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Old 18-Apr-2017, 7:07 AM   #1
lifespeed
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Adding VHF, diplexer and antenna recommends

I need to add a VHF antenna to my UHF only setup. TV fool report here. It is kind of a long story, but if you look at the report it appears UHF covers all stations by pointing at San Francisco 316 degrees and Fremont 357 degrees. Turns out the KGO VC7.1 RF 35 repeater at 357 degrees has problems at the transmitter end, but the operators are unlikely to fix it. So I need to try and get VHF 7 for KGO instead of the UHF 35 repeater.

Any suggestions for a high quality VHF/UHF diplexer and long range VHF antenna? I am one-edge to Mt. Sutro, in the shadow of a small hill.

Here is a photo of my current setup. The XG91 Yagi points at Mt. Sutro in SF, with the DB4e bowtie aimed at Mt. Allison in Fremont. Each connects to a separate Silicondust HDHR4-US network tuner.


Last edited by lifespeed; 19-Apr-2017 at 6:00 PM.
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Old 18-Apr-2017, 11:33 AM   #2
ADTech
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Add our ClearStream 5 and our UHF/VHF diplexer.

You could try the minimalist approach of our simple VHF dipole first, it's much less expensive and includes the diplexer already integrated into the module. The math on your plot says it will work, but signals behind hills are notoriously fickle compared to the mathematical models.
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Old 18-Apr-2017, 12:42 PM   #3
JoeAZ
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You may wish to try one of the MCM Electronics Hi-VHF antennas.
They are far less expensive and likely to do a good job for you.
For maximum gain, I'd run two separate RG6 cables, each dedicated
to one antenna with a low loss A/B switch.
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Old 18-Apr-2017, 1:05 PM   #4
ADTech
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For maximum gain, I'd run two separate RG6 cables, each dedicated
to one antenna with a low loss A/B switch.
As noted in a different thread, that arrangement is overly complex, is inconvenient, and really doesn't have any advantage for the antenna user when a separate UHF and VHF antennas are used. Now, if the separate antennas were both of the same band or were combo antennas aimed in different directions, it does make sense to use an A-B switch* to prevent combining glitches that are endemic when using a common splitter for combining. Still inconvenient, but it's a proper application of the A-B switch.

The actual difference in insertion loss from a quality UVSJ and a "low-loss" (whatever item that might be selected) A-B switch is going to be negligible, perhaps a few tenths of a dB at most. If you happen to have a favorite A-B switch, you're welcome to send me a sample and I'll run it across the network analyzer to characterize it for you and give a comparison that shows the relative performance between it and a UVSJ.

* Note: Using separate tuners for individual antennas as the OP has done is another alternative to avoid the aggravations of combining like-band antennas.
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Last edited by ADTech; 18-Apr-2017 at 2:30 PM.
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Old 18-Apr-2017, 5:30 PM   #5
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In laboratory settings, you may well be correct.
In practice however and in the field, unexplained
issues frequently come up. The engineers for several
of the major Phoenix television stations, with whom
I am in frequent contact, would agree.
My only intent here is to provide people with the best,
most likely to work and lowest cost recommendations.
What is yours?
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Old 18-Apr-2017, 6:01 PM   #6
ADTech
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My purpose is to provide accurate information to the interested members of the public, both customers and non-customers alike, so that the information provided best meets their needs. As someone who has only recently arrived at this forum, you probably do not yet know how diverse my recommendations can be. Other users who have been here awhile and who have been observant will attest to my flexibility in interactions with forum posters. I do not leave any doubt or question regarding my being an employee of Antennas Direct.

I've been combining antennas using the UVSJ device for a very long time and I cannot think of a single instance where an A-B switch would have been a necessary and appropriate alternative. I've also discussed issues such as this with a number of station and industry engineers and the use of the UVSJ is both the recommended and accepted practice.

Go ahead and feel free to saddle your own customers with an inconvenient solution, but I will continue to advocate for the elegant simplicity of the device that was invented for the express purpose of eliminating such a switch.

Best of luck!
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Old 18-Apr-2017, 7:23 PM   #7
lifespeed
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Although the Clearstream 5 is a nice antenna, I have little use for the broad beam and UHF gain. The Stellar Labs 30-2476 does look like a good choice, and is higher gain.

