2023 TV Antennas & Equipment

[WHJ]

TELEVES SMARTKOM 531981 TV AGC AMPLIFIER

I have been trying to evaluate all the TV RF preamplifiers and use the best of those. Until now I have avoided the Televes Smartkom 531981 preamp due to it appearing to be made more for cable TV companies rather than weak-signal home viewers. That is best shown by it having a noise figure of 6.0. But, after experimenting with a circuit around an Analog Devices AD8368 AGC IC I thought that it was time to try Televes better Smartkom AGC amplifier. It can have up to 32 different single channel filters activated with a separate AGC for each channel. This is enough for almost all 35 of the currently available on-air channels. All but the very weak signals will have the same level at the Smartkom’s output.

Jumping quickly to the results, this morning’s tropo opening to Kansas City seemed like a good time to see its use in action. To leave enough space for labeling my spectrum analyzer’s display, below are the stations being received on the upper 100 MHz of the UHF TV channels while beaming towards KC.
Most of the above stations are from Lincoln (14 – 25 miles from me), Omaha (57 miles), and Kansas City (190 miles). Omaha’s ATSC 3.0 KXVO had significant interference from KMBC in KC. That is KMBC’s ATSC 1.0 pilot on channel 29.

I was expecting the AGC level would be frozen after the automatic programming had been activated. However, the AGC appears to always be active responding to changes in the received signal level. The above reception was this morning after 7 AM compared to the automatic programming last night. That was quickly followed by activating all UHF and high VHF channels whether they were receiving signals or not. There were not any KC stations being received then. That programming is shown below.

The default output level of the Smartkom is 85 dBuV (which I measured as 81 dBuV). That provides my HDHR Flex 1K with a 100% signal. So, almost all the signals will be at a green level. The quality might be lower, like it was for KXVO above. With all signals being at about the same level, strong signal interference won’t be as bad for adjacent channels, but that high level still worried me. Setting the Smartkom output level to 70 dBuV reduced the HDHR level to 92% (still green). I decided to go with an output of 65 dBuV for now. There is obviously a lot of reserve to cope with the loss of any passive splitters which are being used.

I ran my standard RF preamplifier evaluation tests. Not surprisingly, its weak signal sensitivity for a 15 dB MER was poor. With its 6.0 noise figure that was expected. However, its strong signal capability and dynamic range were both the best that I have measured! With my existing tower mount preamplifiers left in place to handle weak signals, it is likely to be used inside. Combining the Smartkom results with the Analog Devices AGC and three of my most used preamplifiers is below.

The dynamic range of the Smartkom goes down on the high VHF (90.8 dB) and low VHF (to a marginal 82.9 dB). There is a small regular picture of the Smartkom above. However, what’s inside? That is shown below.

I also used my spectrum analyzer’s tracking generator to provide some measurements. That provides a swept frequency output which can confuse the many single channel AGC’s. With things adjusted to minimize those negative effects, the frequency response of the preamplifier with all UHF and high VHF channels activated is shown below. Any RF outside of the broadcast frequencies is not going to cause any problems.
The frequency response of the AGC with just the 536 – 542 MHz channel 25 being shut off is shown below.

With just channel 6 activated, the response and FM attenuation is shown below.
Neither quite meet the >30 dB rejection +/- 1 MHz specification, but it is still pretty good. FM signals above 89.5 MHz should not cause any problems.

Below are a bunch of figures which show the output dBuV with a varying input level. I used my Rohde & Schwarz SFQ test DTV transmitter and EFA test receiver to make output level and MER measurements. It also shows the noise output level without any input.

Finally, a more complete chart of my preamplifier evaluations is shown below. Many different versions of the preamplifier models being used have been tested. A close look will show missing figures for the Televes Avant X Pro. I found one available for a good price. I will see how the European model for their 8 MHz channels works here. It should arrive shortly.

[WHJ]

I just completed checking the level from 12 of my TV antennas. I increased the level from some of my antennas and decreased others.

