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Digital AM receivers

V

vchimpanzee

I'm referring to an analog receiver which shows the 3- or 4-digit frequency in a display.

I wasn't at home or in the car, but I was close enough to a 1000-watt AM that I could pick it up with my "digital" car radio if the power lines weren't a problem. However, when I was at someone's house with what looked like a very sophisticated piece of equipment, I picked up almost nothing. I finally, FINALLY heard Sean Hannity, but I shouldn't have. I was looking for Paul Harvey.

Never mind. I just did a search for the man and found out where Hannity's nearest affiliate is. I can see the tower out of the window of where I was!
 
vchimpanzee said:
I'm referring to an analog receiver which shows the 3- or 4-digit frequency in a display.

I wasn't at home or in the car, but I was close enough to a 1000-watt AM that I could pick it up with my "digital" car radio if the power lines weren't a problem. However, when I was at someone's house with what looked like a very sophisticated piece of equipment, I picked up almost nothing. I finally, FINALLY heard Sean Hannity, but I shouldn't have. I was looking for Paul Harvey.

Never mind. I just did a search for the man and found out where Hannity's nearest affiliate is. I can see the tower out of the window of where I was!
Click to expand...

I'm not sure, what you are talking about, but do you mean an analog-tuned with digital display receiver ?
 
It sounds like an antenna issue. A bad antenna can ruin the performance of a sophisticated communications receiver - making it seem like a piece of junk.
 
rbrucecarter5 said:
It sounds like an antenna issue. A bad antenna can ruin the performance of a sophisticated communications receiver - making it seem like a piece of junk.
Click to expand...
My aunt was turning some square-looking device on the top. I don't know ... I thought I was hearing a station at 1270 AM.
 
700WLW said:
I'm not sure, what you are talking about, but do you mean an analog-tuned with digital display receiver ?
Click to expand...
Probably.

Anyway, I have the same thing in the car. This radio had FM as well.

In my car (I'll probably start a new thread for it) I want to listen to 98.3 but often end up getting what sounds like Charlie Bown's teachers coming from a very strong station at 98.1 which should never have been allowed to be so close to the station at 98.3.
 
Modern AM radios have no RF tuning ahead of the mixer. There is no way to keep strong signals from "walking through" the mixer.
It would be too expensive for manufacturers to put actual physical coils and capacitors (or shielding) into consumer radios, and
most folks don't live in the shadow of an AM tower, so they never know any better.
If this is a problem, just get a radio built before 1980 or so. They have actual physical tuning components, and some have RF pre-selector
stages before the mixer, so they are good for dx-ing, too.
The GE super-radios, I think, had RF preselector circuits. Maybe it would work for this situation.
 
My aunt was turning some square-looking device on the top. I don't know ... I thought I was hearing a station at 1270 AM.

Was it a large loop of wire? Your aunt may be utilizing a box loop antenna for AM. Those offer tremendous gain on the AM band, but have to be manually re-tuned every time you change stations. It would be very tough for even an expensive AM receiver with only a built in ferrite bar antenna to give the same level of performance. Loops larger than 2 feet will supercharge every AM radio near them! Loops 4 to 5 feet or larger are routinely able to capture AM stations 1000 miles away in the daytime - provided the transmitting station is high power. If you want more information on box loops, I can help you. I have a definitive page describing them. They are easy and inexpensive to make.
 
vchimpanzee said:
In my car (I'll probably start a new thread for it) I want to listen to 98.3 but often end up getting what sounds like Charlie Bown's teachers coming from a very strong station at 98.1 which should never have been allowed to be so close to the station at 98.3.
Click to expand...

This is a separate issue from your AM issue. As luck would have it, there IS a fix for your FM issue, but it involves a bit of soldering. Many of us have done a "narrow ceramic filter" modification to our radios to improve the selectivity. This is also one of those rare cases in electronics where it is entirely a "win-win" scenario, because it also really improves sensitivity, lowers noise, etc. The ONLY reason why receiver manufacturers don't do this is (1) the FCC in making stupid rules and (2) manufacturers don't want to match filters. The second reason is probably the main one.

I can help you with this, too, if you want. Incidentally, I had an identical situation when I lived in central Florida. A local 98.1 was slopping onto adjacent frequencies. After installing narrow ceramic filters, I could hear a 250 mile distant 98.3 without interference from the local 98.1.
 
