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Radio gets FM but not AM

Posted: Sun Aug 22, 2021 8:56 pm
by Oldslowandugly
My dock neighbor has a 1965 Whaler. He installed an AM/FM radio in the console. I think the radio came from a car. He rigged up an inexpensive antenna. All he gets is FM, no AM stations at all. He says the radio worked fine before. What could the trouble be?

Re: Radio gets FM but not AM

Posted: Mon Aug 23, 2021 8:14 am
by jimh
Assuming no defect in the radio, the lack of reception of AM broadcast signals is likely due to the antenna in use being inappropriate for that band.

Also, the signals in the AM Broadcast band are always vertically polarized. Any antenna orientation other than vertical will add additional attenuation to a cross-polarized received signal.

The wavelength of signals in the AM Broadcast band is extremely long, so there is no possibility of having an effective antenna that is any significant portion of a wavelength. The AM Broadcast band receivers are usually configured to use an antenna that is more or less a highly amplified voltage probe and detects the electric wave in the signal. Some AM Broadcast band receivers try to receive the magnetic wave of the signal using a inductive loop formed on a ferrite core.

Re: Radio gets FM but not AM

Posted: Mon Aug 23, 2021 12:10 pm
by Oldslowandugly
I am familiar with the ferrite loop type Antenna. It is usually hung off the rear of the radio chassis on the outside. But most automotive and marine radios I see now do not use that.

Or it is inside the case?

I know an automotive radio relies on the antenna shielding to be grounded to the car body. A boat antenna can't have that.

He used an actual marine antenna, and I think it was made by DUAL.

How does that type get grounded?

My own boat has a Standard Horizon AM/FM radio and uses a similar DUAL antenna also. I get great reception on both bands.

Could it be the car radio does not work well with a marine antenna?

Re: Radio gets FM but not AM

Posted: Tue Aug 24, 2021 6:45 am
by Don SSDD
Where I live there are no more AM stations to receive. Are there AM stations in range of where this boat is being used?

Automobiles have additional grounding of the body to the frame along with condensers to shield the radio signal from ignition static, radio still works without the added grounding but has static. This is on 50’s and 60’s automobiles that I am familiar with, not sure what has been changed with static control now.

Re: Radio gets FM but not AM

Posted: Tue Aug 24, 2021 8:56 am
by jimh
Oldslowandugly wrote:My dock neighbor has a 1965 Whaler.
The manufacturer of the boat and the year of its production really do not influence how AM Broadcast band signals will be received. The only element of the boat that could affect radio reception of ground wave signals from AM Broadcast stations is the non-conductive nature of the fiberglass hull.

Oldslowandugly wrote:He used an actual marine antenna, and I think it was made by DUAL.
I am not familiar with that antenna manufacturer. I am not familiar with the "actual marine antenna" produced by that manufacturer. I cannot offer any advice about that particular antenna or its suitability for use with an AM Broadcast Band receiver designed to be used in a car with a car antenna.

Oldslowandugly wrote:Or [the ferrite loop antenna] is inside the case?
There is no way for me to know anything about the particular radio your friend has removed from an automobile. In general, radios in automobiles use a voltage-probe antenna and employ the metal car body as a counterpoise. A magnetic-loop antenna would not work well encased in a metal housing which was encased a metal car.

Oldslowandugly wrote:How does [a marine antenna for the AM Broadcast Band on a fiberglass boat] get grounded?
An marine antenna for the AM Broadcast Band on a fiberglass boat does not get "grounded" because there is no ground when at sea. Freshwater is not very conductive. Saltwater is a much better conductor, so if at sea in saltwater in a boat with a metal hull, there is a possibility to have a reasonably good electrical bonding to the seawater from the metal hull. My assumption is that an antenna designed for installation on a fiberglass boat would be essentially a vertical voltage-probe antenna with perhaps some sort of internal passive impedance matching circuitry that would attempt to increase the voltage output from the antenna and match to the impedance of the coaxial transmission line for connection to the AM Broadcast Band receiver input.

Oldslowandugly wrote:Could [the cause of no reception on the AM Broadcast Band on the radio your friend has removed from an automobile and installed on his boat] be the car radio does not work well with a marine antenna?
Yes, that could be the cause of the problem. I mentioned this in my initial reply above.

