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Author Topic: need help on HF listening (read please)  (Read 725 times)
MUVR2007
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Posts: 33




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« on: November 23, 2007, 09:45:14 AM »

This sample is recorded in 6.628Mhz in USB mode. My radio is a yupiteru mvt-7100 and the antenna is 30m (telephone cord) long, is basically mounted as upper as possible in my house. The problem is that I hear a little bad the conversation. This frequency is used in nat-e zone(pilot communicating in atlantic ocean). Hope someone can help me, telling what can I do to achieve a better reception. Thanks!

here the link to download the sample voice recorded with the present situation:

http://download.yousendit.com/27B551D828254122
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VE3LXL
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« Reply #1 on: November 23, 2007, 03:25:32 PM »

The two simplest things you can do are to get your antenna outside, and to put up a better antenna. Indoor antennas pick up tons of household electrical noise, and if you're in a steel frame building, the building itself will be blocking some of the signals you're trying to hear. So even if you just moved your present antenna outside it would probably help. And a better antenna would help even more.

There is tons of information on the web about antennas for listening. I'm sure Google will be able to find you what you need.


 
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W3LK
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« Reply #2 on: November 23, 2007, 04:30:56 PM »

With all due respect, your radio is a hand-held scanner that is designed for VHF/UHF reception. That it covers some HF frequencies does not make it a good HF receiver.

I agree with getting an antenna outside, but no matter what you do for an antenna, this will be a poor performing radio on all but the very strongest HF signals.

A receiver actually designed for HF would be a much better choice.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
N3OX
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« Reply #3 on: November 23, 2007, 08:09:25 PM »

I agree that a better RX and an outside antenna might work but I think the most important thing is a better antenna.  

That doesn't mean an antenna with more output, necessarily.  You need an antenna that rejects local noise better.

I would recommend a small, tuned loop antenna often called a "magnetic loop"

The easiest and cheapest way, especially if you're trying to use a small handheld radio is probably this antenna:

http://users.erols.com/k3mt/hla/hla.htm

If you have good results with it, you should build a sturdier version with wire and a capacitor, like this one:

http://n3ox.net/projects/rxloop/

A small tuned loop will overcome some of the disadvantages of a cheap RX... it will add some extra frequency selectivity because it has very sharp tuning and it won't have so much output as to overload the radio.

- - - - - -

Your fundamental problem appears to be noise pickup and buying a $1000 HF RX isn't going to fix that.  A balanced antenna like a small loop coupled to a small handheld radio running on batteries might.

The most important thing, though, might be figuring out what is causing your noise and shutting it off!

I have that RX loop on my homepage because I built it while living in an apartment so I could try to hear some DX on 80m.  It worked very well for nulling some massive noise I had.  I found a very sharp null in one particular position, and kept using the loop until one night when it finally clicked... I looked at the position of the loop and the layout of my apartment... followed the null to the next room... and found that the noise culprit was MY OWN DESKTOP COMPUTER.

Don't let this happen to you.  Make sure it's not your own TV, computer, or other appliance that's causing your interference!

Make sure you unplug any candidate devices.  Sometimes they make noise even if they're turned off.

Now, it's possible that your noise is something harder to take care of, like power line noise or a neighbor's plasma TV.  In that case, the small tuned loop could be a great solution.  Just put the null on the neighbor.  

A new radio might enhance the HF listening experience overall, but if you can't find and eliminate the noise I hear in your file, a new radio won't help at all.

73,
Dan






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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
MUVR2007
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Posts: 33




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« Reply #4 on: November 24, 2007, 05:02:35 AM »

Thanks very much for your attention regarding my question. I have also buyed a Realistic DX-302 but only in a month I will get it in my home (my brother has it in UK and deliver to me when he comes). I know it's an old receiver but in terms of performance, I think he won't be worse than my actual radio. As N30X said, I also think that the antenna is the most important part for someone who want to have a really good listenings. My radio has a good sensititvity for a wideband radio(0.27microV at SINAD 12DB FOR 6mHZ in SSB.)The problem is that I don't have much time to build some of those loop antennas you mentioned to me and, so, I would prefer buying an antenna like that but already mounted. This ensure it will work more properly and I wouldn't spend much time building it. In terms of AM reception, i receive much radio broadcasts and other from all over the world: china, russia, and so on and hear very clearly (must have them has a full signal strenght).
Talking about the electrical noise, the radio is currently ~10m away from my laptop and ~2m from tv (not plasma). I don't know if my neighbours has a plasma tv.. Smiley
I am ~400m from a local train station..this can may a cause of the high levels of noise in reception?

