Antennas: again to the longer term

TV receiving antennas are one of the most popular topics based on the number of emails I receive from readers. Often times they will request additional information on antennas that I wrote about years ago – the Gray Hoverman, which was covered in 2008, or the high-gain wire rhombic I covered in 2006.

In the meantime, I often learn new things from readers. Bill Robbins, a wireless television viewer in Florida, was concerned about reception from his antenna setup. I have found that trying to level or adjust a TV antenna using the quality indicator on a TV or the signal level on a test tool is difficult, slow, and does not always find the best orientation. A spectrum analyzer is a better choice.

Fortunately, these no longer cost thousands of dollars. I recommended Robbins to take an Airspy SDR and use his free Spectrum Spy software to view the spectrum of the incoming signals and point the antenna on the desired channels for the best level and flatness (least multipath). He bought an Airspy R2 and sent me a screenshot of the bottom line. It looked good. He uses a Winegard LNA-200 (one that I also found works fine) and RG-11 coaxial cable from the antenna to his in-home distribution setup. However, I had never heard of the TV antenna he was using – the HD stacker. When he asked my opinion, I looked into it and found it quite interesting.

DIGITENNA AND HD STACKER

In some markets there is a mix of UHF and VHF stations – mostly with a high VHF value (7–13) – but also after repackaging, sometimes with a low VHF value (2–6). Unfortunately, the last time I checked, the most common option for people who need high FM gain was a monstrous, low FM UHF antenna that was the size of a Volkswagen. You know them: you have low VHF elements in the background, followed by high VHF elements, followed by a long UHF section.

The HD stacker has low VHF elements (Fig. 1) which require a width of 60.3 inches but are only 70 inches long compared to lower VHF and UHF monster antennas which are longer than twice as long. I didn’t find any gain specs for the antenna, but I suspect the gain on VHF and UHF is comparable to the monster antennas. Denny’s Antenna Service (dennysantennaservice.com) did a comparison of the outdoor antennas and found that the HD stacker worked just as well as the huge Winegard HD8200U (Fig. 2), except for some low-UHF channels.

Fig. 2: HD8200u (Image credit: Doug Lung)

This test was performed prior to repackaging as it includes stations over channel 36. The comparison included the DigiTenna DUV-XF, which, with the exception of VHF and high UHF (via channel 36), ran at least as well as the HD stacker. The DigiTenna contains an amplifier with a second input that can be used for a high gain antenna and only VHF to create a stack. However, when I was looking for one of these antennas for another reader, it looked like antennas only for VHF had been discontinued at least by the major manufacturers of consumer antennas.

DigiTennas’ performance on lower UHF channels should improve somewhat as Brad Eckwielen, President of DigiTenna, told me he was changing the dipole driven fan element design to optimize performance between channels 14 and 36 and ignoring channels above 36 Perhaps more Eckwielen is important for viewers who need a preamplifier in areas with weak signals. He has modified his amplifier to offer LTE filtering of 20 to 30 dB over channel 36 (608 MHz).

Most filters now allow through signals up to 698 MHz (channel 51). This is important because T-Mobile and other network operators are setting up cell sites in the 600 MHz band. TV tuners that still cover channel 51 (if not channel 69) can be overloaded when using a preamplifier. Further information on the preamplifier can be found at digitenna.com/Products.

NEW NANOVNA DESIGN

In my January column (“Checking Out TV Antennas with a VNA of $ 130”), I used a NanoVNA to check a number of different indoor antennas and found that most of them had increased return loss at low UHF . It would be interesting to see what the new DigiTenna controlled element looks like after being optimized for less UHF, and I wonder if other manufacturers like HD Stacker, Winegard, Channel Master, Antennas Direct, etc. will change their designs to improve performance in the cut UHF band.

Since the VNA article, I’ve learned more about the different varieties of NanoVNA. Some new versions have come out, the software has improved, but unfortunately it has become much more difficult to get products from China due to the drastic drop in flights between the US and China due to COVID-19. Products ordered from China are usually shipped via ePacket or a similar service that depends on space available on flights to the US and being handed over to the US Post Office for delivery. Of the two products I ordered this year, one made it to me in about two months. The other was sent back to the sender after a little over two months, apparently because the sender couldn’t find any flights. When ordering equipment from China, use DHL, UPS, or any other service with your own plane.

