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Old 9-Sep-2011, 5:46 PM   #21
GroundUrMast
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Regarding coax, the only wire I have ever had trouble with was purchased at Radio Shack. That experience was many years ago. The shield had bunched up under the outer insulation during manufacture.

Splitters... most are quite similar in performance. Gold plating and fancy looking cases are cute but don't improve the performance. Look for the loss specification (nominal is about 3.5 dB per port on a 2-way split) and bandwidth should be nominally 5 to 1000 MHz. Additional bandwidth (satellite splitters) buys you nothing in OTA performance.

Regarding grounding, I encourage you to get the most from the relatively small amount of time, money and effort that is usually needed to do the job. Ideally, your tower ground and the coax ground block would be tied to the existing electrical service ground. http://forum.tvfool.com/showthread.php?t=901
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Last edited by GroundUrMast; 9-Sep-2011 at 8:43 PM.
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Old 9-Sep-2011, 6:40 PM   #22
Ziffster
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Thanks!

Everything but the tower is on order and should be here next week!

Since the tower will be a local pickup I just need to decide which one to get - the $650 50' Delhi GN18 @ 150lb or the $880 50' Rohn G25 @ 210lb.
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Old 9-Sep-2011, 8:08 PM   #23
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Thanks!

Everything but the tower is on order and should be here next week!

Since the tower will be a local pickup I just need to decide which one to get - the $650 50' Delhi GN18 @ 150lb or the $880 50' Rohn G25 @ 210lb.
I'd rather climb a Rhon if I had to choose.
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Old 9-Sep-2011, 8:26 PM   #24
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I'd rather climb a Rhon if I had to choose.
Me too, except for Rohn's HDX tower. Sharp edges on the cross bracing of the HDX design cuts into your hands.
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Old 14-Sep-2011, 4:48 AM   #25
Ziffster
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Yikes!

When the parts arrived they had substituted a CM7778 for the CPA19. I called and the reason was that the CPA19 was out of stock. If I really want the CPA19 I can ship it back and they will pay the return shipping and to ship the CPA19 when they get it in about 2 weeks.

Should I return the CM7778 or is it like they claim about the same as the CPA19 plus has the advantage of supporting seperate UHF & VHF antenna without a combiner and built in surge protection / lightening protection?
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Old 14-Sep-2011, 7:34 AM   #26
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Given the vast number of changes in the Canadian markets, it's tough to know what the current situation is regarding which analog stations have been shut down. I picture the TV Fool staff working some looooong hours these days dealing with database edits.

Is CBLN still on the air on channel 40? If so, any consumer grade amplifier would overload.

If you consider only the top seven pending digital database entries, add antenna gain (about 9 dB), it looks like you will be delivering a total of +40 dBmV to the amplifier input. That does not account for any signal from FM or fire/police radio. The CM-7778 is rated for 23 dB gain on the UHF band, and a maximum UHF output of +50 dBmV... that's infers that the maximum input would be 27 dBmV (50 - 23). So, I think the 7778 will overload due to being over-driven by 10 to 15 dB.

Honestly, I think the CPA-19 will be on the edge of overload as well.
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Old 14-Sep-2011, 6:35 PM   #27
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Is CBLN still on the air on channel 40? If so, any consumer grade amplifier would overload.

If you consider only the top seven pending digital database entries, add antenna gain (about 9 dB), it looks like you will be delivering a total of +40 dBmV to the amplifier input. That does not account for any signal from FM or fire/police radio. The CM-7778 is rated for 23 dB gain on the UHF band, and a maximum UHF output of +50 dBmV... that's infers that the maximum input would be 27 dBmV (50 - 23). So, I think the 7778 will overload due to being over-driven by 10 to 15 dB.

Honestly, I think the CPA-19 will be on the edge of overload as well.
CBLN has moved from 40 to 23 and also reduced power to 24 kW (85% reduction). After the change the signal is now so weak that we have trouble picking up CBLN.

That was my feeling, that 23 db was too much, but the seller claimed that overload shouldn't be a problem since we will have 150' of cable and a three way splitter so cabling loss will be around 14 db more than if we had the antenna hooked up directly to the antenna. BTW the CPA-19 was added to offset these losses, realizing the if not for these losses a booster wouldn't be needed.

Sine the pre-amp is really needed for the VHF range more than the UHF range. To eliminate risk of overload (and since the only week stations are VHF) can the joiner be added after the booster rather than before it?
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Old 14-Sep-2011, 7:15 PM   #28
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Quote:
Originally Posted by Ziffster View Post
CBLN has moved from 40 to 23 and also reduced power to 24 kW (85% reduction). After the change the signal is now so weak that we have trouble picking up CBLN.

That was my feeling, that 23 db was too much, but the seller claimed that overload shouldn't be a problem since we will have 150' of cable and a three way splitter so cabling loss will be around 14 db more than if we had the antenna hooked up directly to the antenna. BTW the CPA-19 was added to offset these losses, realizing the if not for these losses a booster wouldn't be needed.

Sine the pre-amp is really needed for the VHF range more than the UHF range. To eliminate risk of overload (and since the only week stations are VHF) can the joiner be added after the booster rather than before it?
I would be inclined to aim the VHF antenna directly at CH-13 to reduce the amount of power from CH-10. Install the CPA-19 on the output of the VHF only. As you say, combine the amplified VHF with the unamplified UHF.

If you run into overload problems you can still add a UVSJ ahead of the CPA-19 with the UHF port terminated by a 75 ohm 'F' terminator cap. That would suppress the UHF power received by the VHF antenna another 20 dB or more.

The UVSJ used to combine the signals from both antennas would need to pass power through the VHF port or be located downstream of the CPA-19 power insertion block (which needs protection from the elements, it's designed for indoor installation).
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Last edited by GroundUrMast; 14-Sep-2011 at 11:30 PM.
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Old 14-Sep-2011, 9:31 PM   #29
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I would be inclined to aim the VHF antenna directly at CH-13 to reduce the amount of power form CH-10. Install the CPA-19 on the output of the VHF only. As you say, combine the amplified VHF with the unamplified UHF.

If you run into overload problems you can still add a UVSJ ahead of the CPA-19 with the UHF port terminated by a 75 ohm 'F' terminator cap. That would suppress the UHF power received by the VHF antenna another 20 dB or more.

The UVSJ used to combine the signals from both antennas would need to pass power through the VHF port or be located downstream of the CPA-19 power insertion block (which needs protection from the elements, it's designed for indoor installation).
Thanks! That got me thinking - what about using an actual attenuator like:

http://www.summitsource.com/eagle-10...k-p-10481.html
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Old 14-Sep-2011, 11:36 PM   #30
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Thanks! That got me thinking - what about using an actual attenuator like:

http://www.summitsource.com/eagle-10...k-p-10481.html
There is no reason to attenuate the output of the UHF antenna and a broadband attenuator in the VHF section of your system would make reception of the weaker VHF signals that much more difficult. I'm not worried about tuner overload... just the preamp.

Try to keep things as simple as possible. Use the UVSJ as a band pass filter only if you prove the need.
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