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 Post subject: How to build an AM antenna optimized for a single frequency?
PostPosted: Sep Sat 11, 2021 10:46 pm 
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Joined: Jun Fri 26, 2020 9:35 pm
Posts: 76
Location: 98020
Hello-

Hockey season is just about to start and I will be enjoying all the away games of my favorite team (Everett Silvertips!) via radio broadcast. I live in an area that makes reception of the station broadcasting their games rather difficult after dark, regardless of the antenna I use. There is a long-wire antenna strung up in my attic, I've tried a C. Crane powered antenna, I have the Grundig AN-200 tunable loop, and I have the special powered type that used to be built by a guy in Florida until he passed away last year. All of these can have trouble at times with providing good reception for this station.

But I also wondered if the fact that these are all designed to cover the whole broadcast band might limit how well they work for each particular frequency. It begs the question: can an antenna be designed and built that would optimize reception of a single frequency? All these other antennas work great for everything else I care to listen to, but ideally I'd like to build one that will really do the best possible job for just the one particular frequency. This happens to be 1380KC.

So, confessing that antenna-design is essentially black-magic to me, how would I go about designing an antenna that will be optimal for 1380KC? Is this something that could really work, or just a silly fantasy?

Thank you and best regards-

Troy
Edmonds, WA


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sat 11, 2021 11:23 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
Normally 1/4 wavelength antennas are used. Find the wavelength of your frequency, google frequency wavelength calculator, and then use a piece of wire 1/4 wavelength long for your reception. It should be ideally going up or vertical. But it's gonna be more than 120 feet long, just an approximation. It will also pick up noise and interference, not practical.

Or

Build an active whip antenna and use a band pass filter at its output to select your particular frequency of interest. No need of a long wire 1/4 wavelength antenna. Circuit of active whip antenna attached.


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Last edited by Dare4444 on Sep Sat 11, 2021 11:41 pm, edited 3 times in total.
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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sat 11, 2021 11:36 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
https://rf-tools.com/lc-filter/

Then connect this band pass filter between your receiver and active antenna's output port. I chose center frequency = 1380KHz and Bandwidth 1360 - 1400 KHz. Files attached. Use readymade 4.7uH axial inductors. You'll have clean reception of 1380KHz.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sat 11, 2021 11:50 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
Active antennas...


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 12:13 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 799
Location: Colorado Springs, CO 80917
Quote:
I live in an area that makes reception of the station broadcasting their games rather difficult after dark, regardless of the antenna I use.

This may be an important clue, I think. I see you're in Edmonds, WA. Where is the station transmitter you want to listen to? The distance & night time propagation may be the issue. Building or buying a complicated active amplified antenna may not be a cure-all (and given that you've tried a few already) for propagation.

EDIT:
Here's part of the problem. His location is ~220 deg azimuth from radio station KRKO. They're 50kW day & night but at sunset they go to a directional antenna beaming ~110 deg with reported beamwidth of 20 deg. That puts him ~110 deg off of pattern boresight.

Looking at the FCC's pattern data I guess the signal in his direction drops 14dB or so when the antennas are switched - not including day/night propagation effects. There also appears to be mountains along the line of sight between his place & the station.

Unfortunately we don't know the orientation of his attic long wire. It might be suboptimal for the KRKO station direction, too. Seems like a combo of the longwire + a tuned pre-amp might be a good experiment.


Last edited by hwhall on Sep Sun 12, 2021 1:26 am, edited 2 times in total.

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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 12:22 am 
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Joined: Sep Wed 03, 2014 11:06 pm
Posts: 328
Location: Poulsbo, Wa
1380 in that part of seattle is flame thrower KRKO (50k watts). I can get them in poulsbo roughly 27 miles NE of me
with only a dipole. You must be in one very deep valley. I use a EWE antenna to focus (very narrow lobe) what i get
and gets rid of a lot of noise.

Not sure it would work in your situation...but KRKO is LOUD and CLEAR here with mine.

Bill

I also built a larger tunable loop then the grundig 200 i have and you will see much more reception from it. Not nearly as much as long wire or EWE though.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 12:50 am 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 5183
Location: Tucson, Arizona U.S.A.
soloapollo wrote:
Hello-

Hockey season is just about to start and I will be enjoying all the away games of my favorite team (Everett Silvertips!) via radio broadcast. I live in an area that makes reception of the station broadcasting their games rather difficult after dark, regardless of the antenna I use. There is a long-wire antenna strung up in my attic, I've tried a C. Crane powered antenna, I have the Grundig AN-200 tunable loop, and I have the special powered type that used to be built by a guy in Florida until he passed away last year. All of these can have trouble at times with providing good reception for this station.

But I also wondered if the fact that these are all designed to cover the whole broadcast band might limit how well they work for each particular frequency. It begs the question: can an antenna be designed and built that would optimize reception of a single frequency? All these other antennas work great for everything else I care to listen to, but ideally I'd like to build one that will really do the best possible job for just the one particular frequency. This happens to be 1380KC.

So, confessing that antenna-design is essentially black-magic to me, how would I go about designing an antenna that will be optimal for 1380KC? Is this something that could really work, or just a silly fantasy?

Thank you and best regards-

Troy
Edmonds, WA

Is this the only thing you want to hear from this station? If so, check if they have an internet broadcast. That would solve the problem quite nicely.

It sounds like you already have a nice selection of good antennas. Other than building a vertical Yagi pointed at the station (do you have enough land for that?) the internet sounds like your only choice. I suppose you could read about the game in the next day's paper though (not quite the same).

