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Old 29-Apr-2016, 4:13 PM   #101
tripelo
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The HDTVi Antenna as a Reference

(continued from previous post)

Part 4. The HDTVi Antenna as a Reference

Another way of comparing gain of the antennas is to directly compare received signal levels to that of the HDTVi antenna. The HDTVi antenna was selected as a reference antenna mainly because it was thought that itís gain would be relatively flat across the UHF band. Also it was thought that the SWR of the HDTVi would be relatively good (close to 1). Part of the reason for the above assumptions is that Log Periodic antennas can be designed to meet the criterion: flat gain and favorable SWR. The physical appearance of the HDTVI suggest as much.

A 4NEC2 analysis of the HDTVi tends to support the assumptions of flat gain and favorable SWR.

Below are images of the results of 4NEC2 analysis




Top Image shows Gain in dBi (recall dBi=dBd+2.15), Lower image shows SWR


The above simulation SWR results agree favorably with the actual measurements. If the HDTVi gain were to be measured, likely it would also agree. If that were the case, than a direct comparison of the higher gain antennas with the HDTVi might provide insight.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:






The above image illustrates the tendency of increasing gain of the four higher-gain antennas with increasingly higher frequencies.

As can be seen in this image and a preceding image, there is a discontinuity at channel 20 and channel 31. These two channels have lower signal strength than most of the others and also have been observed to exhibit multipath effects. The effects that were related to multipath were observed as part of a previous field test performed in May 2012, some results shown in a previous post (Ch 20 & 31 data were not presented).

UHF Signal Strength vs Antenna Height (AGL)

Omitting those points (Ch 20 & 31), the overall data might look smoother, but they were included for completeness.

The following image represents a best-fit linear approximation to the measured data and could illustrate some trends. Caution when interpreting this linear approximation; for a specific channel, it might be better to refer back to the raw data averages (shown earlier).




Both Yagis show increasing gain with increasing frequency (channel number). The 8-bay bow tie, or panel array, antennas show a flatter response with some increased gain with increasing frequency.

CM4228 and DB8

Notable is the approximately 2 dB difference in gain between the CM4228 and the DB8. This difference could partially be explained by the increased SWR of the DB8 (about SWR=4 at mid band), an SWR of 4 could cause approximately 2 dB loss. Some of the signal strength difference and transmission line matching could be attributed to baluns. The DB8 balun was supplied by the manufacturer (Antennas Direct). The CM4228 balun was a homebrew hand-wound ferrite-core balun with a measured loss of less than one dB.

91XG and HDB91x

The measured signal level difference between the gains of the two Yagi style antennas is less pronounced. The HDB91x shows a clear advantage at the top end of the band, however this indication is partially an artifact of the linear approximation. Note the raw data average show signal levels from the two antennas to be fairly close near the upper end of the band. The reason for the overall differences is unknown, but could partially be related to a better impedance match to the transmission line. The S11 measurement of the HDB91x reveals a better impedance match starting at ~500 MHz (Ch 19) and upwards. It is known that the 91XG has an ~microstrip balun that in some ways resembles a usual half-wave loop (but is markedly different). The factory-supplied balun of the HDB91x has not been inspected.

After a first set of data on the 91XG was collected, it was thought something might be amiss. The 91XG balun housing was opened and inspected; a nut that holds the driven element to the balun seemed to not be tight. The nut was tightened and a second set of data was collected. The results of the second 91XG data set were close to that of the first set.

Overall, the appearance of the 91XG and the HDB91x seems similar. But, close inspection shows most component parts of the HDB91x are in some way different than the 91XG. There are measurable physical and electrical differences that may account for some of the difference in performance.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed with received signal on some channels. This is probably a result of the first Fresnel zone not being clear.

A repeat of each measurement probably helped reduce effects of brief transitory multipath effects. The individual data sets were fairly consistent. Measurements using the HDTVi at both beginning-of-test and end-of-test somewhat verified data consistency. The HDTVi final-measurements were about 0.2 dB lower in signal strength than the beginning-measurements. A scaled correction factor could have been incorporated into the data but was deemed unnecessary.

