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I managed to blow two of my GPS Disciplined Oscillators. I explain how that happened and what you can do to avoid it.
I also talk about the DIY bench power supply project which is underway again.
I give an overview of my project on building a cheap high accuracy quartz clock.
If you are looking for a cheaper / lower priced but excellent Low-jitter GPS-locked precision frequency reference (GPSDO):
www.leobodnar.com/shop/index.p...
Some GPS antenna splitters here:
www.gpssource.com/collections...
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You can use a cheap type F splitter for CATV and use a DC blocker on one of the outputs. That allows the voltage from only one to go into the splitter and antenna. I’ve done it many times. You just need an antenna with a high gain LNA.
But the big thing is an inline DC block adapter which is less than ten bucks.
Thanks Martin! Even if I don't really care much about a project that you are doing, I still find it interesting.
Great to see these topics, I'm just revisiting my GPSDO and clock projects too but PCB layout is taking time... Thanks Martin.
My pleasure, thanks for posting good man.
I knew exactly what you'd done immediately! Another poster mentioned you might be able to repair the bias-T on the blown unit. Now I've never let the magic smoke out of anything....NOT! You may want to think about distributing the 10MHz system around your workbench. Mini-Circuits passive power dividers will work but at some point fan-out occurs. Powered distribution amplifiers make life really easy. Thanks for sharing Martin. 73 - Dino KL0S
Cheap way to get those distribution amplifiers is to look for video distribution amplifiers, which are going to have a reasonable response up to 10MHz, and will have a gain after termination of 1. most have 75R BNC connections on them, a decent power amplifier with a gain of 2 and a really low impedance output to series 75R resistors to each output. Easy to change the termination resistors to 50R, either by putting in a new resistor or solder a 150R resistor across the original output ones, and change input resistor as well. They also will do at least 5V peak to peak for the better units with 15V power rails, and many are also DC coupled as well if they are studio equipment, though the more common AV amplifiers are AC coupled input and output, so you are protected against feeding DC back into the unit, though the capacitor might complain long term and pop.
@@SeanBZA Yep, lots of guy do exactly that. TAPR still makes a dedicated 10MHz 6-port distribution amp although unfortunately they no longer offer the case to put it in. I actually have three of them to go out to all the test gear around the bench and radios at the ham desk. And of course you can cascade them as well depending on your physical layout. As with all the rats nest of cables it pays to mark them and keep a schematic of how everything is connected.
Splitter is not a normal RF term. Divider or circulator. If I needed a active antenna with signal I would have one good LNA connected to one good passive antenna. Split the LNA output to whatever unit you need, it's just a RF signal.
I immediately suspected what he did and at the same time I was thinking, what a newbie mistake...
Even without the DC power issue, there's the impedance problem. At 1575MHz the Y wire will introduce reflections that are probably very bad on gps signals. This may prevent proper reception and localisation (and timing)...
Well.. mixed 50 ohm and 75 ohm cabling + splitter do actually work.. not going to recommend it.
You can use a power divider, LNA, and DC blocks - But those antennas are so damn cheap, running a few of them seems to be a great solution. I'd love to have a little RF building that sounds awesome.
Bulova Precisionist wrist watches, with their 262 kHz oscillator, are supposedly accurate to better than 10 seconds per year. My first one was Cdn$130, and my second one, the Lunar Pilot, was Cdn$230 (both on sale at about 50% off street price). I just checked them against NTP, and they're both about 2s fast after being set about four months ago (with the time change for DST). I'd say that they meet their specified performance.
You can use a DC block on one of the units rather than the GOS 2:1 splitter. I can't really determine what the connector on the antenna ports are, but they look like SMAs. SMA DC blocks are used on Spectrum Analyzer ports, Network Analyser ports, etc., to prevent damage to the front ends by DC voltages. When I last bought them, they ran about $40/ea. If the company still exists, Pasternack Enterprises is where I used to buy them.
Thanks for the info.
Very useful video.
