We were doing some overnight maintenance on one of the class A AM’s in New York the other night. The aged Automatic Transfer Switch on the electrical service entrance needed to be replaced, thus the power to the entire facility needed to be cut while the old switch was removed and the new switch installed.
During this period, we took the opportunity to do some maintenance on the main and aux towers. All went well. We also notified the National Radio Club that the station was going to be off the air so that their members could log some rare DX. My thought process here was that we might also find a few daytimers who were still on the air or a DA night who was operating with their daytime facilities. A quick look at MW list shows that there are several such stations on 770 KHz:
Alas, the answer was no, nobody was on the air who should not have been. Reports from Cape Cod, Massachusetts; New Foundland, Canada; Manassas, Virginia; West Union, South Carolina; and south west, Ohio have Cuban and South American stations on the air (Radio Artemisa, Radio Rebelde, Radio Oriental) but all of the east coast daytimers are off.
The 180 degree main mast for WABC is in good shape. You can deride AM and say it is outdated. However, it still gets out and covers vast distances.
We just finished installing one of these units on Mount Beacon for WSPK. Mount Beacon is around 1,500 feet high and is accessed by a road which is a little bit rough. After the snow flies, the only way to get there is a snow machine or perhaps a helicopter. Thus, whatever is installed there needs to be reliable.
My first comment, I recall 10 KW FM transmitters being much larger. This unit is pretty compact and we probably could have fit two of them in this Mid Atlantic rack had we wanted to.
The transmitter itself is pretty simple, four RF modules powered by seven OEM switching power supplies with two fan power supplies, one for each fan unit. This is driven and controlled by a STXe 500 watt exciter.
The back has a 1 5/8 inch EIA flange output, some power connections, remote control interface, etc. Pretty simple overall.
I can also say, there was a noticeable improvement in the audio quality when this was placed in service.
Recently, I pried open my wallet and plunked down the sum of $150.00 for one of these little devices. Now, to be certain, this is not a replacement for a real VNA, especially at a high power broadcast site. However, it can be used for basic trouble shooting and I have had a good deal of fun fooling around with it.
First, a few quick specifications:
Type: SSA-2N NanoVNA V2.2
Frequency range: 50 KHz to 3 GHz
Power output: -50 to +10 dB
Measurement points: 201 (or 1024 with software and computer)
Measurement types: S11, S12 and S21
Screen Size: 4 inch touch screen
Traces: up to 4
Battery: 3000mAh Lithium Ion
Software OS (VNA-QT): Win 7, Win 10, Linux, MacOS
The unit I purchased came with a small carrying case, calibration loads and test jumpers. The software is downloadable and is easily configured.
What I really like about it is the internal battery and the touch screen.
So what can it be used for?
Test a coaxial cable
Measure the length of a coaxial cable
Figure out what frequency an antenna is designed for
Tune a 1/4 wave stub to make a notch filter
Measure the characteristics of a crystal/holder
Measure a capacitor
Measure an inductor
Tune a parallel resonant LC circuit to make a notch filter
Tune a filter can
Test a high pass, low pass or band pass filter
Sweep an antenna (Simple AM, FM, RPU, STL, WiFi)
Check isocouplers for proper circuit functioning
Pretty much anything you need to know about RF antennas, filters and transmission lines can be learned with a VNA. One thing to keep in mind; the measurement points are limited, especially in the stand alone mode. Thus, the smaller the frequency span, the better the measurement resolution will be.
While this is a very inexpensive device designed mainly for Amateur Radio, it can be useful to diagnose antenna and transmission line problems. Would I depend on it to make precise measurements? No. Especially things required by the FCC like base impedance measurements on an AM tower or channel filter measurements for a TV station. Would it work at a high RF transmitter site with multiple AM/FM/TV transmitters? No and chances are you might burn out the front end. Those types of things are best done with professional equipment that has much better accuracy and resolution.
It is a pretty good little tool for basic troubleshooting. One can look at the individual components of an AM ATU for example, or measure the input impedance to see if there has been a shift (should normally be 50 ohms). It is small enough that it can be included in a basic tool kit. It is self powered. Not bad at all for the price.
I just finished a full alignment of my Kenwood R-2000 receiver and tonight I am treated with the pleasing tones of “Jazz from the Left,” on WRMI. Jazz from the left means the west coast sound, aka Smooth Jazz as I am given to understand. I spent some time on the west coast and beyond. I have fond memories of those years.
It is amazing to me still, that a simple AM receiver demodulating +/- 4.5 Khz audio bandwidth from 1,057 miles (1701 km) away can sound that good. That is being received directly; no Internet Service Provider, no satellite service, just a transmitter and a receiver.
There is an art to all this, which is being forgotten. A few minutes with a manual, a volt meter, a tone generator and a non-conductive screw driver can bring something that was neglected back to life sounding as good as the day it left the factory 35 years ago. Try that with with your very expensive iPhone 10,000,000x! Of course, you will need those tiny pentalobe tools to get the screws out. Apple would rather you return your expensive i device to their expensive i store so that their i geniuses can fix it for you.
I don’t know, maybe I am an old fart. Perhaps the right to repair the appliances that I purchased and therefore should own is an old fashioned point of view. After all, all of these corporations have my best interests at heart, right?
I recommend you support your not so local shortwave stations by listening and supporting their programmers. Even in 2021, there are still many shortwave broadcasts that are worth listening to!