I would like to see some specs on frequency response and gain of a VHF/UHF diplexer, but that may be wishful thinking. Some of the signals I receive are in the sub 20dB noise margin range, so I have tried to be very careful with short RG6, no splitters, etc.

A dedicated tuner for the VHF antenna is a possibility, but it would be much nicer to keep all 4 tuners (2 per physical tuner) available for all channels using a VHF/UHF combiner. If the loss from a diplexer pushes me over the edge I can dedicate a tuner to the VHF antenna instead. At $90 per tuner it isn't the cheapest approach, but not totally unreasonable for good RF performance.

I do understand @JoeAZ preference for minimizing loss after the antenna, and generally agree. If you have strong signals it surely does not matter, but my case is not really the strong signal case. Diplexer specs might help me make a good decision without climbing the antenna pole for another reconfiguration The networked tuner arrangement is ideal for direct connection per antenna, just have to pay the price.

Last edited by lifespeed; 19-Apr-2017 at 5:40 PM. Reason: noise margin text unclear
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Old 18-Apr-2017, 7:55 PM   #8
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Quote:
Although the Clearstream 5 is a nice antenna, I have little use for the broad beam and UHF gain.
The UHF is going to get stripped of by the UVSJ anyway so it's a non-issue. To achieve narrow beamwidth requires a lot of metal up in the air, generally an array of elements that cause it to have a more focused reception pattern. Typically, that means more real estate that the antenna's elements must occupy in some dimension.

Quote:
I would like to see some specs on frequency response and gain of a VHF/UHF diplexer, but that may be wishful thinking.
See post #7 in this thread from last week. I just happened to have provided that data.
http://forum.tvfool.com/showthread.php?t=16265
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Last edited by ADTech; 18-Apr-2017 at 7:58 PM.
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Old 18-Apr-2017, 8:35 PM   #9
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Quote:
Originally Posted by ADTech View Post
The UHF is going to get stripped of by the UVSJ anyway so it's a non-issue. To achieve narrow beamwidth requires a lot of metal up in the air, generally an array of elements that cause it to have a more focused reception pattern. Typically, that means more real estate that the antenna's elements must occupy in some dimension.
Yes, that VHF Yagi w. reflector (?) is huge. But there is plenty of room up there, nothing but birds anyway. I'm not one to get too concerned over antenna aesthetics, if it works it's beautiful.

Quote:
Originally Posted by ADTech View Post
See post #7 in this thread from last week. I just happened to have provided that data.
http://forum.tvfool.com/showthread.php?t=16265
Good data, thanks! UHF loss is more than VHF of course, although still less than a dB. Extra credit if you post the input and output match plots, S11 and S22

Right now I'm pulling in a 10dB noise margin station without preamp on the XG91 UHF antenna, so not a lot of room for added loss. If I run separate 20' runs of RG6 into the attic and do the diplexing there it is an easy experiment vs. separate tuners without UVSJ loss. Whether the long cable runs before the UVSJ degrade the signal or not really depends on the match between the antennae and the UVJS I believe. Experimenting with the UVJS up on the pole fed by short <3' RG6 runs is a lot more work.
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Old 18-Apr-2017, 8:59 PM   #10
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Extra credit if you post the input and output match plots, S11 and S22
I can do that tomorrow. Already have the VNA set up for that.

In the meantime, you can peruse the data that our lead engineer did a few years back - https://www.antennasdirect.com/store...Combiners.html under Specifications
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Last edited by ADTech; 18-Apr-2017 at 9:02 PM.
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Old 18-Apr-2017, 9:12 PM   #11
lifespeed
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Quote:
Originally Posted by ADTech View Post
I can do that tomorrow. Already have the VNA set up for that.

In the meantime, you can peruse the data that our lead engineer did a few years back - https://www.antennasdirect.com/store...Combiners.html under Specifications
I missed the return loss specs. VHF at 18dB is great, UHF at 12dB just OK. It is a tricky design task, especially when it is supposed to cost nothing and have zero loss.

At least you guys provide specs, all the other UVSJ I have seen guarantee nothing.

PS - did you see the added zip ties on the DB4e? LOL.
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Old 18-Apr-2017, 11:03 PM   #12
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PS - did you see the added zip ties on the DB4e? LOL.
Well, gotta say that, if you looked at the instruction sheet, I put explicit instructions somewhat to that effect when I wrote the QuickStart a few years back. The biggest thing is to prevent damage to the balun PCB from the coax either hanging from or flapping around in the wind and your placement of the ties does that job.

