OT Bizarre receiver operation

[632 Regal]

K, I have an old receiver in my barn/shop. reception was real bad so I installed an antenna on the roof (old car antenna with coax).

Well... the tuner squished all the stations between 92-104MHZ. like 101 fm is at 98... So I went out and picked up one of them high quality 120.00 antennas, risked my life crawling way up there again and hooked that one up...same freaking deal with the squished stations.

If I disconnect it and hook the old antenna up with a wire in the barn the stations correct themselves. I used 1 peice of shielded coax cable to do the long run to the peak of the roof if that matters any.

I dont mind or anything, I get a few stations now VS 1 staticy religeous talk show, just wondered WTF caused this.

[whiskychaser]

K, I have an old receiver in my barn/shop. reception was real bad so I installed an antenna on the roof (old car antenna with coax).

Well... the tuner squished all the stations between 92-104MHZ. like 101 fm is at 98... So I went out and picked up one of them high quality 120.00 antennas, risked my life crawling way up there again and hooked that one up...same freaking deal with the squished stations.

If I disconnect it and hook the old antenna up with a wire in the barn the stations correct themselves. I used 1 peice of shielded coax cable to do the long run to the peak of the roof if that matters any.

I dont mind or anything, I get a few stations now VS 1 staticy religeous talk show, just wondered WTF caused this.

It may have something to do with the physical length of the coax you are using not being 'tuned' to the frequency you are using. The coax may now be acting as the antenna itself but as you dont have a big lump of flat metal, like a car roof, into which your antenna is bolted, you are missing a big part of the antenna system (ground plane). Hence weak reception. Sorry if you fell asleep half way through that :-)

[632 Regal]

the coax is ran along the side of the barn up to the roof and the barns walls are steel so would that count as a ground plane?


It may have something to do with the physical length of the coax you are using not being 'tuned' to the frequency you are using. The coax may now be acting as the antenna itself but as you dont have a big lump of flat metal, like a car roof, into which your antenna is bolted, you are missing a big part of the antenna system (ground plane). Hence weak reception. Sorry if you fell asleep half way through that :-)

[Jr ///M5]

How many beers did it take to get the courage to crawl up on the roof? :D

[attack eagle]

it has to be analog tuner then right?
I have 0 technical idea on this but to float an Idea:

Prerhaps in adding the long coax run you somehow affected the inpedence the unit was designed to have on the antenna, and thus the tuning is off?

[632 Regal]

just an old stereo hooked to a stage system amp and 4 speakers.

the coax is the same as a direct sheilded wire and the antenna is supposed to be dead nuts on (full FM hertz range) Maybe I do need a ground block or some ****. I guess this is one advantage of living in the stix but not sure why yet.


it has to be analog tuner then right?
I have 0 technical idea on this but to float an Idea:

Prerhaps in adding the long coax run you somehow affected the inpedence the unit was designed to have on the antenna, and thus the tuning is off?

[Vanguard]

Jeff,

I suspect that your problem is in the receiver itself. Many old recievers use a wire, a rubber band or a cord to tie the analog indicator to the dial. It's likely that yours has slipped or stretched and while the tuner is at 98 the indicator is 3 steps off. I used to have an old Marantz tuner that this happened to.

[ryan roopnarine]

what is the ohm-age of the cable that you are doing this with (colloquially, rg-58, rg-59, rg-6). did the antenna you bought have a balun or transformer to convert from twinlead to coax? having done far too much of this mess between the ages of 10 and 14, it sounds like it is a receiver problem, not a decoupling or antenna problem.

[632 Regal]

naww, works right on if I hook a lamp cord into the car antenna inside the barn, dont get good reception in here tho.


Jeff,

I suspect that your problem is in the receiver itself. Many old recievers use a wire, a rubber band or a cord to tie the analog indicator to the dial. It's likely that yours has slipped or stretched and while the tuner is at 98 the indicator is 3 steps off. I used to have an old Marantz tuner that this happened to.

