As you told that story, Neil, I could actually hear that old Olds radio in my head with all the blazing punch of dashboard rock and roll. Right up until you mentioned those leaky caps.
After that reception faded fast and all I could hear was a clock ticking somewhere.
I could actually hear the vibrator supply until you pulled it out.
I tried for a long time to get good AM reception on an "in the house" car radio. I tried loading coils and long and short antennas; I tried a lot of things. I tried all kinds of matching networks and some snake oil too. Nothing really worked; the AM reception was like dead or very weak at best and loaded with AC buzz (not from power supply)
Here is what did work for me. I have an outside 5/8 wave FM broadcast antenna, (for testing purposes only of course). The antenna does have a loading coil which is tuned for my FM operating frequency. The Loading coil has no effect on AM broadcast band frequencies. I have the antenna connected to the house with RG 8 which is also the transmission line for my FM "lab"
I do run RG59 (ok, slight mismatch) from the point of entrance after the FM connection (when used) to the FM/AM car radio.
I found that the coax has to be run right up to the radio chassis in order for the AM tuner to provide the same level of performance as if it were mounted in a vehicle.
If there were so much as a few inches of open wire from the center pin of the coax to the input jack on the radio performance on AM dropped off seriously. I am not sure why this is but it makes a huge difference to have that coax with shield go right up to the radio chassis and grounded to the chassis.
I always thought ok, all I would need was few feet of wire on the antenna connector will work just fine, well, for FM it does but on AM nothing but power line buzz and hash.
I have about 80 feet of coax from the antenna, to the radio, and the length doesn’t cause any problems or signal loss, then I have coax switches which select the antenna and direct the signal to two other radios, one in the computer room and on in an upstairs bed room, very little loss of AM signal and nearly 100% electrical interference noise free on most days.
The antenna feed has to be isolated from each radio input by the switch or else there is a signal loss.
Its great to have this kind of reception for AM
Radio Joe
Here in the UK their is a company that sells large fm receive antennas, and they also do an outdoor/chimney stack mounted am antenna.
This am antenna is helically wound fibreglass whip type, i am guessing it may be one of those long car antennas that were the rage in the 70/80's here, that was mounted on the front wing/fender, and clipped to the gutter towards the back of the car.
This is the only company here i have seen offering an outdoor building mounted am antenna for home use.
Paul.
Car radios have a trimmer to tune the AM receiver to the antenna. Often this is hidden behind one of the knobs, tuning or volume/tone, and will be visible if the knob is removed. Other times it is somewhere on the chassis accessable through a hole.
The procedure is to tune to a blank spot near the high end of the band and turn the trimmer until the background noise peaks.
Though RadioJoe's AM problem seems more severe than this is likely to fix, it is worth a try.
Neil
The best tuner I had was not a Macintosh but a Yamaha, believe it or not. This was back in the seventies and eighties with FM sensitivity of .9uV for 30db quieting and 2.0uV for 50db quieting and ajacent(not alternate) channel selectivity of 40db. AM was 100uV/M, about the same as the GE super radio. But not as good as a car radio. Image rejection of strong signals was something like 80db.
This, believe it or not, is better than the current tuner Macintosh makes. I checked on their site and was surprised at this as the FM sensitivity was 2.0uV for a listenable signal and AM was 320uV/M....not too good for a several thousnd dollar tuner!
Mark
I think Radio8 is on the right track, I bet the car radio AM section uses the car body as part of the antenna (lots of metal), so the long coax run is "mimicking" the now gone car body. I had completely forgotten about the radios actually being tuned.
I wonder if performance would enhanced if the coax shielding was making direct contact with the chassis.