HFU HF Underground
Technical Topics => Equipment => Topic started by: tybrad on April 16, 2014, 2041 UTC
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Previous antenna (past 8 months- I am new to this): 100', 30ga. bare wire around the roof periphery. Decent, but not as good or as quiet as I'd hoped.
Current antenna: strung it up on Sunday, temporarily connected it this afternoon- test, and for tweaking. This one is a longwire loop- 450' of 14 ga. insulated wire strung tree-to-tree in the woods out back at about 30' off the ground. It forms a general loop, terminates both ends at a tree in the back yard where I have a 45' coax feed strung from there to the roof, 15 coils about 10" in diameter as a choke sitting on the roof, and then down to the room in the house (the full coax run is 100' but will be shortened significantly after tweaking everything).
I still need to construct a pole to help support the tree-to-roof run, fine tune the choke, solder and seal the antenna/feed connection in the tree, and make a permanent run through an external wall to my receiver.
This is night-and-day over my first try! Quiet, good grab- I was hearing things that I had not heard before; got a ham in TX at 3PM local here, S09, and many other hams in 10/11m. Lots of latino stations. Time stations now clear and strong.
Prior, there was mostly noise at this time of day. Can't wait until this eve/night!
Yay!
(http://1.bp.blogspot.com/-QdtWsRHiESE/T9DNS6aePgI/AAAAAAAAGYQ/2wOA02fTtyU/s1600/dance-smiley-face.gif)
Tyler
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I am hearing audio on LW that I have never heard before- it was mostly noise and a beacon or two. Hearing some Christian and latin stations, as well as beacons more clearly.
The one question that I have is the chugging noise across most of the 150-400KHz band. It sounds like a higher pitch chugging locomotive (in AM) that is louder at certain freq's (150, 157, 165, 174, 181), then starts to become less of a problem higher up. Interesting that they are spaced relatively constant- might be a clue
Any ideas? Local to me? Atmospheric?
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As far as I know, there are no longwave broadcast stations on this side of the Atlantic. I suspect you're overloading the receiver and hearing images of shortwave stations.
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Interesting. Aren't there tropical stations that use this band n the Western Hemisphere?
Would a resistor in series with the UHF/VHF transformer at the receiver solve this potential problem?
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No, but a preselector would help!
+-RH
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Well then, have I made my antenna to be too efficient? I would rather not add an antenna tuner to my setup- it's a simple setup and I already have too much gear in that room.
My DX160 has an antenna knob on it for tuning- that's it's function, correct? I do not think that it's a bandpass filter though, as preselectors are. What say you?
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You could certainly be picking up local QRM from switching power supplies, TVs, computers, etc. No way to tell for sure without turning things off or flipping breakers. It could also be from nearby houses.
I had some pickup issues as well, which I solved through the use of ferrite cores: http://www.radiohobbyist.org/blog/?p=1374
Congrats on the loop antenna though, they really are good performers.
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Just stumbled upon this thread. What Chris said, loops are awesome for all around radio use. I use mine for hamming on 10-80 mtrs and general swl'ing. Now that your antenna is up, have some fun. WOOHOO!
Steve
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DX-160's are great receivers, but for longwave you probably need an antenna tuner.
What you are probably experiencing (the Latin stations on LW, etc.) is AM band stations bleeding over into the LW spectrum on the DX-160, or possibly some shortwave stations, as Pope Jim suggested. There aren't any longwave broadcasters in the Western Hemisphere.
The DX-160's antenna trimmer just control matches the antenna impedance to the RF section of the DX-160, which helps improve performance, but it won't eliminate or reduce images from local AM stations that are probably bleeding over into the LW spectrum on your radio.
For that, you will need an antenna tuner, or build a tuned loop for longwave (like a box loop with a tuner across it, and a sense loop hooked up to the radio).
You could also turn down the RF Gain a little bit, it might reduce the images and still let the LW beacons through. The RF Gain is also useful for SSB -- sometimes the DX-160's AGC (even when set to 'slow') will overreact on strong sideband signals. Backing the RF Gain a little bit can often make it easier to clarify strong SSB.
As for the chugging noise, it is probably RFI of some kind.
Glad to hear you're getting better reception with the new antenna, and getting some good reception with your DX-160.
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Thanks for the responses, everyone! I no longer hear voice on LW- just beacons and the noise to which I referred.
CHRIS: the longwire comes no closer than 45' to any house (which is mine). Would AC and other electronic noise be a problem at these distances? If I do it, do the ferrite cores belong on the longwire or the coax?
I am playing around with some antenna things and have an update.
Once I finished the installation:
450' woods loop on braided 14 ga. insulated wire ->
Soldered 42' coax feed (ends connected to shield and center) ->
Coax lightning arrestor connected to Earth ground wire outside of house (presumably terminated on cold water pipe, but not sure- it's underground) which also has the cable TV and I think, electric breaker box inside all connected to it ->
Coax coil choke at the arrestor point ->
Into an A/B coax switch for disconnecting the antenna during electrical activity ->
Into a VHF/UHF transformer ->
Into the DX-160 with one conductor on 'antenna', the other on the other screw terminal that is jumped to the ground screw, and this ground screw is connected to electrical ground on a power bar.
QUESTIONS:
1. With the arrestor connected to Earth ground via the water pipe, the signal at the receiver is attenuated. Why?
2. With Earth ground connected, when I unplug the elect. ground- no difference. Why not?
3. With Earth ground disconnected, signal is high again. Why? Makes no difference if elect. ground is connected. I have it connected as a matter of precaution since Earth ground is disconnected. But perhaps they are electrically connected, as I surmised in the statement above.
4. I am not using the A/B switch any longer, thinking that losses or connex problems might be there. Thoughts?
So the problem appears to come from Earth ground being involved. Why is this?
Thanks everyone! You're all great. ;)
Tyler
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I have no idea why you are experiencing what you are experiencing.
I don't know what your lightning arrestor looks like, but depending on proximity of the 'gap' between antenna and ground I suppose it's conceivable that grounding the arrestor could provide some sort of capacitance or proximity effect
'Proximity effect' is when you place a radio's whip antenna within an inch or so from a longwire, you still pick up a lot of stations that way -- so maybe your lightning arrestor could be somehow bleeding off some signal towards the earth ground in the same manner; the proximity of the arrestor element to the antenna could be interacting with the antenna -- or course, this is just a guess. Others here who are more up on antennas probably could have a much better explanation.
I myself never used a ground with my DX-160. And any time I have tried using grounds, I never have had better results -- although I know others swear by them.
I personally only use grounds to ground an outdoor antenna when it is not in use, for safety reasons.
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It sounds to me as if you need a choke balun at the feedpoint of your antenna. By grounding the shield of the coax, your pulling one side of the antenna to ground, and that could be causing your signal loss.
Also, the VHF/UHF transformer is not suitable for much below 50 MHz as the core material is optimized for higher frequencies. Try a real HF transformer for this application.
It also appears you violated the star ground principle by grounding equipment at more than one point, and that can cause noise ingress problems. By code, electrical ground in your house is at some point tied to earth ground. That's probably why you notice no difference between the two.
+-RH