AM Passive Antenna

[trusty]

Being in the market for an AM antenna booster, I have spent the last few hours gathering information on both the Terk Advantage and the Select-A-Tenna so I could make an informed decision.

And then I stumbled onto info that said the Select-A-Tenna has been discontinued, thereby making my decision easier.

Or harder. (Maybe there is something that's better, and I've been too focused to see it.)

Do you have any suggestions? I have a Sony SW-7600GS, so I need a passive (inductive) antenna for MW (unless an active antenna will work on my radio (The Sony active antenna only works on SW and turns off the radio's ferrite bar and telescopic antennas.)

Also, I read that Terk (and S-A-T) could be attached to the end of a longwire antenna which would be perfect for my situation. Has anyone tried this?

Thanx for all responses.

 

[audioguy]

I would suggest making your own loop. It's easy to do and very inexpensive. Check the thread on box loops. There's nothing that critical about the exact shape of the loop or the type of wire. The main part you need is a broadcast variable cap salvaged from an old radio. I have used copier paper boxes very successfully.

 

[boombox]

I have the Select-A-Tenna and the Radio Shack loop (now discontinued). Both are pretty close in performance. The S-A-T having a slight edge in sensitivity. I have never tried the Terk.

I have a couple home built loops but find the S-A-T and RS Loop more handy to use, or take with me on road trips (less bulky).

There is a review online by a radio engineer comparing the Terk and S-A-T, he found them to be quite similar. You could probably find it by typing the two words into Google.

I never have tried attaching my S-A-T to a longwire.

I've found that if you need to inductively couple a wire to a small portable, it's much easier to just wrap some of the antenna lead around the radio, or even wrapping the lead around the radio's whip can work (I've done that with two of my digital portables with good results).

 

[Steve Green NEPA]

♫ I'm no techie, that's for sure
All the DXing I can catch
Comes up through this dirty floor ..... ♫

Apologies to Springsteen.

That said, Trusty, it occurs to me that your decision probably will be a choice based on either sensitivity or directionablity -- and perhaps both.

I agree with AudioGuy here. Home-brew!
If you have a real cooker of a radio, and need the space, the spiral diamond-shaped National Radio Club mini-loop is a wonderful aide for nulling out adjacents and co-channels.
It's easy to tilt, as well. A techie pal of mine (lifelong pal, EE degree) said he achieves that third-dimension tilt by 'putting a book under it' , hi.

If your priority is gain and you are not into soldering, then the standard NRC four-foot box loop is your quest. Like the mini-loop, the four-foot one can be tilted too, only with a bit more effort and proportionately additional elbow room.

Speaking far more from hit-and-miss experience than from any other approach, my estimate is that you'd be able to get a fairly rugged variable capacitor from just about any old table tube radio -- whether the radio even turns on or not. I've preferred the varianle capacitors with more than one row of flanges, and many old radios have them.

With a few sticks of spare wood or dowels, neither loop should run you much more than 20 dollars. The manufactured loops for the public -- the cheaper and unamplified ones, at any rate -- all work on the same principle.

 

[Tom Wells]

Read the thread on box loops!

 

[OKCRadioGuy]

http://www.scott-inc.com/html/lp3.htm

 

[OKCRadioGuy]

Yeah. It's 500 dollars, but it will keep lots of man-made noise from bothering your reception. My house is a noisy RF environment. This antenna cut about 80 percent of the garbage right out.

 

[boombox]

Re: building your own: like the others have said, the main issue would be getting a variable capacitor. But they are available online. Or you can get one from a junked AM radio.

Wire is reasonably priced, and you could build a Box Crate Loop, using a plastic milk crate as a frame. I got my crates for 6 bucks each at a local box store.

I built two box crate loops this week, one using a single crate, and two days later I built another one using two crates secured together with zip cord.

Putting a box crate loop together is rather simple -- it takes less than an hour to make one.

