# AM21 Sensitivity Reduced - Why?



## gcd0865 (Jul 23, 2008)

Hi All:

The OTA sensitivity of my AM21 and my tv's OTA tuner have always been quite comparable, even on the respective signal meters. Over the past two weeks or so, however, I think something has happened that has reduced the sensitivity of my AM21. If it makes any difference, I believe this happened before the June 12 DTV switch date, and none of these stations switched channel assignments or anything like that at the DTV switch date. 

I have an antenna going into an A-B switch box for switching between my tv and my AM21. On my three distant channels (at night), I'm getting signal strengths of 45, 55 and 88 on my tv's signal meter and all three stations come in fine using the tv's tuner. All three of these stations used to also come in on the AM21, with approximately the same signal strengths. Now, two of these three stations don't come in at all on the AM21, and the third station (that registers an 88 on my tv's meter) comes in at 40-43 on the AM21. I knew that the two tuners were quite comparable previously because the two weakest of these stations would always appear in the evening at exactly the same time on both my tv's tuner and the AM21, as signal strengths came up (meaning that both tuners had approximately the same reception threshold based on signal strength).

To check for possible connection problems, I reversed the A-B switch, took the switch out of line, substituted the short coax going to the AM21, checked the cable going from the AM21 to my HR21, did a full reset followed by a new OTA setup, but couldn't trace any problems.

This is an all-of-a-sudden performance drop for my AM21. Could something have happened to my AM21 (heat?) that would reduce its sensitivity? Thanks in advance for any comments.


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## litzdog911 (Jun 23, 2004)

First time I've heard of a problem like this. I'm guessing you have a defective AM21.


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## IDRick (Feb 16, 2007)

gcd, check your cables. You may have a loose connection, particularly between the AM21 and the a/b switch. In my case, a 45% signal strength really means that I have little margin to spare (on order of 3 to 5 dB before pixelating/dropout occurs). A pre-amp may help you. Need much more info before I can recommend a specific pre-amp. How many tvs? How many splitters? Total length of cable run? Which antenna are you using? Where is the antenna located? Can you post tvfool.com results from your actual address? We won't see your address, just the zip code and city.


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## gfrang (Aug 30, 2007)

It sounds to me like the am21 but what i would do next is pull the plug on the hr21 and am21 for a couple minutes and pull the usb plug and reinsert it.Plug it back in and see what happens.


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## dodge boy (Mar 31, 2006)

Mine does this too, I split the cable from the antenna to my TV and my AM21, my TV picks up all kinds of channels the AM21 wont, and I put the right zips in so all the same channels show up in the guide, just the AM21 won't tune them.


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## ciurca (Apr 14, 2009)

Same here, not so dramatic. Daytime, I would be around 88% for one and 75% for the other. Now I'm at around 80% and 65% respectively. My local cbs stated on June 12 that they would be upping their digital signal after shutting down the analog monster. I've only seen a decrease.


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## gcd0865 (Jul 23, 2008)

Thank you for all the comments. When time permits, I will check all the connections again (I had bypassed my switch and temporarily connected the AM21 to the antenna directly, with no change). I'm wondering if something has happened to the USB cable connecting the AM21 to the HR21 (I'll have to try a temporary substitute for that as well). I'll also try unplugging the units as suggested. The funny thing about this is that this isn't really an antenna or reception issue; my tv tuner and AM21 were exactly equal to each other two weeks ago, until one day, the AM21's sensitivity just went to crap all of a sudden.


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## David MacLeod (Jan 29, 2008)

I have had a usb issue on one, different cable fixed it.
my signals were lower than normal and jumping a lot.


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## Davenlr (Sep 16, 2006)

Two things to consider...the AM21 has two tuners and a built in splitter, which will send a signal half as strong as the signal going to the tv, to each tuner.

Signal readings are dependent upon software on the host receiver. Did your software get updated at approx the same time this signal issue cropped up?


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## ciurca (Apr 14, 2009)

Davenlr said:


> Two things to consider...the AM21 has two tuners and a built in splitter, which will send a signal half as strong as the signal going to the tv, to each tuner.
> 
> Signal readings are dependent upon software on the host receiver. Did your software get updated at approx the same time this signal issue cropped up?


So, there are probably no real changes in signal quality, just the measurement parameters?


