This one is targeted mostly toward my European readers (however, read on).
I received the following email from Olkesandr in Ukraine, it seems the Russians stole his transmitter:
My name is Oleksandr (last name redacted). I am chief editor of Ukrainian radio station CCR 648 AM. We are looking for an used am transmitter 25 or 50 kwt. Probably Your company has one for sale?
That is interesting. I asked for a few more details and received the following:
I am originally from Crimea. But in 2014 I had to leave my native town. I have been living in Kyiv since 2014. In 2017 our team of journalists launched informational broadcasting to the occupied Crimea from Chongar (it’s 1 km from Crimea in Kherson region). First we started broadcasting on 105.FM 5 kwt. But in 2018 our signal had been jammed by russians occupants. In 2019 we started broadcasting on 648 AM (10 kwt). In 2021 we increased the power to 25 kwt. But in February 2022 our transmitter was captured by russians. Now we are looking for an 25-50 kwt AM transmitter. We are going to install it in Kherson region (in controlled by Ukraine territory). I supposed we’ll be able to cover by our signal all Kherson region, Zaporizhzhya and Crimea.
Digging around, I found two news stories about it: Apparently, the Russians removed the Transmitter. By the way, Krym (pronounced cream) is Crimea in Ukrainian and Russian.
Missing Harris DX-50 transmitter, serial number MPS104705-00001
That is an interesting setup; the FM antenna is a stack of six, looks like 1/2 wave spaced six-element yagis, vertically polarised. The AM is a slant wire that goes almost to the top of the tower.
That area is still occupied by the Russians. As it is one of the two usable land transportation routes, it is likely that it will be unusable for some time after it is deoccupied.
So, here is the ask; I know that many Medium Wave transmitters have been turned off in Europe over the last several years. Is there any in that power range that is available to be moved to Ukraine? Preferably something that is still in good working order and on or close to 648 KHz. It is a long shot, but worth asking.
This is an important question these days. We are running into more situations where timing is important, especially when audio and video codecs are concerned. If there is too much time differential, the codec will unlock. More often, digital transmission methods require precise timing to prevent jitter and dropouts. Some equipment has 10 MHz or 1PPS inputs. Some equipment does not and relies on NTP to keep things in sync.
While searching online for GPS time sever, I came across this post where Austin built a Stratum 1 level time sever with a Raspberry pi and an inexpensive GPS receiver. I thought to myself; damn that sounds interesting. While a Raspberry pi is a hobbyist toy, the same setup can be done with a more serious computer to create a solid NTP server for a facility or LAN.
A little about NTP time servers; Stratum 0 server is directly connected to an atomic clock. Since GPS satellites have atomic clocks, that makes them a Stratum 0 server. Stratum 1 servers are connected to Stratum 0 servers. Stratum 2 servers are connected to Stratum 1 servers and so on. The time accuracy for a Stratum 1 server is 10 microseconds.
First, I wiped my SD card and loaded a fresh install of Raspberry pi OS. Then followed along with the instructions. For this install, I opted for the cheaper GPS receiver, the GT-U7 (not an affiliate link) from Amazon for $10.99. It comes with a cheap little antenna, which actually worked sitting inside on my desktop while I was configuring the software.
This little module is designed for a drone but works well in this application. The 1PPS output looks clean on the scope. Here is the pinout between the GT-U7 and the Raspberry pi:
I found this really nice aluminum case in a pile of disused junk at a transmitter site. It used to be for a digital TELCO STL circuit. I figured it would be nice to put the Raspberry pi and GPS receiver in a suitable home.
Raspberry pi 3 is mounted on a piece of scrap sheet steel designed to slide into the aluminum case.
We have several of these nice Panasonic GPS antennas left over from various installs. I pressed one into service on the roof of my house.
Panasonic CCAH32ST01 GPS antenna
I think a high-quality antenna is pretty important to get consistent good performance from this setup. There are three slight problems, however. Unfortunately, this antenna has been discontinued by the manufacturer. Also unfortunate, the GT-7U boards have one of those little IPX RF connectors. Fortunately, I found a short jumper with an F SMA connector. Finally, it requires +5 VDC and the GT-7U runs on 3.3 VDC. The pi does have a 5-volt rail, so I used this 2-way power divider to feed 5 volts to the antenna from one port and the received RF from the antenna goes to the GT-U7 from the other port.
If you are interested, here are the commands to get this thing running:
The next step is to make sure the serial port is turned on and enable the ssh login shell since this is going to live in the basement and I don’t want to run down there to fool around with it.
Then go to interface options, serial interface, and enable. The login over the serial interface can be left off. If ssh access is needed, enable ssh, then exit.
Once those packages have been downloaded and installed, some config file editing is needed. You may use whichever method you like, I tend to use nano. First, the /etc/config.txt and add the following to the file:
Next, there are a few more configuration files that need to be edited.
