Magnavox 537, 535, 533, 515, 513, 2160A, 2160, 2080 & Philips 3576, 3575 - Page 682

The CM7778 pre-amp has an FM trap which you can set to "IN" (where it attenuates or "traps" FM signals) or "OUT" (where FM signals remain untouched).

I set it to "OUT" since I wanted to feed my Marantz receiver the FM signals.

Tell me more about this low pass filter. I need a 1GHz MoCA filter for my Ceton tuner. If the Magnavox tuner does the same thing it would save me $15.

For greater clarity, I don't run the coax through a surge protector.

There's really nothing special about the Antenna, it's not uncommon for UHF/VHF combos to have the ability to pick-up FM signals (same MHz range).

Before I had the pre-amp, the Mag picked up WETK just fine. Then I removed the pre-amp, and it didn't pick it up anymore. And now, with pre-amp back on, no joy.

But I see the signal improvement on all channels (especially in terms of stability) in the TV tuner. WFFF being the best example, without pre-amp I'd be lucky to catch it late at night once in a while around 35%, with pre-amp it's always on at 60+.

I don't need it to stop anything from getting out of my house over coax since I'm on fiber optic. I just need it to block the noise above 1GHz on the coax run going to my Ceton tuner.

We're clear on that

I may be way off base here and I haven't followed the thread completely but interference may be coming from an outside source in the home. I had a laptop power supply knock out channel 3 on my OTA antenna and had a heck of a time finding that out.

Friday pm: down to 12.
the beave

hey rx -

how are you powering the preamp in your antenna ??? are you using a power supply and powering through the coax ?

if so, you might wat to DC block the input to the mag..... if the feedline into the mag is carrying voltage, the mag may not like that at all !!

DC blocks for F-Type connections are quick and cheap...

alternate test would be maybe a 0.1uF cap in series with the F-connector on the back of the mag...

rgds,
ron g

Seconded.

Two TVs back, I had a set go belly up because it'd gotten juice coming in thru the coaxial.

Naturally, Radio Shack no longer carries the voltage blocks for coaxial runs , so you have to poke around on the net to find them.

Here's an odd one. Mag 513. Recorded from front AV (vid + L/R audio) from cable box. Deleted commercials. Played from HDD fine. Archived to DVD-R - high-speed dub. Play DVD in 513 -> long stretches of audio gone silent (starting at or near some of the deleted commercial/chapter marks). Analog CCs remained visible. Played same after finalizing on the 513, and also on a 515. When disc played in a Panasonic DVD-R, the no-audio section was much reduced in length - i.e. sound came back much faster. Re-did HS dub onto a different brand DVD-R - same. (Regular dub fine.)

Wondering if it has happened before but not noticed since didn't play the DVD.
Any comments appreciated.

well, 1st guess = problem with mag 515 writing to DVD ( regardless of disc )... try calibration process to ensure that's eliminated...

2nd guess = dirty laser - clean with moist swap to eliminate...

the fact that dead spots are of shorter duration in the panny indicates that there is, for sure, some corruption on the DVD images, that the corruption is most likely from the burn process, and that the panny's error recovery simply works better...

try running thru the content on the HDD and listen carefully. the HDD's response time is much faster than a DVD's, and your corruption COULD be in the HDD image, but may be recovering much faster... the dead spot while listening to the HDD image might be so minute that you might not even notice it when it flies by...

a bit or 2 error on the HDD image might not even be discernable, while the same error might cause the slow poke DVD drives to take longer to recover.

you might also try a direct dub, as opposed to hi speed. a direct dub will lay down the image slower, but if the error or corruption is on the HDD image, a direct dub will burn the faster recovered and corrected audio. the hi speed dub lays data down exactly, including any errors in the image...

rgds,
ron g

agreed....

i HATE cheap switching supplies...

rgds,
ron g

This is sort of a wild guess, but in the Magnavox setup menu, under General Setting/Playback/Disc Audio/Dolby Digital, try setting it on PCM rather than Stream. I have had the Stream setting result in loss of audio during playback before. I don't think it would explain everything you described, but I wonder if it might help.

