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Locked Quick and easy AM broadcast antenna

 

THE STORY:
I bought a new Sharp compact stereo and the AM reception is worse than horrible with the supplied 8-loops-of-wire-on-a-plastic-form "AM antenna." My 20 year old Aiwa that I replaced had the same exact plastic antenna but with 6 loops of wire.

I went to Goodwill and bought a $3.99 clock radio thinking I'd take the ferrite rod antenna out, wrap some wire around it, and voila, plug it in as an external antenna. While looking closely inside, I see that the ferrite rod is actually connected to the tuning capacitor and is part of a resonate circuit so I put the the radio back together, checked it for working again, and I'll use the in-store credit to buy a shirt.

GETTING CLOSE TO THE QUESTION:
Last night I got on Ebay and found 200' of 10/46 Litz wire for $7 and ordered it.? This hair-brained idea is to wind the small Litz wire on the stock wire - loop form and get better reception (more turns is better, right?)

THE QUESTION:
Can I use 200' of small Litz wire, when it arrives, in place of the supplied antenna of the short 8 wire loop and get better AM reception? I really don't want to have an antenna that I have to tune with an external capacitor.? Of course I'm OK with spinning it around to adjust for maximum signal.

Thanks in advance.
 

On 12/8/2014 8:32 AM, Gordon Quickstad ceeohtoo@... [loopantennas] wrote:
THE STORY:
I bought a new Sharp compact stereo and the AM reception is worse than
horrible with the supplied 8-loops-of-wire-on-a-plastic-form "AM
antenna." My 20 year old Aiwa that I replaced had the same exact plastic
antenna but with 6 loops of wire.
How do you know the antenna is at fault? What specifically
is the problem with reception? "Modern" AM tuners are of
the "tuner on a chip" variety, and the newer designs eschoo
passives so the whole tuner is indeed on the chip. This
results in inferior performance to older designs.

I think you answered your own question. The 20 year old
Aiwa has the same antenna (except for the unimportant detail
of the number of turns) and works great.

Both the historical GE Superradio's and the current ones use
ferrite rod antennas. But the electronics in the current ones
are junk.

If your only problem with the Sharp is insufficient sensitivity,
simply replace the supplied loop with a larger one with fewer
turns to maintain the inductance. Doubling the size will
magically give you 6 dB more signal.

Rick N6RK
 

Thanks for the help.

To expand a little, the problem is poor signal to noise ratio on (probably) all stations. ?Other old discrete electronics portable radios that I own in the same location pull in the stations clearly with their ferrite antennae. ?I bought the Litz wire because I'm thinking that using low-loss Litz wire on the stock antenna form, and lots of turns, will help. ?I didn't know that using a physically larger loop would give 6db in itself. ?Yes, you're right, both the AM and FM electronics on the radio are in a very small shielded enclosure right where the antennas plug into in back and it's about "chip" sized (I saw it when I had to fix the CD changer on the newly purchased system because A. I'm mechanically inclined and B. don't like waiting for repairs, so I took the risk and broke the warranty and went inside with success but no future warranty).

Shouldn't just using more turns on the stock form intercept more signal and improve the SNR? ?And how about more turns AND also changing to a larger antenna form to wind turns on? ?Since it's a shelf stereo, I'm size limited on space for spinning the antenna around to the best reception.?

There are some neat talk programs on AM because air time is so cheap so I do like to break away from the typical FM fare but can't stand just 50% signal with 50% static noise which I currently have.
 

Increasing the number of turns increases signal VOLTAGE
but also increases inductance. If the radio electronics
are resonating out the inductance, you don't want to mess
with the value of inductance. (If the radio electronics
are NOT resonating out the inductance, no wonder you have
such poor sensitivity). If you double the diameter, but
use 70.7% as many turns the inductance will remain the
same. You can also make the loop taller but not wider.
This will still give you more pickup area but will not
exceed the space behind the radio.

Rick N6RK

On 12/8/2014 10:57 AM, ceeohtoo@... [loopantennas] wrote:

Shoul! dn't just using more turns on the stock form intercept more
signal and improve the SNR? And how about more turns AND also changing
to a larger antenna form to wind turns on? Since it's a shelf stereo,
I'm size limited on space for spinning the antenna around to the best
reception.
 

I had the same problem with a $150 Sony stereo. The AM reception is really terrible. I live east of Los Angeles and the AM band is chock full of stations but the stereo will hardly pick up any except the 50000 watters. Also it acts like there is no AGC. High power stations like KFI come in only fair and weaker ones like 10000 watts are too poor and noisy to listen to. The volume must be turned up high to hear them like the 50 kW stations. Then you have to remember to back down the volume before changing stations.

Anyway I "solved" it with an external outside active antenna. But I was still not happy. The no AGC problem bugged me so I now use a $100 Drake PRN 1000 100 kHz - 30 mHz SW AM only receiver with the active antenna and feed the audio to the "portable" input.

You can use the extra little loop to couple another antenna with some wire connected to it to your rx by placing the two loops close together and changing the orientation for best reception. Maybe that will help without spending a bunch of $$$.