[632 Regal]

RG-6 cable. The antenna came with a length of cable (RG-6) but it was about 15 feet too short so I had to make a longer one.

The receiver I have has only 1 lead for antenna and 1 ground, I hooked the coax direct and with a filter tieing both together and made NO difference.

Im thinking the new antenna is making the receiver stoned and not able to comprehend a good antenna.

You are probably onto something with a transformer and my receiver only having 1 antenna lead. Maybe it's just too old but it sounds freaking awesome with the current setup....maybe its just the combination of amp and speakers.

Just too weird how it "compresses" the dial into a smaller range. Its all there just compact now...lol


what is the ohm-age of the cable that you are doing this with (colloquially, rg-58, rg-59, rg-6). did the antenna you bought have a balun or transformer to convert from twinlead to coax? having done far too much of this mess between the ages of 10 and 14, it sounds like it is a receiver problem, not a decoupling or antenna problem.

[632 Regal]

it's vodka not beer but a few shots. I fell off tall things 3 times and am not looking forward to another time. With Sals ITP (low platelets and nose bleeds) I have had a lot of nightmares of falling so simply climbing onto the roof freaks the hell outta me these days. When I was younger i had no fears, even climbed one of them real tall power towers, layed on the top on my stomach and pretended I was swimming...not these days however.


How many beers did it take to get the courage to crawl up on the roof? :D

[ryan roopnarine]

do you know the brand/model of the antenna or know of the website for it?

i'd think that a impromptu ground might do some "compression". i'm sure that back in the ancient daze when people your age roamed the earth you played with a crystal radio at some point. same effect, the better the ground, the better separated the "smooshed" together signal got/could be differentiated.

[whiskychaser]

the coax is ran along the side of the barn up to the roof and the barns walls are steel so would that count as a ground plane?

I'm assuming you are using a simple car aerial with a car radio? If so at least two bits match :-) Ideally you should use the right kind of coax but this is more important if you are transmitting-and you arent. Because you are using a long length of coax you have to cut it to the right length for it to work at its best. Otherwise you can get 'harmonics' which are different frequencies coming in and confusing the fck out of your radio. If your barn roof is also flat, made of steel and your aerial is bolted through it, you have one fantastic ground plane!:-) If you got your aerial INSIDE all that steel, you are stopping it from receiving signal. Ask anybody else who did the ARA exam. Sure you must know someone local who did the ARA exam and can be even more boring in person :-) And without the appropriate risk assesment...zzzzzz

[Ross]

I suspect the co-ax cable is not agreeable to the recvr. Have you tried the flat stuff? Twin lead I think it's called. How about one of those matching transformers that TVs used to come with before everyone had cable?
Also if the antenna is attatched directly to the metal barn that would become part of the antenna. No?

[whiskychaser]

I suspect the co-ax cable is not agreeable to the recvr. Have you tried the flat stuff? Twin lead I think it's called. How about one of those matching transformers that TVs used to come with before everyone had cable?
Also if the antenna is attatched directly to the metal barn that would become part of the antenna. No?

It occurs to me we dont even know what kind of receiver this is :-) Maybe the tuner out of an old midi system or something? In which case a few metres of door bell wire, split after about 3ft into a V shape would do nicely. And you dont need to climb on the roof:-)

[632 Regal]

i said it was old, sorry about not clarifying. It's a Zenith receiver with a turntable and 8-track player <- yes. It works great and thats what powers the power amp.

thought about the T-wire antennas but stapling it to the barn wall which is metal wont help much with reception. I am in the boonies sourrounded by hills and trees and crap and thats why I chose the peak of the barn. It is mounted to a 2x4 nailed to the roof and not metal. Also a dual wire antenna would only be able to connect to 1 antenna screw on the receiver. I am pulling in a station thats 75 miles away and used a marker to draw the location on the dial thingie.