Re: Radio gets FM but not AM

Posted: Tue Aug 24, 2021 9:10 am
by jimh
Because the signals from AM Broadcast Band stations use amplitude modulation, and because marine engines use spark ignition, and because marine engines often lack particular effort to suppress the electrical noise generated by the high voltage spark ignition signal, the reception of AM Broadcast Band amplitude modulated signals can be severely degraded by the presence of electrical noise generated by the engine. A simple test for the presence of interference caused by the spark ignition in the engine is to compare the received signals with the engine off and the engine running at operating speeds.

Re: Radio gets FM but not AM

Posted: Tue Aug 24, 2021 6:21 pm
by Oldslowandugly
There are many AM Broadcast Band stations here in New York city. Listeners use them mostly for traffic and weather information.

I like my Standard Horizon AM-FM because it has the NOAA weather channels.

This is the DUAL marine antenna I use.

As you can see it looks just like a car fender antenna.

Re: Radio gets FM but not AM

Posted: Sat Sep 04, 2021 8:30 am
by jimh
Thanks for the link to a DUAL-brand antenna.

Re AM Broadcast Band antenna for a boat being similar to a “car fender” antenna: modern automobiles don’t have vertical whip antennas mounted on the fender anymore. Some have a radio antenna embedded in the windshield. More often on modern cars I see a small housing on the roof that contains the antennas for the AM and FM broadcast bands, for satellite reception including subscription music and weather services, for navigation systems, and for an integral cellular radio transceiver (as in the GM OnStar system).

Re: Radio gets FM but not AM

Posted: Sat Sep 04, 2021 9:28 am
by jimh
Oldslowandugly wrote:There are many AM Broadcast Band stations here in New York city

New York city AM Broadcast was typically the home of the big-three network stations, WNBC (660-Hz), WABC (770-kHz), and WCBS (880-kHz), and also of pioneer WINS (1010-kHz) owned by William Randolph Hearst, then later Powel Crosley, then Westinghouse, and others.

New York AM Broadcast radio featured many famous personalities, such as Murray the Kay, Dan Ingram, Don Imus, Wolfman Jack, Cousin Brucie, Casey Kasem, and others.

About the only use I have found now for reception of AM Broadcast stations on a boat is in the fall when many college football games are broadcast and the weather is still suitable for boating.

For another business interest of Powel Crosley see

The Fisher Price Bearcat Outboard ... arcat.html

Re: Radio gets FM but not AM

Posted: Sun Sep 05, 2021 7:09 am
by Don SSDD
I grew up on Prince Edward Island and we could get the NYC stations on AM when the sky was overcast. Once heard the Grand Old Oprey from Wheeling West Virginia, not sure if it was replayed by a station closer to us. This was in the middle of the night when not much happening in the mid 60’s on the airwaves.

We also had an old multiband radio, likely made in the 1920’s or 1930’s. We could get Radio Moscow. The Vietnam war was quite different from the USSR reports as compared to the news we got from CBC/NBC/CBS and newspapers. There would be completely opposite reports after any significant events. It made me question any news reports.

The world is a much more informed place today. We have live streaming and surveillance video for almost everything. There is way less control of the news than when we all listened to AM radio.

Re: Radio gets FM but not AM

Posted: Sun Sep 05, 2021 7:53 am
by jimh
The radio program Grand Ole Opry was (and still is) broadcast live from Nashville, Tennessee on WSM, 650-kHz on Saturday evenings.

WSM is a 50,000-Watt clear-channel station. Its signal can be heard at night all over North America. It is a very famous AM Broadcast station. If you drive through the Nashville area on Interstate 65, you will go past their iconic radio transmitting tower.

The technical details of the antenna’s structure and electrical properties are very interesting. See ... wsmtwr.htm

Re: Radio gets FM but not AM

Posted: Sun Sep 05, 2021 10:14 am
by Don SSDD
Thanks Jim, very interesting.

There were 13 Radio Canada International towers built in Sackville, NB, in the 1930’s, they carried Radio Free Europe during WWII, as well as broadcasting RCI programming. The towers were about 400 ft each and local people reported getting radio broadcasts from their sink, toaster, or refrigerator.