It was interesting checking the level from my channel 6 antenna. The BROADBAND level after my FM filter was 80 dBuV maximum while before the filter it was 104 dBuV. My HDHR tuners are fine with 80 dBuV but would overload with 104 dBuV.

[WHJ]

Recent good openings have made me wonder if all of the strong signals added up causing collective overload of my equipment. I considered adding a RF AGC to prevent that. I have one Televes preamplifier with built in AGC. It can prevent overload of other equipment which has a limited dynamic range, but the preamplifier's dynamic range is just typical of other preamps.

I did not find too many other options. I considered the Analog Devices AD8367 and AD8368 IC's. See: AD8368 (Rev. C) (analog.com) The AD8367 is just rated to 500 MHz and the AD8368 has a worse noise figure (10.0), I thought that I would experiment with both. They are meant to have a now noise amplifier before the AGC's as in done in the Televes preamplifiers.

I purchased some of the low-cost evaluation boards on eBay and tested them using my preamplifier standards:

I did not like the AD8367's limited frequency response and 200-ohm input impedance. The AD8368's noise figure concerned me, but I liked it having its AGC voltage available which can be converted to a measurement of its collective input level.

I added 75 to 50-ohm input matching and a 50 MHz high pass filter to the AD8368 and added a voltage measurement display.

I connected one of my Winegard HD7698P antennas to the unit and first measured 0.378 volts. That translates to 85 dBuV. I measured the overload level of HDHR5 and Flex 4K tuners as being 92 dBuV. That's a small safety margin. I later measured the same antenna with the AD8368 measuring 0.533 volts/92 dBuV--precisely at the limit. I then pointed the antenna directly at my local DTV stations. That read 0.749 volts/99 dBuv. That is what I expected--over the limit at worst case antenna heading!

My upgrades to some of my Flex 4K's has improved the situation. That increased its overload level to 104 dBuV. I need to make additional tests to more antennas.

[WHJ]

The vertical dipole appears to have more advantages than I first thought. I was worried that they never would be better than my horizontal Yagi's due to their added gain and directivity. At least when an opening is just to one signal, the vertical dipole was occasionally better. Also, having an omnidirectional antenna is useful to point to a new opening. That occurred a couple of times over the weekend when there was an opening to Las Vegas when my directional antenna was pointed to the southeast states.

The Yagi's have long been useful during openings in multiple directions. That permits reception of both southeast states or New England depending on my antennas heading.

Due to the advantages of having the vertical dipole I have added it to my third HDHR tuner. My equipment connection diagram in my first message has been altered to reflect that change. My HMC421 antenna switch control will be set most of the time to alternate between feeding my channel 6 Yagi or my vertical dipole to my third HDHR tuner. Depending on conditions, I can switch to feed only one of the two during an opening. When my fourth tuner has been connected to TV BandScan, I can have all four permanently connected to a tuner.

[WHJ]

The elevation lobe compression depends on the number of antenna bays (effectively dipoles) which are vertically stacked. It's best if those are one wavelength apart. That distance is the inverse of the frequency ratio. You show the elevation pattern of a 24-bay channel 49 (683 MHz) antenna. A 24-bay 97.5 MHz FM antenna would need to be seven times the size of your UHF example. That's not practical. FM antennas generally have a 12 or 14 bay maximum. Some elevation patterns of FM antennas are below:

Due to power licensing, a 4-bay antenna will require much greater transmitter output power than a 12-bay antenna for 100 kW ERP. Both will produce the same signal at the coverage extreme. The power bill will be much lower when the 12-bay antenna is used. However, everybody inside the coverage extreme will have a stronger signal with the 4-bay antenna.