You should see my sons antenna setup in the house, **** you should see his systems...wires all over the place, speakers all over too. I couldn't let him win the stereo compettition could I? His systems (2) do still have more throbbing boom though...lol


It occurs to me we dont even know what kind of receiver this is :-) Maybe the tuner out of an old midi system or something? In which case a few metres of door bell wire, split after about 3ft into a V shape would do nicely. And you dont need to climb on the roof:-)

[pingu]

Coax cable should be 75 ohm impedance for radio and TV aerials. The length of the coax won't make any difference (except that the coax will slightly attenuate the signal from the aerial). The coax won't be affected by running near a metal barn - coax is shielded.

Coax can also come in 50 ohm impedance. This is the wrong impedance for use on a radio. If you've somehow got 50 ohm coax then the length of the coax will form resonances (as mentioned by whiskychaser).

Some radios use balanced, 300 ohm, flat wire instead of coax. If you've wired coax (even if 75 ohm) to a connector on your radio that is expecting 300 ohm flat cable then the radio and the coax won't be getting on too well - you'll be getting the resonances.

Does the conector on your receiver specify the impedance (75 ohm or 300 ohm)? Is the connector a coax plug/socket or two wires (i.e. for flat 300 ohm cable)?

Is the aerial suited for 75 ohm coax or 300 ohm flat wire? If the aerial is for 300 ohm then you can convert this to 75 ohm (and plug it into 75 ohm coax) using a special type of transformer called a "balun".

The fact that a station at 101MHz is coming at 98MHz is nothing to do with the coax cable: cables don't shift frequencies. Your dial is off a bit.

Hope this helps!

[632 Regal]

I think your onto something here, the radio does say 300 ohm. The antenna and cable are 75 ohm. The dial is off yes, the upper range is packed into the middle ie: 88fm comes in at 88 but all stations above 104 are squished below 104.

balun...must look into this




Some radios use balanced, 300 ohm, flat wire instead of coax. If you've wired coax (even if 75 ohm) to a connector on your radio that is expecting 300 ohm flat cable then the radio and the coax won't be getting on too well - you'll be getting the resonances.

Does the conector on your receiver specify the impedance (75 ohm or 300 ohm)? Is the connector a coax plug/socket or two wires (i.e. for flat 300 ohm cable)?

Is the aerial suited for 75 ohm coax or 300 ohm flat wire? If the aerial is for 300 ohm then you can convert this to 75 ohm (and plug it into 75 ohm coax) using a special type of transformer called a "balun".

The fact that a station at 101MHz is coming at 98MHz is nothing to do with the coax cable: cables don't shift frequencies. Your dial is off a bit.

Hope this helps!

[632 Regal]

I have something like this deal hooked up, it doesnt make any differences in the dial or reception. Balun... < word of the day

http://upload.wikimedia.org/wikipedia/en/thumb/b/bb/Tvbalun.jpg/180px-Tvbalun.jpg

[pingu]

Tha' she blows - that's a balun!

I presume that the 300 ohm end (the end with the flat wire) of the balun is plugged into your receiver?

And that the 75 ohm end (the coax plug/socket) of the balun is plugged into 75 ohm coax all the way to the aerial?

Is the aerial 75 ohm? (The aerial might be 300 ohm and might not be getting on too well with the 75 ohm coax.)

[632 Regal]

yes yes and yes but it doesnt seem to make a bit of difference with it on or off. do these things go bad? maybe I need something specificly for this situation?


Tha' she blows - that's a balun!

I presume that the 300 ohm end (the end with the flat wire) of the balun is plugged into your receiver?

And that the 75 ohm end (the coax plug/socket) of the balun is plugged into 75 ohm coax all the way to the aerial?

Is the aerial 75 ohm? (The aerial might be 300 ohm and might not be getting on too well with the 75 ohm coax.)

[pingu]

Baluns are just miniature transformers - unless your balun has been bashed about a lot it won't have worn out or anything.

Yes, yes, yes: so everything ought to be OK but it isn't.

Have you tried a different receiver? If your receiver is of unknown provenance then the receiver might be duff between 92 and 104MHz.