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Attached Images
File Type: jpg HDTVi 4NEC2 Gain SWR.jpg (81.0 KB, 1899 views)
File Type: gif 4 Antenna Compare HDTVi.gif (16.2 KB, 1911 views)
File Type: gif 4 Antenna Compare - Linear.gif (11.6 KB, 1961 views)
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Old 6-Jul-2016, 3:30 PM   #102
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Compare: Antennas Direct C5 & Televes Yagi B-III

A series of antenna tests conducted on July 1, 2016.

Objective: Compare performance of selected VHF antennas while receiving DFW TV channels

Antennas:

1. Antennas Direct C5
2. Televes Band III Yagi

Antennas Direct C5: Driven element is a loop design (contains two loops, inner and outer) with reflector screen. The balun is ferrite core design.

Televes Band III Yagi: Folded-dipole driven element with reflector and five directors. The balun is sealed in metal can.

Images of antennas shown below:

Antennas Direct ClearStream 5 (C5)




Televes Yagi B-III





Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations, both VHF channels (8 and 9) located on same transmitting tower.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration

Test Equipment:

Same as previous*, except:

1. Sencore SLM1456CM instead of Sencore SLM1456
2. 3dB attenuator at input of Sencore SLM1456CM
(From antenna perspective, improves coax cable match to 75 Ohms)


*Previous similar test: Compare Received Signal Strength of 5 UHF Antennas

Test Procedure

1. Calibrate VNWA, with the 40ícoax cable (refers measurements to antenna/balun connection).

Starting with Antennas Direct ClearStream 5 antenna:

2. Mount antenna w/coax and ferrites to mast, raise center of antenna to 25 feet
3. Align antenna for peak signal on Channel 8
4. With 1456CM scan DFW VHF stations (Channels 8 & 9) for signal strength and MER.
(repeat scan 9 times while in this configuration, record times).
5. Take at least 2 Photos
6. Turn antenna ~90 degrees, disconnect coax from 1456, connect to VNWA
7. Measure S11 (input impedance, SWR/Return Loss) for the band
8. Lower Mast remove antenna
9. Mount Televes Yagi B-III, repeat steps 2-8
10. Then again, for each antenna, repeat steps 2-9


The test location and setup was similar to that described in previous posts:

Televes DAT-75 vs. Antennas Direct 91XG


Credit:

Thanks to Stuart Sweet of Solid signal for providing the Televes Yagi B-III.

(To be continued)

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Attached Images
File Type: jpg Antennas Direct ClearStream 5.jpg (60.3 KB, 1613 views)
File Type: jpg Televes Yagi B-III.jpg (26.5 KB, 1568 views)
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Old 6-Jul-2016, 3:31 PM   #103
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Part 2. Images of the Two Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows Antennas Direct ClearStream 5 and Televes Yagi B-III.





(To be continued).

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Attached Images
File Type: jpg Antennas Direct C5 & Televes B-III.jpg (98.0 KB, 1544 views)
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Old 6-Jul-2016, 3:32 PM   #104
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Part 3 (continued from previous post)

Attached are Graphs depicting a summary of data analysis.

1. Average received power levels, (Image below):

An average 9 measurements of each channel (8 & 9) for each antenna (ClearStream 5 and Televes Yagi BIII).





2. Average Relative Gain per Channel (image below)

A nine-scan average of both antennas.





3. Average SWR 5 Antennas (image below)

SWR was derived from measured S11 (Return Loss). The curves represent the
smoothed scan averages for each antenna.





For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis


No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.


========== Comments ====================

The Antennas Direct ClearStream 5 (C5) and Televes Yagi BIII provided nearly the same average signal strength for Channel 8 and 9, with an approximately 0.1 dB advantage for the Televes antenna. Since 0.1 dB is near the measurement accuracy limits of the test configuration, the difference may not be very significant.

The per channel data shows that the Televes antenna provides a higher signal on channel 9 (by about 0.2 dB) relative to the Antennas Direct antenna. This could be a result normally expected of Yagi type antennas, that is the gain increasing with increasing frequencies, up to the design limit.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed at UHF with received signal on some channels. However, effects of multipath have not been explored at VHF frequencies, and there have been no symptoms to suggest it might be prevalent.