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## Davenlr (Sep 16, 2006)

I would say thats totally possible, except you said (I think) that you no longe get stations you used to?). If IRC, OP said "at night". Tropo enhanced reception can vary greatly, and cant be relied on. If you cant get a station at 2pm, but can at 8pm, its likely tropo enhanced reception and is out of your normal viewing range... In a case like that, the -3db splitter loss in the AM21 could be a deal breaker, and require you to "make it up" at the antenna (with more height) or (more capture area) or with a ln amp (channel master 7777) to overcome coax loss. This should get your -3db margin back.


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## gcd0865 (Jul 23, 2008)

Hi All:

As an update, last night I unplugged the USB cable from the AM21 and did a full reset and new initial setup of the AM21. No difference. I then substituted a different USB cable between the AM21 and HR21; no difference there either. I didn't power down the units yet, as it's more difficult for me to reach back to do that (but I'll try that next).

To answer the other questions posted, the signal quality on the AM21 remains fine (for the stations that come in), just that the sensitivity of the AM21 has dropped substantially (and the signal meter now reads much lower). Before this all started, both my tv's tuner and my AM21 acted about the same: both would hold a stable picture at signal levels (on the respective signal meters) of greater than about 37; between 33-36 the picture would pixelate; and from 32 down, no picture and signal level would be at zero. Both my tv tuner and the AM21 would receive the exact same number of stations, and they would come in and fade out with nighttime/daytime passage at about the same time. Then, two weeks ago, something happened (instantly, one day) to the AM21.

Last night, distant stations were particularly strong, coming in mostly at 60-70 on my tv tuner. None of these would come in on the AM21 (but they all used to just fine, two weeks ago), except for one distant station registering 85 on my tv's signal meter; it registered about 45 last night on my AM21's meter. Local stations seem a little lower on the meter too, but not as much as the distant ones. So the AM21's sensitivity seems to have suddenly just dropped by 10-20 points for local stations, and up to 40 points for distant ones. The threshold for the AM21's tuner to lock on stations is the same as before (around 37), but since the sensitivity is now reduced so much, the number of channels received is less. I know it seems like I just have a bad coax cable or switch box, but I reversed the cables (no difference), substituted another cable (no difference) and took the switch box out of line to connect directly to the antenna (no difference).

Regarding the comments about antennas, amps, reception, tropo, etc., they are of course all factors in over-the-air reception, and I do still have some antenna system improvements to work on. But this is just a sharp all-of-a-sudden dropoff in my AM21 compared to what I reliably had before, so i'm just trying to diagnose that problem at this point.

I'll power down the units shortly and report back. But I'm suspecting that something in the circuitry of my AM21 just went bad one day about two weeks ago.

Thanks again for your interest and comments...


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## Davenlr (Sep 16, 2006)

Unless your DVRs software got updated at exactly the time this signal drop started, I would concur with you.

You might check the system info on the DVR and see if the data of the last software upgrade matches the date your problem started.

Are both tuners reading the identical signal level? It seems odd both would fail at the same time.

Hopefully unplugging and restarting will fix it up.


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## gcd0865 (Jul 23, 2008)

Yes, both of the AM21's tuners are reading the identical signal level. Thanks for the additional tip; I'll also check the last software upgrade date.


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## gcd0865 (Jul 23, 2008)

Hi All:

Wanted to give everyone an update on my AM21 situation, in case this happens to anyone else. I had double and triple-checked all my AM21 connections and became convinced that my AM21 was slowly going bad. Over the additional time since my last post, the signal strength numbers and the ability of the AM21 to receive stations continued to gradually decrease. Back in June, I had only lost my distant channels that were 50-65 miles away. But more recently, I gradually lost another station 25 miles away (it first started to pixelate, right at the threshold of being received, then I lost it altogether). This was a station that initially had an 85 signal strength that gradually declined to 34, then disappeared altogether on the meter. Then, I started to lose one or two of my local channels (8-12 miles away). Signal strength numbers continued to slowly decline through this time on the AM21, but my antenna was fine, as my tv's tuner still received everything just fine, with no signal strength change on the tv's meter.