Don KPC6NDB
Upland, CA
34.10 -117.63 1250ft
FRG-100B FunCube Dongle Pro+
ICF2010 Perseusx3 WR-G31DDC
R70 R71A w/250Hz R75x2 w/250Hz
SDR-IQ SPR-4 SSR-1
SR-AF & LPF DSP599zx MFJ-784B
HD-1418 AF-1 MSB-1
PA0RDT Mini-Whipx2 @ 25ft
RYO Active Antenna @ 25ft
ALA100Lx2 Z1501F @20ft w/9ft Whip
Solarcon A-99

On 08-Dec-14 08:32, Gordon Quickstad ceeohtoo@... [loopantennas] wrote:


THE STORY:
I bought a new Sharp compact stereo and the AM reception is worse than
horrible with the supplied 8-loops-of-wire-on-a-plastic-form "AM
antenna." My 20 year old Aiwa that I replaced had the same exact plastic
antenna but with 6 loops of wire.

I went to Goodwill and bought a $3.99 clock radio thinking I'd take the
ferrite rod antenna out, wrap some wire around it, and voila, plug it in
as an external antenna. While looking closely inside, I see that the
ferrite rod is actually connected to the tuning capacitor and is part of
a resonate circuit so I put the the radio back together, checked it for
working again, and I'll use the in-store credit to buy a shirt.

GETTING CLOSE TO THE QUESTION:
Last night I got on Ebay and found 200' of 10/46 Litz wire for $7 and
ordered it. This hair-brained idea is to wind the small Litz wire on
the stock wire - loop form and get better reception (more turns is
better, right?)

THE QUESTION:
Can I use 200' of small Litz wire, when it arrives, in place of the
supplied antenna of the short 8 wire loop and get better AM reception? I
really don't want to have an antenna that I have to tune with an
external capacitor. Of course I'm OK with spinning it around to adjust
for maximum signal.

Thanks in advance.
 

¿ªÔÆÌåÓý

Assuming this is a typical digital AM receiver, the original ferrite "loop" antenna is untuned and feeds an FET RF amplifier as a broadband antenna.? That's why it's not particularly sensitive.? Good results can be obtained winding about 5 turns of hook-up wire around the existing coil (no direct connection) to serve as an inductively-coupled pickup.? The ends of the added pick-up coil can then be used as the connection point for a simple dipole or another loop.? A long wire can be connected to one lead of the added pick-up coil, but the remaining lead should be grounded.

Regards,

Dexter

On 12/8/2014 11:32 AM, Gordon Quickstad ceeohtoo@... [loopantennas] wrote:

?
THE STORY:
I bought a new Sharp compact stereo and the AM reception is worse than horrible with the supplied 8-loops-of-wire-on-a-plastic-form "AM antenna." My 20 year old Aiwa that I replaced had the same exact plastic antenna but with 6 loops of wire.

I went to Goodwill and bought a $3.99 clock radio thinking I'd take the ferrite rod antenna out, wrap some wire around it, and voila, plug it in as an external antenna. While looking closely inside, I see that the ferrite rod is actually connected to the tuning capacitor and is part of a resonate circuit so I put the the radio back together, checked it for working again, and I'll use the in-store credit to buy a shirt.

GETTING CLOSE TO THE QUESTION:
Last night I got on Ebay and found 200' of 10/46 Litz wire for $7 and ordered it.? This hair-brained idea is to wind the small Litz wire on the stock wire - loop form and get better reception (more turns is better, right?)

THE QUESTION:
Can I use 200' of small Litz wire, when it arrives, in place of the supplied antenna of the short 8 wire loop and get better AM reception? I really don't want to have an antenna that I have to tune with an external capacitor.? Of course I'm OK with spinning it around to adjust for maximum signal.

Thanks in advance.
 

One more thing that was implied but not stated:
The radio will pick up most efficiently at resonance, which requires both the inductance and the capacitance of the final (tuned circuit+antenna system) to be matched {Fr = 1/(2*pi*sqrt(L*C))}. If you increase the inductance of the antenna beyond the range of the variable capacitor (either external or internal varactor) you don't buy yourself anything except worse performance (the loop will act as a pre-selector and mute the signal of interest). Make sure you keep the inductance of the antenna system roughly the same, which means as stated earlier in this thread increasing the area enclosed by the loop if you increase the number of turns. Inductance increases roughly by the square of the number of turns so you need to increase the area accordingly (as stated earlier in the thread).

73s,
Bob Cavanaugh - AG6YK


On Monday, December 8, 2014 11:12 AM, "'Richard (Rick) Karlquist' richard@... [loopantennas]" wrote:


?
Increasing the number of turns increases signal VOLTAGE
but also increases inductance. If the radio electronics
are resonating out the inductance, you don't want to mess
with the value of inductance. (If the radio electronics
are NOT resonating out the inductance, no wonder you have
such poor sensitivity). If you double the diameter, but
use 70.7% as many turns the inductance will remain the
same. You can also make the loop taller but not wider.
This will still give you more pickup area but will not
exceed the space behind the radio.

Rick N6RK

On 12/8/2014 10:57 AM, ceeohtoo@... [loopantennas] wrote:
>
> Shoul! dn't just using more turns on the stock form intercept more
> signal and improve the SNR? And how about more turns AND also changing
> to a larger antenna form to wind turns on? Since it's a shelf stereo,
> I'm size limited on space for spinning the antenna around to the best
> reception.

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