Yes, filtering the stronger signals from FM and DTV signals can aid reception--that's part of the reason that I am using so many filters. Go to the following web page to see my recent 24-hour low VHF receptions: https://forums.wtfda.org/forum/wtfda...ot-frequencies

[Crazy Monkey]

I do not have excessive FM overload, but enough to limit things. I have two 100 kW FM stations about 14 miles away and a low power FM 8 miles away. 1.5 to 2 miles away your local FM signals should be beaming over your head (depending on the transmit antenna height and gain). It is the combined strength of all the signals going to your tuner and its filters which matters.

For comparison, I made field strength measurements on a channel 23 DTV station which use an antenna about 450' high. I made measurements along one azimuth radial. Starting close to the tower, its signal strength went up as went further from the tower. Only after I reached ten miles from the tower did the strength start going down with increased distance.

Ok, thanks.

I've come across some graphs in the past which showed just how much power was reaching the ground at a certain angle beneath the tower, but I haven't been able to find these graphs for FM. From my understanding (and I was told), FM signals don't have this tight pattern like DTVs do. But maybe someone can provide actual graphs for this. It seems from my experience, the FMs here are far worse overload. But I do notice that filtering out the strong 1 to 2 mile DTV transmitters raises the signal quality of some of the weaker DTVs by 10 to 20%.

Here is an old example of what I'm referring to...

[WHJ]

I do not have excessive FM overload, but enough to limit things. I have two 100 kW FM stations about 14 miles away and a low power FM 8 miles away. 1.5 to 2 miles away your local FM signals should be beaming over your head (depending on the transmit antenna height and gain). It is the combined strength of all the signals going to your tuner and its filters which matters.

For comparison, I made field strength measurements on a channel 23 DTV station which use an antenna about 450' high. I made measurements along one azimuth radial. Starting close to the tower, its signal strength went up as went further from the tower. Only after I reached ten miles from the tower did the strength start going down with increased distance.

The chart shows the low band filters that I use. I fortunately have four different low band antennas. My channel 2 & 3 antenna uses a Mini-Circuits SCLF-65 filter:

As the graph shows, even 88.1 FM is down by 30 dB.

My channel 4 & 5 antenna uses a Mini-Circuits BPF-A69 filter:

By the time that you get to my first close 100 kW station's frequency (96.9 MHz), it's down 25 dB.

My channel 6 antenna uses a CirQTel FBT filter:

It's down a bit further on that first station.

[Crazy Monkey]

Can you elaborate more on what you're using for the FM filters and tell me exactly what stations are causing overload? How far are these stations from your receive antenna? You seem to be doing rather well with DTV Es while I struggle.

I'm particularly curious because my situation sounds similar. I have broadcast stations of 12 kW and 16 kW with transmit towers 1.5 and 2.0 miles from my receive location, and trying to get a clean low-VHF band seems to be impossible (particularly on channel 6 due to local 88.1).

[WHJ]

It has still been a slow start to the Es season this year. And most of the tropo openings have not been far enough west and/or north to help my location. I changed my 2023 equipment diagram at the top to show what is currently being used rather than my planned changes. I need my fourth HDHomeRun tuner added to TV BandScan before I can go much further. My three active tuners scan channels 2 - 36 rather than the default 2 - 51. My fourth tuner just scans channels 2 - 6.

[WHJ]

I figured out why KMCI has jumped to the easiest Kansas City station to detect. They have changed their ATSC 3.0 core layer from the same 256QAM 9/15 as their programing has to QPSK 4/15. Below shows the difference between their original signal in late 2021 to their current one.

That makes their signal 21.5 dB easier to detect. The video will still take a stronger signal to view, but it should speed recapture of a weak signal.

When reception is marginal, it is more commonly received as follows.

The basic PLP0 information is received due it only requiring a -0.3 dB SNR. Since the enhanced PLP1 QAM256 programming requires a 21.2 SNR, the video cannot be viewed. The Flex 4K Development dBm strength and dB SNR data makes easier to see the point of reception. The first two receptions were made on a Flex 4K without the Development enhancement.

An example of KMCI reception in the middle of the afternoon without any significant opening is shown below.


