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Receive Antennas (below 30MHz) For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

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  #1 (permalink)  
Old 08-10-2014, 10:39 PM
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Arrow The Idea of AM Ferrite Coil Antenna on Ham It Up Upconverer

Heya RR folks. I am inquiring about if anyone had any luck using a AM ferrite coil antenna extracted from a parts radio who had success using it on the antenna input of the Nooelec Ham It Up Upconvertor. the device only has a SMA connector. I have a spare 75 ohm BNC connector.that I can use on the SMA to BNC adaptor. How will I terminate the AM ferrite coil antenna to the device?

It was kind of fuzzzy to me where to post this thread because it deals with antenna's below 30mhz, but also, it deals with a SDR "add-on" so to speak.

If anyone has a schematic that will be nice thanks. I can receive AM signals as it is now but not strong enough to my liking. Just 1 AM station is strong the other 6 or 7 in my area are rather weak.

I am aiming toward MW medium wave USA frequency allocation. 535 khz to 1705 khz. Can't expect reception in the long wave band because nothing here is below 535khz

Last edited by screamin72; 08-10-2014 at 10:44 PM..
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Old 08-11-2014, 12:43 PM
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Ferrite bar antennas are not that efficient on MW. You'd be far and away better off building a box loop or if you're not all that handy, getting something like an unamplified loop like the Grundig or similar.

It would take a little wiring to put a BNC connector on the output cable from the loop, but either should work like gangbusters. And you get the ability to rotate and null away any junk coming from your PC.

To me that's a win-win...Mike
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Old 08-11-2014, 1:19 PM
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It's easy to shrink the radios but more difficult to shrink antennas especially for the HF spectrum. There are some fractal designs out there but I'm not sure of their efficiency. I'm feeding my 120' dipole using the SMA to BNC adapter and pick up the AM band fairly well but I really only concentrate on the HF band. The bottom line is that you really need big antennas for HF and lower!
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Old 08-11-2014, 2:28 PM
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Not on MW and below, unless you have LOTS of room for efficient antennas. That's why many folks use box loops and the like - not everyone has that kind of space!

Sure, a 120 foot antenna (in fact, most any wire antenna without coils...) will hear MW, but you won't have the nulling capability that a loop provides.

Mike
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Old 08-11-2014, 3:30 PM
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Actually, a loopstick antenna can be quite "efficient" on MF. What's needed is that the loop primary turn needs to be tuned. This is why portable AM radios generally have a ganged tuning capacitor. One section tunes the LO, the other section tunes the antenna.

A tuned loopstick can deliver almost as much RF voltage to the receiver as a full size antenna. The tradeoff is it has a VERY narrow bandwidth, thus the requirement that it be tuned.
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Old 08-11-2014, 5:04 PM
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None of you answered my question. You all hijacked my thread. I asked for a schematic how to connect the MW ferrite coil to the Ham it up. I didn't ask if it was deficient!

Just because it makes sense doesn't excuse it from being moderated!

The reason I say every single reply to me has hijacked my thread is because they answered a question not asked!!!!
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Old 08-11-2014, 5:12 PM
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Maybe this will work for you:

Twin Coil Ferrite® AM Antenna Signal Booster > Antennas > AM Antennas | C. Crane
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Old 08-11-2014, 5:24 PM
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I asked for a schematic not a complete product I would have to modify for sma connectors or bnc female to sma male. I want to make it. I cannot find on google anywhere that explains how to terminate a AM ferrite coil from a parts AM radio to a Ham It up up converter via a bnc.
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Old 08-11-2014, 6:22 PM
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Simmer down, screamin. Some of us are suggesting alternatives precisely because it might be a little on the tough side. Without seeing what you have, it's a little hard to suggest a way to proceed.

As zz mentioned, you would need a variable cap to tune the loopstick. Did you happen to rip that out of the radio you took apart for parts? Mike
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Old 08-11-2014, 6:59 PM
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I have this

NooElec - Ham It Up v1.2 - RF Upconverter For Software Defined Radio - Software Defined Radio
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Old 08-11-2014, 8:33 PM
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Yep we got that - back to the question - did you take the variable cap out of the radio you were stripping for parts? See zz0468's comment in message 5 of this thread.

