Wierd question about a radio

flatheadfan

flatheadfan

Well-known member
One common thing working on old cars is the wierd things that happen. The other night I was installing a radio in a '36. It is an open car with the antenna under the runniing board. Once the radio was installed I turned it on and the reception was poor, at best. I set my trouble light on the transmission tower and suddenly the radio's reception improved. I lifted the light off the tower and the poor reception returned. It appears that the light (and its' cord), were working as an antenna without being attached to the radio. In fact, the antenna lead to the radio is no where near the trans tower. My question is this, do I have a grounding problem, if so do I need a body to frame ground?

Any help would be appreciated!

Thanks

Tom
 
Amplitude modulation is very susceptible to noise interference. If the car is in a building with flourescent lights on, there will be interference. Electric motors and the car's ignition & generator can be sources of RF noise. Your drop light may have been acting as a filter rather than an antenna. Antenna connections need to be what the manufacturer intended too in order to act as a good frequency gathering device.

I asume this radio set is of original type design used by FoMoCo in 1936. Whether it has been restored with modern electronics or not can have a difference in the way it functions. More modern radio sets have better filters and antennas so interference is generally not much of a problem compared to the early designs. If it has a solid state voltage inverter rather than the old ******** then polarity of electrical connections can have an effect. I doubt though if it would have worked very long if it was connected with reverse polarity with a solid state inverter tube. The fact that it worked at all, it's a good sign.
 
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My guess is that the antenna being under the running board is a problem. AM antenna needs to be open to the air.

Mine won't even work inside my garage.
 
An under the running board antenna is pretty much directional. My roadster had an under board antenna & if I went to town the siganal was fine but comming home was a lot weaker. The radio is history. I prefer the sound of the exhaust & wind. The drop light wires connected to the building wiring were probably be used to bring in the stronger signal. Back in the day some cars used the chicken wire that supported the roof.
That's my thoughts on that.
 
Fords starting in 33 or 34 used the chicken wire in the roof which was insulated from the surrounding sides.I think the open cars used an antenna mounted on the rear spare tire carrier.The running board antennas are rather low for good reception.Original radios drew a lot of amps.
 
Have you adjusted the antenna trim screw, usually it is close to where the antenna wire goes into the case----it can make the difference between only getting stations in the next close town to getting stations from the next state.

Follow these steps to adjust the trimmer:

1) Turn on the radio and tune to a weak station on or near 1400 kHz on the AM dial while the engine is off. Make sure there is ample volume so you can hear any differences while adjusting the trimmer. This process should be done in a fairly open area where large objects aren't around to affect normal reception.

2) Make sure all the sheet metal on the car is in place and shut the doors. Remove the tuning knob and knob behind it from the radio. Above the tuning control shaft you will see a small hole, inside is the trimmer adjustment. (Use the above picture as a guide).

3) Use a very small screwdriver that will fit the adjustment screw inside. Because the screwdriver is metal, you will have to make only slight turns at a time and then pull the screwdriver out each time (the screwdriver is metallic and slightly alters the trimming process) before listening to the radio's output from the speaker(s).

4) The idea is not to tighten or loosen the screw completely (remember this is a fragile component), just turn it a little in a direction that gives you the loudest output from the weak station tuned in.

5) Once you have the antenna "trimmed" properly (loudest output achieved), don't adjust the antenna itself (raise or lower the mast if it's telescopic) or you will have to repeat the process again for optimum reception. If you have a windshield antenna, this process can also optimize your reception. If you have a factory rear power antenna, don't worry about "loosing your settings" because the antenna should always extend to the full length every time the radio is on.

6) Install the knobs back on the radio.
 
Guys-

First, I appreciate the responses! I now have some directions to investigate. However, one thing that keeps coming up is "antenna trimming." I understand the need but I can't see any way this can be done on this radio model short of taking the radio out of the car which separates the radio from the antenna you want trimmed. Enclosed is a picture of the antenna hook-up inside the radio. Any ideas? Again, thanks for the help.

Tom
 

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On older radios, I usually could find the trim screw behind the tuning knob. I would remove the tuning knob by pulling it off carefully, then with a flashlight, look in alongside the shaft to the rear (bottom) of the shaft to locate the small trim screw.

From there simply follow the previous directions above.

When trimmed or tuned, simply retplace the knob.

There may be other other locations for the trim screw but this is the most common that I have found. I do believe that I had a radio once that had the tuning / trim screw on the outside of the case and it was marked.

Perhaps if you can find an owner's manual or an older radio repairman that may assist you better.
 
Antenna trimming will tune the dial and station together. Say for your 57 Ford, tune for your favorite station at approximately 1/2 the dial and it is supposed to be at 1100. You tune for 1100 but the station reception is weak at this point, but tuning the radio slightly higher or lower on the dial makes the station much clearer. Re-tune to 1100 and then you adjust the antenna trimmer so the station reception is peak at this point. For the 36 radio again tune the dial to 1100 and if the station is weak or far off from the dial setting you then tune so the station is clear then remove the tune cable from the radio box, readjust the dial for 1100 and then plug the cable back in. This is just a matter of syncing the station and radio dial together. Your drop light electrical cable is acting as a huge antenna allowing stronger station signal to the antenna of the car, the result is better reception in an enclosed area. Your not going to play the car radio in the garage so move the car outside and see if reception improves.
 
I get a kick out of those old sets. All hard wired and easy to do solder repairs. If a circuit board on a later model radio gets burned, you have to replace or remake the circuit board. there aint no circuit board in those old ones, just a chassis.

It seems like those radios have a cable from the head to the unit. The antenna may be tuneable but a person would be well off with some instructions from some original literature on that model. I wonder if more than one manufacture was involved with the 35/36 radio sets from FoMoCo?
 
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More than anything else, it's the location of the antenna that causes the issue. On my 39 coupe, I have dual antennas mounted under the running boards. If I'm in a populated area the radio works just fine. But out in the "sticks" where I live, reception is rather poor. Lousy, actually! Listen to the pipes.
 
The best thing I ever did to my AM radio was to tap in an input for my iPhone. I like to listen to music (as opposed to talk radio) and have a collection of period-correct music for cruising. The music is amped by the old amp and speakers giving it that low-fidelity sound that we loved so much.
 
Why the signal got better.

Unlike the electrical system we are familiar with, radio frequency signals do not need a direct connection - in the sense we usually understand it.

Simply having a long wire in proximity to the antenna is enough for the transference of signal - it doesn't need an electrical connection. In fact the ground part of an antenna isn't really that important (yes sounds like heresy, but true).

I _think_ the radio is a Philco FT-6, I do have a schematic of this radio attached as a PDF. Sorry for the poor reproduction. The antenna trimmer is in the lower left corner.

Regards

Henry
 

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AM antennas are designed to be vertically polarized. Your mounting point works OK for FM (with an optional antenna length of 30") but is really not recommended for AM. Even with a perfectly tuned vertically polarized AM antenna reception is still dependent on many more factors than FM.
Good luck.;)
 
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