another bolt signal strength thread

When I connected a new Bolt to my TV it lost 4 of my channels, that my Premiere easy got. Tivo sent me a new replacement Bolt and now I get all my channels fine. After reading some of the same posts you have, I think there is a quality control issue with the Bolt.

 

Tivo's most advanced DVR the "Bolt", can't pull in signals on it's own like older Tivo's can and they want you buy equipment to get it to do what it's supposed to do out of the box...seriously?

 

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I was hoping to use my Bolt for OTA. Got in on the recent deal before I moved across country, then got around to testing it. Got a few channels but then after a couple days it completely stopped getting any channels. The coax connection was burning hot. Ugh.. even tried different antennas.

 

Run a TVFool report and look at the Noise Margin figures for the stations you are trying to tune in. Anything over 40dB will not be helped by the use of a preamp, and the higher up that scale, the more that the overloaded signals from a stronger station can affect weaker station reception in the same antenna direction.

The attenuator would be installed after the preamp- basically, you're adding signal loss back into the system to weaken the system gain. If you need to add 6dB of attenuation to your coax plant, IMHO you don't need a preamp. Without knowing the preamp model number, I assume that the amp is adding 15dB of signal amplification to UHF channels, with a noise factor loss of 2dB. You are now being advised to reduce that 13dB net by another 6 dB of attenuation. At that point, an amplified drop splitter would make more sense than a preamp (a four port drop amp will typically add a net of about 5dB per drop)- assuming amplification was needed in the first place. A properly balanced system would apply only enough amplification to make up for the losses in your coax plant.

It never hurts, at this point, to build a insertion loss table for your coax plant. From the Noise Margin report, add the antenna gain, subtract the loss from the length of coax from the antenna to the Tivo, subtract the loss from the splitter port, subtract 3dB for the balun (matching transformer at the antenna), and any other losses in the signal path (LTE filter, POE filter, lighting arrestor) and subtract 0.5 dB for any coax connector (wall plate or cable connector). Subtract 7dB for the tuner noise figure. The sum of those figures can then be removed from the TVFool Noise Figure. If that net figure is below 30 dB, then a preamp may help.

Finally, an amplifier is going to do little to help if the signal issues are a result of multi-path reception issues. You can run an evaluation- with the antenna pointed in the desired direction, tune each of the TiVo tuners to a different station- pick out three that are problem reception, and one that is good. Go to the diagnostics screen (Tivo>Settings&Messages>Help>System Information>Diagnostics). You will see the tuner information for each tuner (listed as 0 through 3), showing signal strength (%) and SNR (dB) for the four stations. On the problem stations, when observing the readouts for a few minutes, if you see the numbers bouncing around, it's an indication of multi-path issues, where the UHF line of sight signal is being blocked by buildings, nearby trees (trees are death to a UHF signal), etc. A pre-amp will not cure this- you can try relocating the antenna, or if the signals are strong enough, changing the direction of the antenna so that it's off angle from the primary direction, etc.

Keep in mind that the Bolt has an automatic gain control circuit, and the typical maximum sustained signal strength that you will see for OTA is a value of "72". A good rule of thumb is when that value drops to 50 or below, you will likely experience blocking and drop-outs. The signal strength scale is not comparable to your TV (that is, a "65" on the TiVo is not the same as a "65" on your TV). There is an argument to be made that the TiVo tuners are not as sensitive as those in some television sets, but it's a different animal in design.

 

Assuming your antenna is something like the Solid Signal Xtreme Signal 8-bay, the gain between 500 and 650 Mhz (UHF frequency) is ~ 14dB to 16.5dB. Lets call that 15dB for an average value.

Assume an average TVFool NoiseMargin for UHF channels ~ 45dB. Add the 15 dB for the antenna gain. Subtract 3dB loss for the balun. Subtract another 5dB for the attic penetration loss. Subtract 1.5 dB for the 30' of RG6 coax. You mentioned a splitter, but not how many ports- assume 4dB loss for a 1:2 splitter. Your net noise margin to the tuner is 46.5dB, or about 39.5 dB including an assumed NF of 7dB for the tuner. In other words, you DON'T need a preamp in your setup, and a distribution amp may not be necessary at all.

You can drop your values into this worksheet posted on the TVFool forum to calculate this on your own.

If you are convinced that you need a distribution amp, find a reputable amp (Winegard, Channel Master, or PCT) with the same number of output ports as the splitter. The two port Winegard HDA-100 is a 15dB Amp with a 4dB Noise Figure. You would replace the 1:2 splitter with the drop amp. That would increase the NM to 48 dB (the amplification is enough to overcome the second stage NF of the tuner). It's likely not necessary- I suspect your issues are either with a defective TiVo Box (it happens) or you are seeing multi-path issues.

In no case in your plant should you run BOTH a preamp and distribution amp.

Verify that your problems aren't multi-path related. The Bolt has a built in diagnostic screen which will allow you to verify that, as noted above:

If you are seeing the signal strength and SNR numbers bounce around in a couple of minutes of observation, you've got multi-path reception issues.

 

The SNR and Signal Strength numbers move in tandem (they shouldn't, but they do). The Bolt has an automatic gain control, so the maximum signal strength that you will see for OTA will level out at "72", with a corresponding SNR number of 29dB. In my experience, a drop in Signal strength below 50 (SNR of 20) usually results in macro-blocking, pixellation, drop-outs, etc. Unfortunately, an amplifier won't always cure that.

Multi-path is just as it sounds- the signal is blocked from one direction, and takes a different path before converging on the antenna. Nearby trees in the signal path are a notorious cause. The signal is blocked off and on, and the varying strength levels at the antenna cause the "bounce" that you see in the scale, and the problems associated with that.

The best cure is to relocate your antenna. I recognize that you have this in your attic, but an antenna enjoys fresh air, and eliminating the penetration loss will strengthen the signal. In any case, if you can visualize the attend direction in your attic, if it's pointing through the attic, and then through a nearby tree or into an adjacent structure, see if you can move the antenna so that the view of the horizon in the direction of the towers is unobstructed.

There is a scenario where a distribution amp may help you. You might rotate the antenna so that the compass orientation is strongly off axis. The hope is that you can null out part of the signal that is variable in strength, and pick up a weaker, but steadier signal. Somewhat like you, I live within 20 miles of the transmission towers, and and average UHF NM for me is 61! I have a fair amount of insertion loss- about 14 dB from the antenna to the most distant tuner. Even with that, my NM numbers were in the mid 40's... in other words, plenty of signal. My problem is that the LOS to the towers takes me right through a 70 year old Sycamore tree, less than 40' away, and about as broad. I have a Yagi style antenna, which I changed out for a lower gain Yagi. I aimed the antenna off-axis: nearly 25 degrees magnetic from the TVFool direction, pointing it through a LOS gap that is relatively clear of foliage.

I added a distribution amp with a 6.5 dB gain and a NF of 4 dB- it also had an integrated POE filter, so I eliminated the splitter insertion loss of 6 dB, and 1.5 dB for the POE filter- for a system gain of 10 dB. I changed to a lower gain Yagi, and the Noise Margin for the amplified system improve to the mid 50's, over the mid 40's range without. The Tivo strength numbers on my problem stations increased by about 10. There is still the a multi-path bounce, but the low-end of the bounce is now above "50" on the TiVo strength scale, with lower amplitude, so the picture is generally stable. Your mileage will certainly vary, but it's an option.