AM Signal Very Weak on Stock AM/FM Radio

[lonetreesteve]

I looked through the archives, but couldn't find the problem I'm experiencing. I've tried 3 different stock 240Z AM/FM radios (I know, I'm a pack rat) and the FM is very strong, but the AM is extremely weak, in fact only the strongest AM signal in Denver (the mighty 850 KOA) is barely there. So obliviously, it must be the antenna, but I only have one working stock antenna. the good thing is that I do have some spare stock antenna parts. Any help on this would be greatly appreciated.

Thanks!

[geezer]

There should be an antenna trimmer adjusting screw on the bottom of the radio. It may have come loose and is out of adjustment? FM waves travel differently from AM waves so the radio needs to be set for the area you live in. This comes under the category of "stuff I used to know about", but am guessing now.

[lonetreesteve]

That's a good point, Ron. However, after 3 radios I was convinced that it must be the antenna, so #3 is in the dash and I don't want to take it out until that is the only possible solution. I figure what are the chances of having 3 radios that all need the trimmer screw adjusted? Is there anything else that it could be?

[geezer]

I think the trimmer adjustment matches the radio to the antenna and your locations signal strength so it seems logical to me that all 3 radios would react the same and possibly need the same adjustment made. I think a different antenna would garner different results. Don't take this response seriously though, I'm just grasping straws.

One other thing. Do you have a good ground to the radio chassis/case?

Edited November 16, 2008 by geezer

[EScanlon]

Ron;

You're correct about "trimming" the antenna, but I don't recall if there is an antenna trim screw on the OEM radio and the schematic / owner's manual doesn't say anything about it. The way I "trim" my antenna is to raise or lower the antenna to the height that gives the best reception, both in AM and FM.

FWIW

E

[Carl Beck]

Hi Ron:

I like that - "things I used to know" qualifier. So I'll use it as well.

AM broadcast radio signals are capable of going around the world as they bounce off the earths upper atmosphere - and are broadcast with various amounts of out put power from the sending unit. In almost every case the longer/larger the antenna the better. (as the lower frequency wave lengths are longer).

Depending on the quality/sensitivity of the receiver - and the band separation of the tuner dial - it may be necessary to damp out weak signals, so that the signal seeking radio will stop only on strong signals.

FM on the other hand works best with an antenna length of limited length (30 to 32 inches comes to mind - but I wouldn't bet anything on that memory), or one that has a resister built in to filter out high frequency noise.

Be that as it may - you are correct - the AM radio's in the Z's have an "antenna trimmer" screw - located just forward of the antenna input on the case. I just looked at two of the one's I have in the house.

BTW - did you used to hook your crystal radio set to the steel bed springs of your bed?

FWIW,

Carl B.

Edited November 17, 2008 by Carl Beck

[Arne]

My OE AM radio is out of the car now. (I have my old Pioneer Supertuner in it instead. AM radio sucks in my parts.) While I can't say for certain that the AM/FM has it as well, the AM radio does have an antenna trim screw, as does my Pioneer, and most every other AM receiver I can recall. On the AM radio, the trim screw is on the bottom, near the antenna lead.

The AM trim instructions for older radios that I recall were all pretty simple. Tune into a station (as weak as you can get a steady signal). and turn the trim screw back and forth for best signal. C'est tout.

[Unkle]

I have been chasing this as well . AM radio does not improve with the stainless antenna used as far as I know ! The antenna is for FM reception.

AM reception comes from an internal '' ferrous rod '' wound with a wire . Google this , and you will see tons of info on this subject .

[lonetreesteve]

Thanks for all the info, guys!

[geezer]

Well Steve, your initial thoughts of the antenna being at fault are probably true. I know that there are signal amplifiers (pre-amps) available, that can be connected between the radio and antenna plug in, where it wouldn't be seen, but with a good stock antenna that shouldn't be nessesary.

Carl - Your right about me having a crystal set, except mine was connected to a long wire going out the window and strung up a tree. You probably remember bringing bags of tubes to the corner store to test for any signs of life also. I still have an old shortwave that my grandfather bought new in the 20s that I keep in top working order. All the parts can still be found fairly easy today.

[EScanlon]

Nice to learn about the trimmer screw!

E