The NanoVNA device I recommend right now is the one with the 4.3 inch LCD that I showed in the January column. This turned out to be NanoVNA-F. Details on the design of the device can be found at https://github.com/flyoob/NanoVNA-F. Note that the latest version has an output of 0 dBm at the base frequency of the generator (up to 300 MHz) and works up to the fifth harmonic and allows measurements up to 1.5 GHz.

Its dynamic range is 70 dB in the 10 kHz to 300 MHz band and drops to 60 dB in the 300 MHz to 900 MHz band. I had no problem updating the firmware in my device to the latest firmware for 2019 – it’s as easy as copying a file to a flash drive – but I couldn’t take advantage of the extra output (older devices were -13 dBm) and the improved RF bridge in the latest hardware version.

If you want the latest hardware, order at www.aliexpress.com in the DeepElec Store and use DHL shipping. If you want to order from a US source like Amazon or eBay, check the version on the DeepElec store (pictures, specs, etc) and make sure the version you ordered sees the same version, specs, and same just like the DeepElec NanoVNA-F. The price should be higher too, assuming people are buying these units from DeepElec and not importing a no-name clone that may not offer the same performance.

I recently heard about a new NanoVNA, the NanoVNA-V2. This device has a smaller screen, no battery and no case as can be seen on the official website at https://nanorfe.com/nanovna-v2.html and also at https://groups.io/g/NanoVNA- . V2. The websites claim to work up to 3 GHz with a dynamic range of 40 dB at that frequency. The website www.tindie.com/products/hcxqsgroup/nanovna-v2/ currently sells official units starting at $ 59.95. A calibration kit and an acrylic housing are available at an additional cost. Special software for Windows, Mac OS and Linux is available for NanoVNA-V2 at https://github.com/nanovna/NanoVNA-QT/releases.

The latest version of NanoVNA-Saver also runs on Mac OS, Windows or Linux and works with most NanoVNA hardware, including NanoVNA-F and NanoVNA-V2. This is the software I used in the January article. The software is updated regularly and remains my choice to operate the NanoVNA from a laptop or PC.

If you don’t want to go to the hassle of installing software to run NanoVNA, a web-based client is now available that works with NanoVNA-F and a few other devices. Cho45’s software, available at https://github.com/cho45/NanoVNA-Web-Client, should work on Mac OS, Windows, Linux, or Android. I’ve tested it with the NanoVNA-F on Windows, Linux, and Android and it worked well, with surprising functionality.

Fig. 3: NanoVNA WebClient (Image credit: NanoVAN)

Fig. 3 is a recording of the web client connected to my NanoVNA-F, showing the frequency response of a Channel Master LTE filter. Due to COVID-19 and travel restrictions, I was unable to return to Los Angeles where most of my RF adapters are stored. Therefore, the accuracy of this chart may not be the best as it was done without the use of at least 50 to 75 ohm loss pads or transformers. Follow the instructions on the web client website. You may need to change the settings in Chrome or make sure your user is in the same serial device group as the NanoVNA on Linux. I had to add myself to the “uucp” group for it to work.

For more information on NanoV-NA, see my column in the IEEE Broadcast Technology Society magazine for March 2020 (you can search for it at https://resourcecenter.bts.ieee.org). It’s free for IEEE BTS members. In the article I show a block diagram of the device and describe how it works. A key component is a Texas Instruments FM stereo digital matrix decoder!

One final note: I finally got around to updating my Transmitter.com website. It’s still a work in progress, but there are now links on the home page to folders with some of the tools I created and mentioned in previous articles and what I hope to create a monthly feature – highlighting an article on the website television technology that I wrote more than 20 years ago. The current one is a self-made frequency standard and calibrator from March 1994. WWV and WWVH have fortunately received funding to continue operation so that the device can be built and still works 26 years later!

As always, I look forward to your comments and questions. Let me know what i missed! Send me an email at dlung@transmitter.com.

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