Another possibility is that your barn aerial is so close to the corrugated iron (I presume your barn is corrugated iron?) of the barn that the aerial is no longer "seeing" what physicists call "free space" (air is pretty much the same as a vacuum as far as radio waves are concerned); this could conceiveably be effecting the aerial and causing a resonance in the 92 to 104MHz range. How close is the aerial to the corrugated iron?

[632 Regal]

The barn wall is steel, the antenna is vertical with that wall directly at the peak appx 20 feet tall. the dot represents the antenna

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How close is the aerial to the corrugated iron?

[BobHarris]

If you have some 3 foot long welding rods you could imrove the ground plane by fixing them to the base of your antenna so that they form a horizontal X. I used to do this with a CB radio setup using a car antenna I had when I was a kid.

[pingu]

So your aerial is immediately above the steel barn wall?

It seems as if the proximity of the aerial to the barn wall could be the cause (have you been able to try a different receiver?) of the problems.

TV and FM aerial are designed to work in "free space" - i.e. a significant distance away from large conductors (such as barn walls). To be a "significant" distance away, the aerial should probably be at least one wavelength (preferably 5 wavelengths) away from the barn wall.

At 100MHz, a wavelength is 3 metres. So if your aerial is closer than that to the barn wall then it's certainly plausible that the steel barn wall is upsetting your aerial. Could you use some sort of mast to raise the aerial well above the steel barn wall?

If it's a PITA to access the aerial then I expect you'll want to try a different receiver first, just in case the problem is something other than the steel barn wall.

[632 Regal]

the steel walls peak is 1.5 inches below the base of the antenna so this makes sense. Cant really move it much farther away so I guess I can live with it as is. The receiver works perfect with an antenna inside but the reception is very bad.


So your aerial is immediately above the steel barn wall?

It seems as if the proximity of the aerial to the barn wall could be the cause (have you been able to try a different receiver?) of the problems.

TV and FM aerial are designed to work in "free space" - i.e. a significant distance away from large conductors (such as barn walls). To be a "significant" distance away, the aerial should probably be at least one wavelength (preferably 5 wavelengths) away from the barn wall.

At 100MHz, a wavelength is 3 metres. So if your aerial is closer than that to the barn wall then it's certainly plausible that the steel barn wall is upsetting your aerial. Could you use some sort of mast to raise the aerial well above the steel barn wall?

If it's a PITA to access the aerial then I expect you'll want to try a different receiver first, just in case the problem is something other than the steel barn wall.

[whiskychaser]

the steel walls peak is 1.5 inches below the base of the antenna so this makes sense. Cant really move it much farther away so I guess I can live with it as is. The receiver works perfect with an antenna inside but the reception is very bad.

Been out in the sun for a week so forgive me if I lost the plot. Just to recap:
Your receiver gets poor FM reception but as you are surrounded by hills and FM travels line of sight, I would say thats normal. (If you have it, you will probably get AM stations better but you wont get them in stereo.) If you have managed to get your aerial/coax/receiver to match with no improvement, you could invest in a small pre-amp to fit in between your aerial and your receiver. It may also amp up some unwanted signals but could well give you the edge you need

[632 Regal]

didnt match it, just going to live with it. the reception with the antenna on the roof is very good.


Been out in the sun for a week so forgive me if I lost the plot. Just to recap:
Your receiver gets poor FM reception but as you are surrounded by hills and FM travels line of sight, I would say thats normal. (If you have it, you will probably get AM stations better but you wont get them in stereo.) If you have managed to get your aerial/coax/receiver to match with no improvement, you could invest in a small pre-amp to fit in between your aerial and your receiver. It may also amp up some unwanted signals but could well give you the edge you need

[DaveVoorhis]

Have you tried a different receiver? The band compression problem doesn't sound like an antenna problem to me, it sounds like an old and rather poorly-engineered Zenith receiver being affected by the inductance of the big antenna.