I finally decided to call DirecTv, and was told that there is no warranty (at all) on the AM21, that they would not replace it, and that I had to purchase another one from them for $50 plus $3 tax. Since I could no longer reliably record shows over-the-air using my present AM21, I caved and bought another unit. Hooked up the new AM21 last night, using all of the original cables from the previous AM21, and it works perfectly (as good as the previous unit when it was brand new, getting all of my 50-65-mile stations again, and pretty much equivalent again to my tv's tuner).

Something gradually went bad with my original AM21 starting around May or June, where the unit resolved a picture just fine, but gradually lost its sensitivity, eventually getting to the point where it became useless. I had the AM21 directly on top of my HR21 receiver, as the AM21 manual says you can do. But when I removed the old AM21 to install the new one, the old one was quite warm overall, and was actually rather hot on the rear portion of the lower surface (maybe where the internal power supply is?). Perhaps the heat gradually affected some components inside that first AM21 over time. If it might be any issue, I seem to remember my HR21 showing a 117-degree internal temperature when I checked it a while back, which I was told was normal.

In any event, I installed the new AM21 in a different location, not directly on top of my HR21, and maybe others might want to consider the same, since there's no warranty on the AM21. If anyone else is noticing gradual reduced reception performance from their AM21, maybe the same thing is happening to yours. From how hot my AM21 was when I removed it, I don't think DirecTv should say in its manual that you can put it directly on top of your regular receiver. I also think it's a ripoff for DirecTv to not replace this unit for me at no cost. Even though the AM21 was a purchase, and not a lease, it ought to be covered in this kind of situation. Cable companies also lease their equipment to you, and if any equipment ever goes bad, they just replace it, because you are paying them a monthly fee for their service, which needs to work properly or you won't be satisfied.

I'd like to complain about this some more to DirecTv, but don't know who to contact. I'll certainly keep this in the back of my mind when cable HD offerings catch up to DirecTv (which looks like it will happen soon). I'd appreciate hearing anyone else's thoughts about this, or about their similar scenarios (if any). At least I feel a little better from venting. Hope this is helpful to prevent this from happening to anyone else...


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## tcusta00 (Dec 31, 2007)

gcd0865 said:


> Hi All:
> 
> Wanted to give everyone an update on my AM21 situation, in case this happens to anyone else. I had double and triple-checked all my AM21 connections and became convinced that my AM21 was slowly going bad. Over the additional time since my last post, the signal strength numbers and the ability of the AM21 to receive stations continued to gradually decrease. Back in June, I had only lost my distant channels that were 50-65 miles away. But more recently, I gradually lost another station 25 miles away (it first started to pixelate, right at the threshold of being received, then I lost it altogether). This was a station that initially had an 85 signal strength that gradually declined to 34, then disappeared altogether on the meter. Then, I started to lose one or two of my local channels (8-12 miles away). Signal strength numbers continued to slowly decline through this time on the AM21, but my antenna was fine, as my tv's tuner still received everything just fine, with no signal strength change on the tv's meter.
> 
> ...


Thanks for your update.

I would explain the situation in an email to the office of the Sr. VP of Customer Relations, Ellen Filipiak. While they may not be in a position to do anything about your situation now since it's resolved, they will probably take it under advisement and hopefully work to fix what's wrong with the AM21 itself and the warranty (or lack thereof). (Of course the forum trolls will respond otherwise)

The email to her office is [email protected].

I think the tone of your thread and posts remained professional while getting across your criticisms, which is important in getting someone to listen to you at DirecTV and ultimately effect some change.


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## CCarncross (Jul 19, 2005)

While I see your point, since the AM21 is just an add-on ATSC they will sell you that does nothing to receive SAT signals, when and if they go bad D* really shouldnt have to replace them after the initial 90 day warranty or whatever they have. If they leased them fine, but they don't, they are purchased, and everyone should know they are purchased when they buy them. My understanding is the PP doesnt cover them either.


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## tcusta00 (Dec 31, 2007)

I have to disagree. Most electronics have a one-year warranty. 

Additionally, the capability that that AM21 provides to HR21/2/3 users is included in HR20s at no additional cost. If they're asking the customer to pay $50 to add this onto the receivers to get the same capability as older receivers then the least they can do is give a 1 year warranty. I understand the rules as they're currently written and hope to never have an AM21 go bad, but I must respectfully disagree with them.


