91XG or DB8e

[welkin]

Hello all,

Here is my tvfool report:

http://www.tvfool.com/?option=com_wr...b97d707e909613

Here is my original thread for reference:

http://forum.tvfool.com/showthread.p...ighlight=8200U

Here is a flow chart of my setup:



This setup worked great until RF19 started their repack process and has lowered power. Since this has happened, reception is very poor, but it is still watchable, sometimes. RF19 is eventually moving to RF25. After that RF44 is moving to RF19 and back to full power, RF23 is moving to RF16, and RF49 is moving to RF22. I will have 2 RF22s in opposite directions when this happens. All this is supposed to happen by the end of 2018. Fun times.

Anyway, after the repack, my highest frequency will be RF28. Do you think I should change out one or both of the 91XGs to increase gain at these lower UHF frequencies in an attempt to make RF19/RF25 watchable, or will I lose directional capabilities and get too much multipath interference? Is there another option you would suggest?

Thank you for your advice!

[rabbit73]

Hello again, welkin

Do you think I should change out one or both of the 91XGs to increase gain at these lower UHF frequencies in an attempt to make RF19/RF25 watchable,

The DB8E does have more gain than the 91XG for the low UHF channels according to the specs:



The DB8E must have both panels aimed in the same direction, which should be obvious. Also, both panels must be equally illuminated by the incoming signal, which might not be true. The 8-bay has a larger capture area than the yagi.

or will I lose directional capabilities and get too much multipath interference?

The 91XG does have an excellent F/B ratio. It is not clear if it would make a difference with your UHF antennas aimed in different directions.

Is there another option you would suggest?

A custom built yagi for the UHF low channels 14 - 36, in particular a loop yagi that has a horizontal loop for the driven element. It has superior rejection of off-aim signals. G0KSC calls his Loop Fed Array the Low Noise Yagi or LFA Yagi:
https://www.google.com/search?q=G0KS...k1.bNCN0I0-jCw

http://www.g0ksc.co.uk/2013-yagis/11...-lfa-yagi.html

The last resort would be a method of combining that avoids using a splitter in reverse as a combiner.

[welkin]

I think I'll wait and see what happens when they move RF19 to RF25. The gain of the 91XG improves about 1 DB and signal seems to get better the cooler the weather. If it's not better after the repack is finished, I'll move on to other options. I have to be able to get my AntennaTV and watch Johnny Carson. Thanks for your time.

[ADTech]

Several points for consideration:

Please also use call signs, RF channels alone are no longer sufficient in Springfield to identify what's going on.

The TVFool plot provided is woefully out of date (2015 database). Probably an old link.... However, as the consequences of the recently complete spectrum auction unfold, the changes will be coming in hot and heavy as stations who were bought out go off the air and as channel sharing agreements are implemented. Given that this site's owner hasn't implemented changes submitted for quite some time, it remains to be seen whether or not such updates will be made in the future. Just don't know...

Gray pretty much threw the channel and programming assignments in Springfield into a Cuisinart and I'm still trying to sort out the details since I hadn't looked at the market in quite some time.

Since Antenna TV is only available on low-powered digital stations (15 kW or less) ERP and you're 70 miles away, the odds of ever picking them up reliably is probably somewhere between slim and none except under rare atmospheric conditions. That you're picking up the channel 19 signal at all is, in itself, quite an accomplishment.

Regarding your concerns for having a co-channel issue on channel 22 when KRBK moves, I wouldn't worry about it. I'd suspect that KQFX-LD will be displaced and will have to file for a new operating channel when that filing window opens.

You can likely improve your system noise figure for your UHF antennas by around 4 dB by amplifying them separately before combining the signals in your reversed splitter. An improvement in the system NF by that magnitude would provide the same improvement as would an antenna with an increase of gain of 4 dB on your channel of interest.

[jrgagne99]

Originally Posted by ADTech

You can likely improve your system noise figure for your UHF antennas by around 4 dB by amplifying them separately before combining the signals in your reversed splitter.

He would need splitter that passes power through both ports, right? Does such an animal exist? Can the CM-7777 power inserter supply enough current to power two pre-amps? He would also need a UVSJ that passes power through the UHF side (or passes power through both ports and put a DC-blocker on the VHF port), right?

[ADTech]

He would need splitter that passes power through both ports, right? Does such an animal exist?

Yes, you can buy one at Walmart. Every splitter on retail store shelves that I've examined that are labeled for "satellite" use are diode steered DC pass, regardless of their packaging or labeling.

Can the CM-7777 power inserter supply enough current to power two pre-amps?

The CM7777 would probably have to go. Too much gain for a hybridized, multi-amp system. Some amount of additional research would be needed to optimize the system. There are ways to power multiple amps off a single power supply/inserter, some assembly WILL be required as will careful selection of components. Keep in mind that there's no "free lunch".

