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 Wide Band AM Radios
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 Return to top of page · Post #: 1 · Written at 7:12:26 AM on 21 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

Some flagship pre-war US console radios had wideband AM tuners (before FM was popular.) One that comes to mind is the Scott 16A which also had a dynamic range expander. I think Scott himself actually came from New Zealand.


 
 Return to top of page · Post #: 2 · Written at 3:54:44 PM on 21 January 2024.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2405

AM stereo (Motorola system) was used in Australia for a number of years. I recall an Autovox car radio that supported it, along with wide audio range. Sounded nice if the station wasn't pushing the compressor too hard. But very vulnerable to noise.


 
 Return to top of page · Post #: 3 · Written at 4:22:38 PM on 21 January 2024.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2039

The EA stereo AM kit was wideband. I still have mine, but hasn't been used for years. The plan is to throw it out when I get around to it, since AM stereo is no more.


 
 Return to top of page · Post #: 4 · Written at 5:02:19 PM on 21 January 2024.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 1284

Still have EA kit too. The stereo FM packed it in eventually and it was put away then.

I also have a pioneer car tape/radio that has AM stereo. The AM stereo would go pop and drop out to mono, and then come back again a few seconds later, then repeat the excercise. Very annoying. This was upposedly due to bugs getting fried on the transmitting antenna. But maybe that was myth.


 
 Return to top of page · Post #: 5 · Written at 9:38:06 PM on 21 January 2024.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2405

The bugs story is not a myth.

There is a spark gap at the base of the tower to protect the transmitter from lightning strikes. These towers are often in marshy areas (where there are lots of bugs) for a more effective ground plane. Bugs build up around the spark gap and are eventually incinerated in a flashover across the gap. The signal is momentarily interrupted as the transmitter recovers from the overload. The stereo at the receiver then needs to re-sync.


 
 Return to top of page · Post #: 6 · Written at 3:52:04 AM on 22 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

When I was with AWA in the early 70s, they had a wideband AM tuner called the "AM3". I wanted one badly but couldn't afford it.

The AM3 was a matching component of AWA's Ortho-Fidelity hi-fi series, made in NZ (it may have been cheaper to make in NZ and Aust may have had a free-trade pact with NZ - but not Asia - at the time.)

In order to justify the high price of the Ortho-Fidelity series they added a level of European Sophistication: they had the back panel connectors done only with DIN connectors. Later, I see them opening the cartons and adding DIN-RCA adapters before shipping out because Australians were not taking to the DIN standard very well at all. Just one of the stupid ideas that contributed to the fall of AWA.


 
 Return to top of page · Post #: 7 · Written at 8:32:50 AM on 22 January 2024.
BringBackTheValve's Gravatar
 Location: Linton, VIC
 Member since 30 December 2016
 Member #: 2028
 Postcount: 472

RCA connectors over DIN any day. From fault finding to kit building, equipment using RCA connectors is a joy to work with.

I may be wrong, but I am stuck with the idea anything from Europe, including cars, seems deliberately built to give service technicians maximum grief.

I note RCA connectors are still with us, haven't seen DIN for a long time---good!


 
 Return to top of page · Post #: 8 · Written at 12:00:22 PM on 22 January 2024.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6720

QUOTE: Australians were not taking to the DIN standard very well at all


I've had an abiding dislike of DIN connectors since primary school days when the 16mm projector's connection to its remote speaker was via a DIN plug and it became my job to hold the damn thing in throughout the film so we had sound.

IMO, DIN connections can only be made once and left like that.

And don't get me started on mini DIN and bent pins!


 
 Return to top of page · Post #: 9 · Written at 2:57:59 PM on 22 January 2024.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2039

I didn't mind DIN connectors, the problem was that they weren't very widespread so adaptors had to be used. I was used to soldering DIN plugs because I used to service CBs in the day and they often had a DIN connector for the microphone plug.

If you don't mind mono on AM, a wideband receiver is still a good idea because the stations transmit a wideband signal. It just isn't stereo.

In my experience, the momentary dropouts on stereo is because of overmodulation. AM stations tend to overmodulate especially on the negative excursions to make the signal more "punchy", and be more understandable at a long distance. However the Motorola system is predicated on no overmodulation, and the stations don't want to restrict themselves. So it's either good stereo, or good coverage.


 
 Return to top of page · Post #: 10 · Written at 10:59:15 PM on 22 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

There's more ironies with DIN/RCA: the German Pro video connector, called a "Fernseh" plug (which also didn't catch on) was like an oversize RCA (they were actually quite good!)

Also "Ortho-Fidelity" was partly borrowed from RCA ("Orthophonic") like AWA borrowed the word "Radiotron".


 
 Return to top of page · Post #: 11 · Written at 11:30:02 PM on 22 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

In the 1980s at an NAB convention I stumbled by a Motorola booth, they were pushing their new compatible AM Stereo. There was no-one stopping as music was by then mainly FM in US. But I halted and the lonely guy said "take a listen to AM Stereo" (via headphones as they couldn't demonstrate speaker stereo in that compact space)(they must have had a hidden encoder coupled directly to a decoder, then to headphone amp.)

I listened and it was stereo all right, but I said to him "why is the treble so bright?" He said "oh we boost the treble in the encoder to compensate for the [severe] treble roll-off in typical AM tuners" Smile


 
 Return to top of page · Post #: 12 · Written at 5:19:50 AM on 24 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

The bandwidth of the AWA AM3 is 8.7kc (Wide mode) at -3db points.


 
 Return to top of page · Post #: 13 · Written at 10:07:49 PM on 24 January 2024.
NewVista's avatar
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

In the 90s I got a flagship Sansui TU-X1 tuner from ebay for FM DX'ing. It has Wide/Narrow modes for both FM & AM!
I had never tried its AM until I wanted to test it before selling and was shocked: it didn't work! I found out it had a blown IC--it used two of these National Semiconductor ICs for AM demod --one of the most complicated AM tuners but very low AM distortion of only 0.5%.

When fixed, its AM (in Wide mode) sounded like FM! It only had one special 455kc variable bandwidth IF coil that can not be purchased as a component. Its circuit & alignment are shown here: https://youtu.be/d01h0gk_owk?t=565


 
 Return to top of page · Post #: 14 · Written at 2:48:04 PM on 29 January 2024.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 830

QUOTE: The bandwidth of the AWA AM3 is 8.7kc (Wide mode) at -3db points.

Much wider and you'd start picking up out of town AM radio carriers.

I've modified the AM section of AM mono_FM stereo receivers (What stereo shops call those big boxes that contain a big audio amp, an AM/FM radio receiver, phono preamp. and input jacks for your CD player and such).
See my page https://www.wa2ise.com/netcom/Higher%20fidelity%20in%20AM%20radios.html#solidstate

This mod should allow you to hear most of what AM stations broadcast, about 8kHz of audio. However, this is for listening to strong local stations. If you go DXing distant stations, you may hear a fair amount of "monkey chatter" (frequency inverted human speech or music).


 
 Return to top of page · Post #: 15 · Written at 7:29:06 PM on 29 January 2024.
BringBackTheValve's Gravatar
 Location: Linton, VIC
 Member since 30 December 2016
 Member #: 2028
 Postcount: 472

Nice site, well presented as well as informative.

Good work Wa2ise.


 
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