Signal Amplifiers (Amps, Preamps, Distro Amps) - See Chart in Post #1

[roger1818]

The cascade system noise calculator guesses at the noise factor of the first stage amplifier in your tuner. This can vary widely from model to model. If its NF is as good or better than your HDP 269, the pre-amp won't improve your SNR (given that you only have 30ft of coax and no splitters). That is why some say adding a pre-amp is only useful if you have more than 50ft of coax or a splitter, but this rule of thumb is a bit of an over simplification.

[balm]

Ok, thanks Roger, and Majortom,

I will have to do more tests.


I put in a receiver Noise = 3, in the spreadsheet, it gives me system noise= 6.2 without preamp, and system noise = 4.6 with preamp

[balm]

Then make sure something else like interference or multipath isn't at play to begin with, insert an attenuator (2 way splitter)
inline at the receiver, you should lose signal lock. If ya do, use this channel as ur baseline.

did something similar, but not quite right,

I turned the antenna slightly off the channel with SNR 15, then it was trying to drop out, then I put in the preamp, and it didnt seem to improve any

but I will retry using your methodology, thanks...

so if it doesnt improve, and assuming the receiver noise is worse than the preamp, that means there is other issues at play, like multipath...?

BTW, im using a CM4228HD.

[majortom]

3dB NF receiver isn't likely for a consumer device.
I'd probly plug in sumthin double that and say 6dB.

[roger1818]

^^^I am not so sure about that. In the old days, TV tuners have very low NFs, but as more and more people got cable TV, they started to cut corners. Now there is a wide variation from model to model. 3dB isn't an unreasonable design spec, especially for a STB where they know it will be used with an antenna.

[majortom]

Originally Posted by balm

so if it doesnt improve, and assuming the receiver noise is worse than the preamp, that means there is other issues at play, like multipath...?

yeah, the purpose of the attenuator in the before test is just to rule out other factors like external interference, multipath degrading the sensitivity on the channel ur tuned to, etc. if ya can't get there, use a different channel.
In a lab environment that wouldn't be necessary, but this is real world.
The purpose of the additional attenuation in the after test is to validate the improvement over long coax runs.

For the indication of SNR, are you using your Hauppauge 950Q PC based tuner?

[balm]

so if I insert the splitter (attenuator) before, and the signal DOESNT drop out, this indicates there was multipath to begin with ?


EDIT: yes, using the 950Q

[majortom]

well, let's just assume it's not limited by weak signal strength alone.
To get an idea what your receive sensitivity is ya have to receive a signal that is at or near the sensitivity threshold, and below AGC control in strength to begin with. So ur trying to find one without the aid of a Spectrum Analyzer. If ya have to add more attenuation, 2way 3.5 dB + 4 Way 7 dB = ~ 10 dB. Certainly ya can make it drop out using some combination of those on a weak station. For me here I use the distant Canadian stations. I have an adjustable 75 ohm attenuator, 1,2,4,8 dB steps so up to 15 dB atten.

950Q - uses an Xceive XC5000 tuner
http://db.tt/xzTxtesC
I'm not 100% sure but I think my LG tv uses the same silicon tuner

The inDtube PC tuner I use is similar but uses an Xceive XC3028L
http://db.tt/pgy3Iryl

So in theory your tuner is ~ 1dB better NF wise than mine.

[Miike]

I've acquired a Phillips MANT310 VHF/UHF/FM amplified indoor antenna and am wondering if it would be possible/advisable to use the internal parts as a preamplifier for my home built 4 bay bowtie reflector antenna (Mclapp 4 9x9) which is mounted in the attic of my two storey house.

I'm not sure if it will help or even be possible. I reliably receive all local digital channels in the Ottawa area (I have a separate folded dipole to receive global on 6.1). All I really have to gain is PBS, maybe a long shot at CBS.

I'm not even sure how I might connect the preamplifier. Inside the housing there is a circuit board with two yellow wires connected to the rabbit ears and two black wires connected to the UHF loop. Could I simply attach these leads to my VHF and UHF antennas? Would I need to use a balun on the antennas, or is it built in to the circuit board?

Here are my TV Fool results:

http://www.tvfool.com/?option=com_wr...de65c7a5fcddd2

[stampeder]

Miike, we'll deal only with your amplifier questions in this thread, but everything else about your reception in your area is already covered in this one:

http://www.digitalhome.ca/forum/showthread.php?t=126060

So read through it and read the replies to your recent post there, and if you still have amplifier questions then come back here to this thread.

