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Old 06-29-2017, 07:21 PM   #16
It's the Antenna!
 

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The point that I was trying to make is just because the connections are good enough for the signals, doesn't mean that they are good enough for the DC current for the preamp.

I'm glad that you are getting signals for the 7777hd inside, but I really want to know why the Juice preamp didn't work like it should have.
Quote:
I suppose I should have ran another coax up the hill
Yes, running another good length of coax would have been a good test to see if the original coax has a problem. Coax that is in a below ground pipe can go bad submerged in water from condensation.
Quote:
I believe the coax is the copper clad...it is the RG6.
RG6 can come either way, copper clad steel or solid copper. Most of it is copper clad steel.
Quote:
I think you said RG11 is the full copper.
I didn't bring up the topic of RG-11, Terryl3 did. I think it is too hard to work with and should only be used as a last resort.
Quote:
I running about 60 per cent on the Tivo meter for my main stations. I think when it drops below 40 on the yellow signal they drop off...these are low powered UHF that I'm trying to receive.
That's normal for a TiVo. You need a preamp at the antenna to improve that. The technical reason for that is because a preamp at the antenna improves the system noise figure.

Why not try an extension cord for the preamp AC power supply to see if a preamp at the antenna would help with the marginal channels?
Quote:
I'll try to send you a pic....
Yes, I see the picture, you showed it to us before in your first post. It is inside; you need a preamp outside near the antenna to improve the reception of the weak signals, if it is possible at your location.



Quote:
I don't think the Juice is any better than some of the other items....
The Juice is a very good preamp. It has a low noise figure that helps with the reception of weak marginal signals and it resists overload from strong local signals.

Quote:
the girl immediately said they would let me keep it at 50%.
That's a good deal.

Quote:
I told her it didn't work on long runs so I sent it back....
Big mistake. All you know is that it didn't work on your long run. You should have tried it with a new run of coax and with an AC extension cord while you had it.
Quote:
probably an overrated product like some of the others....
It's not overrated; you underrated it without giving it a fair chance.
Quote:
I wish they could make an amp with a reset.....
A reset for what?
Attached Images
File Type: jpg machinery-manHDF7777_1.jpg (131.3 KB, 50 views)
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Old 07-04-2017, 06:19 PM   #17
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Default Voltage Drop Calculations



I did some calculations of voltage drop with different kinds of coax to find how much there would be at 100 and 200 feet for a preamp that uses 5 volts and draws 200 mA (0.2 A).

Belden 1694A RG6
18 AWG solid .040" bare copper conductor,
tinned copper braid shield (95% coverage).

Center Conductor DC Resistance:
(Ohm/km) 20.9984, 0.64 ohms/100ft

Outer Shield DC Resistance:
(Ohm/km) 9.1868, 0.28 ohms/100ft

0.64 + 0.28 = 0.92 ohms round trip

E = I x R
E = 0.2 x 0.92 = 0.184 V
5 - 0.184 = 4.8 V for 100 ft
5 - 0.368 = 4.6 V for 200 ft., 7.4% drop

Perfect Vision RG6
Center conductor CCSteel 98 ohms/Km, 2.94 ohms/100ft

Braid Al 60% 43 ohms/Km, 1.29 ohms/100ft

2.94 + 1.29 = 4.23 ohms round trip

E = I x R
E = 0.2 x 4.23 = 0.85V

5 - 0.85 = 4.15V for 100 ft
5 - 1.7 = 3.3V for 200ft, 34% drop

Belden 8233 Triax - RG-11/U Type
14 AWG solid .064" bare copper conductor, gas-injected foam HDPE insulation, bare copper double shields (95% and 80% coverage), polyethylene jacket.

CenterConductor DC Resistance
20C (Ohm/1000 ft) 2.600, 0.26 ohms/100 ft

Outer Shield DC Resistance
20C (Ohm/1000 ft) 1.500, 0.15 ohms/100ft

0.26 + 0.15 = 0.41 ohms round trip

E = I x R = 0.2 x 0.41 = 0.082 V
5 - 0.08 = 4.92 V for 100 feet
5 - 0.16 = 4.84 V for 200 feet, 3.2% drop

Comscope 4136903 RG11
Center Conductor Material Copper-clad steel wire 14 gauge

Center conductor DC Resistance 11.00 ohms/kft, 1.1/100 ft

Shield (Braid) 60% Aluminum
Shield DC Resistance 6.90 ohms/kft, 0.69/100 ft

1.1 + 0.69 = 1.79 ohms round trip

E = I x R = 0.2 x 1.79 = 0.36 V
5 - 0.36 = 4.64 V for 100 feet
5 - 0.72 = 4.28 V for 200 feet, 14.4% drop

The type of coax you use will make a big difference in the voltage drop for the preamp.

