outside of the ham bands which a highly accurate reference oscillator will not save you from the FCC.

Lastly not all transceivers use a 10 MHz clock oscillator nor does the microprocessor care. In the case of the newer Icom's, you can change the SDR percentage offset to move your master frequency in any direction. This is why transceivers made in the last thirty years have a receiver RIT.
« Last Edit: February 25, 2021, 07:46:45 PM by K6AER »
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KB5ZSM

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Re: Garman GPS as frequency reference?
« Reply #4 on: February 25, 2021, 11:14:22 PM »

I think I know what your thinking. It would be able to give you a reference to test the accuracy of a VFO or other such divices (kind of like a marker generator). You could see how well your VFO would track while using an old boat anchor. It is a fun and usefull addition to any work bench so don't let the elders snub you. Keep on experimenting and learning. Hands-on is the best teacher. I'll want to look at the QRPLABs myself. Sounds kind of like a neat place & Keep asking Questions.

73s   Win  (KB5ZSM)
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N4OGW

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Re: Garman GPS as frequency reference?
« Reply #5 on: February 26, 2021, 09:08:03 AM »

QRPLabs (qrp-labs.com) sells GPS kits to stabilize the frequencies of some of their rigs. They (Hans Summers, G0UPL) participate in the groups.io site  groups.io/g/QRPLabs/topics. You might get answers to some of your questions there.

Hans also has a website that has a lot of his earlier efforts and experiments www.hanssummers.com/

Ted, KX4OM

I am using the QRP labs OXCO (http://qrp-labs.com/ocxokit.html) and GPS receiver (http://qrp-labs.com/qlg1.html) as a GPS frequency reference for my Elecraft K3. This has worked well and was cheap. I mounted them in a small box and have them running 24/7. Insulating the OXCO helped its stability a lot- I wrapped it in bubble wrap. I also found an external GPS antenna on ebay.

As to why one would need the frequency accuracy and  stability, one reason is weak-signal digital modes on VHF/UHF. Being on frequency is critical when operating 2m meteor scatter using MSK144.

Tor N4OGW


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KX4OM

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Re: Garman GPS as frequency reference?
« Reply #6 on: February 27, 2021, 08:38:36 AM »

A GPS project I'm working on is a 10 MHz GPS-disciplined oscillator combined with an ovenized OCXO. It is from instructables.com by author yannick99.

https://www.instructables.com/GPSDO-YT-10-Mhz-Lcd-2x16-With-LED/

It consists of a PC board (artwork provided, as well as gerbers) and is based on an Atmega 328P (HEX and source code provided), an inexpensive GPS module, an LCD and the OCXO. It has been a popular project, and the author continues to update it. The only significant cost outlays are the ubox Neo-6M module GPS and the OCXO. The GPS module built up on a PC board, with antenna, is under $10 on eBay. I bought the surplus Isotemp OCXO model from the article on eBay for less than $30, I see there is currently one listed there for $14.98 from China.

There are several examples of builds by others shown in the instructable.

My build was interrupted by having to move out of my house for 6 months due to a tree fall; we just moved back in, and I am currently reassembling my lab and ham station in the basement.

Ted, KX4OM 
« Last Edit: February 27, 2021, 08:58:26 AM by KX4OM »
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KD6VXI

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Re: Garman GPS as frequency reference?
« Reply #7 on: February 28, 2021, 07:45:15 AM »

Even I'm old enough to remember zero beat on wwv or chu to ensure I was on the frequency displayed.

Sheesh, we are now looking at ppm accuracy.

What a great time we live in!

--Shane
KD6VXI
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KM3F

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Re: Garman GPS as frequency reference?
« Reply #8 on: March 05, 2021, 08:27:43 PM »

First basic frequency check is right on the radio.
Tune in the highest WWV frequency you can receive.
Set the VFO on that frequency.  Example 15.0000 mhz.
Then switch to CW mode.
Listen to the CW beat tone frequency.
Then switch to the other reverse side's tone.
They should sound the same or nearly so.
Believe it or not your  percieved difference can be less than 5 hertz on mutiple reversals checks.
Your hearing on a compairision like this is very accurate and good enough for any mode as long as it's stable.
If both sides don't sound the same pitch, then you can make adjustment of the master oscillator until they are the same, and don't need a frequency counter that may not even be as good.
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