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## DarinC (Aug 31, 2004)

tcusta00 said:


> If they're asking the customer to pay $50 to add this onto the receivers to get the same capability as older receivers then the least they can do is give a 1 year warranty.


Although, as you probably know, 90 days is all they give on a DVR as well. I know, because I had a drive die in a new owned box, which they wouldn't help on. Actually, was bad from day one, but it wasn't until it completely died into the 4th month that I realized it was a bad drive, and not just flaky HR21 issues. Unfortunately, you can't get warranty service direct from the drive manufacturer, because the serial# maps to an OEM.


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## David MacLeod (Jan 29, 2008)

got spare am21 ready to go just in case


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## gcd0865 (Jul 23, 2008)

Hi All:

I know this is an old thread, but I wanted to provide yet another AM21 update, in case anyone else is experiencing the same situation. My second AM21 (in use since August 2009) failed on a recording about a month ago due to insufficient signal strength, on a 25-mile station received at a signal strength of 83-85 on my tv tuner, and at pretty much the exact same level on both my first and second AM21s when they were new. Unfortunately, the signal strength numbers declined over time on my second AM21 (just as they did for the first unit), and I again lost my 50-65-mile stations first, and then my intermediate (25-mile) station. Signal level on that 25-mile station (that had originally been around 83-85) was in the mid-30s on the AM21 (but still 83-85 on my tv's tuner) when the first recording on that station failed a month ago.

I did the usual checking of the antenna connections and wiring to/from my main receiver (upgraded earlier this year from HR21 to HR24), and was convinced that the same gradual degrade was occurring to this second AM21 unit as happened to the first. I called DirecTV, and they ran me through a series of reboots of both my main receiver and unplugging and replugging of the AM21 connections, with no change. The DirecTV rep was unable to find the AM21 on their system, but assured me that I could order a new unit from them, and the rep credited me $10/month on each of my next 6 months' worth of invoices to cover the replacement cost (which was actually $53, including shipping).

A few days later, the new unit arrived, in the exact same kind of AM21 box as for my two previous units, but this time containing the new AM21N version of the unit (matte exterior instead of glossy, and labeled on the back as AM21N). No markings on the exterior of the box show the "N" version, though. I removed my existing (second) AM21 unit from my console, and hooked up the new AM21N without changing any of the existing wiring, using everything exactly as before (as I did previously when swapping out the first unit for the second one). Powered up the new unit, entered in two zip codes for two markets, and all over-the-air stations (even the farthest 50-65-mile stations) instantly came in again just fine (just as they did the last time when I replaced my first unit). On this (third) unit, however, I do note that the signal levels are about 2-3 points lower than they are on my tv's signal meter (I'm pretty sure they were identical before), but I guess that's close enough.

One difference I noticed with this new AM21N unit - where the signal strength meters on both of my previous AM21 units could not show any numbers below 30 (below that, they would just drop instantly to zero), this new AM21N unit can display signal strength numbers in the 10s and 20s, even though a picture can only be decoded correctly (without dropouts) with a signal strength above about 35 (same as before).

Like the second unit, I've placed this third AM21N unit away from my main (now HR24) receiver to avoid any possibility of heat being an issue, but I don't think that's been the cause of this recurring problem. Only thing I can think is that some component in these units must be degrading over time, making the units less usable and eventually non-usable.

In any event, I wanted to share this with the forum in case anyone else is experiencing the same problem, and perhaps DirecTV is aware of this issue, since they readily volunteered covering the replacement cost this time (unlike the previous time, where I eventually got it covered, but at a later time). It'll be interesting to see if the AM21N version of this unit has the troubled component(s) upgraded to avoid future issues.

Hope this is helpful to others...


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## ciurca (Apr 14, 2009)

Very interesting. I wonder if others have experienced the same.


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## tuff bob (Mar 5, 2007)

I think I've run into it - got an AM21 that is not receiving and channels now, they are all 792. Checked antenna, tried different antenna. Don't know what else to try.


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## usnret (Jan 16, 2009)

Ditto the above fm Tuff Bob. Mine just "went away" today.


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## jamieh1 (May 1, 2003)

I got a AM21 and a AM21N. Ive notice that on the AM21 I have a station that is 100%. Then if I hook the AM21N to the same reciever the signal is about 87%.