Re: Radio gets FM but not AM

Posted: Sun Sep 05, 2021 11:05 am
by Jefecinco
Villa Acuna, located across the US/Mexican border from Del Rio Texas was, if I remember correctly, the site of a 100,000 watt radio station, XERF, in the early 1950s. There are conflicting stories that the station was later authorized to transmit at up to 500,000 watts. The broadcasts were in English and the DJ would say they were broadcasting from Del Rio or Villa Acuna. They were a mostly music station playing a lot of early rhythm & blues and down and out blues, AKA gut bucket blues as well as country music. I listened to the broadcasts from my bed using a small portable radio, perhaps an early transistor radio. To a 13 year old it was fun to get away with listening to "naughty" music late into the night.

Re: Radio gets FM but not AM

Posted: Sun Sep 05, 2021 5:39 pm
by jimh
Don SSDD wrote:There were 13 Radio Canada International towers built in Sackville, NB, in the 1930’s...

Back then there was a lot of medium- and high-frequency radio broadcast stations. The antenna arrays were very interesting. They often employed variations on the STERBA CURTAIN or RHOMBIC antenna arrays, where are very direction.

Today there is not much HF or MF broadcasting left. Everyone listens on the internet.

A few years ago we were in Quito, Ecuador, the home of the VERY famous high-frequency broadcast station HCJB. HCJB was run by a Christian organization, and they would say the call letters stood for "Heralding Christ Jesus's Blessing." They had a phenomenal signal all over South America. They used loop-fed antennas because the high elevation was causing corona arching at the ends of dipole elements in the antenna array. The closed-loop driven elements reduced the tendency for corona arching. The station was running very high power, perhaps 100,000-Watts or more. The air at 10,000-feet was too thin for conventional antennas.

Eventually the proselytizing for adoption of the Christian Faith in South America was very successful--about 99-percent of the population of South America identifies as Christian. The city of Quito, which is at about 9,000-feet elevation decided it needed a new airport. The new airport was to be located outside of the center of town, and, as it happened, the towers of HCJB were in the path for the runway approach. HCJB had to remove its famous antenna arrays to accommodate the new air port.

The transmitters were removed, too, and sent to be re-tuned to new frequencies for a new station in Malaysia, where there were a lot more potential converts to Christianity than in South America.

When we were planning the trip to Quito, I was hoping to be able to visit HCJB. Unfortunately, I got there several years too late. The station, the transmitters, and the huge antenna arrays were all gone.

We did have a very nice approach and landing at the airport, and departure several days later. The high altitude was quite an obstacle to overcome when visiting.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 6:27 am
by Don SSDD
I worked in Newfoundland in the early 1980’s at a bank. I had a fellow who wanted to finance small cable-satellite cable-TV for small remote communities. He had worked for years doing maintenance on Candian Coast Guard radio towers in Newfoundland and Labrador. He had set up his own transmitter where he lived and was streaming satellite tV free to the community as a trial while he applied for a Cancom license. There was a communication tower there and he was pulling TV channels off a satellite.

He had the electronics inside a small building and for power, he used an old car up on blocks. It would start and produce electricity to charge a bank of batteries, then shut itself off. He only had to keep it full of gas. He had an tape player which he used to play an advertisement across the TV screen asking people to support his license application.

To get licenses in the various communities he recruited a local person in each community and ended up with a group of about 15 to 20 people. They were successful getting licenses but the business failed when they couldn’t all agree on business operation, like putting more money in. This was about 1982. He was an early adopter.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 9:30 am
by jimh
Regarding reception of television signals from satellite, in 1973 to 1976 I was living in Connecticut. A friend of mine went to work for a new company that was installing a very large, 10-meter, satellite dish in Connecticut to be able to downlink signals from a commercial relay satellite between the USA and Europe. They were using C-Band at that time for the frequency, and C-Band was known as "Crummy Band" because there were so many terrestrial high-power point-to-point links authorized in that same band. Because microwave signals do not bend from atmospheric refraction much at all, to minimize interference the big dish was located well below the prevailing terrain. In this way all the terrestrial signals would just be passing overhead and would not be received or cause interference. This dish was actually sited not very far downstream from a large dam.