Quote:
At least you guys provide specs, all the other UVSJ I have seen guarantee nothing.
Yeah, I know. I tested and posted test results 5-6 years ago for the Holland, Pico, and Radio Shack devices. the first two seem to have gone extict and who knows how long RS will still be around.
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Last edited by ADTech; 18-Apr-2017 at 11:06 PM.
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Old 18-Apr-2017, 11:12 PM   #13
lifespeed
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Quote:
Originally Posted by ADTech View Post
Well, gotta say that, if you looked at the instruction sheet, I put explicit instructions somewhat to that effect when I wrote the QuickStart a few years back. The biggest thing is to prevent damage to the balun PCB from the coax either hanging from or flapping around in the wind and your placement of the ties does that job.
There was a tie on it, wasn't flapping.

Quote:
Originally Posted by ADTech View Post
Yeah, I know. I tested and posted test results 5-6 years ago for the Holland, Pico, and Radio Shack devices. the first two seem to have gone extict and who knows how long RS will still be around.
I would ask for a link, but it is academic with stuff disappearing.
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Old 19-Apr-2017, 2:14 AM   #14
rabbit73
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ProjectSHO89 tested the RS Gold UVSJ:



When I tested it with my signal level meter the insertion loss in the passbamd was about 0.5 dB.

Here are the Holland specs:

http://www.hollandelectronics.com/ca...-Diplexers.pdf

The UVSJ contains a high pass filter and a low pass filter, which are inherently low loss.
Quote:
Originally Posted by lifespeed View Post
Right now I'm pulling in a 10dB noise margin station without preamp on the XG91 UHF antenna,
so not a lot of room for added loss.
You can add the antenna gain to the NM to make it more positive.

Nice photo of your antennas, but it makes your thread hard to read because the posts are very wide. I try to limit my images to
about 800 pixels wide.

Quote:
Originally Posted by lifespeed View Post
Some of the signals I receive are in the sub-20dB noise margin range, so I have tried to be very
careful with short RG6, no splitters, etc.
It impossible to receive signals with a NM lower than -15 dB; they are buried in the thermal noise floor below -106 dBm.

If you are able to receive a signal with a NM lower than -15 dB, either the TVFOOL report is wrong or the signal has been
enhanced by Tropospheric Propagation.



With so many factors involved, try the easy way first with the UVSJ down below.

If you are concerned about the insertion loss of the UVSJ for UHF, you have a choice of two UHF antennas to combine with the
VHF antenna; pick the one that will do the least harm to UHF reception.
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Last edited by rabbit73; 19-Apr-2017 at 5:14 PM.
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Old 19-Apr-2017, 5:17 PM   #15
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FYI, the TVFOOL NM calculation assumes that a preamp will be used. If you look at a report you will see that the difference
between the NM and the signal power is a constant of about 91 dB. This allows for the minimum required SNR of 15 dB above
the Thermal Noise Floor which puts the a 0 dB NM signal at -91 dBm.

If you do not use a preamp, then you must allow for the minimum required SNR of 15 dB and the NF (6 dB average) of the tuner,
placing the minimum required signal at -85 dBm (+6 dB NM) where most tuners drop out. With a preamp, the tuner NF is buried
in the amplified Thermal Noise Floor, because the amplification is prior to the tuner input, and the tuner noise is internal.

These two diagrams show why a signal of at least +6 dB NM is needed at the tuner input to allow for the tuner NF when a preamp
is not used.

Version 1 is usually how it is shown, but Version 2 is more accurate because it shows the tuner noise added to the Thermal Noise
Floor before adding the minimum required SNR of 15 dB.




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Last edited by rabbit73; 19-Apr-2017 at 5:57 PM.
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Old 19-Apr-2017, 5:59 PM   #16
lifespeed
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Quote:
Originally Posted by rabbit73 View Post
You can add the antenna gain to the NM to make it more positive.
Yes, that is how it works. The UHF antenna gain is 12 to 14 dB, so even with a noise margin of 10 dB (KBCW RF45 VC 44.1) I still get error-free reception. So (10+12)-15 leaves about 7 to 9dB for coax loss and tuner noise figure. Both of these must be doing OK, as I get this station clearly.