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## mloiterman (Aug 20, 2007)

I can confirm that the AM21 is a major piece of junk. I'm on my third one and they all have died after about a year for the same reason.

The behavior is exactly has been described by others - out of the box the unit is able to lock onto a wide range of signals. The unit will operate fine for about year or maybe 18 months and then it gradually becomes unable to lock on to signals that it did when it was new.

Each time I have had to replace the box for $50.00 bucks. Sigh...


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## CCarncross (Jul 19, 2005)

Both mine are over 2 years old...work the same as the day I got them.


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## Surveyor40 (Jan 5, 2006)

I've been using the AM21 for about 3 years without issues on 4 of my DVR's. I would consider there maybe other factors causing the failure of the AM21, and not rule out an antenna system or electrical problem.


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## say-what (Dec 14, 2006)

I have 2 AM21's. One I got as soon as they were available, the other 3 to 6 months later. I've used these two on various HR2x's over time (HR21, HR23, HR24 and HR34) and neither has had a problem and I use a small indoor antenna. The only problem I've had is when I've moved the antenna to clean and that affects the TV also.


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## jamsys (Oct 28, 2007)

I am having horrible problems with my AM21 and the HR34. Some days it finds the channels, some days it doesnt....

My peeve is that on page http://www.directv.com/DTVAPP/content/support/protection_plan it states protection for ALL your DIRECTV devices.... I am paying $5.99 a month for this. After 5 calls and the same answer I dont know what to do...... They say that since its not a Sat box, it isnt covered, but I tell them to look at their web page and it says all devices!

Thoughts?


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## CCarncross (Jul 19, 2005)

jamsys said:


> I am having horrible problems with my AM21 and the HR34. Some days it finds the channels, some days it doesnt....
> 
> My peeve is that on page http://www.directv.com/DTVAPP/content/support/protection_plan it states protection for ALL your DIRECTV devices.... I am paying $5.99 a month for this. After 5 calls and the same answer I dont know what to do...... They say that since its not a Sat box, it isnt covered, but I tell them to look at their web page and it says all devices!
> 
> Thoughts?


Exact words from the standard PP: *All active DIRECTV™ Receivers, remote controls, dish antenna, wiring, connectors, switches, and dish antenna realignment.*

It does not say all devices. It is not a Directv receiver, it does not fall under any of that wording. Are you perhaps looking at the wording for the Premier plan which is like $20 month?


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## texasbrit (Aug 9, 2006)

jamsys said:


> I am having horrible problems with my AM21 and the HR34. Some days it finds the channels, some days it doesnt....
> 
> My peeve is that on page http://www.directv.com/DTVAPP/content/support/protection_plan it states protection for ALL your DIRECTV devices.... I am paying $5.99 a month for this. After 5 calls and the same answer I dont know what to do...... They say that since its not a Sat box, it isnt covered, but I tell them to look at their web page and it says all devices!
> 
> Thoughts?


Your problem is almost certainly because your signals are too weak. The Hr34 is the only DVR that scans for signals instead of using a fixed database. The good news is that you can receive stations that are not in DirecTV's database. The bad news is that stations that have marginal signal can come and go, just as you are describing. With the other DVRs, you can only get stations that are in the database, but if the signal is low you might still receive them.
You almost certainly need a better antenna.


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## chrisjmccord (Jan 17, 2013)

Does it matter what kind of antenna you get to hook up to the AM21? I guess for looks sake I'd want to get one to put in the attic, but would need to run or fish a cable down the wall to the TV. What kind of antenna would you but for up in the attic? I'm not too far away from our towers here, maybe 5-8 miles?


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## moghedien (Dec 3, 2007)

texasbrit said:


> The Hr34 is the only DVR that scans for signals instead of using a fixed database.


According to the Solidsignal website, the THR22(Directv TiVo) will also scan with the AM21. Is anyone here able to confirm or deny this?


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## Scott Kocourek (Jun 13, 2009)

chrisjmccord said:


> Does it matter what kind of antenna you get to hook up to the AM21? I guess for looks sake I'd want to get one to put in the attic, but would need to run or fish a cable down the wall to the TV. What kind of antenna would you but for up in the attic? I'm not too far away from our towers here, maybe 5-8 miles?