Thanks but, that's not the problem. All the other tuners (3 different brands) are just fine, it's only thr Mag's screwing up.



Yes, the DC runs through the coax from the power supply to the pre-amp on the antenna mast. But the pre-amp comes with it's own "power inserter" which acts as a DC blocker.


Radio Shack has left the country about 10 years ago.

We have a few indie electronics retailers, but finding OTA gear is of heroic caliber in our Northern land.

hi rx -

not to seem picky, but have you actually confirmed 0 DC (as well as hi resistance) on the center conductor of the connector feeding the mag ?

also, some equipment ( splitters as well as antennas ) present a low DC resistance, such as an output coil to ground, even though they're tuned to represent a 75 ohm load at RF frequencies. perhaps this might be causing havoc...

i've had simpler stuff mess me up, but i do still think that AGC saturation is the better argument...

rgds,
ron g

I agree about tha AGC, but this stuff is giving me headaches. I mean, the 2 stations I'm having issues with are the 2 weakest stations. So, hard for me to understand they could be saturated. I mean, I have a heard time understanding how OTHER stations saturating are giving me reception woes with DIFFERENT stations.

Oh well.

I mean, as I stated before, when I have a chance I'll go set my FM trap to OUT, but that'll pretty much be it after.

I don't record anything on FOX (I just watch football live) so not having WFFF on the Mag isn't enough of a deal to continue scratching my head - I'm losing enough hair as it is with aging...

For PBS (WETK), I must admit it pains me a little, as they do have concerts/documentaries that I'd record, but again I'm starting to weight the pros and cons of pursuing this and... I have to move on with life.

hi rx -

your weak stations are NOT saturating anything.... the strong stations are doing the damage and making your weak stations disappear...

ok, the AGC process is essentially an an ANALOG process...

depending upon receiver design, AGC can be affected by stations you are NOT tuned to....

in addition, RF receiver front end circuits, while being broadly tuned circuits, are typically WIDER in bandwidth, than an actual RF frequency you might be tuned to...

a tuner has a receiver front end, a mixer, and an ' IF ' section... no matter what it's used for... turn 'em upside down and they all look the same...

it is in the IF section where receiver ' selectivity ' is essentially accomplished. selectivity is the ability of a receiver to discern a single channel over all others that it is NOT tuned to...

so, for example, lets say your mag is tuned to RF channel 12....

again, depending on receiver design, the RF front end, if it has an active preamplifier, can be completely overloaded by a local strong signal at, say, RF channel 11, or 10, or 9, or 13, etc.... a front end overload causes the receiver to be ' de-sensitized ' , with the result being the lack of ability to bring in the weak channel you are trying to see... this is because the noise floor is being raised so high that the little weak signal drowns in it... orrrrr, the amplifier may be receiving such a strong signal as to throw it out of its linear gain range ( a DC level where the device is designed to function as an amplifier ).

also, again depending upon receiver design, AGC circuits can act the same way. if a strong local signal exists that is not too far away, and the receiver's ' IF ' section is of a relatively wide bandwidth design, that AGC can be affected by the stronger signal, and will reduce the amount of overall sensitivity, again, possibly killing your ability to receive the weaker, more distant signal that you might be tuned to...

i'm assuming you're not a tinkerer at this point, so best thing to do is to order up a set of fixed F-Type attenuators ranging between 1 and 10 dB, eg, 1dB, 3dB, 6dB, and 10dB....

start stacking them at the input to your test mag in sequence as follows....

1 - 1dB only
2 - 3dB only
3 - 1dB + 3dB
4 - 6dB only
5 - 6dB + 1dB
6 - 6dB + 3dB
7 - 10dB only

you get the idea...

gradually add attenuation to see if you can properly affect the level of the aggrigate signals such that your Mag receiver performs as best it can....

i would do this without the antenna preamp, since the antenna preamp is a wideband device that will amplify EVERYTHING, including the noise floor...

preamps can be helpful, but they can also hurt things, raising the noise floor of the aggrigate signal being received...

