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Series-tuned antenna experiment (it works very well!)

J

JasonW

Guest
(NOTE: The following was an *experiment*--I don't advocate doing this for continuous Part 15 AM broadcasting except perhaps during emergency situations.)

Hello All,


While rummaging around early this morning I found a TalkingSign www.talkingsign.com transmitter that I had stashed away years ago. I had never been crazy about it because the modulation level is rather low (unlike with the Talking House www.talkinghouse.com , "line out" audio doesn't work well because it is too soft) and its audio sounds like a 3 kHz telephone line--muddy.

However, since the TalkingSign transmitter has a built-in RF ammeter to enable tuning the 3 meter wire antenna, I decided to experiment with using a longer antenna both with and without a variable capacitor in series between the antenna and the RCA antenna jack on the back of the transmitter.

I have a ~28 foot insulated #19 gauge wire antenna running around my ceiling, which includes an 8 foot vertical section that comes down to the floor. I first connected this antenna directly to the transmitter using a male RCA/female BNC adapter and a male BNC/binding posts adapter connected together. Using the TalkingSign's built-in antenna matching network variable capacitor, at my chosen frequency of 1600 kHz (carrier only) I was unable to get a good match--the RF ammeter needle never moved farther than about 20% of the way from zero. The transmitter's adjustable antenna matching network clearly wants to "see" a 3 meter antenna. (I briefly tried the unit's 3 meter wire antenna, and it easily tuned up with no problems.)

Next, I connected an AM radio receiver-type 160 pF variable capacitor in series between the TalkingSign and the ~28 foot wire antenna. At maximum capacitance, the RF ammeter tried to go violently "off the scale" when I adjusted the transmitter's built-in antenna matching network variable capacitor. Backing off the 160 pF variable capacitor by about 1/10th of a turn enabled me to obtain a perfect, "needle-gentle" match using the transmitter's variable capacitor. The longer antenna not only increased the radiated power (the signal didn't fade out past the end of the block [~250 feet] as it did with the 3 meter wire antenna), but the audio now sounds *much* better--as good as the Talking House. The longer antenna definitely has greater bandwidth than the supplied 3 meter wire antenna. -- JasonW
 
Just for giggles you should try a 2 inch diameter 10ft copper pipe in place of that 28ft wire. use the variable cap that you used in the previous setup and write back and let us know the results :)


> (NOTE: The following was an *experiment*--I don't advocate
> doing this for continuous Part 15 AM broadcasting except
> perhaps during emergency situations.)
>
> Hello All,
>
>
> While rummaging around early this morning I found a
> TalkingSign www.talkingsign.com transmitter that I had
> stashed away years ago. I had never been crazy about it
> because the modulation level is rather low (unlike with the
> Talking House www.talkinghouse.com , "line out" audio
> doesn't work well because it is too soft) and its audio
> sounds like a 3 kHz telephone line--muddy.
>
> However, since the TalkingSign transmitter has a built-in RF
> ammeter to enable tuning the 3 meter wire antenna, I decided
> to experiment with using a longer antenna both with and
> without a variable capacitor in series between the antenna
> and the RCA antenna jack on the back of the transmitter.
>
> I have a ~28 foot insulated #19 gauge wire antenna running
> around my ceiling, which includes an 8 foot vertical section
> that comes down to the floor. I first connected this
> antenna directly to the transmitter using a male RCA/female
> BNC adapter and a male BNC/binding posts adapter connected
> together. Using the TalkingSign's built-in antenna matching
> network variable capacitor, at my chosen frequency of 1600
> kHz (carrier only) I was unable to get a good match--the RF
> ammeter needle never moved farther than about 20% of the way
> from zero. The transmitter's adjustable antenna matching
> network clearly wants to "see" a 3 meter antenna. (I
> briefly tried the unit's 3 meter wire antenna, and it easily
> tuned up with no problems.)
>
> Next, I connected an AM radio receiver-type 160 pF variable
> capacitor in series between the TalkingSign and the ~28 foot
> wire antenna. At maximum capacitance, the RF ammeter tried
> to go violently "off the scale" when I adjusted the
> transmitter's built-in antenna matching network variable
> capacitor. Backing off the 160 pF variable capacitor by
> about 1/10th of a turn enabled me to obtain a perfect,
> "needle-gentle" match using the transmitter's variable
> capacitor. The longer antenna not only increased the
> radiated power (the signal didn't fade out past the end of
> the block [~250 feet] as it did with the 3 meter wire
> antenna), but the audio now sounds *much* better--as good as
> the Talking House. The longer antenna definitely has
> greater bandwidth than the supplied 3 meter wire antenna.
> -- JasonW
>
<P ID="signature">______________
Oldies 1610 AM Stereo

