Quick question,

What would be the cause of overlapping stations? On my radio, at around 900KC and higher on the dial (which I do notice there are more stations up there than the lower end) I hear a bunch of unclear stations overlapping each other. For example, two newscasts happening at once. I have a roughly 25ft antenna wire attached that goes out the window and straight through the air to the top of our flagpole, about 15ft high.

I really wanted to hear an old radio show on CHML 900 late last night, but it was just a bunch of fuzz/static/stations right on 900KC . I heard from a friend who's less than 100 miles away that CHML 900 was booming in for him last night.

Any ideas? Thanks in advance.

I don't know the first thing about antennas, so feel free to ignore this. Hopefully someone who actually has lots of knowledge and experience setting up antennas will answer you.

However, today I was reading this article...
http://www.nostalgiaair.org/PagesByMode ... 015945.pdf
...which is about RCA's recommended antenna setup for some of their mid-1930s radios.

On the 2nd page under alternative arrangements, RCA's writer makes the side note that you could build the same antenna vertically instead of horizontally, but that would turn it into a "practically non-directional antenna" with a "somewhat inferior... noise ratio".

So, when I read your post, I wondered whether the fact that your antenna is vertical could have something to do with it?

Just a thought,
Rodney

Here's another thought. If skip conditions were really good, especially
after dark, you might have been in a position where more than one
station on 900 were coming in. A lot of modern transmitters are so
accurately tuned, you sometimes can't even hear a beat note...
Nelson

Hi

Many stations across the country are assigned same transmitting frequencies. At night several may be received at the same time. Only exceptions were clear channel stations. They are usually high power 50KW stations like KOMO, 1000KC, in Seattle. Even those frequencies now have a few smaller stations assigned.

A long antenna may cause radio selectivity to broaden.. Try adding a small cap, 47 pf, in series with your antenna.

Here in Albuquerque a local station was forced to modify their antenna array because they were interfering with a New York station at night, even though they were severely cutting their power.

Lower power local stations are assigned the upper frequencies to a large degree, usually from about 1200 Kc and up. Because there are so many of them, they can tend to sometimes interfere with each other, with distant ones coming from different directions at night.

One way to maintain control over them is with a tunable loop, such as a Select-A-Tenna (or you can build one on a wood quilting loop, along with using a variable capacitor) which can be tuned to the frequency desired for best gain, and then turned to null out RF from other directions.

Okay so it sounds like an antenna problem. And not the radio, phew . Thanks guys!

Now you've sparked my interest. I hope it's okay to digress here. I don't want to clutter the forum up with dumb questions. I did some research on the Select-A-Tenna, but to be honest, I think I'd like to make my own. They look neat and don't look too expensive to make. I did a quick search of the forums and google and all of the instructions seem over my head.

What exactly do I need to make one for use on the AM BCB only (I'll worry about shortwave later )?
--Gauge/length of wire?
--What kind of variable cap?
--I'll need a knob of some sort
--What else?

Where can I get these supplies? I'll be at Kutztown in 2 weeks.

I'm definitely capable of building one. My dad will enjoy helping out as well. I think it could be a very cool project. I'd make a wood box and mast and then stain it a nice dark color.

Simple but works well! Talk to me like I'm an idiot, please

Thanks guys.

Roughly 80 feet, gauge doesn't matter, diameter doesn't matter either.
365pF tuning cap from an old radio.

There was a discussion here on this topic, perhaps 2 months ago? Maybe 3.

Ferrite core antennas work just as well and are smaller, but not as eye-catching.

Thank you Alan.

Anyone have any recommendations on gauge from past experience? If it doesn't matter I'd like to use a pretty thin wire, because it's easy to maneuver.
When you say roughly 80ft. could I use 75 - 85ft. How much off of 80 can I be? Why 80ft? Does this have to do with inductance and capacitance and the BCB?

I'll be at Kutztown so I'll keep my eye out for a 365pF variable cap. Must it be exactly 365pF?

What knob should I get? Any other hardware I need?

So far I have:

thin uninsulated copper wire (80ft)
365pF variable cap
scrap wood
knob

Is there a schematic/blueprint somewhere for what I'm trying to do?

I hope I can find everything I need when I go, and I'm sure there will be plenty of people to help me out.

I definitely like the loop antenna "mast" design. Will look pretty neat sitting on top of my radio.

Sorry for all the questions. Thanks again.