From ' Receiver 101 ' - if a signal is below the noise floor, you're not going to ' pull it out ' of the floor using a wideband amplifier. you can only ( and then even difficult ) grab a signal out of the noise floor with a TUNED amplifier, since that amplifier serves to reduce that portion of the noise floor being caused by other signals...

the ability to receive a signal, regardless of its strength, is a function of the S/N ratio for the given signal.

you are attempting to do something that is difficult to accomplish without doing some hi-tech stuff... sadly, it is most likely due to the Mag receiver system design, and the only way to make the thing work how you might want it to is going to involve some hi-tech solutions, short of not using the receiver system in the mags...

OTA set top boxes may end up being a better choice, but you'd have to buy or borrow one to test the theory...

ordering up a few cheap attenuators to try the ' snap-train ' attenuation approach is probably the cheapest way to test, to see if you can get a good combination of strong vs weak signals in order to make the mag tuner work for you.

also, i'm sure it was mentioned previously, but it goes without saying that you should be using low loss coax that is at least double shielded, and should probably be of the ' flooded type ' that is used by cable and satellite folks. this type of cable resists moisture contamination...

were i in your situation and serious about what i wanted to do, i'd be using some Andrew FSJ superflex 1/4 inch product for my main long run feeds. stuff like this has a completely solid shield, and it ain't gonna let anything strong get in...

in your ( i believe ) ocean environment, if your feedline is conventional RG-6 and is anything more than a few years old, you can bet it's contaminated.

you should also be inspecting whatever structure you have your antenna mounted on. ANY corrosion or rust near mounting bolts and other connecting metal parts can QUICKLY turn those pieces into diodes, which will generate lots of noise and interference from locally strong signals, regardless of their frequency as it might relate to the channels you are trying to hear.

i worked in a commercial environment for a bit under 30 years and spent many-a-time, trying to help folks who were being bombarded with interference from local adjacent signals. for 90% of the time, the complainers were using grocery store things like RG-59, or RG-6 feedline that was years old and turning green...

of course, they never had any noticable issue until folks like ' local paging carriers ' installed in a building 2 blocks away...

this is just an example...

bottom line is to make sure you maxmize the shielding, and minimize the loss in the cable ( per 100ft )... the loss can vary widely across different cable types.

rgds,
ron g

rkg22: You're right in saying I'm no tinkerer, but from hours of reading this and other forums, I still have somewhat of a clue how things work.

That's also why, in my post above, I said I don't understand how these 2 channels I'm having issues with are the only 2 that DON'T have adjacent channels. While the other 2 US stations that I have no issue with DO have adjacent local channels. Sounds like it should be the opposite : problems with channels that have adjacent local channels, and not with those that don't. I understand, from a logical standpoint, the signal-to-noise ratio, but again according to my tvfool I should be in the clear for these channels, and I am on all my other tuners, except the Mag's...

As for the cable run, I recycled/reused an existing RG6 cable that was professionally installed some 10 years ago for a satellite dish we briefly subscribed to. So, I'm not sure about quad shield and this and that, but I'm positive it must be of somewhat professional quality, and visually it still looks fine. It's not "turned green"
Once it reaches indoors, after the 4-way splitter, it uses RG6 cable that was installed by the cable company, about a year ago back when we still subscribed to these robbers. Seems like good indoor quality cable... not that I really can tell the difference, though.

Anyway, it's a never ending story and I fear some members will start to feel I'm going off-topic here with my OTA woes (it's happened a few months back) so for now I'll leave it at that and keep trying things out... as I said my next attempt will be with the FM trap set to IN. Might actually happen later on Today.