_________________
Jim Mueller

Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 1:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 39559
Location: SoCal, 91387
poulsbobill wrote:
1380 in that part of seattle is flame thrower KRKO (50k watts). I can get them in poulsbo roughly 27 miles NE of me
with only a dipole. You must be in one very deep valley. I use a EWE antenna to focus (very narrow lobe) what i get
and gets rid of a lot of noise.

Not sure it would work in your situation...but KRKO is LOUD and CLEAR here with mine.

Bill

Easiest solution is just to move in with Bill! :wink:


poulsbobill wrote:
I also built a larger tunable loop then the grundig 200 i have and you will see much more reception from it. Not nearly as much as long wire or EWE though.

I built a 23 inch diameter tunable loop, and it's RF gain is equal to the 240 foot random length long wire on my back acre. In addition, I can angle it to null interference or increase gain, something I can't do with the long wire.

DX can fade in and out, and it matters not what antenna you use; the signal is either gonna be there, or unintelligible, and that can change by the minute.

I would recommend a tunable loop, larger of course than the Grundig, one of which I also have. Here's a link to my construction thread;
https://www.antiqueradios.com/forums/vi ... 4#p2024254

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 1:44 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 799
Location: Colorado Springs, CO 80917
poulsbobill,
You seem to be on an azimuth from the station where the line of sight is largely over water & what looks like lowlying land, whereas the OP seems to have some mountains in his line of sight. You probably get a little more signal strength, but I think I'd agree that if the OP is going to use a loop it needs to be a lot larger than the Grundig.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 5:52 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2831
Location: Saskatoon
The easy solution involves no antenna at all. Just stream it online:
https://tunein.com/radio/Everetts-Great ... 80-s35018/
:)


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 6:24 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 799
Location: Colorado Springs, CO 80917
Quote:
The easy solution involves no antenna at all. Just stream it online:


No, that's the solution to, "How can I hear their audio vibration?"
The problem is how to build an antenna to pull in that radio station.
They want to play a _radio._
Not pretend it's radio.
And become like Marconi again
So they've taken The Path of Pain.
"You need more antenna wire!"
"But, it's _wireless,_ sire."
:D


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 8:03 am 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 1485
Location: Montreal, Quebec
At those frequencies, most "long wires" aren't. So you won't be able to match the antenna to frequency..

A loop has the advantage of you can aimit. And since it's tuneable, it does match the frequency. A bigger loop would beat a small loop.

Active antennas won't help. They are more like a probe, and you still have a small antenna. They function like tube era car radios, coupling to the too of a tuned circuit, where the imledance is really high. Some shortwave portables have an active antenna built in.

A big yagi is way too big at that frequency, even if the issue isdkrectionality.

Nothing's said abiut the radio. Some will be better than others, thiugh that seems less tye case here, when it's a signal in the wrong lication.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 8:56 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 799
Location: Colorado Springs, CO 80917
mblack, good points. I wonder if it would be worthwhile to lash together a little antenna tuner & see if that might increase the signal usefully.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 10:14 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
10dB gain booster for MW band.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 10:24 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
Loop antenna 0.5 to 30MHz with gain. This looks interesting!

https://www.lz1aq.signacor.com/docs/wsm ... ntenna.htm


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 10:36 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 799
Location: Colorado Springs, CO 80917
I noticed none of those preamps have any front end tuning (or even middle or back end). Couldn't a strong local station (or maybe even noise source) could cause some problems? I note that nearly all the ham radio designs I'd ever seen had some tuning but these designs seem more like consumer grade stuff (e.g., "the user isn't smart enough to peak up the desired station, just put an on-off switch & an LED on it").

In "10dB gain booster for MW band" schematic, it seems really odd that they seem to have at C1 a 1uF 400V cap (electrolytic? It's polarized it seems) coupling RF from the antenna. Maybe a typo? But then there's C2 at 0.33uF that also seems more like an audio frequency coupling value than RF. The CON3 output to the served radio set is only 33pF. Why such "fat caps" on the way into T1 but only a skinny one on the way out? The other schematics only have a few 100 pF for input coupling caps.


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 11:34 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
hwhall wrote:
I noticed none of those preamps have any front end tuning (or even middle or back end). Couldn't a strong local station (or maybe even noise source) could cause some problems? I note that nearly all the ham radio designs I'd ever seen had some tuning but these designs seem more like consumer grade stuff (e.g., "the user isn't smart enough to peak up the desired station, just put an on-off switch & an LED on it").

In "10dB gain booster for MW band" schematic, it seems really odd that they seem to have at C1 a 1uF 400V cap (electrolytic? It's polarized it seems) coupling RF from the antenna. Maybe a typo? But then there's C2 at 0.33uF that also seems more like an audio frequency coupling value than RF. The CON3 output to the served radio set is only 33pF. Why such "fat caps" on the way into T1 but only a skinny one on the way out? The other schematics only have a few 100 pF for input coupling caps.


Full article here

https://www.electronicsforu.com/electro ... -am-radios

It's from a Russian designer. I feel that active antenna followed by a narrow BPF using 4.7uH coil given above by me is the way to go. Fc is exactly 1380KHz and Bw is 40KHz. It's a very narrow filter!

The loop antenna with preamp presented above is also a good idea. Simply connect its output to BPF. Current is 39ma through each 2n2222 so it won't overload by input signals.


Last edited by Dare4444 on Sep Sun 12, 2021 12:04 pm, edited 1 time in total.

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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 11:45 am 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
See the narrow response. It should filter out the 1380KHz


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 12:04 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
The active whip. Performance is similar to a half wave dipole!


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 Post subject: Re: How to build an AM antenna optimized for a single freque
PostPosted: Sep Sun 12, 2021 12:10 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 796
Improved version. This + band pass filter = pure 1380KHz signal to your receiver. There are no shortcuts in life.


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