A solid copper center conductor is better than a copper clad steel center conductor because it has lower resistance.

A copper high percentage braid is better than an aluminum lower percentage braid because it has lower resistance.

The question that still remains is: How low can the voltage go and still have the Channel Master 7777HD Amplify preamp work properly?
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Last edited by rabbit73; 07-04-2017 at 06:33 PM..
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Old 07-04-2017, 07:54 PM   #18
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I would estimate around a .5 volt drop and the amp should still work to a point.
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Old 07-15-2017, 12:25 PM   #19
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Quote:
Originally Posted by Terryl3 View Post
I would estimate around a .5 volt drop and the amp should still work to a point.
That seems like a good estimate, but I will never know until I test it.

Channel Master is running a 4th of July Freedom sale from July 4 to July 20.

Half price for a 7777HD Amplify preamp; I couldn't resist.
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Old 07-15-2017, 12:36 PM   #20
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Default Coax measurements with CM 7777HD Amplify preamp

I made some measurements with four different 100 ft lengths of coax connected to a CM7777HD preamp, one at a time, with no signal.

Later, I connected three of them together in series with a signal, to see what would happen to the voltage at the amp and the signal. I tried to simulate what was used by machinery-man at his location.

100ft Solid Signal Custom RG6 Quad with solid copper center conductor

Output of power inserter
with amp connected: 5.187V

Voltage at amp: 4.990V, using "T" adapter

Voltage drop: 0.197V

Current for amp: 169 mA, measured with Fluke 115 DMM; 14 mV drop across meter

100ft Solid Signal Custom RG6 with solid copper center conductor, not Quad shield

Output of power inserter
with amp connected: 5.187V

Voltage at amp: 4.902V

Voltage drop: 0.285V

Current for amp: 165 mA

100ft Channel Master 3713 with copper clad center conductor

Output voltage of power inserter without amp connected: 5.274V

Output of power inserter
with amp connected: 5.190V

Voltage at amp: 4.667V

Voltage drop: 0.523V

Current for amp: 153 mA

100ft Solid Signal Tech Choice 3035 (Monoprice) RG6 copper clad center conductor

If you look at the Q&A at the Monoprice site you will see that the 3035 is not rated for outdoor use, but its CL2 rating means that it has a fire rating for in-wall use.

Output of power inserter
with amp connected: 5.192V

Voltage at amp: 4.563V

Voltage drop: 0.629V

Current for amp: 149 mA
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Last edited by rabbit73; 07-15-2017 at 01:30 PM..
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Old 07-15-2017, 12:37 PM   #21
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What ever happened to good old fashioned line amps, all the new stuff looks to be way under powered.

We use to have some very nice line amps in the CATV business, ran on 24 volts AC, right on the coax. Cant find good stuff anymore.
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Old 07-15-2017, 01:38 PM   #22
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Quote:
Originally Posted by Terryl3 View Post
What ever happened to good old fashioned line amps, all the new stuff looks to be way under powered.
The manufacturers seem to be fascinated with 5V USB power connections.
Quote:
We use to have some very nice line amps in the CATV business, ran on 24 volts AC, right on the coax. Cant find good stuff anymore.
There is still some good commercial-grade equipment, but with consumer-grade equipment, the manufacturers no longer try to make it better, they try to make it cheaper.
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Last edited by rabbit73; 07-15-2017 at 07:47 PM..
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Old 07-15-2017, 01:50 PM   #23
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Default Voltage Measurements for CM7777HD Amplify Preamp at Different Coax Lengths

I made some voltage measurements with the CM7777HD preamp and different lengths of coax. I also monitored the signal reception with a 32" Sony TV and signal power with a Sadelco DisplayMax 800 Signal Level Meter at the different lengths.

Tests with OTA signal, channel 40

Equipment used:

GE 34792 Attic/Indoor Antenna, indoors at ground level
Channel Master 7777HD Amplify Preamp
100ft Solid Signal 3035 RG6 with copper clad center conductor
100ft Channel Master 3713 RG6 with copper clad center conductor
100ft Solid Signal Custom RG6 with solid copper center conductor
Jumper cables, F-81 adapters, 2-way splitter, and a type F coax T-adapter (f-f-f) for voltage measurements under load at preamp
Sadelco DisplayMax 800 Signal Level Meter (SLM)
Fluke 115 DMM
Sony 32BX320 TV

100ft Solid Signal 3035 RG6 with copper clad center conductor

Voltage at preamp: 4.553V, measured with "T" adapter
SNR 31 dB
Signal Power: -0.2 dBmV (-49.0 dBm)

I then added:

100ft Channel Master 3713 RG6 with copper clad center conductor

Voltage at preamp: 4.205V
SNR: 28 dB
Signal Power: -6.1 dBmV (-54.9 dBm)

And then added (for a total of 300ft plus jumpers):

100ft Solid Signal Custom RG6 with solid copper center conductor

Voltage at preamp: 4.051V
SNR: 27 dB
Signal Power: -9.1 dBmV (-57.9 dBm)











As you can see, the preamp LED is still on at 4.051V, with 300+ feet of coax.