The above was from https://rabbitears.info/tvdx/all_tuners

[WHJ]

Until my TV Band Scan tuner names have been changed and my new tuner is added, I think that I have found a better way of connecting my antennas. Two of my three tuners shown on TV Band Scan will just have one VHF/UHF antenna connected (Winegard HD7698P's) along with either my 9-element channels 2 & 3 Yagi or my new 7-element Channels 4 & 5 Yagi. The two Winegard antennas are at different heights on different towers controlled by different rotators. Additional details are shown below.

The third 4K tuner will have a new custom circuit to automatically cycle between up to six different UHF antennas, or a Stellar 30-2476 VHF antenna or my custom 10-element channel 6 antenna. The UHF antennas will be changed every two minutes. For now, just 4 antennas will be connected, concentrating on the first two.

A chart of my interim connections is shown below. The no longer appropriate TV Band Scan names for my Garland, NE receptions are shown in red.

With some TV band combiners having around just 30 dB of isolation, I often have filters added to prevent the directivity of a band's antenna from being compromised by other connected antennas.

I am not sure why the reception of the Kansas City stations has changed this year. Originally KCTV-24 was the first KC station received. Local KSNB moving to channel ended that. Then, KPXE-30, WDAF-34 and KSHB-36 were all pretty close in being the first KC stations received. KMCI-25 and KSMO-32 were a little bit behind those three. Both of those two stations going to ATSC 3.0 did not seem to change things much. For about the last three months however, KMCI has been the clear winner as the first KC station being received.

[WHJ]

Today I got my second HD HomeRun tuner converted as close as possible to my new connections shown on the chart. I will need to have my fourth tuner added to BandScan and complete my construction of the Agilent 8765F RF switch control circuit to go further. This circuit will allow the continual connection of a selected antenna or have either of the two antennas alternated every two minutes. The second tuner receptions can be viewed at https://rabbitears.info/tvdx/one_tun...0A0E179/tuner0 I need to get revised names for those tuners.

I better tested my new channel 4 and 5 antenna today. The receive strength of semi-local KNHL (channel 5) 74 miles away was 100% / -44 dBm when beaming towards it. With the antenna pointed in its normal SSE heading the station could not be received at all. The difference is shown below.

So, if KNHL or other local stations are not shown as being received, it probably is because the best antenna is not pointed towards it.

[WHJ]

I have added some new TV antennas and associated equipment. All of the new antennas have been mounted but some custom antenna selection equipment needs to have its construction completed. The equipment is summarized below:

The combination of filters and selective combiners is used to prevent mixing of unwanted local signals from off-frequency antennas hurting reception of DX from the more directive antenna. The selectivity of the HD HomeRun tuner seems to be worst of the low VHF channels. The filters there help prevent overload and IMD from FM stations hurting low VHF reception. The installation to the 10A3F120 tuner has been completed. Its reception can be observed at https://rabbitears.info/tvdx/one_tun...0A3F120/tuner0

I will include some pictures of my new antennas. I have long had a 9-element custom antenna for channels 2 and 3 and a 10-element custom antenna for channel 6 and the lower FM frequencies but nothing specifically for channels 4 and 5. Using some surplus tubing that I have a 7-element antennas channel 4 and 5 was recently installed.

The top antenna is a Winegard HD7698P with the new channel 4 & 5 antenna just below that. A fixed direction Stellar 30-2440 is side mounted on the tower.

I redesigned the Televes 149783 UHF antenna. Twelve elements were added, and the length of all directors was extended.

My 10-element channel 6 antenna is on top.

I thought that I would try something different and install my first vertically polarized TV antenna. It is just a side-mounted vertical dipole tuned best for channels 2 and 3. It is spaced from the tower to produce the following pattern:


It is shown below with my 9-element channel 2 & 3 antenna just above it.


There has not been much tropo or Es opening recently (or expected in the next week) hurting evaluation of the new antennas.