/ect/default/gpsd – there is a default file that comes with the package, it needs to be modified to start the daemon automatically and look for the pps signal on ttyS0.
Now check and see if the GPS module is working by typing cgps or gpsmon. The output should look something like this:
It did not take the module too long to find and lock onto GPS. If you don’t see something like this in five minutes or so, go back and check your wiring, and make sure that the data connections are made right. The GT-U7 has a little red LED that is lit when the PPS pulse is not being sent. If this light is not on at all, check your power connection. If it is on steady, check your antenna. If it is flashing, but you are not seeing any output in cgps or gpsmon, check your data connections.
Next and last configuration file is the /etc/chrony/chrony.conf file. At the top of the file, I added the following lines:
#custom lines for PPS
server time-a-g.nist.gov iburst
# add refclock pps
refclock SMH 0 delay .1 refid NEMA
refclock PPS /dev/pps0 refid PPS
#my home network
Leave the rest of the file alone. Basically, the time servers are added to compare the GPS time and act as a backup. The hosts on my home network are allowed to query this host and use it as an NTP server.
sudo systemctl restart chrony
Wait a couple of minutes and check the chrony console to see what is happening: chronyc sources. Should look something like this:
This was after the server had been running for a day. Chrony is great because it measures the hardware performance and creates a delay file. This is used to anticipate any hardware-added delays that the system might have. The last sample column is of interest, the number indicates the offset between the local clock and the source at the last measurement. The far column is the margin of error or greatest variation +/- of the expected values. A value of 0.0000000042 seconds or 0.042 microseconds is pretty good for an $11.00 piece of hardware. Now every host in my house is syncd to satellite within 0.042 microseconds, in lockstep through the time-space continuum.
If I were to do this professionally, I would use better hardware. I think the pi 4 has better serial and ethernet interfaces, more RAM, and a quad-core processor. Last I looked they were $75.00 at Newark.
The GPS module was the cheapest I could find on Amazon. I am slightly concerned about the longevity of this device. Perhaps it will run for a long time, or perhaps not. A quick search brought up several “hats” (plug directly into the 20-pin header). These range in price from about $30.00 to $60.00. What is required of any GPS module is 1PPS output. The configuration would be about the same although some use GPIO 4 instead of 18.
I have been reading with interest the ongoing discussion about AM radios in Electric Vehicles. Rather than rehash the what, I thought it would be nice to dig into why it is happening.
My first thought is that many of the electronics use PDM or PWM to control various stages of charging, converting, or discharging the storage system. I quick review of a typical EV basic diagram shows that there are several systems involved
Searching through various chip makers’ data sheets on Li-ion battery chargers, DC voltage to voltage converters, regenerative braking systems, traction motor inverters, and so on shows that all of those systems use PWM. Some of those PWM frequencies are right in the AM band, while others are not. That explains why different manufacturers have different takes on AM radios in EVs.
All of those electrical components are controlled by an electronic system that handles battery charging,
This basic diagram shows several sections that rely on PWM to function. The traction inverter is very complicated, with sensors running to each motor and each wheel for traction control, etc.
I imagine the average EV driving down the road in a cloud of PWM-based electrical noise. Whether or not that creates interference with AM reception depends solely on the PWM frequency the chip manufacturer chooses. That is not all, even when sitting in the garage charging, the Li-ion battery chargers use PWM.
It seems a monumental task to attempt to mitigate the noise issue. The real question is; does the general public and more specifically, those who want to own an EV care about AM broadcasting?
There are many alternative entertainment options these days. I would say the average Tesla driver listens to iTunes.
It would be interesting to test MA-3 reception in a Tesla. That would be a real-world test to see how the HD Radio codec stands up to electrical noise. I would say the same about DRM, but you would need to find a receiver first.
Occasionally, I get to go for a nice walk in a snowstorm. No, I am not being sarcastic. It is the middle of March and winter has decided to make an appearance. One of the FM stations we take care of went off the air and the remote control was not able to get the transmitter to come back on, so a stroll through the woods was necessary. This station is located at Sam’s Point Preserve, in Craigsmore NY.
The site is owned by Vertical Bridge. There are a few tenants on the tower and fortunately, somebody left the gate open before it snowed. I was somewhat dreading trying to wrestle with it when I got to the site.
The problem itself seems to be due to a power hit; the main transmitter was off and the remote control, a wheezing Genter VRC-2000, was not able to control either the main or the backup. Those should be replaced at some point.
There are several other towers up here for various cell carriers, 911 dispatch, etc.
My SO decided to come along.
My phone said we walked 2.7 miles round trip, which sounds about right. The station is back on the air. When I can get up there with a vehicle in a few weeks, I will look into the remote control problem.