Mike

[edit] Giving this a little thought - I've never tried this, but the theory is sound - I would connect the variable cap across the loop (1 end goes to one side of the cap, the other to the opposite side), then take a length of wire, wrap it around the opposite end of the loop about 4-5 times and feed that to the output. This method uses inductive coupling to accomplish the signal transfer.

Unfortunately I don't have any software for doing the schematic, but it should work.
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Last edited by ka3jjz; 08-11-2014 at 9:00 PM..
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Old 08-12-2014, 12:26 AM
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Quote:
Originally Posted by screamin72 View Post
None of you answered my question.
Sure I did. I gave you a concept. Take it and run with it.

We can't give you a schematic because we don't know what you're using as an organ donor to get your loopstick antenna. Look at it. Try to understand what it is before you tear it out of the donor radio. There are two coils on the ferrite core - a large one, and a small one. The large coil goes to the capacitor. The small one goes to your receiver.

I did the hard part. Now go finish it. It'll work.

Last edited by zz0468; 08-12-2014 at 1:04 AM..
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Old 08-12-2014, 1:12 AM
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I don't need to run a variable cap because the radio is tuned with software connected to the RTL2832U R820T). I am in a small studio apartment not big enough for a huge antenna. I have yet to find a junk AM radio so I can remove what I need to make a passive antenna for the AM band. The board operates the frequencies 150khz to 55 mhz non stop. The ferrite AM coil I will be taken from the radio will need to be direct connection to the antenna or RF input of the board with some kind of minimal circuit. I have to be very careful with this because I never applied a loop anything to a digitized circuit like this. The board is just a week old.

Last edited by screamin72; 08-12-2014 at 1:22 AM..
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Old 08-12-2014, 2:53 AM
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The variable capacitor is to tune the antenna, not the receiver. In a portable AM receiver, the loopstick has two coils. One is in series with one section of the multi section capacitor, and the other coil is the antenna terminal to the receiver. Without tuning the loopstick with the capacitor, the antenna won't develop enough signal to drive your receiver.

When you recover the loopstick from the junque radio, you need to also recover the main tuning capacitor. Those are the only components you will need from the radio. It doesn't get much more passive than that.
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Old 08-12-2014, 3:37 AM
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Quote:
Originally Posted by zz0468 View Post
The variable capacitor is to tune the antenna, not the receiver. In a portable AM receiver, the loopstick has two coils. One is in series with one section of the multi section capacitor, and the other coil is the antenna terminal to the receiver. Without tuning the loopstick with the capacitor, the antenna won't develop enough signal to drive your receiver.

When you recover the loopstick from the junque radio, you need to also recover the main tuning capacitor. Those are the only components you will need from the radio. It doesn't get much more passive than that.
OKay that's good for a beginner like me. I also want to know is there a simpler variable cap that has a knob that can tune it? I have no problem going to Radio Shack to see if they have one.
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Old 08-12-2014, 5:40 AM
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Sad to say RS stopped carrying things like this a LONG time ago. If you didn't rescue the cap from the radio, it's likely you'll need to dig one up on the web. Mike
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Old 08-12-2014, 1:51 PM
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My local Radio Shacks still carry parts. No variable caps, though. At least not that I've seen.

They might have knobs in their parts drawers, though. Just use the bigger section of the tuner cap from your junk radio.

I think there are single gang 365 pf tuner capacitors you can get online, also.
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Old 08-13-2014, 5:02 PM
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Like this you mean...



The two grey wires just go off to the AM terminals on my stereo but you will need thinner coax and the proper plug for the SDR. There are two coil windings on the rod - the larger one goes to the variable cap and the smaller one goes to the radio. I have only used one section of the variable cap.
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Old 08-14-2014, 2:50 AM
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That's exactly what I've been talking about.
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