MW Attic Antenna Options

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Fizz306

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Hello all,

I've become fascinated in listening to far off AM stations, as many of you have. I'm currently using a slinky antenna in the attic, fed with 50 ohm RG-58 and an ugly-balun, and I'm looking for a reasonably cheap upgrade to this specifically for LF/MF listening.

I'd prefer something that is coax fed, and since it will be placed in the attic, I'm not all that interested in a loop antenna. At this point, I'm thinking it would be a longwire antenna, but I've yet to find any good plans on the net that cover this type of antenna specifically for AM reception.

I'll shortly be building and installing a multiband dipole after upgrading to my general, to start to get into HF. It'll be a 40-20-17-10 multiband, but I would imagine that I'll be able to do better with LF/MF (receive only) using some sort of longwire in the attic.

Does anyone here have plans, or are aware of plans on the internet, that lay out longwire attic antennas, coax termination, etc. for AM-based applications?

Your opinions are greatly appreciated!

Rob
 

zz0468

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Since an attic space is too small for anything that would qualify as a "long wire", and you're not interested in a loop, I'd suggest that you look into active antennas. Designed and built properly, they can rival a true longwire , and don't bring in as much noise.

Why not consider a loop? That would be ideal for what you're trying to do.
 

n3ouc

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I was going to say the same in that why not try a loop. If you have an attic large enough to install a multiband dipole, a loop running along the entire inside wall area of the attic would probably work well. Get a 4 to 1 balun and use some rg6 or rg59 75 ohm coax and you should be set to go..
 

WA0CBW

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Just an FYI but an antenna doesn't know the difference between digital, analog, fm, SSB, CW etc. For a simple receive antenna string a wire from one of the attic to the other and connect it to your radio with a piece of coax.
BB
 

Fizz306

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Just an FYI but an antenna doesn't know the difference between digital, analog, fm, SSB, CW etc. For a simple receive antenna string a wire from one of the attic to the other and connect it to your radio with a piece of coax.
BB


Thanks for the input everyone. And yes, I am aware that the antenna doesn't differentiate between different forms modulation. I was referring to AM meaning the broadcast band, not the modulation.

A little more background. This antenna's sole purpose will be AM band reception. ~500 kHz thorough ~1700 kHz. This is why I was thinking about a longwire in the attic, like attaching 300 feet of small gauge wire along the rafters. The attic runs about 40 feet long and 20 feet wide.

Due to fencing and structural layout, I cannot string 300 feet of wire around the property a la longwire. I do have a large oak tree branch (90+ feet tall) directly above the chimney-mounted mast. This 75ish foot vertical longwire is an option, but not particularly cost effective considering the need for an additional lightning arrester (~$60) and grounding supplies.

I have also looked at and considered options like:

AM-DX.COM - Large Ferrite Loop

AM-DX.COM - Antenna Overview

And it's my understanding that this was a loop design. I can't imagine practical for an attic install considering the need for frequent manual intervention:

http://www.benlo.com/ham/uz-8dx-1.jpg


I feel I'm in with n3ouc on this compromise vs. convenience design. Easy enough to build a choke, and just run a few hundred feet of wire around the attic perimeter a few times. Anyone have experience with this concept they would be willing to share?
 

zz0468

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...Easy enough to build a choke, and just run a few hundred feet of wire around the attic perimeter a few times. Anyone have experience with this concept they would be willing to share?

As a non-resonant loop, it will pick up signals, and probably be relatively low in noise pickup. If you have the ability to tune it, the voltage delivered to the receiver will be substantially higher.

It's cheap, it's easy, and if you're not happy with it, you can change it cheaply and easily. Start with one turn, and see what happens when you add another. Predicting results in any particular installation would be close to impossible. At some point, while adding more turns, it becomes just a random hunk of metal, which may or may not behave as an effective antenna.
 

Fizz306

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As a non-resonant loop, it will pick up signals, and probably be relatively low in noise pickup. If you have the ability to tune it, the voltage delivered to the receiver will be substantially higher.

It's cheap, it's easy, and if you're not happy with it, you can change it cheaply and easily. Start with one turn, and see what happens when you add another. Predicting results in any particular installation would be close to impossible. At some point, while adding more turns, it becomes just a random hunk of metal, which may or may not behave as an effective antenna.

All of the antenna analyzers and tuners that I'm considering are for amateur HF operations, and really only go down to 1.8 mHz. Obviously I could cut an antenna to be resonant, but man-oh-man, that'd come to about 670 feet for a 700 kHz center. Probably unrealistic for an attic deployment.

Thanks for the insight, I'm looking forward to playing around with this over the next few months and seeing what happens. I'll be sure to touch back and let everyone know my results...

Rob
 

k9rzz

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May I suggest using a simple phasing circuit to combine your two antennas for REAL versatility. It appears to be a lost art in this 'high tech' day (pfffft!), I use RLC circuits but check out this super simple set up: Simple Phasing System

Check out the other articles on that site too, like the audio phasing, which sounds really neat!
 

Fizz306

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May I suggest using a simple phasing circuit to combine your two antennas for REAL versatility. It appears to be a lost art in this 'high tech' day (pfffft!), I use RLC circuits but check out this super simple set up: Simple Phasing System

I do remember reading a post by you (I believe) talking about how you phased a vertical and a horizontal long wire to attenuate high-angle skips and focus on low-angle receiving closer to the horizion. Thanks for the link, I'll be sure to look into it.

When you say combine two antennas, are you referring to the multiband dipole I plan on installing? Or more along the lines of the long wire in the attic coupled with a long wire vertical suspended in the trees above the house?

Another thing to note is that I do have an old GE SuperRadio that I could pull the ferrite rod out of...