The plans are available on line -- but it's basically just winding 23-24 loops of wire around a single crate, 16 or 17 around the dual crate. Secure the variable capacitor to the crate with double backed tape or zip cords, tape the ends of the wire loop to the crate to hold them securely, connect the ends of the wire loop to the variable capacitor with alligator clips, sit the radio inside the crate and DX away.

Both of my crate loops have more gain than my Select-A-Tenna. The second one (the two crate version) took 15 minutes to put together, and 20 minutes to 'tune' -- I had overwound it on purpose, as I wasn't sure how many windings would cover the band. I had to remove about three windings to get the loop to tune to above 1600 khz.

Even though the two crate loop doesn't fine tune well above 1600, it still boosts signals above 1600 well enough to outperform the Select-A-Tenna.

 

[rbrucecarter5]

With loops, physical size (area of the loop) is everything. The best loop I have is 4 turns around an 8 foot square frame. I tune it with a varactor and mount the loop part outside. I have a little control box inside that generates the tuning voltage. I have a sense winding around the loop which I bring back inside with a twisted pair. Gain is nothing short of spectacular.

I haven't published the web article, but the rest of my loop stuff is here:

www.earmark.net/gesr/loop

Its been a long time since I revised that page - I've been thinking about a re-vamp for a while. I find now that separating the turns tends to reduce parasitic capacitance and make it easier to cover the band. So that kind of leaves out ribbon cable loops unless they are three feet and under. But by all means give that a try because it simplifies construction of smaller loops.

After you get the cross sectional area as large as you can, then make the wire as low a gauge (larger wire cross sectional area) as you can. I know of one fellow that used copper tubing with good results.

 

[boombox]

^^^ So you're the guy with that Superadio page? It's a great web site. Very informative.

I especially liked the info on the Realistic TRF.

 

[rbrucecarter5]

^^^ So you're the guy with that Superadio page? It's a great web site. Very informative.

I especially liked the info on the Realistic TRF.

Yep - same borrowed web space. Thanks for the nice comments!

 

[trusty]

Many moons ago, my relatives, who pick up EVERYTHING anywhere because ("...you never know when you're gonna need one of those..."), talked me into taking this tabletop from off the side of the street. I put it in the basement and kept it to someday make a table.

Well, scratch the table idea. You see, the thing is basically a six-sided frame of a tabletop designed to support 4 glass tabletop "panes", so it's fairly light. 40 inches in diameter. The thing screams to have wire wrapped around it, attached to a base and set on a lazy susan. I just need to get the proper capacitor and find a place to put it.

Until then I'm looking for something a little more portable. I like the box crate idea - specially if it out-performs the S-A-T.

Thanks!

 

[boombox]

I'd say the box crate idea is definitely worth looking into... After building a couple, I'm a box crate loop believer. ;D

One of the cool things is that box crate loops can be expanded rather easily. You just add crates, rewind the wire around them...... It's a very flexible concept, and they're very lightweight also. You can build more than one, and re-use the variable capacitor, move it from loop to loop if you use zip cords and alligator clips.

I'm having a lot of fun with the two I've got.

 

[kenglish]

It looks like the Select-A-Tenna is discontinued, according to Universal Radio's website.

I have a couple of the Grundig AN-200 loop from Radio Shack (recently discontinued from RS), and I was playing with them a few days ago. I noticed that, at least in passive/un-wired mode, they did not resonate up very high in to the expanded band. One seemed to cut off at about 1610, the other at 1640. They worked down to 530.

I'm going to have to find those 12" ferrite bars I have at home, and try to build a McKay-Dymek .

 

[nocomradio]

I have two of the Grundig AN-200's as well. For a bit, Radio Shack was clearing them out for $7.98 each in store only. I stop and check every RS I pass now, but I don't find them much anymore.