[Miike]

Hi Stampeder,

Thanks for the response. I'm really only interested in the amplifier side of things here. I just mentioned the reception details for context.

Any advice on how to wire up the amplifier would be appreciated. I recognize that it is not of great quality. I'm mostly curious to know if it is possible - specifically regarding how and where to connect the internal leads, and whether or not a separate balun would be required.

[roger1818]

Miike, It should work, though as you said the amp is likely of poor quality. If you do it, I would replace the "yellow and black wires" with proper 300ohm twin lead. The wires that connect to the rabbit ears can go to your folded dipole and the wires the connect to the loop can go to your Mclapp 4 9x9. Just don't use baluns as it sounds like the amp has them built in.

[Miike]

Hi Roger1818,

Thanks for the advice. I might try it out this weekend. If so, I'll try to remember to report back the results.

Would it be helpful if I could provide a picture of the circuit board?

Miike

[re_nelson]

As noted a few posts back (check it for the TV Fool data), a Terk HDTVi, the passive antenna, was recently obtained so that I could use a rather modest antenna in order to compare preamps. Time constraints allowed me to test only three preamps:

Winegard AP8700
KitzTech KT-200
Research Communications RC9263

The format and methodology of these SNQ measurements using a Silicon Dust HD Homerun follows the model I've used in previous posts. And each preamp was rotated into service for a period of 20-25 hours before being replaced by another in the cycle.

This is the first such test where the absence of any preamp made a discernible difference that the average viewer might notice. When no preamp was in use, both channel 27 and 31 (each of which is an LPTV facility) would suffer an occasional dropout. It was momentary and occurred at a rate of about once every quarter hour. Adding any of the three preamps tested cured that problem. The television where the dropouts were observed is a Sylvania-branded LC195SLX.

The report shown here is confined to only those channels that present something of a reception channel. All of the others are so solid that they are of little interest.

SNQ scans from 2012-04-17 21:00 to 2012-05-06 23:00 

CH       NONE   AP8700 (Diff)   KT-200 (Diff)   RC9263 (Diff)
--       ----   -------------   -------------   -------------
 9       80.2     82.5 ( 2.3)     86.3 ( 6.1)     90.6 (10.4) 
12       63.7     72.4 ( 8.7)     69.5 ( 5.8)     74.7 (11.0) 
18       65.2     77.9 (12.7)     74.9 ( 9.7)     82.4 (17.2) 
20       55.3     76.2 (20.9)     74.2 (18.9)     75.3 (20.0) 
21       75.0     90.0 (15.0)     90.4 (15.4)     93.9 (18.9) 
25       50.0     83.1 (33.1)     83.1 (33.1)     92.3 (42.3)
27       41.0     67.4 (26.4)     73.7 (32.7)     80.0 (39.0) 
28       49.0     70.1 (21.1)     76.2 (27.2)     80.2 (31.2) 
31       43.2     65.5 (22.3)     68.5 (25.3)     69.4 (26.2)
34       57.7     84.8 (27.1)     82.7 (25.0)     85.8 (28.1)
50       43.2     67.2 (24.0)     77.0 (33.8)     81.0 (37.8) 
51       40.0     66.9 (26.9)     79.8 (39.8)     79.0 (39.0) 
         ----   -------------   -------------   ------------- 
Average  55.3     75.3 (20.0)     78.0 (22.7)     82.1 (26.8)
         ----   -------------   -------------   -------------
NumScans   37      106             104             106

[HWP]

I have some questions about pre-amps that are not on the Pre-Amp Chart.

These pre-amps are all brand-name pre-amps that probably deserve a mention on the pre-amp chart.

Specifically, these pre-amps all claim to be designed for places where there are a combination of strong and weak signals. They claim to have a high tolerance for strong signals and resist overload well.

The only one on the Chart is the Winegard. I want to get one of these types of pre-amps but I'm not sure which one(s) might be good options.

Winegard hdp 269
Antennas Direct PA19
Antennacraft 10g201 (combined output), and
Antennacraft 10g221 (separate VHF/UHF outputs)

Does anyone have any experience with these pre-amps, and/or understand how to interpret specs related to overload resistence - assuming those specs can be found?