Martin, can you do a review of the Leo Bodnar frequency reference. i.e. output range, signal quality, stability, accuracy, pros, cons, possibly a tear down?? I'm interested in getting one as a home lab standard but can't decide between a Leo Bodnar or a BG7TBL GPSDO.
I have destroyed the active antenna on a couple of receivers. I'm 99% sure I zapped it with an static discharge.
Leo Bodnar makes some really nice electronics ... I'm familiar with their sim racing products (-8
WOW, too bad about blowing up those 2 GPS devices! Without looking inside seems like it should have current limiting on antenna port would protect it. I have connected 2 GPS like you have and had NO problem, maybe I just lucked out ? 73
Very interesting and useful, but please when holding something in front of the camera for your viewers to look at: hold it STILL , not waving it around and when pointing at a part hold your finger STILL and do not keep poking at it; the blurred image is very distracting and difficult to observe in detail.
👍 You can include me in the count.
Awesome
👍
Antenna bias messing up your day?
3.3V and 5V is common, not so sure the GPS like to be powered via the antenna port.
Also: Connect the antennas before connecting power.
There is a bias-T (current via inductor, capacitor for RF) inside the module, and a sharp ramp may kill the RF input.
If you mix, at least make sure they use the same antenna voltage!
And yes, using a splitter do work
How accurate are we talking? The Dallas DS3231 or DS32KHZ should supposedly be accurate to less than a minute a year over typical indoor temperature ranges, and I'm pretty sure there are clock kits out there using the former. Doing better than that will probably be hard.
They are using GPS to syncronize to The United States Naval Observatory's atomic clocks.
The occilator is adjusted by the GPS, so time is less than 100 ns off, and frequency is better than 100 ppb accuracy.
(more like
I think that it's an AWESOME IDEA! Diciplined quartz /oven
And also so cool if it showed GMT as a separate pair of digits (could be different colour) and then a local 12 or 24 hour clock format. Even cooler? Big led digit format, kind of a NASA Apollo meets Back to the Future kind of display: Year Month Day Also seems STRANGE to me that there aren't software competitors to Geochron Clock... Is is just me?
73 DE W8LV BILL
So you want accurate timekeeping with GPS?
Then try this experiment:
Setup one of the GPS you have already, log the data, just time and position and accuracy from the GPS.
Then get a precision antenna with a choke ring, leobodnar have one: www.leobodnar.com/shop/index.php?main_page=product_info&products_id=286 Some info on choke ring: en.wikipedia.org/wiki/Choke_ring_antenna
Log the same data with this antenna, and you will most likely see much more stability in the position, the main reason is that you GPS antenna is very sensitive to ghost signals, that can be from reflection of the signal from foreign objects around the antenna, these objects can be anything, threes, buildings, posts, and even the surface the antenna is standing on.
So by reducing ghost signals (GPS signals that is out of timing because they travel of a non direct path) you get a more precise timing.
@12m25s: The question... Answer with another question: What is that crazy Y-cable?
Even ignoring the issue with the DC "bias" voltage, you shouldn't split RF with parallel connections like that.
There is some possible solution posted on this electronics forum about the power-supply stability issue that may be worth looking into.
www.edaboard.com/showthread.php?354838-Power-Supply-Stability-and-Troubleshooting
1st boom
The input should still be working normally the power supply for the antenna is what fails. As the power is fed to the antenna, the dc is not wanted on the input to the receiver. You should find the receiver is decoupled from the DC with a cap.
You just put a capacitor in line before the oscillator
He has so much expensive equipment and seems to know his stuff but also still sometimes makes horrible rookie mistakes & doesn't even seem to know how to build a DC block for a bias T :)
Sure, given he isn't hotplugging the cables. Hotplugging would give a pulse of bias voltage into the reciever. (given one of them is unpowered, or they have different bias voltage)
erlendse correct but if he is hot plugging why have the splitter just hot plug a single cable as you need lol
@@brianwild4640 no reason given, just bad practices during assembly.
Bit boring video