They work well with most radios I have tried them with, but as kenglish mentioned, they don't seem to do much above about 1650. For as cheap as you can find them, they aren't a bad thing to have around, but I am also planning on building a box loop too. I do like having other options.

BTW, has anyone ever tried building the Ramsey SM-100 unit?

http://www.amazon.com/Ramsey-SM100-Signal-Magnet-Antenna/dp/B0002NRL8E

Pricey I know, but what kind of performance could you expect?

 

[rbrucecarter5]

I have two of the Grundig AN-200's as well. For a bit, Radio Shack was clearing them out for $7.98 each in store only. I stop and check every RS I pass now, but I don't find them much anymore.

They work well with most radios I have tried them with, but as kenglish mentioned, they don't seem to do much above about 1650. For as cheap as you can find them, they aren't a bad thing to have around, but I am also planning on building a box loop too. I do like having other options.

BTW, has anyone ever tried building the Ramsey SM-100 unit?

http://www.amazon.com/Ramsey-SM100-Signal-Magnet-Antenna/dp/B0002NRL8E

Pricey I know, but what kind of performance could you expect?

I have some giant ferrite bars. After seeing a lot of ads for active antennas based on them, I did some designs ranging from totally passive to active. What I found was - in every case the Terk AM Advantage was better than a large tuned ferrite. I discovered that any varactor tuning scheme is extremely sensitive to power supply noise, so you should probably power from batteries. Not a huge deal because the current is so low it hardly matters.

 

[trusty]

I have some giant ferrite bars. After seeing a lot of ads for active antennas based on them, I did some designs ranging from totally passive to active. What I found was - in every case the Terk AM Advantage was better than a large tuned ferrite. I discovered that any varactor tuning scheme is extremely sensitive to power supply noise, so you should probably power from batteries. Not a huge deal because the current is so low it hardly matters.

Thanks for all the info; it has filled in some blanks.

I will probably build a loop after the first of the year. I went ahead a bought a Terk because I had to have it before Christmas. It works pretty well, but not as well as I had expected. But, to be fair, I haven't had the time to really test it out. We have some of the worst ground conductivity in the world (N. Ga.), and I THINK that probably affects the Terk's performance.


OK. I have a couple of questions on a longwire. I want to receive from all directions. I can put up a 92ft. wire running east-west or an 82ft. wire north-south, OR both.

I've thought about putting up both and tying them together with a coax at the point of entry into the house. I tried this when I was a kid, but, because we were living in an apartment, I only could string 20 ft. of wire each way. (I picked up KFI while in Atlanta one night at 2am ET using this setup - but that was in the mid '60s. )

I guess my main question would be if I NEED to put up 2 wires (?); would they enhance or restrict each others' reception?

Again, thank you for answers and comments.

 

[boombox]

OK. I have a couple of questions on a longwire. I want to receive from all directions. I can put up a 92ft. wire running east-west or an 82ft. wire north-south, OR both.

I've thought about putting up both and tying them together with a coax at the point of entry into the house.

I guess my main question would be if I NEED to put up 2 wires (?); would they enhance or restrict each others' reception?

Again, thank you for answers and comments.

At MW wavelengths, your 92 ft and 82 ft wires would be too short to be very directional. You could probably get away with using just one for MW. But it would be worth putting up both and seeing if either antenna gives better reception. Some times other factors (surrounding terrain) can influence an antenna's reception.

I have a 100 ft. low wire that I sometimes use for MW. It works well. It seems to receive equally from all directions.

I'd put both antennas up and use a switch, to switch between them. 90 foot antennas would be directional at SW band wavelengths.

They shouldn't restrict each other's reception. If you used them both at the same time (i.e. one wire to the center of the coax, the other wire to the braid) they would act similar to a V-beam in the shortwave bands.

 

[KB1OKL]

I second the NRC 4' box loop, it is not real easy to build but if I can build one anyone can. It's fairly sensitive and will null very good, it can be tilted and turned 360 degrees. You do need some space for it though.