He would also need a UVSJ that passes power through the UHF side (or passes power through both ports and put a DC-blocker on the VHF port), right?

As an example, our UHF/VHF combiner (UVSJ) already does both of those.

[welkin]

ADTech, Thanks for your input. I appreciate it. The Longley-Rice coverage map for the future home of KYCW-LD doesn't give me much hope, but it will be broadcasting from a 2000' tower, so I've got to try. I'm getting 32 channels/subs reliably now. I acquired a 50' Rohn 25G, so I'm going to gain 15' in height soon, which should help.

http://www.rabbitears.info/contour.p...2.941138888889

Originally Posted by ADTech

You can likely improve your system noise figure for your UHF antennas by around 4 dB by amplifying them separately before combining the signals in your reversed splitter. An improvement in the system NF by that magnitude would provide the same improvement as would an antenna with an increase of gain of 4 dB on your channel of interest.

Should I get another 7777 and run another coax in the house and combine them inside? Eliminate the UVSJs and go with something like an RCA TVPRAMP1Z? Can two preamps be ran off of one power supply? Something else?

Also, I think I know the answer, but is there a method of combining the 4 antennas that doesn't introduce the loss of a splitter/combiner? Multiple tuners are not an option.

Thanks!

[rabbit73]

is there a method of combining the 4 antennas that doesn't introduce the loss of a splitter/combiner?

The method that ADTech suggested, combining after amplification, doesn't eliminate the combiner loss, but it does make it irrelevant because the signals are stronger before that attenuation.

So, having two preamps and having two coax lines would allow you to combine after the two power inserters and avoid a custom power supply needed to power two preamps through one coax.

No matter where the combiner is located, after the UVSJs or after the power inserters, you are still combining two UHF antennas aimed in different directions and two VHF antennas aimed in two different directions. This means that if two antennas pick up the same signals, when they arrive at the combining point they will interfere with each other if they are not in phase.

The only way to avoid that is with single channel amplifiers, single channel antennas if necessary, and combine into one coax like a CATV headend.

[ADTech]

KYCW-LD is using the antenna previously used by now-gone KSPR at just a bit over 1800' AGL.

I have to tell you I generally despise the 7777 because it's used so inappropriately so often. Too many people think that more gain is better and it usually isn't. If that thing was kept behind the pharmacy counter and sold only by expert prescription, I'd have a very different perception about it.

Powering multiple preamps with a single line can be done, it does require some knowledge about the amps in use, some creativity and it's not without its possible drawbacks.

[Tower Guy]

There is still a sensitivity problem if a splitter used as a combiner after both preamps. It occurs because any front end noise contributed by the preamp connected to the mis-aimed antenna adds to the noise of the preamp of the marginal signal. To get any advantage, you could either notch out channel 19 from the mis-aimed preamp output, or attenuated the output of that preamp by enough to allow the desired signal to override the undesired noise. If you opt for an attenuator, a good place to start would be 6 db.

If you opted to filter the noise from the mis-aimed antenna, Warren electronics says that they still have some channel 19 Jointennas. http://www.warrenelectronics.com/ant...Jointennas.htm

A Jointenna may only allow channel 19 through, or not; you'd only know if you tried it.

[ADTech]

Warren Electronics has closed (owners retired).

[Tower Guy]

If this is real, they have some NOS channel 19 Jointennas.

https://picclick.com/Channel-Master-...718785944.html

[rabbit73]

If a 2-way splitter, used as a combiner, has to pass power to two preamps and it has diodes, will the diodes be reversed biased and not pass power?
https://www.amazon.com/Valley-2-Way-.../dp/B001X3MGFU

http://www.homedepot.com/p/Ideal-2-4...-332/202276264

This will work:



This will not:

[ADTech]

Those are both examples of incomplete markings that don't include the diode symbols. Sat splitters have to pass power from any of the "output"" ports back to the "input" port so the receiver can power the dish-mounted electronics.

The Ideal splitter you indicated is one of my favorites as is the Holland HFS-2D whose label does properly indicates the internal function.



If polarity matters for DC-passthrough (and it would in the case of the splitter that is performing antenna combiner duty), there is at least one splitter out there that does not used DC-blocking capacitors on the output so it doesn't need diodes. That would be the Channel Plus 2512A.

[rabbit73]

Yes, the Channel Plus 2512A might work. I wonder what is inside and how much current it will pass?



1 GHz bandwidth
• 3.5 dB insertion loss (as a splitter)
• Passes DC IR signals on the coax
• Use as a signal splitter or combiner
• DC and I/R passing
• Provides a 1 GHz bandwidth
• Ideal for antenna and coax operations

If the 2512A is used as a splitter between the preamp and the power inserter, would it be necessary to put a DC block on the output for the second TV?