Thanks for the insight and explanation as I'm just starting to develop a knowledge base in antennas!
 

Boombox

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I guess I'm suggesting the obvious here, but unless you have an actual 'longwire' (by my definition it would be at least 100 ft. or more), or an outdoor 'Wellbrook or similar antenna, your best option for long distance AM band listening is a loop. Just sayin'.....

Most MW DXers I know of (including myself) who don't use long outdoor antennas use loops. They're fairly compact, can be built rather cheaply, and you could put that Superadio to better use DXing with it, rather then using its loopstick as a part for something that may not give you better performance than a Superadio and loop will give you on MW.

Part of the reason for using a loop (aside from it's cheap cost, compactness, and performance) is that it is directional, and to seriously DX the AM band one needs a way to null out stations, something that just isn't done with a fixed antenna without phasing equipment.

Maybe you could buy or build a Wellbrook and put it in your attic. There are guys that swear by those antennas....

FWIW, you can DX the AM band on shorter or moderate length wires if you've got the receiver to pull in the signals (which it sounds like you do). You just can't null out stations. So anything you put up in your attic will DX, it's just that if you really want to get into MW DX a loop or some sort of directional antenna is a preferable way to go.

Either way, good luck with MW DX. It can be a real fun hobby.
 

Fizz306

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I guess I'm suggesting the obvious here, but unless you have an actual 'longwire' (by my definition it would be at least 100 ft. or more), or an outdoor 'Wellbrook or similar antenna, your best option for long distance AM band listening is a loop. Just sayin'.....

Most MW DXers I know of (including myself) who don't use long outdoor antennas use loops. They're fairly compact, can be built rather cheaply, and you could put that Superadio to better use DXing with it, rather then using its loopstick as a part for something that may not give you better performance than a Superadio and loop will give you on MW.

Part of the reason for using a loop (aside from it's cheap cost, compactness, and performance) is that it is directional, and to seriously DX the AM band one needs a way to null out stations, something that just isn't done with a fixed antenna without phasing equipment.

Maybe you could buy or build a Wellbrook and put it in your attic. There are guys that swear by those antennas....

FWIW, you can DX the AM band on shorter or moderate length wires if you've got the receiver to pull in the signals (which it sounds like you do). You just can't null out stations. So anything you put up in your attic will DX, it's just that if you really want to get into MW DX a loop or some sort of directional antenna is a preferable way to go.

Either way, good luck with MW DX. It can be a real fun hobby.

Thanks, Boombox.

While I would love one of these:

Active Loop ALA1530S+ Imperium

After factoring in shipping, along with a rotor for the attic and we're getting close to $500 USD.

I'm focusing most of my money at this point on my ham equipment (IC-7100, AT, SWR meter, etc.), which is primarily why I'm really trying to find something cheap and easy to play with while I work up my MW DX chops.

An active loop like that is certainly something on my to-buy list, but not for a while at this point.

I can easily fit a few hundred feet of wire in the attic a la open loop style:

http://easyweb.easynet.co.uk/~msdawson/62matticopenloop.jpg
 

Token

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A little more background. This antenna's sole purpose will be AM band reception. ~500 kHz thorough ~1700 kHz. This is why I was thinking about a longwire in the attic, like attaching 300 feet of small gauge wire along the rafters. The attic runs about 40 feet long and 20 feet wide.

Due to fencing and structural layout, I cannot string 300 feet of wire around the property a la longwire. I do have a large oak tree branch (90+ feet tall) directly above the chimney-mounted mast. This 75ish foot vertical longwire is an option, but not particularly cost effective considering the need for an additional lightning arrester (~$60) and grounding supplies.

I think you mean a random wire antenna, not a longwire antenna. A Longwire is, by definition, one wavelength or longer at the lowest frequency of interest. So we would be talking 1900'ish feet for the AM BCB band.

I know you are shying away from an active loop like the Pixel Pro or the Wellbrook, primarily because of cost. However, a loop is a killer tool on MW. If one of the prebuilts are not in the cards, how about a home brew mag loop and a cheap rotor in the attic?

T!
 

zz0468

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...If one of the prebuilts are not in the cards, how about a home brew mag loop and a cheap rotor in the attic?

The loopstick antenna from a portable AM radio would be cheap, easy, and work quite well.
 

Fizz306

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I think you mean a random wire antenna, not a longwire antenna. A Longwire is, by definition, one wavelength or longer at the lowest frequency of interest. So we would be talking 1900'ish feet for the AM BCB band.

I know you are shying away from an active loop like the Pixel Pro or the Wellbrook, primarily because of cost. However, a loop is a killer tool on MW. If one of the prebuilts are not in the cards, how about a home brew mag loop and a cheap rotor in the attic?

T!

Thanks for the clarification, as I do mean a random wire.

A home brew mag loop sounds like fun and would be a neat weekend project for sure, but how would I get around having it in the attic when it comes to tuning the capacitor?
 

Boombox

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Thanks for the clarification, as I do mean a random wire.

A home brew mag loop sounds like fun and would be a neat weekend project for sure, but how would I get around having it in the attic when it comes to tuning the capacitor?

There's a guy on another forum who worked out a remote tuning control for a loop that's home built but is basically an outdoor MW box loop, mounted on a pole on his roof. I think he used a small motor and attached it to the tuning control.
 

Fizz306

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There's a guy on another forum who worked out a remote tuning control for a loop that's home built but is basically an outdoor MW box loop, mounted on a pole on his roof. I think he used a small motor and attached it to the tuning control.

I'll have to look to see if I can't find that...
 

Boombox

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I'll have to look to see if I can't find that...

It's a guy on the Antique Radio Forum. Can't remember which thread. Might be the Listening Post thread on the main part of that forum, or one of the AM radio DX threads.
 
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