TheRadioBoard

Had anybody tried it? will it be useful in regenerative receiver with RF amplifier?

I once made a loop for a SW regen. I set it up with a plug that could plug into the existing rf amp coil socket.

It didn't work very well. I attribute most of that to it being indoors compared to an outdoor random-wire. Loops aren't very efficient antennas to start with.

I've used my Hoop Loop up to about 3 MHz. Above that frequency the direction and polarization of a sky wave seems to fluctuate over time, making the nulling ability of a loop less useful. A small, single-turn loop, sometimes called a "magnetic loop" may work, but they are very lossy even when built well, due to the very low radiation resistance. A small resistance in connections is significant in relation to the radiation resistance. This type of loop has a very narrow bandwidth (if losses don't create the appearance of wider bandwidth!) and must be constantly retuned.

I assume you aren't referring to a full-wavelength loop. They have a large capture area and work very well, but they won't fit in an average house.

If size is a concern, try a whip and an active matching stage (which isn't a preamplifier, it only matches the high radiation resistance of a short whip to an impedance suitable for connection to a receiver). Here's one example: http://www.qrp.pops.net/probe1.asp The disadvantages are, susceptibility to locally generated noise, because the signal capture area is small relative to the difference between desired signal strength vs noise.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

I guess regeneration of loop antenna should help.
In "Radio" from 2007 was described receiver


Approximatly 9 cm coil of regenerative contour was serving as antenna in the same time. An people were satisfied with performance.
What about to repeat it with tubes?

For what its worth, I have built a few SW receivers using 3-4 inch air coils instead of smaller plug-in coils. They have always impressed me the most because they can actually receive signals with the antenna disconnected.

That's not to say that you "don't need an external antenna" but it is nice to be able to hear many signals without an external one.

You have to stay clear of the antenna if you make it part of the regen's tuned circuit, as body capacitance will retune your radio. Some radio stations might sound better if listened to as a Theremin, though!

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

I have been using a low-noise 40m shielded coax loop with a solid-state regen with an untuned RF preamp stage.

http://web.archive.org/web/200608051813 ... gloop.html

(Note: some of the images in that link appear to be broken, but if you click on them, they will appear.)

In this design, the antenna is balanced, so it connects to both the antenna and ground terminals of the receiver. For antenna comparison testing, it is possible to remove the ground connector and the antenna will become a random wire antenna.

I have this antenna mounted indoors on the 2nd floor, and when using the antenna as balanced loop, I can receive 40m CW when the band is open. The directionality of the antenna also has also come in handy for nulling out some broadband hash noise (probably from neighbors' plasma TVs or similar appliances) that would sometimes suddenly start up and wipe out the band.

If I disconnect the ground connector as mentioned above, turning the antenna into a random wire, it becomes impossible to receive nearly all stations; the noise level jumps dramatically. I'm not sure how to interpret the drastic jump in noise level when disconnecting the antenna's ground (shield) connection. It may be that the that when acting as a random wire, the antenna becomes wide-banded and overloads the receiver with off-band signals, whereas when acting as a balanced loop, the bandwidth is narrower, thus avoiding overload.

Anyway, I'm pretty satisfied with the above loop for its low-noise and directionality. Currently I'm using it without an antenna tuner, though the article recommends using a tuner. I did some preliminary experiments with a homebrew T-type tuner and they did seem to improve performance.

The braid acts as a Faraday shield. It has to be open at the top so it doesn't appear as a shorted turn. The purpose of the shield is to reduce electric-field pickup from local noise sources, while allowing magnetic-field rf signals to reach the inner loop.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/