Try these guys for your antenna questions. http://www.solidsignal.com/p/ota.asp?mc=03&d=antenna-help


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## palmgrower (Jul 18, 2011)

I added amplifiers after the off air antennas to drive the signal, zero issues with AM21's since and marginal locks are solid locks, good luck

I used a Winegard HDA100 15 dB Distribution TV Antenna Amplifier (HDA-100)


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## Garyunc (Oct 8, 2006)

jamieh1 said:


> I got a AM21 and a AM21N. Ive notice that on the AM21 I have a station that is 100%. Then if I hook the AM21N to the same reciever the signal is about 87%.


+1. Amplifier is the way to go.

This is the one I got.
http://www.radioshack.com/product/index.jsp?productId=2103093


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## veryoldschool (Dec 10, 2006)

Garyunc said:


> +1. Amplifier is the way to go.
> 
> This is the one I got.
> http://www.radioshack.com/product/index.jsp?productId=2103093


If you're going to go with an amp, this one might be a better choice: http://www.solidsignal.com/pview.as...mplifier-(HDA100)&c=Amplifiers&sku=1579839664

Why is because it has a noise figure of 3 dB, and the radioshack doesn't bother to list theirs, which means it might be as high as 8 dB.

BTW I also have a Radioshack very similar to that one [with only one output] and it barely makes a difference to my weak channels.


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## texasbrit (Aug 9, 2006)

moghedien said:


> According to the Solidsignal website, the THR22(Directv TiVo) will also scan with the AM21. Is anyone here able to confirm or deny this?


Yes, that is apparently true although I don't have one to confirm it.


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## P Smith (Jul 25, 2002)

texasbrit said:


> Yes, that is apparently true although I don't have one to confirm it.


 then why not provide a link to your source ? we will follow there to see its credibility ...


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## tigerwillow1 (Jan 26, 2009)

veryoldschool said:


> If you're going to go with an amp, this one might be a better choice: http://www.solidsignal.com/pview.as...mplifier-(HDA100)&c=Amplifiers&sku=1579839664
> .


As an "enhancement" to this suggestion, this is the Winegard HDA100. Look also at the HDA200, only a few bucks more. In addition to more gain (and :-( higher noise figure), it has an adjustable attenuator. I used the HDA200 with my AM21 and found that it was just as bad receiving signals that were too strong as those that were too weak. The amp had to be adjusted "just right" for me to pull in the stronger and weaker stations at the same time. I've posted before about the AM21 being a "weak" receiver, with it not picking up at all stations that were solid on two other receivers split off of the same antenna. With a Dish DVR now using the same connection that the AM21 formerly was, OTA reception is much more reliable, and the gain setting on the amp doesn't make a bit of difference except for changing the reading on the signal meter.


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## veryoldschool (Dec 10, 2006)

tigerwillow1 said:


> As an "enhancement" to this suggestion, this is the Winegard HDA100. Look also at the HDA200, only a few bucks more. In addition to more gain (and :-( higher noise figure), it has an adjustable attenuator. I used the HDA200 with my AM21 and found that it was just as bad receiving signals that were too strong as those that were too weak. The amp had to be adjusted "just right" for me to pull in the stronger and weaker stations at the same time. I've posted before about the AM21 being a "weak" receiver, with it not picking up at all stations that were solid on two other receivers split off of the same antenna. With a Dish DVR now using the same connection that the AM21 formerly was, OTA reception is much more reliable, and the gain setting on the amp doesn't make a bit of difference except for changing the reading on the signal meter.


You bring up a good point [that I don't agree with :lol:]

First: not all solutions will work in every situation.

You can over amplify the signals for the strong stations as you're trying to boost the weak stations.
Dynamic range of the tuner [any tuner] is what comes into play here.

The HDA200 has a 4.5 dB NF and a max gain of 24 dB
The HDA100 has a 3 dB NF and gain [fixed] of 15 dB

So the question sort of comes down to how much gain do you need for the weak signals verses how much noise are you adding, thus reducing the noise margin, which is what this is all about.

The best solution is using a larger antenna, as its gain doesn't add any noise.
The next is to use a low noise amp, and add another amp if you need more gain for distribution losses [cable & splitters].