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements using the Antennas Direct ClearStream 5 at both beginning-of-test and end-of-test somewhat verified data consistency. The Antennas Direct ClearStream 5 final-measurements averages were within a few hundredths of a dB of the signal strength of the beginning-measurements average.



(To be continued)

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Attached Images
File Type: gif Compare C5 & Televes B-III.gif (5.0 KB, 1485 views)
File Type: gif C5 & BIII per Channel.gif (5.2 KB, 1656 views)
File Type: gif SWR - C5 & Televes BIII.gif (7.6 KB, 1683 views)
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Old 6-Jul-2016, 3:32 PM   #105
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Part 4 (continued from previous post)

4NEC2 Analysis and Discussion

Antenna simulation software (4NEC2) could be useful in comparing antennas. Generally, software analysis is not a substitute for field tests. Choices must be made of available approximations that are necessarily incorporated in software models. Without some field measurement data to guide the design of a simulation model, rarely does a simulation model account for all factors in an antenna design.

In cases where field data is limited, but available enough to help confirm the models and if one can be fairly sure the software model something close to reality, then software analysis can provide insight.

The physical dimensions of both antennas; the ClearStream 5 and the Televes Yagi B-III were measured and software models created in 4NEC2.

The gain values shown in the following 4NEC2 results do not include balun loss or mismatch loss.

Below are images of the results of 4NEC2 analysis

Top Image, Gain in dBi, Lower image SWR

(Recall dBi=dBd+2.15)





The above simulation SWR results agree favorably with the actual measurements.

If the Antennas Direct ClearStream 5 gain were to be measured, likely it would also agree.

Below is an image that shows the Televes Yagi B-III antenna gain and SWR:







The shape of the Televes SWR pattern above above is in reasonable agreement with actual measurements (see previous post). Overall, the SWR is lower than measured. No explanation has been found. It could be that the software model does not account for some factor that could alter the SWR values. Another possibility is that the balun (not modeled) could contribute to the SWR difference. For example; In some cases LC components are added to a balun to improve response at band edges at the expense of impedance match at center band.

The above image illustrates the tendency of increasing gain for higher frequencies, often seen in Yagi-type antennas.

These simulation results are also in fair agreement with data present at the two manufacturers websites:


Antennas Direct ClearStream 5

Gain and SWR (simulations of both, plus measured values of SWR at 10 ft AGL),

Located in this document:

https://www.antennasdirect.com/cmss_...with%20uhf.pdf


Televes Yagi B-III (Gain),

Located in this document:

https://www.televes.com/sites/defaul...ennas_en_0.pdf


Azimuth Beam Width

The following images show the computed azimuth (horizontal) antenna patterns of the two antennas at three frequencies representing lower end of the band (174 MHz), mid band (194 MHz), and upper end of the band (216 MHz).






Note the C5 has a somewhat broader beamwidth, especially evident at the upper end of the band, than the Televes antenna.








The difference in gain at 216MHz is mainly related to increasing gain from the Televes B-III. The Televes B-III is advertised to cover up to 230MHz, so it is expected the gain would be higher at the upper end of the band.


(To be continued)

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Attached Images
File Type: jpg Antennas Direct ClearStream 5.jpg (72.2 KB, 1572 views)
File Type: jpg Televes Yagi B-III.jpg (68.3 KB, 1496 views)
File Type: jpg Azimuth Patterns C5 & B-III @174.jpg (107.7 KB, 1512 views)
File Type: jpg Azimuth Patterns C5 & B-III @194.jpg (107.0 KB, 1490 views)
File Type: jpg Azimuth Patterns C5 & B-III @216.jpg (108.0 KB, 1477 views)
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Old 6-Jul-2016, 3:33 PM   #106
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Part 5 (continued from previous post)

Specifications, Measurement, Analysis and Discussion


In an effort to reconcile the various gain and SWR numbers available for these two antennas, the following chart was composed.

For each of the two antennas and each channel (8 and 9), the gain and SWR are presented. The sources for the gain and SWR are listed in the left column.

The manufacturers numbers are derived from the technical documents found in the links provided in a previous post. Antennas Direct lists gain figures as dBi, very likely the Televes numbers are also in dBi.