"Proud User of Chris Cuff's Alfredo Lite 100mw"

http://www.part15.us
Largest Part 15 Website in the World</P><P ID="edit"><FONT class="small">Edited by easthill on 03/01/06 09:39 PM.</FONT></P>
 
I think a "fat" 3.05 meter antenna like that would tune up perfectly without using the 'extra' 160 pF variable capacitor, but its increased bandwidth would almost certainly make the audio sound better than the supplied 3 meter wire antenna.

Using a 10' tall stack of electrically-connected 55-gallon oil drums as an antenna--now *that* would be the ultimate broad-banded Part 15 AM antenna! :) -- JasonW

> Just for giggles you should try a 2 inch diameter 10ft
> copper pipe in place of that 28ft wire. use the variable cap
> that you used in the previous setup and write back and let
> us know the results :)
>
>
> > (NOTE: The following was an *experiment*--I don't advocate
>
> > doing this for continuous Part 15 AM broadcasting except
> > perhaps during emergency situations.)
> >
> > Hello All,
> >
> >
> > While rummaging around early this morning I found a
> > TalkingSign www.talkingsign.com transmitter that I had
> > stashed away years ago. I had never been crazy about it
> > because the modulation level is rather low (unlike with
> the
> > Talking House www.talkinghouse.com , "line out" audio
> > doesn't work well because it is too soft) and its audio
> > sounds like a 3 kHz telephone line--muddy.
> >
> > However, since the TalkingSign transmitter has a built-in
> RF
> > ammeter to enable tuning the 3 meter wire antenna, I
> decided
> > to experiment with using a longer antenna both with and
> > without a variable capacitor in series between the antenna
>
> > and the RCA antenna jack on the back of the transmitter.
> >
> > I have a ~28 foot insulated #19 gauge wire antenna running
>
> > around my ceiling, which includes an 8 foot vertical
> section
> > that comes down to the floor. I first connected this
> > antenna directly to the transmitter using a male
> RCA/female
> > BNC adapter and a male BNC/binding posts adapter connected
>
> > together. Using the TalkingSign's built-in antenna
> matching
> > network variable capacitor, at my chosen frequency of 1600
>
> > kHz (carrier only) I was unable to get a good match--the
> RF
> > ammeter needle never moved farther than about 20% of the
> way
> > from zero. The transmitter's adjustable antenna matching
> > network clearly wants to "see" a 3 meter antenna. (I
> > briefly tried the unit's 3 meter wire antenna, and it
> easily
> > tuned up with no problems.)
> >
> > Next, I connected an AM radio receiver-type 160 pF
> variable
> > capacitor in series between the TalkingSign and the ~28
> foot
> > wire antenna. At maximum capacitance, the RF ammeter
> tried
> > to go violently "off the scale" when I adjusted the
> > transmitter's built-in antenna matching network variable
> > capacitor. Backing off the 160 pF variable capacitor by
> > about 1/10th of a turn enabled me to obtain a perfect,
> > "needle-gentle" match using the transmitter's variable
> > capacitor. The longer antenna not only increased the
> > radiated power (the signal didn't fade out past the end of
>
> > the block [~250 feet] as it did with the 3 meter wire
> > antenna), but the audio now sounds *much* better--as good
> as
> > the Talking House. The longer antenna definitely has
> > greater bandwidth than the supplied 3 meter wire antenna.
>
> > -- JasonW
> >
>
 
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