Quote:
Originally Posted by rabbit73 View Post
Nice photo of your antennas, but it makes your thread hard to read because the posts are very wide. I try to limit my images to about 800 pixels wide.
Fixed and clickable.

Quote:
Originally Posted by rabbit73 View Post
It impossible to receive signals with a NM lower than -15 dB; they are buried in the thermal noise floor below -106 dBm.

If you are able to receive a signal with a NM lower than -15 dB, either the TVFOOL report is wrong or the signal has been
enhanced by Tropospheric Propagation.
That was a hyphen, not a minus sign. Not clear, edited to "sub 20 dB".

Quote:
Originally Posted by rabbit73 View Post
With so many factors involved, try the easy way first with the UVSJ down below.

If you are concerned about the insertion loss of the UVSJ for UHF, you have a choice of two UHF antennas to combine with the
VHF antenna; pick the one that will do the least harm to UHF reception.
In hindsight this seems obvious, good idea! The way to maintain tuner quantity, as opposed to dedicating an entire dual tuner to VHF to receive two channels, would be to diplex VHF with the DB4e aimed at Fremont 12 miles away. Although this antenna does not receive all the San Francisco stations like the Big Yagi it does receive quite a few perfectly. This would help with the occasional DVR wanting more tuners issue. Unfortunately I don't have room for three antennae on that mast. Three antennae, something doesn't seem right here. Anything worth doing is worth overdoing.

Last edited by lifespeed; 19-Apr-2017 at 6:04 PM.
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Old 19-Apr-2017, 6:05 PM   #17
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I grabbed an EU385 out of the returns box at random and ran it though the usual battery of measurements.

I just zipped the files so you can download and peruse them. The file name identifies the measurement.

Note: Unused terminals were capped with 75 ohm terminators for each measurement.

Cheers!
Attached Files
File Type: zip EU385CF-1S_CHARACTERIZATION.zip (103.3 KB, 29 views)
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Old 19-Apr-2017, 6:53 PM   #18
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Quote:
Fixed and clickable.
Thanks for reducing its width; much better.
Quote:
That was a hyphen, not a minus sign. Not clear, edited to "sub 20 dB".
Thanks; I guessed wrong.
Quote:
I don't have room for three antennae on that mast. Three antennae, something doesn't seem right here.
Anything worth doing is worth overdoing.
I overdo it frequently, especially with wood.

Would you consider replacing one of the UHF antennas with a UHF/VHF-High combo antenna like the Winegard HD7698P?
It would have to be the 91XG, because that is the same direction as for KGO RF7, I think.

Another alternative would be the VHF Kit on top of the DB4e as suggested by ADTech.

If that isn't enough gain, another alternative would be a modified MCM 30-2475 between the 91XG and the DB4e.
Remove the upper and lower reflector rods, leaving just one; its 33-1/8 length should be sufficient for channel 7.
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Last edited by rabbit73; 19-Apr-2017 at 8:53 PM.
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Old 19-Apr-2017, 8:21 PM   #19
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Quote:
Originally Posted by ADTech View Post
I grabbed an EU385 out of the returns box at random and ran it though the usual battery of measurements.

I just zipped the files so you can download and peruse them. The file name identifies the measurement.
Interesting images.

It downloaded as a php file, so I had to change the file extension to zip and extract.
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Last edited by rabbit73; 19-Apr-2017 at 8:25 PM.
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Old 19-Apr-2017, 10:45 PM   #20
lifespeed
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Quote:
Originally Posted by ADTech View Post
I grabbed an EU385 out of the returns box at random and ran it though the usual battery of measurements.

I just zipped the files so you can download and peruse them. The file name identifies the measurement.

Note: Unused terminals were capped with 75 ohm terminators for each measurement.

Cheers!
Plots are much better than a single number. The UHF antenna would actually see a very nice load up to 600MHz (-16dB R. L.). Your UVSJ performs well, especially over the UHF band once it is cut down to channel 37 608MHz.

The combined port match isn't as good, but the tuner probably presents a decent 75 ohm load so this may be less important than the port facing the UHF antenna.

It seems unlikely the slight loss and mismatch would cause an issue, I'll try your UVSJ first as the most likely solution vs. a dedicated tuner. It would be nice to preserve 4 tuner availability for most channels. Even though they aren't terribly expensive, it seems silly to have more than two of those units sitting up in the attic.

Are you using a Fieldfox handheld VNA/SPA?
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