Thanks again for all of you who are helping me a lot!
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MUVR2007
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Posts: 33




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« Reply #5 on: November 24, 2007, 05:06:13 AM »

Thanks very much for your attention regarding my question. I have also buyed a Realistic DX-302 but only in a month I will get it in my home (my brother has it in UK and deliver to me when he comes). I know it's an old receiver but in terms of performance, I think he won't be worse than my actual radio. As N30X said, I also think that the antenna is the most important part for someone who want to have a really good listenings. My radio has a good sensititvity for a wideband radio(0.27microV at SINAD 12DB FOR 6mHZ in SSB.)The problem is that I don't have much time to build some of those loop antennas you mentioned to me and, so, I would prefer buying an antenna like that but already mounted. This ensure it will work more properly and I wouldn't spend much time building it. In terms of AM reception, i receive much radio broadcasts and other from all over the world: china, russia, and so on and hear very clearly (most of them have a full signal strenght).
Talking about the electrical noise, the radio is currently ~10m away from my laptop and ~2m from tv (not plasma). I don't know if my neighbours has a plasma tv.. Smiley
I am ~400m from a local train station..this can be the cause of the high levels of noise in reception?

Thanks again for all of you who are helping me a lot!
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N7IOH
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Posts: 116




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« Reply #6 on: November 25, 2007, 09:24:56 AM »

Hi Joao, I would agree with the others about a better antenna as it sounds like you are going to have a better receiver soon.  I don't know what you have for room as far as antennas are concerned, but here are some thoughts.  The receiving loop would be a good starting place.  These are very easy to build and can be built in a few hours.  A vertical antenna will tend to pick up more man made noise than a horizontal antenna.  If you could build a horizontal antenna for the frequencies you most listen to that should help.  Then of course get it outside and as high as possible if that won't be a problem.  If you are really into short wave listening I would have 2 or 3 antennas and buy the MFJ-1026 to use along with them.  The MFJ-1026 can do wonders when properly set up with 2 antennas.  What it does is works one antenna against the other to phase out the noise.  Another item that can help is an inexpensive antenna tuner.  These can help put your antenna at or near resonance and work kind of like a preselector.  Here are some links to information about the MFJ-1026.

http://www.hard-core-dx.com/nordicdx/antenna/special/mfj1026.html

http://www.astrosurf.com/luxorion/qsl-mfj1026.htm

http://www.k0to.us/HAM/Noise/NoiseExample/MFJ-1026_example.htm

http://www.k0to.us/HAM/Noise/adjusting_MFJ-1026.htm

http://www.angelfire.com/mb/amandx/mfj1026.html

Al, n7ioh
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MUVR2007
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Posts: 33




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« Reply #7 on: November 26, 2007, 10:27:58 AM »

Thanks N7IOH. However, for now I'm not considering buying MFJ-1026 as I don't have enough money..maybe later. I would like to start from a loop antenna as you told, but where can I get ideas of how to build one? Are there any tutorials or something like that for help me building it?
Btw, have you already tried to listen to the aircraft/atc frequencies in atlantic ocean? In affirmative case, can you tell me or send me a sample of what you can listen? If not, I can give you some frequencies for you to test..

Thanks again!
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VE3LXL
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« Reply #8 on: November 26, 2007, 03:39:21 PM »

W3LK is right. Many of those handheld scanners have really terrible reception at HF and MF frequencies. That's likely a big part of your trouble. I don't know anything about that Yupiteru radio, but that old Realistic DX-302 will almost certainly perform much, much better, even with your current antenna.
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MUVR2007
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Posts: 33




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« Reply #9 on: November 26, 2007, 03:46:24 PM »

Yes, the radio doesn't help very much I know, but I think that with a better antenna this radio will perform better than is actually performing. The problem is making it as good as it should be. Do you really think that is probably that with this antenna the DX-302 will really do a much decent job?
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