CONCLUSIONS:

The preamp seems to have a circuit that compensates for low voltage from the coax.
Quote:
Originally Posted by machinery-man View Post
I hooked it up the bottom of the tower and the power inserted in the house but the amp did not light up as noted by instructions. I checked the power and found the 5.8 volts out of the inserter and 5.8 volts at the end of the rg6. Puzzled why it didn't light up...I then connected leads in the house and simply powered the unit at the antenna with a battery and inverted. It lite up and got the signals as needed......I really don't think there is any problem with the line as I have it in conduit and I do get good signals. Does anyone have any take on this. Any input would be appreciated. Best Chuck
You must measure the voltage for the preamp near the preamp with it connected. This is called voltage under load, which is less than open circuit voltage. A T-adapter will allow you to measure the voltage between the center conductor and the shield when the preamp is connected.



If your C7777HD preamp didn't work at the antenna and the Antennas Direct Juice preamp didn't work at the antenna, maybe there is something wrong with your coax.
Attached Images
File Type: jpg CM7777hdTest1.jpg (114.6 KB, 28 views)
File Type: jpg CM7777hdTest2.jpg (124.1 KB, 28 views)
File Type: jpg CM7777hdTest3.jpg (140.0 KB, 28 views)
File Type: jpg CM7777hdTest4.jpg (160.7 KB, 28 views)
File Type: jpg Loc2noRefl.jpg (100.9 KB, 28 views)
File Type: jpg T-Adapter.jpg (23.5 KB, 21 views)
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Last edited by rabbit73; 07-22-2017 at 05:30 PM..
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Old 07-15-2017, 02:54 PM   #24
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The amp's internals may run on +3 volts DC, thus the amp's still on line with a DC voltage drop of almost a volt.

Man I wish I still had access to the old engineering test lab, I could have some fun.
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Old 07-19-2017, 09:46 PM   #25
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Default CM7777HD Amplify Power Supply Protection from Coax Shorts

The original CM7777 preamp with two antenna inputs used the CM0747 power supply/power inserter that had a solid state fuse (self-resetting) that protected the power supply if there was a short in the coax.

I sent an email to Channel Master asking if the CM7777HD had similar protection:
Quote:
With a DIY antenna installation, a short in the coax is not unusual. The CM0747 power supply/inserter for the original CM7777 had a solid state resettable fuse (PTC) to protect the power supply if there is a coax short. Does the power supply for the CM7777HD have any protection if there is a coax short? If yes, exactly what type of protection is used?
This the answer I received:
Quote:
Our 12VDC power supply for the amplifiers does have load protection and automatically restores when incorrect load is removed. If you have one, you can short it at the output of the coax cable and you will see the green light/LED go out and hear the protection relay activate. Hopefully this info helps. Thanks!
Well, I was a little confused by that answer. The CM7777HD Amplify preamp uses a 5V power supply, not a 12V power supply. But, it does have a green LED, so I thought I would risk a test.

I measured the voltage to the preamp and then shorted the coax with the current shunt in my Fluke 115 DMM to measure the short circuit current. Ordinarily, it's a bad idea to connect a current meter to a voltage source, but I calculated that since the current shunt could handle 10A continuous and 20A for a short time, the risk to the meter was small.





The reaction of the power supply was interesting. When the current reached a peak of about 1.2A, the power supply shut down; it's rated for 1A output. A few seconds later it tested for a short and if it was still there, it would shut down again.

I didn't hear any relay clicking; it is probably a solid state circuit that shuts down the switchmode power supply (SMPS) when there is a short.

The Fluke DMM is able to record the MAX, MIN, and AVG current:



CONCLUSION:

The power supply for the CM7777HD Amplify preamp does have short circuit protection.
Attached Images
File Type: jpg CM7777HDshort1.jpg (214.2 KB, 15 views)
File Type: jpg CM7777HDshort2.jpg (204.7 KB, 15 views)
File Type: jpg CM7777hdPSscc.jpg (112.1 KB, 7 views)
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Last edited by rabbit73; Yesterday at 07:05 PM..
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Old 07-21-2017, 08:54 AM   #26
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I received a reply from Channel Master that corrected their instructions. They had given me the instructions for testing the 12V power supply for the CM7777 (with one antenna input) instead of the 5V power supply for the 7777HD that I had asked for.
Quote:
Tier II Tech Support (Channel Master Support)
Jul 20, 5:19 PM MST

Sorry for the confusion.
The 12vdc supply for the CM7777 CM7778 and our distribution amps is what I'd described.
I've not done long term over current/shorted cable testing. Sorry.
I'll get that on our list in the lab.
Thank you!
Kind regards,
Tier 2 Technical Support
support@channelmaster.com
1-877-746-7261
This is the perfect example of why it isn't a good idea to use the same model number for three different amps.