The 4NEC2 results are from simulations described in the immediately previous post. The gain numbers (dBi) listed here are calculated to include mismatch loss due to SWR.

The DFW Measure numbers are a summary of actual measurements at 25 ft from a location in Garland TX (described in a previous post). The units of values listed as gain are dB, either positive or negative relative to that averages of the two antennas (per channel).





Summary and Discussion

These two antennas are of different design, but for the channels tested yielded relatively close gain and SWR numbers.

The Antennas Direct antenna consists of driven element loops (inner and outer) with a screen reflector. The loop is made of relatively thick conductor that helps to broaden frequency response (flattens SWR). This design is in some ways similar to two stacked dipoles (top element fed at ends instead of center fed). This stacking effect tends to compress vertical beam width, thus for a given amount of total gain, allows for a slightly wider horizontal beam width. This C5 antenna being a relatively broadband design tends to have a flat gain and SWR response across the entire VHF high band.

The Televes antenna is a conventional Yagi design with folded dipole driven element. This design tends to have increasing gain with increasing frequency, up to the design limit. According to Televes literature the design limit is 230 MHz (the upper channel in the European band). Conventional Yagi designs tend to have a flattened oval shaped aperture (area over which signal is gathered). This flattened oval-shaped aperture shape means more of the antenna gain is a result of horizontal beam becoming narrow. So, one would expect the beam width of the Televes antenna to become more narrow at higher frequencies (where the gain is highest).

Since much of the data presented in the above preceding chart is in agreement.

The above chart for these two antennas tends to indicate:

1. Antennas Direct and Televes gain figures are consistent with each other.

2. Manufacturers gain numbers are consistent with 4NEC2 simulation results.

3. Antennas Direct SWR values are consistent with actual measurements (at 25 ft. AGL).

4. Computer simulations combined with field measurements can be used to characterize antenna performance, in some cases.

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Attached Images
File Type: jpg Rationalize Specs & Data-C5 & BIII.jpg (68.9 KB, 1505 views)
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Old 24-Jun-2017, 1:14 PM   #107
tripelo
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Compare: Antennas Direct DB8e & CM-4228HD

Antenna tests conducted on June 15, 2017.

Objective: Compare performance of selected VHF antennas while receiving DFW TV channels.

Antennas:

1. Terk HDTVi (as reference)
2. Antennas Direct DB8e
2. Channel Master 4228HD

Terk HDTVi antenna measured as reference (see previous posts).

Both Antennas Direct DB8e and Channel Master 4228HD are panel type antennas, also known as 8-bay antennas.

Main differences between the two panel antennas are feed system design and reflector backplane.

Images of antennas shown below:

Antennas Direct DB8e



Channel Master 4228HD (below)




Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration

Test Equipment and Test Procedure:

For details of test equipment & procedure, see previous similar tests:

Compare Received Signal Strength of 5 UHF Antennas

Compare: Antennas Direct C5 & Televes Yagi B-III


Credit:

Thanks to forum members ADtech and re_nelson for providing the Antennas Direct DB8e antenna.


(To be continued)

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Attached Images
File Type: jpg DB8e.jpg (60.4 KB, 514 views)
File Type: jpg 4228HD.jpg (45.4 KB, 497 views)
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Old 24-Jun-2017, 1:14 PM   #108
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Compare: Antennas Direct DB8e & CM-4228HD

(Continued from previous post)

Part 2. Images of Three Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows the reference antenna: Terk HDTVi





The image below shows both the Antennas Direct DB8e (left) and the Channel Master 4228HD (right).



(To be continued).

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Attached Images
File Type: jpg HDTVi.jpg (20.1 KB, 493 views)
File Type: jpg DB8e & 4228HD.jpg (55.9 KB, 493 views)
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Old 24-Jun-2017, 1:15 PM   #109
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Compare: Antennas Direct DB8e & CM-4228HD

(continued from previous post)

Part 3. Data Collection & Analysis

The amount of data collected represents:

Number of UHF channels: 23
Measurements per channel
DB8e4 and 4228HD: 9
HDTVi: 12

Total (individual channel measurements): 23 x 9 x 2 + 23 x 12 x1= 690

Attached are Graphs depicting a summary of data analyses.

