14884	2018-06-10 21:59:33	Chuck Hutton	Amplification of ferrite loop array
Message	Date	From	Subject
I am trying to amplify an array of ferrite rods for LW / MW / 160m DXing. This antenna is a circular array of perhaps 20 to 30 ferrite rods and has tremendous signal gathering ability for a small antenna. It works well in a tuned configuration where there are enough turns in a pickup coil to resonate with a standard 365 pF cap. The problem arises when I remove the cap and try to generate an untuned, broadband input for an SDR. With no cap, the gain is so low that amplification is necessary. My first shot was a balanced FET input preamp but that failed to deliver much if any gain. The second attempt was a medium Z preamp - the Wellbrook FLG-100 which has a couple of K input impedance. No luck. I don't know why the FET preamp didn't work. Chuck
14885	2018-06-11 01:00:05	Roelof Bakker	Re: Amplification of ferrite loop array
Hello Chuck, I wonder if this will work at all. I have yet to come across a broadband antenna build with ferrite rods. All examples I have seen used a tuning cap. A simpler approach for a broadband (VLF / LF / MF / HF) antenna is an E-probe. 73, Roelof, pa0rdt
14886	2018-06-11 02:29:24	blumu	Re: Amplification of ferrite loop array
Some earlier DX receivers, notably the Sony icf2010, have a FET RF amp with untuned winding on the ferrite rod. Michael 2E0IHW .................................................................. On Montag, 11. 06 18 09:00, 'Roelof Bakker' roelof@ndb.demon.nl [emrfd] wrote: ... > I have yet to come across a broadband antenna build with ferrite rods. > All examples I have seen used a tuning cap. > > A simpler approach for a broadband (VLF / LF / MF / HF) antenna is an E-probe. > > 73, > Roelof, pa0rdt
14887	2018-06-14 12:07:45	kb1gmx	Re: Amplification of ferrite loop array
I've done work with wideband ferrite loaded antennas for MW/HF. Too many turns makes it so inductive its self inductance inhibits current flow (signal). Lots of turns work for tuned but wideband likely many less. Experiment! The other is the are nominally electrically small so lots of gain is needed. The gain is on the 25-35db range, needed to be able to handle big signals and small as its wideband. Generally fets don't cut it. It needs to be low internal noise. And very importantly the interface to the antenna cannot have one side grounded as that upsets the balance (just like 1M loops) and it will pick up power line and other conducted noise as well as destry directivity. Typical amp will have a balanced input and unbalanced output for coax. Allison
14888	2018-06-14 12:11:31	E-P Mänd	VS: [emrfd] Amplification of ferrite loop array
Dear friends, I have an article (in paper only), Electronics World, August 2002: Calibrating LF antennae using DCF39. [Antennea = latin, in english antennas, strange mix of languages!] Article compares various non-ferrite large loops and ferrite rod aerials at 139 kHz receiving. Main result: Resonating antenna gives at least 8 times more voltage than non-resonating antenna. High-impedance FET amplifier needed to get any results. Low impedance destroys antenna effect. Authors: (possibly, not stated) DK8KW and OH2LX. Kindly, EePee = OH2NFI. Lähettäjä: emrfd@yahoogroups.com [mailto:emrfd@yahoogroups.com] Lähetetty: 11. kesäkuuta 2018 08:00 Vastaanottaja: emrfd@yahoogroups.com Aihe: [emrfd] Amplification of ferrite loop array I am trying to amplify an array of ferrite rods for LW / MW / 160m DXing. This antenna is a circular array of perhaps 20 to 30 ferrite rods and has tremendous signal gathering ability for a small antenna. It works well in a tuned configuration where there are enough turns in a pickup coil to resonate with a standard 365 pF cap. The problem arises when I remove the cap and try to generate an untuned, broadband input for an SDR. With no cap, the gain is so low that amplification is necessary. My first shot was a balanced FET input preamp but that failed to deliver much if any gain. The second attempt was a medium Z preamp - the Wellbrook FLG-100 which has a couple of K input impedance. No luck. I don't know why the FET preamp didn't work. Chuck [Non-text portions of this message have been removed]