I'm no expert either, but I have to suppose some kind of harmonic could be at play. An example might be a weak/problem channel at twice or thrice the frequency of a strong lower channel (or FM, which lies between VHF 6 and VHF 7, which the trap should solve) having an effect similar to a strong adjacent channel. A harmonic from a strong nearby HAM might do it too. How close are you to an airport or military installation? If any of the latter, maybe moving or shielding one side of the antenna would help. It might be interesting to see if a nearby friend or neighbor with antenna would allow you to connect your mag to his long enough to see if problem channel behavior changes.

hi rx -

i do realize and understand about your 2 stations that are presumably in the clear vs those that have adjacents that are working fine....

do understand, though, that it only takes a couple of dB difference in true strength to affect the ' drowning ' syndrome on your problem channels.

if your channels WITH adjacents are 1 or 2 dB stronger ( strong enough to climb out of the noise floor ) they may work, while your trouble stations may still get drowned due to slightly less signal that you might not even notice...

in addition, you may have local ( non-TV ) high level interference giving you headaches...

remember that the signal strength numbers on these devices is not a pure ' level ' indication. it's a measure of S/N that's reduced to a simple number...

indeed, 1 station with a ' higher ' number may simply mean that the actual level might be the same, or even lower, but that the S/N for that station is much better....

the green that i mentioned would not be visible from the outside, but moreso underneath the outer jacket on the shield, or even into the center conductor areas... especially at or inside the f-connectors themselves...

good maintenance would include connector replacement and sealing, assming that the overall cable has not been compromised. again, a fairly cheap thing to do...

i know it's nit-picky, but you'd be surprised how much loss a single problem connector can cause... at the higher frequencies, things like this can represent an almost short circuit, causing many dB of loss at a given frequency...

the commercial cable you described is probably ok, but with 10 years of exposure to the elements, any connections can be culprits...

in addition, whatever structure your antenna is mounted on can be a worse culprit...

any metal-to-metal connection points, especially if those points are made from dissimilar metals, can definitely reek havoc with any substantial local signal ...

an example of this from my working days was with a local FM broadcast station operating in the 88-108 FM band. and this was in the middle of the desert... because of faulty ( corroded ) feedline mounts and the lack of use of stainless steel hardware, that station was causing strong spurious emissions all the up through 900 mHz and wiping out a local link receiver trying to hear something about 50 miles away...

the emissions were caused at the joints of the feedline mounts, which had essentially turned into diodes due to the corrosion, acting like RF mixers with other unrelated signals at the same site as the broadcast station... the broadcast station ultimately had to de-construct and move elsewhere due to its interfering with several public utility communication systems....

things like this are hard and time consuming ( read - expensive ) to find...

things to do that are least expensive include getting the attenuators ( just a few bucks ), as well as ensuring that you've got a HEFTY ground system from your antenna structure ( hefty wire connecting from structure to a good 6 foot rod punched deep into the ground near the structure) , as well as connector replacement on general principle, given a 10 year exposure to the elements. many cable connector installations are ' crimped ' as opposed to soldered, providing such opportunities for corrosion to occur. a single poor crimp along with 10 years of exposure can do a lot of damage.

it's clear ( at least to me ) that you've got some sort of AGC, overload, or interference problem, since the signals coming out of your mags are weaker when you power the mags up. again, not necessarily any defect issue, but simple inability of the mags to handle something strong nearby...

the mag's tuner may be using an IF frequency that is different from your other devices, but happens to be on a frequency that mathmatically evaluates to a mixer product that causes the trouble.

regarding OT, well yes, its a problem that is lengthy to deal with, but certainly not OT as it relates to the capabilities of the mag machines across varying signal conditions...

i would not give up at this point, until you've exhausted at least the less expensive possibilities...

an online order for a few attenuators ( 20 bucks or so ) and a good once over of your antenna structure, as well as a bit of research on non-tv local transmitters might net you a solution...

and DO ensure that there really is NO voltage at the center conductors of both RF input and output of the mags when the antenna is connected...

don't believe your DC blocked power inserter at face value...
guarantee DC isolation by using a DC block at both RF input and output of the mags.

rgds,
ron g

With digital OTA adjacent channels aren't usually adjacent. Example: my channel 3 is actually using channel 22

@rkg 22 & mrmazda:

All your input is greatly appreciated.
I did the FM trap mod earlier today. So far, no change, other than I'm no longer getting that US FM station I was after. I left it in the IN position anyway to see if I get different results later tonight. The weather got so hot and humid today that the US stations would naturally be weaker than normal.
Some of the channels do yield about 2-3% more in the TV's tuner, but no difference in the Mag's.