It causes confusion and errors.

The original 7777 had two antenna inputs and came with the 0747 power supply/power inserter. It was a very good popular design; I miss it.



The second version of the 7777 has only one antenna input and different circuitry for 30 dB gain, making it more susceptible to overload. At first, it came with the 15V APA1260315URH linear power supply and the PCT-MPI-1G power inserter. It now comes with the 12V SMPS512UTRH power supply (higher efficiency) and the PCT-MPI-12 power inserter.



The third version of the 7777, called the 7777HD Amplify, comes with the 5V SMPS105URH power supply and the CM-7777HDXPI power inserter.



Quote:
The 12vdc supply for the CM7777 CM7778 and our distribution amps is what I'd described.
The power supply that came with my last CM3410 distribution amp was the 15V APA1260315URH linear power supply; they had not yet switched to the 12V SMPS512UTRH switchmode power supply. The label on the 3410 says 12 to 16 VDC input.

There are several reasons for these changes:

1. To try to reduce the number of different amps in inventory to meet the customer needs
2. To reduce the number of different power supplies in inventory
3. To replace the low efficiency linear power supplies with higher efficiency switchmode power supplies to meet stricter energy consumption regulations. The older power supplies are level IV; the new power supplies are level VI.

Attached Images
File Type: jpg PCT SMPS512UTRH.JPG (117.0 KB, 10 views)
File Type: jpg OrigCM7777preamp2.JPG (106.5 KB, 7 views)
File Type: jpg 2ndGenCM7777preamp.jpg (51.8 KB, 7 views)
File Type: jpg 3ndGenCM7777preamp.jpg (163.0 KB, 7 views)
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Last edited by rabbit73; 07-22-2017 at 09:04 PM..
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Old Yesterday, 06:58 PM   #27
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Default Voltage and Signal Measurements of CM7777 with One Antenna Input

I made some voltage and signal measurements of the CM7777 preamp, with one antenna input, at different coax lengths. Later, I measured the short circuit current of the power supply to see what would happen during a coax short.

With short coax jumpers:

Voltage at preamp: 13.03V, measured with "T" adapter
SNR 28 dB
Signal Power: +9.6 dBmV (-39.2 dBm)
(OTA channel 40, raining)



I added:

100ft Solid Signal 3035 RG6 with copper clad center conductor

Voltage at preamp: 12.15V, measured with "T" adapter
SNR 28 dB
Signal Power: +3.0 dBmV (-45.8 dBm)

I then added:

100ft Channel Master 3713 RG6 with copper clad center conductor

Voltage at preamp: 11.41V, measured with "T" adapter
SNR 28 dB
Signal Power: -4.0 dBmV (-52.8 dBm)

and finally added, for a total length of 300+ feet:

100ft Solid Signal Custom RG6 (not Quad) with solid copper center conductor

Voltage at preamp: 11.27V, measured with "T" adapter
SNR 27 dB
Signal Power: -8.4 dBmV (-57.2 dBm)
Preamp current: 0.265A (265 mA)

I also measured the gain of the preamp with the OTA signal and my Sadelco DisplayMax 800 signal level meter: 24.7dB.

Since OTA signals constantly vary in strength, I repeated the measurement using the stable video carrier for analog channel 15 from my Blonder Tongue HAVM-1UA Agile Modulator: 24.1 dB (from -8.4 to +15.7 dBmV)

The specs for the 7777 say gain: 30 dB. Either my preamp is out of spec or Channel Master reduced the gain to make it less susceptible to overload.
Attached Images
File Type: jpg CM7777gen2Voltage.jpg (72.3 KB, 8 views)
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Last edited by rabbit73; Yesterday at 09:17 PM..
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Old Yesterday, 07:34 PM   #28
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Default CM7777 (2nd Gen) 5V SMPS105URH Power Supply Protection from Coax Shorts

I shorted the 5V SMPS105URH power supply for the CM7777 preamp, with one antenna input, to see how it would react to coax shorts. As before, I used the current shunt of my Fluke 115 DMM.



I tried it a few times, getting slightly different readings. When the current reaches a certain level, the power supply will shut down. It then waits a few seconds and tries again. If the short still exists, it will shut down again. The photo above shows a MAX short circuit current of 0.250A (250mA).

I did not hear a relay click.

Another set of short circuit readings looks like this:



This power supply also has short circuit protection.
Attached Images
File Type: jpg CM7777gen2sccMAX.jpg (73.0 KB, 8 views)
File Type: jpg CM7777gen2PSscc.jpg (184.3 KB, 7 views)
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