That's the circuit I'd recommend, a multi-turn coil resonated with the variable capacitor, and a separate one-turn coil connected to the radio. It could be more than one turn; it's for impedance matching.

"365pF" is standard for AM broadcast radios but the actual value can vary. If the coil or capacitor is a little off, they won't tune the whole AM band, no big deal.

Any wire will work, insulated or not (bare would have to be spaced so it didn't short).

Here's one I made, on aluminum channel for shielding:

The variable capacitor (from a transistor radio) is at the bottom of the frame, and tunes the multi-turn coil. That coil/capacitor circuit is not tied to anything else. The smaller coil feeds the radio through a length of RG-174 coax.

An unshielded loop won't give a sharp null: it also acts as a short vertical antenna.
The gap at the top is necessary to keep the shield from acting as a shorted turn.

When you say the stations "overlap" do you know if you are hearing stations assigned to the same frequency or that the several stations you hear are on adjacent frequencies. Dx-ing at night in the AM band requires a receiver with better than average selectivity. For example, in my area CHML-900 comes in fairly clearly at night but it isn't especially strong. I usually get a much stronger signal from the adjacent WLS-890 (Chicago). A radio with average selectivity (a set with only one IF stage, for example) will not be able to separate the two stations very well. At the higher frequencies, if the radio does not include a TRF stage, the effect will be even worse.

A loop antenna will help, but if the radio has only average selectivity, the advantage of having the loop might be minimal. What model receiver are you using?

Dave

Like so-

PM sent.



Larry

Take a look at my recent May 1 post:
The project don't have to be elaborate. The one I made is wound on a cardboard box covered with wood grain contact paper.
viewtopic.php?f=6&t=191034&p=1607528#p1607528

Get a variable capacitor with 8:1 gear ratio.
http://www.crystalradiosupply.com/1/page7.html

Thanks for the advice everyone! I appreciate all the help I can get. I've decided at my stage in the radio world, Rocketeer's loop with variable cap seems simplest for me, and seems like it will work nicely. 100ft of wire!

The radio I'm using right now is a Silvertone 6051 AC/DC set. Not the battery op one that shows up on Nostalgia Air. It's nothing special. Here's a link to the SAMS photofact: http://www.scribd.com/vincent_milone/d/ ... rtone-6051 .


By the way, Alan, I really like the idea of designing the loop so it can pivot. Maybe I can incorporate that into the design.

Interesting.

The schematic for the Silvertone shows that it has only a single IF stage plus an un-tuned RF stage. This combination, while it gives the radio good sensitivity, does nothing to improve it's selectivity. Also, your radio already has a built-in loop antenna which could reduce the advantage offered by an external loop antenna. Since you are going to Kutztown, it might be a good idea to be on the look-out for a radio that can provide the type of selectivity you need for nighttime AM DX reception. A sensitive and selective communications receiver, for example, connected to the directional loop antenna that you are building will deliver the kind of performance you need.

Dave

A communications receiver might require a bit above his financial standing.

As an alternative, I would recommend simply looking for a receiver that has a tuned RF stage ahead of the converter, easily ID'd if you can see the chassis, as the tuning cap will have three gangs on it, vs the usual two.

There is NP in using a receiver with a built in loop, BTW. I have found that spacing the external loop at a certain distance or angle from the receiver achieves different results, including pulling a station up out of the mud entirely.

I like to listen to CHML every night,too.Atmospheric conditions are terrible right now.Here in NH,I can usually get that station like it's next door,but not recently.It's been a hard catch on any of my sets, except occasionally after 1:00 am.Luckily,my console has a built in,rotateable antenna,so that helps-sometimes.

The fact that the front-end of my console is as wide as the proverbial "barn door" doesn't help much either.Not very handy when you're trying to listen to a weaker station parked right next to a flamethrower.Does your set have an un-tuned rf stage?

Thanks Dave and Fifties. You learn something every day. As you guys mentioned, using an external loop with an internal loop may reduce the effect of the external. It certainly won't negatively affect the reception, will it? Mike-- Good to know, may it's not my radio. I hear reception gets worse in the summer? My radio has an untuned-RF stage, only two gangs (Thanks Fifties).

Re: My radio has an untuned-RF stage, only two gangs

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It's possible a strong local station is overloading the front end of your radio and causing it do de-sense. Might not be an antenna problem at all.