I have a modded Sony ICF36 rig, with an added-on FM Atlas Elf2A SCA demodulator board. (I can go from main-channel FM and TV to SCA and SAP just by flipping a switch!)

Is there any way to set this up in my rig without screwing up the SCA section or reception?
 
rbrucecarter5 said:
My aunt was turning some square-looking device on the top. I don't know ... I thought I was hearing a station at 1270 AM.

Was it a large loop of wire? Your aunt may be utilizing a box loop antenna for AM. Those offer tremendous gain on the AM band, but have to be manually re-tuned every time you change stations. It would be very tough for even an expensive AM receiver with only a built in ferrite bar antenna to give the same level of performance. Loops larger than 2 feet will supercharge every AM radio near them! Loops 4 to 5 feet or larger are routinely able to capture AM stations 1000 miles away in the daytime - provided the transmitting station is high power. If you want more information on box loops, I can help you. I have a definitive page describing them. They are easy and inexpensive to make.
Click to expand...

Could you post your receiving AM loop antenna web page URL here? I'd love to try receiving a few distant AM Stereo stations with one.


-- Black Shire
 
MotoMuzak said:
I have a modded Sony ICF36 rig, with an added-on FM Atlas Elf2A SCA demodulator board. (I can go from main-channel FM and TV to SCA and SAP just by flipping a switch!)

Is there any way to set this up in my rig without screwing up the SCA section or reception?
Click to expand...

FM has +/- 75 kHz deviation, so you should be OK with 150 kHz ceramic filters. There is a possibility of degradation if you don't match the filters exactly, or use ones that statistically are under 150 kHz. Some people at fmtunerinfo.com sell matched filter sets so you don't have to match your own. I would not recommend 110 kHz filters in your case, because they would probably get rid of SCA.
 
Actually, matching is pretty easy. They are really high, not low impedance at resonance. The matching procedure is to take the inductive part partially back around towards the real axis on the Smith chart with a C in parallel, but not all the way. Next use a resistance in parallel with both the L and C to take the impedance to the 50 ohm circle. Then, put a capacitor in series with the loop, C, and R to go around the 50 ohm circle to land on the real impedance line and 50 ohm point on the Smith chart. Perfectly matched! There are usually several combinations of parallel C and R that work, the values get really critical if you try to get too close to the real axis initially. If you go to the real axis, you may have an antenna impedance (on the real axis) of several k (essentially infinite on the Smith chart).
 
Getting back to my original post on this thread, I drove past my aunt's house, and the tower of the Sean hannity station, and at no time did I lose the Paul Harvey station. I had interference from power lines and what I believed to be different stations on that frequency. The car radio also has the frequency displayed.
 
rbrucecarter5 said:
Actually, matching is pretty easy. They are really high, not low impedance at resonance. The matching procedure is to take the inductive part partially back around towards the real axis on the Smith chart with a C in parallel, but not all the way. Next use a resistance in parallel with both the L and C to take the impedance to the 50 ohm circle. Then, put a capacitor in series with the loop, C, and R to go around the 50 ohm circle to land on the real impedance line and 50 ohm point on the Smith chart. Perfectly matched! There are usually several combinations of parallel C and R that work, the values get really critical if you try to get too close to the real axis initially. If you go to the real axis, you may have an antenna impedance (on the real axis) of several k (essentially infinite on the Smith chart).
Click to expand...

I *think* I'm correctly picturing the schematic you're describing, but the Smith Chart is Greek to me...


-- Black Shire
 
rbrucecarter5 said:
It sounds like an antenna issue. A bad antenna can ruin the performance of a sophisticated communications receiver - making it seem like a piece of junk.
Click to expand...
Okay, I finally thought to ask today. I'm at the house where the radio is. My uncle put an antenna on the receiver that was used for something else. I could ask for specifics.
 
vchimpanzee said:
rbrucecarter5 said:
It sounds like an antenna issue. A bad antenna can ruin the performance of a sophisticated communications receiver - making it seem like a piece of junk.
Click to expand...
Okay, I finally thought to ask today. I'm at the house where the radio is. My uncle put an antenna on the receiver that was used for something else. I could ask for specifics.
Click to expand...
Correction. My aunt said my uncle put another antenna on there but the one that came with the receiver is on there now.

Anyway, it's a Panasonic SA-PM18 with quartz synthesizer tuner.
 
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