My friend was involved with the construction and set up of this very large dish (33-foot diameter), and he invited me to come up for a visit. The dish structure was very impressive, but I thought the location just downstream from an old dam was a significant liability. I think it was an old earthen dam. I wouldn't want to go to work every day at a place just below a large, old, earthen dam.

This antenna was used for downlinking live video and audio feeds of television content from Europe. At that time to get a reliable signal on a relay satellite in the mid-Atlantic you had to be on the East Coast of the USA and you had to have a 10-meter dish, and you had to have a very clear horizon to the northeast.

This was my first introduction to satellite downlink reception. Later in the 1980's I built two 30-foot dishes from kits for C-Band downlinks for a local television station to use. These were not very well made structures. For a parabolic reflector to work properly, the surface of the dish must be a very precise parabolic curve, otherwise the antenna radiation pattern develops many sidelines. When aiming a big antenna at a particular satellite the last thing you want in the antenna pattern is many sidelines. The mounting system was similarly unstable and crude. I gained a lot of practical experience in the fabrication, installation, and aiming of big satellite antennas from those projects.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 9:43 am
by jimh
Don SSDD wrote:I worked in Newfoundland in the early 1980’s at a bank. I had a fellow who wanted to finance small cable-satellite cable-TV for small remote communities.

Canada was an early adopter of satellite television distribution with their ANIK satellites. To get USA-based content, the Canadians would steal American television over-the-air signals. Since Windsor, Ontario was less than a mile away (by water) from Detroit, Michigan, the Canadians used to steal the off-air signals of Detroit TV stations to get the major networks. At that time I worked for the NBC affiliate in Detroit, and our off-air signal was being broadcast to Canada via their ANIK.

The station management did not mind that their signal was being taken and used in Canada. I suspect they might have even negotiated a deal to provide it. I think that may have occurred--I was not privy to any of that sort of negotiations--because one day I was tasked with setting up a direct audio feed via dedicated wired circuits to the Canadians. It seemed they could never get really clean audio for the television signal using an off-air feed. I thought it rather funny that we were giving them so much assistance in stealing our programming.

The irony of this was that throughout Canada, particularly in the remote areas where everyone watched television from ANIK signals, our local Detroit television personalities became quite well-known in Canada. Back then the local anchorman of our newscast was a fellow named Mort Crim. Mort was the classic TV new anchorman. He later claimed that he was inspiration for the fictitious newscaster Ron Burgundy in the famous parody movie Anchorman: The Legend of Ron Burgundy.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 10:23 am
by Jefecinco
Speaking of stealing signals, when we lived in the Dominican Republic in 1983 through 1985 we could not receive any English language signals from over the air television broadcasts. We had agreed long before moving to the DR that we would not waste money on cable TV. However, we learned the price of cable TV, which included English language programming, was very low in the DR. We subscribed and enjoyed the service during our tour there. Some time after subscribing we learned that the local cable TV provider was acquiring the signals without paying for them.

Ethically, we should have discontinued our subscription but we managed to keep watching, as did everyone else in the US Mission.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 12:02 pm
by Oldslowandugly
Don SSDD- That station you heard was WWVA from Wheeling WVA. It was a very popular country music station. When I was a kid in the late 50's early 60's we used to overnight on my uncle's wooden boat on the Youghiogheny Lake which is on the Pennsylvania/Maryland border. We would listen to WWVA while fishing. The neat thing about AM radio was that lightning from an approaching storm would create lots of static. We knew it was time to get off the water.

As for the initial antenna problem, it is solved. The guy used a late model car radio. Late model cars use a different antenna connector than old cars used. The DUAL antenna connector was the old-style Motorola connector that cars used for decades. It required an adapter to plug into the radio. Then he cut the coax cable of the adapter and the antenna. He used coax screw-on connectors to join them with a coax union. When we did continuity tests we found the coax union was defective. Once we changed it out the radio worked fine.

Re: Radio gets FM but not AM

Posted: Mon Sep 06, 2021 8:41 pm
by jimh
Thanks for the follow-up on the actual cause of the poor reception: the antenna connection was modified and was defective.