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1-7 of 7 messages
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Receiving question on my HF radio and antenna.
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by KD0BIE on November 20, 2008
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I have a receive question on my radio. First I am a tech and working on getting my general. Almost there, but for the time being I am listen and monitoring the bands and listening to shortwave broadcasts. I had a random wire antenna to receive about 50 feet. I had it on two pvc pipes about 5 feet off the ground. It worked great. I was able to receive all bands up to 40m just fine. I wanted to get a longer antenna so I got 100 feet of the same type of antenna line to receive higher bands like 80 or 160 but instead put it up a tree then passed it to the peak of the roof. After doing so I am not able to get hardly anything. I don’t know if it’s been a bad week in propagation or could it be where I placed the antenna from the tree to the peak of the roof? Please give me some suggestions that would work with what I have. Would taking that 100 feet of line and doing the PVC pipe for the mast be better? I really appreciate all of your guys help and trust me I have looked everywhere for an answer before I came here.
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RE: Receiving question on my HF radio and antenna.
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by G7MRV on November 21, 2008
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Hi,
that sounds a bit odd. Im quite surprised it did well only 5ft off the ground to start with. It should be much better higher up. Are you using an ATU? It sounds to me more likely that there is a fault, does the wire go over the antenna run and then directly to the receiver in one length or is there any joints? perhaps a joint or connection is bad, or there is a short somewhere or break in the wire (if pvc covered the core could break but the insulation just stretch)
I tend to use just random wires for receiving on my FRG-100 and they are usually just chucked up into a tree top attached to a brick!
Have you checked the settings on the radio? are you sure you dont have an attenuator switched in inadvertently, or the antenna connected to the wrong port? Do you have a signal source you can check the receiver on, or a local ham/club with testgear who could check it for you?
conditions (here in Europe) on HF are poor but theres still usually some strong stations about.
Maritn G7MRV
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RE: Receiving question on my HF radio and antenna.
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by N5LRZ on November 21, 2008
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Recap....
You had a random length SW Antenna barely off the ground 50 feet or so long and heard locals--40 miles is local for Amateur HF/heck anywhere in the contineltal US is local for Amateur HF.
You then increased the length to well over 100 ft and raised the antenna and heard less.
Well there ya go, your answer. Do some research into end fed antennas of 1 wave length or longer. I do believe that you will find that an antenna that is end fed and 1 full wave length or longer will receive in the direction of the wire itself/in the direction it is pointing.
THUS a 125 foot length of wire may receive OK on 80 and 160 much as your 50 foot wire because this length is far less than 1 full wave length for 80 and 160.
HOWEVER even at 40 meters the full wave length of 60 feet would be 2 full wave lengths making the antenna very directional for 40 meters.
AND if that were not enough it would make all the lower bands even worse because that same 125 feet would be many multiples of 1 full wave length.
ALSO you have the problem of resistance itself. For example a quarter wave dipole center fed has a charastic of 70 ohms or so. BUT a full wave dipole for that same frequency has an charistic feed point of THOUSANDS.
The solution is simple though. You might borrow an antenna tuner and use that to tune in your receive signals. External antenna tuners do more than just tune a transmit feed point, they also help with receiving as well. And in fact the instructions of my tuner state as a pretune to adjust all controls for maximum receive noise.
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RE: Receiving question on my HF radio and antenna.
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by WA3SKN on November 21, 2008
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Sounds like it might be shorted to ground somewhere. Check to make sure it is not touching anything metallic.
-Mike.
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RE: Receiving question on my HF radio and antenna.
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by AA4PB on November 21, 2008
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If the change in antenna length from 50 feet to 100 feet made that much difference I would look for some other issue like a broken or shorted wire. The change in length should not have made that much difference.
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RE: Receiving question on my HF radio and antenna.
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by KD0BIE on November 21, 2008
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I do have a Auto tunner. I tried this morning before work and I am getting an awesome signel on 20m. I was suprised about 20m, but again last night I could not getting hardly anything on 40, 80m.
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RE: Receiving question on my HF radio and antenna.
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by K9JH on November 21, 2008
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A few comments that do not directly answer your question...
Bigger antennas are not always better. The concept of "bigger capture area" is wrong. You need to focus on the idea that gain in one direction comes from loss in another. I would recommend playing with the free program EZNEC to see how changes affect the radiation patterns.
You do not have to have a resonant antenna to hear 160m or 80m. A smaller antenna will work fine. You will suffer some loss, but you will hear the vast majority of stations still. You will need to worry about impedences later when you are transmitting.
The biggest thing you can do to have better ears (in my experience) is to get the antenna away from the house. You get so much noise from a a 100 watt dimmer switch that it can completely wipe out a megawatt broadcaster.
K9JH
James
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