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HIGH Q CAPS FOR VLF LOOP ANTENNA?
On Fri, 28 Oct 2005 14:19:14 -0400, TRABEM wrote:
With the current model of parallel loop... If my receiver was 2K input impedance (whether tuned input or not), could I connect it to my loop with a piece of 2000 ohm open wire line and expect the net (or loaded) Q to be around 100 (assuming a 2K impedance open wire line could be built and that my unloaded antenna Q was 200 to start with). Yes or No? You have too many suppositions to give a straight answer. First, there is no such thing as a 2000 Ohm open wire line. As for the gist of the question: Yes. With the current model of parallel loop... If I elected to use a buffer amp with megohms of input impedance, would I preserve the unloaded Q and end up with a net Q of about 200 because I haven't loaded the loop? Yes or No? Yes. However, as Tom has pointed out separately, this may not be the optimal solution. I believe my receiver is microvolt sensitive and that the loop will deliver a relatively good signal to the receiver even though the loop isn't terribly efficient. If I build selectivity into the front end of the receiver, do I really need high Q (200)?? I think the answer is NO..... Well, this is a good opportunity to examine that tumble down the slope to the Q = 2 (caused by the severe loading of your proposed design). The correlative to this is, how much selectivity do you need in a field where stateside VLF is relatively rare? Further, by the action of the strong filtering that usual attends the "I" and "Q" channel processing, you could easily repair any shortfall. However, back to that Q = 2. That still offers respectable (not fantastic) selectivity against signals out at the bottom of the AM band which is 10f (one decade) away. OK, I am with you with respect to the brain filtering out unwanted conversations to let you focus on your conversational partners distant voice. But, I thought traditional binaural receiver meant that the frequencies higher than a certain point went to one ear and that the all the frequencies lower than the same frequency went to the other ear. In this manner the listener has a feeling of 'depth' or 'richness' that isn't present in a mono setup. Binaural is what the fellows in white coats mean by listening with two ears. This is interesting though. And rarely reported for this style of detection. What a pity. Are you suggesting that the brain can also process the I/Q output streams and provide opposite sideband rejection as well as selective frequency and adaptive filtering? The rejection is psychological, not actual. It is what I meant by "mind-space." The vectors do not add up to zero, the mind simply ignores the off-band content like you would at a party listening to that cute office temp's whispers when your wife is yelling across the room at you. Listen to a recording of that same scenario in mono and you WILL hear your wife! The brain reassembles all delay/phase information content at the party to sort out what to pay attention to. When that same information is passed through a monaural channel, the phase information is lost and everything competes equally lousy given the S/N ratio. 73's Richard Clark, KB7QHC |
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