1. Average received power levels, (Image below):

The image below represents an average of 23 UHF channels, nine measurements per UHF channel for each antenna (4228HD and DB8e), 12 measurements per channel for the HDTVi.





The image below shows the received signal strength per UHF channel for the three antennas. Note signal strength is shown in dBmV (dB referenced to milliVolts in a 75 Ohms system. To convert to dBm (milliWatts) subtract 48.75. from the dBmV numbers.





The image below shows the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna. The HDTVi signal strength is referenced to zero on the vertical dB scale.





The image below shows a linear best-fit approximation of the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna.





The following image shows SWR for the three antennas, it was derived from S11 (Return Loss), measured at 25 feet AGL.

The fuzziness of the lines in the SWR graph results from simultaneously receiving the broadcast stations in DFW with the Vector Network Analyzer. The reception of these strong signals caused some interference with the live impedance measurements. The antennas were not turned away from the stations as was done in previous measurements





All three antennas have respectively good values of SWR. No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.

Antennas Direct Technical data sheet indicates the SWR is less than 2 from 470 to 698 MHZ. The SWR measurement shown above for the DB8e is fairly well in agreement with Antenna Direct published specifications. Published SWR specifications for the 4228HD are not available.


For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis


========== Comments ====================

The Antennas Direct DB8 provides highest overall signal strength, with an advantage over the 4228HD at high channels approaching 4-5 dB. TheCM4228HD performs well for channels below about channel 23, with an advantage of more than 1 dB at the lowest end of the band.

The 4228HD appears to have reduced gain as the frequency increases. The reason for this phenomenon was not investigated in this effort. However, it may be related to the transmission line feed for individual driven elements in the 8-element array, and particularly the feed between the two 4-bay segments.

Others have explored this 4228HD gain effect:

HDTV primer: Designed an improved antenna transmission line feed.

Antennahacks: Implemented an improved transmission line feed system.


Test Location and Data Variability

The test site is LOS to the DFW stations, however effects of multipath have been observed at UHF with received signal on some channels

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements with the HDTVi, at both beginning-of-test and end-of-test, somewhat verified data consistency.

(to be continued)

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Attached Images
File Type: gif Compare All Channels.gif (4.8 KB, 499 views)
File Type: gif Avg Sig Strength per Channel.gif (12.3 KB, 509 views)
File Type: gif Per Channel Relative to HDTVi.gif (10.6 KB, 495 views)
File Type: gif 4228HD DB83 HDTVi Linear fit.gif (9.2 KB, 488 views)
File Type: gif SWR Analysis.gif (12.7 KB, 500 views)
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Old 24-Jun-2017, 1:16 PM   #110
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Compare: Antennas Direct DB8e & CM-4228HD

(continued from previous post)

Part 4. Compare 6 antennas (DB8, DB8e, 4228, 4228HD, 91xg, HDB91x)

Having earlier measured four other high-gain UHF antennas relative to the HDTVi antenna, this could suggest that all six could be compared.

http://forum.tvfool.com/showpost.php...2&postcount=99

The main link between the two data sets is the measurements of the HDTVi antenna. The HDTVi was used as a reference antenna in both experiments. Realizing that errors can accumulate, a direct comparison of the two data sets might be somewhat useful.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:





The Yagi antennas (91xg and HDB91x) stand out as having higher gain as the channel number increase. The two Yagis appear to have the highest gain available at the top of the UHF band.

It appears that the older CM4228 (non-HD) is a fairly good match to the newer DB8e, both show a wideband response with relatively high gain at the lower channels.

If the above graph were accurate for every channel (which is doubtful), one could add the gain of the HDTVi to every antenna, to obtain a total gain figures. Previous calculations show the gain of the HDTVi to be about 6.5-7 dBi.

Caveat: Keep in mind that real antenna gain patterns are rarely (if ever) linear, and the above chart (although based on measured data) is an approximation.

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Attached Images
File Type: gif DB8e, 4228HD, & Others.gif (11.4 KB, 493 views)
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