The HDA200 gain ranges from 6 dB [max attenuation] to 24 dB.
At its minimum gain, you've got 6 dB, but you're adding 4.5 dB NF
Not the best solution is it?
It would be better at about 16 dB of gain, as the noise margin would now be close to the HDA100, and it would then work better to the 24 dB output, "if" you needed that much gain.

Now if I needed more gain than the HDA100, adding a http://www.solidsignal.com/pview.as...gain-(SKY38323)&c=Amplifiers&sku=610370581759

Might be a better choice.
The combined NF would be < 3.5 dB and the total gain would be ≈ 26-36 dB.
Again not every solution is best for every situation.

And if you're dealing with trying to find the sweet spot between the strongest and weakest signals, it might only need one of these:
http://www.solidsignal.com/pview.as...ion-1296F&c=Signal Variators&sku=853748001293

YMMV


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## tuff bob (Mar 5, 2007)

CCarncross said:


> It is not a Directv receiver, it does not fall under any of that wording


That's real cheesy to use that as an exception. It a receiver and its got DirecTV written on it.


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## jcwest (May 3, 2006)

In Mobile Al. during the summer "storm season" we frequently have extremely large afternoon/evening storms passing by, hence the need for OTA backup to satellite locals.

I got the AM21 right after I got my first HR21 box (2007 I think) our NBC channel is on the fringe of constant strong signal.
Added the Channel Master 7777 signal amp and have never looked back.
Signal via the AM21 has been rock solid every since.

J C


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## gov (Jan 11, 2013)

A rule of thumb from 'sparky school':

Connect one TV to your antenna (no splitters, no amps) and the stations you get are the stations you are going to get when you're done. RF amps just let you drive more tuners (with appropriate splitters), they don't drag signal out of the noise.

But, remember, for me 'sparky school' was before digital anything. LOL! Maybe ATSC is a little more forgiving ??


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## Davenlr (Sep 16, 2006)

gov said:


> A rule of thumb from 'sparky school':
> 
> Connect one TV to your antenna (no splitters, no amps) and the stations you get are the stations you are going to get when you're done.


Not actually true. By using a mast mounted preamp, any stations above the noise floor at the antenna terminals, will be present after the often rather high coax losses, at the TV. Without the preamp, stations you otherwise would be able to receive, might get lost in the attenuation of the coax. This is especially true when using RG59, or if the stations are on UHF band (which most ATSC stations are).

You are correct in that the use of amps on the indoor end of the coax only serve to boost the signal enough to pass through splitters, but dont improve the incoming signal at all.


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## veryoldschool (Dec 10, 2006)

gov said:


> A rule of thumb from 'sparky school':
> 
> Connect one TV to your antenna (no splitters, no amps) and the stations you get are the stations you are going to get when you're done. RF amps just let you drive more tuners (with appropriate splitters), they don't drag signal out of the noise.
> 
> But, remember, for me 'sparky school' was before digital anything. LOL! Maybe ATSC is a little more forgiving ??





Davenlr said:


> Not actually true. By using a mast mounted preamp, any stations above the noise floor at the antenna terminals, will be present after the often rather high coax losses, at the TV. Without the preamp, stations you otherwise would be able to receive, might get lost in the attenuation of the coax. This is especially true when using RG59, or if the stations are on UHF band (which most ATSC stations are).
> 
> You are correct in that the use of amps on the indoor end of the coax only serve to boost the signal enough to pass through splitters, but dont improve the incoming signal at all.


Seems we all have our take on this.

I don't see either as "wrong", but I still see more to what both are trying to say.

The noise floor starts at about -106 dBm, so you need 15-16 dB SNR/CNR for ATSC.

Your best [primary] gain comes for the antenna.
From here the loss of the transmission lines drops signal, but not noise power.

Using an amp generally defines the system NF, as loss/gain is linear, but cascaded NF is anything but linear, as you can find here: http://www1.sphere.ne.jp/i-lab/ilab/tool/NF_e.htm


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## bflora (Nov 6, 2007)

Amps never improve the S/N ratio at any given point in the line but they can help preserve S/N ratio 'downstream'.


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## veryoldschool (Dec 10, 2006)

bflora said:


> Amps never improve the S/N ratio at any given point in the line but they can help preserve S/N ratio '*downstream*'.


This is true, and the only thing you can play with is what is "upstream" and where downstream starts.


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