Possible HR10-250 OTA Fix?

[wahooj]

It seems (and this is anecdotal evidence so far) that putting a "MODEL 312 VCR / TV SEPERATOR U/V SPLITTER & BALLUN" in between my antenna and Tivo helps my multipath problems. The device itself splits the UHF and VHF signals into 2 inputs. Its original purpose was to connect an antenna with a single coax output to an old-school TV with seperate VHF and UHF inputs. I used the UHF output (2 wires with leads, connecting to a coax adapter). I don't need VHF.

This device seems to improve my multipath problems. Without it, 2 channels came in marginally (hiccups as often as every 10 seconds, long periods of dropout), with it they come in stronger (still an occasional hiccup, so far no dropouts). Brief expirementation on the signal strength meter showed a stronger, more consistent signal strength.

I have some theories as to what's going on:
1) It doesn't really work. Variances in the signal strength occur independently of connecting / disconnecting the device. The signal improves when its connected and degrades when disconnected as coincidence. I need to test longer.

2) It is attenuating the signal. Those 2 channels are too strong. I am not sure how to test this theory.

3) It is acting as an FM Trap +. It is removing the FM, and also the VHF. However, I would think an FM trap would only help with VHF.

4) Removing the VHF frequencies from the signal is the source of the improvement. The OTA tuners in the Tivo tune UHF better without the VHF in the way.

My setup: HR10-250, Terk HDTVo antenna mounted atop 10 foot mast on highest point of roof. Hill, other houses, trees, causing multipath problems. One of the 2 channels affected is 11.6 miles away, the other 71.6 miles.

I don't know why I even tried it in the first place. I was looking through my old cables and junk looking for a coax splitter and saw it. I had an ESP moment and just knew that using it would work.

Does anyone out there with more antenna knowledge than me have an idea why this works (or doesn't)? Or want to confirm (or disprove) my findings?

[Jeremy517]

Probably just the attenuation. You can easily test it with a variable attenuator. Radio Shack has them for under $10 last time I checked.

[litzdog911]

Agreed. The HR10-250 OTA tuners are easily overloaded with strong signals, lowering the "signal reading" even though the signal is plenty strong. Attenuators solve this problem, and a splitter is essentially a fixed attenuator.

[wahooj]

The thing that makes me think its not attenuation is that the signal strength is at best mid 50's. And before I put the antenna up on the mast, depending on where on the roof I put it, it would have a singal strength of 0, or very low and unable to lock. To me that isn't consistent with a too-strong signal that needs to be attenuated.

I think I will go to Radio Shack and get a variable attenuator and possibly an FM trap and see if I can replicate what the UHF / VHF splitter is doing.

[RMSko]

Does it make sense to use both an attenuator and an FM trap?

[spankspank]

The thing that makes me think its not attenuation is that the signal strength is at best mid 50's. And before I put the antenna up on the mast, depending on where on the roof I put it, it would have a singal strength of 0, or very low and unable to lock. To me that isn't consistent with a too-strong signal that needs to be attenuated.

I think I will go to Radio Shack and get a variable attenuator and possibly an FM trap and see if I can replicate what the UHF / VHF splitter is doing.



I'm not familiar with your Terk antenna, but 71 miles is a long way for UHF. I don't think you want to attenuate that signal. The 11 mile signal may be too hot for that attenna. What is the gain for that signal on this Terk? Can you just attenuate that signal?

The signal meter in a Tivo or TV only measures the error rate on the digital stream coming in to the tuner. The number it gives back won't let you differentiate between weak signal/too much signal/or FM interference.

You might have too many db into the tuner (no pre-amp, right?) but I believe your UHF/VHF splitter is reducing interference and improving your signal quality. This is seen on the digital meter as less errors, higher number.

You say you don't need VHF/FM, so leave it out. Also search/post in the avsforum OTA section to see how other people near you did it.

[spankspank]

Does it make sense to use both an attenuator and an FM trap?

In cases where you have too much signal in UHF/VHF and strong FM/police radio, yes.

[TyroneShoes]

Does it make sense to use both an attenuator and an FM trap?
Here is the question that might also help clear up wahooj's questions.

If you look at what is required for digital lock, it is three things:

1. Signal 15 dB or better above the noise floor.

2. A desired to undesired signal ratio that exceeds the threshold a particular tuner needs to work properly.

3. A signal level not so strong as to swamp the tuner.

1 and 3 define the window of operation, too much or too little signal won't work, while anthing within the window has a fighting chance.

An attenuator can only affect where the signal falls within that window. But, it can have no affect on a signal to interference ratio, because it attenuates both the desired and undesired signal a like amount, leaving a net ratio virtually the same.

An FM trap can affect both the window of operation as well as the S/I ratio. It affects the latter by filtering out interference directly, and it affects the window of operation because some times without that interference removed, especially when the interference is stronger than the desired signal (and even when it is not multipath interference) strong unwanted signals can cause the tuner AGC to shift the window of operation in a direction less favorable to the level of the desired signal. Remove the FM interference, the AGC shift returns to normal, and the level of desired signal becomes more favorable.

Bottom line, they do different things, and can be applied together usually without negatively impacting each other. Using both together is quite common.

Wahooj's U/V splitter could be improving things through attenuation, or it could be removing strong, undesired signals off frequency, in much the same way an FM trap removes FM. Both things could be happening at once. What it is NOT doing is improving the S/I ratio of multipath. Nothing filters out multipath, because by definition it is on the same frequency. You need antenna directionality and strategic placement to do that.