When I said there was no "green" on the cable, I meant on the conductor itself, but I admit after 10 years it certainly doesn't have that shiny "bronze" look. I could definitely just cut it off and put new connectors, but the only ones I have are the threaded ones you screw onto the cable, not the crimped ones. I don't have the crimping tools etc. And I know these aren't the best connectors, especially for outdoor use.

I also just wanted to specify that the closest ocean is ... I'd say, 500+ miles away.

As far as military/airport, they're each about 10 miles away, and each are at about 90° each way (one to the West and the other East). They're out of the main range of the antenna, especially the airport which is actually more like 120°, so to the back of the antenna.

The more plausible causes are really the noise levels, saturation etc, and I agree I should probably end up trying attenuators etc. I'll see if I can source some of these parts online in Canada.

I have one friend who I know uses OTA, but only with rabbit ears for local channels. So, no way to test the US stations, or something even close to my installation with the Mag. There is one user on another forum (local) who uses a very similar setup and a Mag DVDR, and he doesn't have the same issues I have, but he's further away from the local transmitters, he's not located in my immediate area. So, comparisons are hard to make.

I'm not saying I'm giving up, but climbing on the roof and in the tower every time I try something different is just a hassle and my wife doesn't necessarily approve it either

The tower is grounded from when it was installed, but I'm not sure the gauge of the wire and where it's actually grounded. I just know it's still attached to the tower itself... not sure where the other end goes. It's a tower I "permanently borrowed" from the neighbor's roof (from a TV service that, back in the day, offered micro-wave TV from the local Mt Royal but that went bankrupt a long time ago). I of course asked my neighbor before taking it

I've had terrible luck with the screw-on and crimp connectors. I get much better results with the compression connectors. The tools cost a bit more but using anything else seems like throwing money away.

I have the Ideal 33-623 tool set. The compression tool and wire cutter seem to be of decent quality but the wire stripper is mostly plastic. The stripper works well enough but it probably wouldn't last very long with heavy use.

hi rx

a thought just occurred to me. this may have been addressed already, but when you test, have you shut down and/or disconnected all of your other entertainment devices not being used for the test ( such as other DVRs and televisions ) ?

i just remembered that i had a situation where one of my devices ( can't remember if it was one of my STBs or if it was another DVR ( panny e95 ), but depending on the channel the offending device was tuned to, it would generate some pretty strong interference ...

i have a kind of complicated setup, with 3 OTA converters, 2 of which being used to feed OTA content to both DVRs via line inputs. the third is fixed on the local CBS OTA affiliate and is used to convert and pass tv guide onscreen service into my panny via a channel 4 inserter at the back of the panny. all of this is in addition to my local COX cable feed...

also, during some early testing when setting up the channel 4 inserter, i did note that when i did simple mixing, using a channel 4 notch filter to clear the channel from cox, and just a plain old splitter running backwards as a combiner, as soon as i connected the cable feed, my channel 4 ( from the STB ) took a nose dive in strength... i had to use the actual channel 4 tuned inserter to calm things down and drop the noise floor being generated from the cable feed...

anyway, the right combination of channels would get in the way, producing sufficient interference to louse up a local channel, making it undesirable for recording... my situation is with all channels ( OTA and cable ) being pretty strong to begin with, so my experience was simply a small amount of ' degradation ', a nuisance for me, but for your situation trying to pull weak signals from afar, maybe something like this could be happening. like maybe one of your dvrs or other boxes connected to the feed around the house might be generating something that the mags don't like ??

just another stab...

rgds,
ron g