Update: This was delivered on May 2, 2025 in good condition. It took 24 days to get here, 21 of which were sitting in Memphis.
A cautionary tale.
I have purchased and sold several things through Ebay over the years. Most of the time the transactions go smoothly. The item is more or less as described and it arrives in a reasonable time period.
All good.
Recently, I saw this very nice looking Agilent E5061B Vector Network Analyzer. The price was right and it even came with this nice hard case. This is great, I need something like this for an upcoming project.
The only very small, almost too small to notice possible issue was; its in Canada. With all the trade rhetoric going around, I thought, perhaps I should look to buy something from the US. Nah, its fine, after all, it is not coming from China.
Nope.
The order went in, the seller shipped the package, it arrived in Memphis, TN and the trail goes cold after that:
I have emailed and called FedEx several times. They say, “all good, we have all the documentation we need, it will be shipped out shortly.” Last time I called, I spoke to a woman in the Philippines who’s phone cut out with every other word.
It seems probable that all international shipments are stuck in some giant FedEx terminal waiting for someone to say okay or calculate some tariff. The pessimistic view is that it has been stolen. I have lost things in transit.
I should have listened to my little voice. While the problem is not with Ebay itself, importing equipment from another country is problematic. I would advise anyone bidding on Ebay to pay close attention to the location of the item you are purchasing.
In the mean time, I still need to finish my project…
I found this obviously used GPS antenna in a storage room at one of our client’s transmitter sites.
How often have you asked that same question about some older piece of equipment lying around? There is a trend among engineers to hold off on getting rid of old equipment because someday, perhaps, it can be used again. Often, these treasures so lovingly stored away for many years or decades do not work when that day finally comes along, leading to disappointment and despair.
This GPS antenna falls into that category.
What to do, what to do…
Fortunately, there is an easy way to test this antenna and do other things with GPS. I had one GT-U7 GPS receiver module left over from a previous project.
Couple that with an FT232RL FTDI USB to serial converter and a bit of software from u-blox. The GPS receiver is a clone of a u-blox M6 GNSS chip, meaning the u-center software will work with it. That is a free Windows software application. The u-center software is great because you can access all of the options on the GPS receiver chip. Since this is to be used for testing, I enabled the LNB voltage sensing and protection features in the antenna configuration menu. Thus, the software will notify if there is a short circuit or open circuit in the GPS antenna under test.
GPS survey receiver parts
I had this nice Hammond 1590WB diecast enclosure left over from a previous project. It’s probably a bit of overkill, any small enclosure would work, but why buy something new?
Mini USB 2.0 Cable, USB A to B Cable, 3 feet, Amazon B00006B6PH, $3.95
The cross-connect between the two modules is fairly straightforward:
GT-U7 pin
use
FT232RL pin
use
2
TXD
2
RXD
3
RXD
3
TXD
4
GND
5
GND
5
VCC
4
VCC
Pin out
Internal mounting
This particular FTDI module has a jumper to set the VCC to 3.3 or 5 volts DC. I left it on 5VDC to run the GPS receiver and provide LNB power to the connected GPS antenna.
I used a piece of packing foam tacked into the inside of the enclosure with gorilla glue, then tacked the FTDI module to the foam with gorilla glue. The GPS module is tucked under the header for the FTDI chip.
The software is pretty easy to use. The most difficult thing is figuring out which com port and baud rate to use. To find the com port, open the Windows device manager then plug the FTDI module in. The new serial device should register automatically. Click on the new device to get the com port information. I find the GT-U7 modules are most often set to 9600 from the factory, but it could be anything. I suggest trying different baud rates until you start seeing data.
Putting all of those things together, we get this miniature USB power GPS receiver with software that can show how well a GPS antenna is working and whether or not the location has good (or good enough) reception. One could also check the coax going to a GPS antenna and make sure that it is working right and not too long. Or check and see if a line amplifier is working, etc.
The answer to the above question is, yes!
u-center software screenshot, GPS antenna under test
The used GPS antenna is picking up plenty of signals from a less-than-optimum position. I’d say this is a keeper.
Device under test; GPS antenna on window sillGPS survey receiver
A little bit of orange paint, also left over, and a few labels and it looks like a professional unit. Not bad for some leftover parts I had lying around.
I found a great resource for learning about test and measurement on Rohde Schwarz’s YouTube channel. Each video is about 5 to 15 minutes long and covers the basics of RF test equipment, measurement parameters, and definitions.
Measuring RF systems is an important part of Broadcast Engineering. Many folks think that RF plants are going away, replaced by all IP content distribution. I disagree; Terrestrial Broadcasting will be around for a while yet. AM and FM radios are still ubiquitous in cars, homes, businesses, etc. There is no other information distribution method that is as simple and robust as over-the-air broadcasts. That is why Federal Emergency Management is still spending money on hardening broadcast facilities.
The Internet and Mobile Data in particular are susceptible to failure in emergencies. Cellular networks were almost useless due to congestion or system outages during the 9/11 attack or a natural disaster such as Hurricane Sandy.
Radio still has a role to play.
As the older Broadcast Engineers retire, there is a dearth of qualified RF specialists who can make accurate measurements on antenna systems, filters, and other transmission system components. There are very few mentoring opportunities, especially in commercial broadcasting. Gone are the days of several engineers on staff, when there was time to teach the younger people some hard-learned lessons. One of the reasons I write this blog is to pass along some of that knowledge to others so that the industry might survive.
By now, most have heard of the passing of Ray Topp, publisher of Radio Guide magazine. I was shocked when I first learned about it in the middle of February. The family has decided to cease publishing the magazine, which is understandable, but also a loss for the industry. The goal of Radio Guide was to provide “real-world technical information.” When I wrote an article, I always thought about the various people I worked with over the years and what they were concerned with.
The last I heard from Ray was the third week in December. He said he had a bout of COVID and there were some complications. He said he was trying very hard to get the January/February 2023 issue done. I sent in my article in early January but never heard anything back, which is unusual. When the publishing date came and went, I thought that perhaps he was still recovering. Unfortunately, that was not so.
My final article for Radio Guide was to be titled: Learning with the Libra VNA