[welkin]

I appreciate your help. I believe you are proposing something like this?

[ADTech]

I wonder what is inside and how much current it will pass?

There's a reference circuit design in this MiniCircuits app note that is pretty much similar to almost every two port splitter I've opened. http://www.minirf.com/pdf/splitters/MRFSP0014DS.pdf Ignore the "external" references in the diagram, those are for the design engineer's use who is using the device for his design. In the collection of splitters I have on hand and have opened, I see one or more differences in capacitors as well as some splitters that don't' bother with the isolation network between the two outputs (two coils and resistor).

Add to the list of potential splitters that include direct pass-through of DC the basic Ideal cable/TV splitter that anyone can pick up from Home Depot for $4 (85-132).

The basic splitters that do not pass DC power simply have a low-value blocking capacitor in series with the output port. For "satellite" splitters, they simply put a diode in parallel with the blocking cap to allow power to pass from either output back to the input. The sat-rated splitters also appear to use higher quality transformers and much better layout and construction techniques so as to extend their bandwidth.

As far as maximum current carrying capability, it's hard to say. It appears the transformers through which power must pass are all wound with a wire somewhere around 28-32 gauge.

Several of the samples I have include DC pass on one port only. All of these simply have a coil connected directly from the input to one of the outputs and include the blocking cap on both output legs.

I believe you are proposing something like this?

Pretty much along those lines although I wouldn't specify use the RCA amps due to my experience with them (poor reliability) plus the need for a different power source in order to run two of them off one source. If you do decide use them, you shouldn't need the HLSJ as a high-pass filter for FM.

[welkin]

Originally Posted by ADTech

Pretty much along those lines although I wouldn't specify use the RCA amps due to my experience with them (poor reliability) plus the need for a different power source in order to run two of them off one source. If you do decide use them, you shouldn't need the HLSJ as a high-pass filter for FM.

Is there a unit you recommend besides the RCA

Thanks,

[rabbit73]

Originally Posted by ADTech

There's a reference circuit design in this MiniCircuits app note that is pretty much similar to almost every two port splitter I've opened. http://www.minirf.com/pdf/splitters/MRFSP0014DS.pdf Ignore the "external" references in the diagram, those are for the design engineer's use who is using the device for his design. In the collection of splitters I have on hand and have opened, I see one or more differences in capacitors as well as some splitters that don't' bother with the isolation network between the two outputs (two coils and resistor).

Thanks for the splitter information; very helpful.

Originally Posted by welkin

Also, I think I know the answer, but is there a method of combining the 4 antennas that doesn't introduce the loss of a splitter/combiner?

As you are finding out, it is not easily done. You first must try your antennas without combining to see if reception is possible. Then, when you combine them, if you are not able to receive all the channels that you had when the antennas were separate, combining doesn't work for you.

There seems to be a difference of opinion between ADTech and Tower Guy about the potential success of combining 4 antennas in this manner. With so many factors involved, I would just have to try it.

Multiple tuners are not an option.

Why not?

[rabbit73]

Originally Posted by welkin

Is there a unit you recommend besides the RCA

The RCA TVPRAMP1R Preamp is inexpensive, works fairly well, but does have quality control problems. In particular, when using separate UHF and VHF antennas, the switch must be set to SEPARATE. In that position, it sometimes makes poor contact with the VHF antenna. The fix is to use COMBINED and an external UVSJ ahead of the preamp input. Also, people that buy an Amazon warehouse special, often get a return that doesn't work because the power supply/power inserter hasn't be checked.

At first I was puzzled by ADTech not suggesting the Juice preamp which is made by the company he works for. The Juice has a low noise figure (good) and is resistant to overload. My guess is that the power supply would need to be custom to power two preamps through one coax. Their power inserter would handle the current for two, but the power supply might not. The PCT SMPS512UTRH for the second generation 7777 might work:



I favor the two coax and combine after the two power inserters approach, because it avoids the power supply problem and allows you to test each antenna system separately.

Also, there is the FM interference problem. The Juice does not have an FM filter and you have a strong local FM transmitter that might cause a problem with VHF reception. I did an FM signal report based on your TVFOOL report, but it isn't accurate enough because you are so close to KMYK:
http://www.fmfool.com/modeling/tmp/5...3/Radar-FM.png

Can you please do an exact address FM signal report so that I can see how close my estimate was:
http://www.fmfool.com/index.php?opti...pper&Itemid=29

Any maybe while you are at it, a more recent TVFOOL report (which will still probably have some errors because the tvfool database isn't up to date):
http://www.tvfool.com/index.php?opti...pper&Itemid=29