Re: Build Experimental Loop for LF to HF.


My working levels came from a DoD receiver specification that was lying around. Take two signals into the receiver front end and vary their identical levels upwards until the 3rd order IMD products were 1uv - if I recall correctly. The test signal level in dBm plus 107 dB is the dynamic range. They were looking for 80 dB. (None of that ARRL horse manure about the sum of the levels - each signal was -27 dBm with IMD products at -127 dBm. So I was testing around -20 dBm to -30 dBm.

(And nothing really beats physical size for antennas. And a simple loop can easily be large enough that you need a LOT of ferrite to get equivalent performance. HOWEVER, there is the detail that if the antenna is 0.1% efficient at MW a bigger antenna will generally not give you better performance.)


On 20201206 09:30:02, Mag loop Simon wrote:

In my honest opinion..

Ferrite antennas are really down on sensitivity compared to tuned mag loops. ( tried it.)

Useful for dfing..but no one uses them for low noise dx Rx antennas..there is a good reason for this ..

Ok if one builds a ferrite antenna from LOTS of bars then they can start to be of use..but y? When can do much better with a rx only multi turn loop. ( less cost more Q etc.)

Re varicap diodes for tuning..been done for years..problem now is finding suitable diodes..and really they make any difference to imds etc with the small voltages developed across loop, ( unless real close to AM broadcast station etc.)

Main issue with remote high Q loop antennas is tuning..this can easy be got around with stepper motor..

I have alot of experience with loop antennas..I use a LARGE one for 160m tx..

Simon g0zen 

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