Re: Tube Hi-Fi directional AM antenna?


Gabriel Velez
 

I say if it works as it is, and provides you with the stations without them stepping on each other, then simply use it as is.

I think the matching transformer would be better for the PL-390, but you would not need it for the Fisher. But use 75 ohm. 50 ohm is generally used for transmitters and two-way HAM gear.

For AM, it is virtually impossible (it is possible, but needs a big back yard) to make 180 degrees directional (but it *is* 90 degree directional, unless one uses a long wire antenna and small non directional coil) for a couple of reasons. One is the wavelength. The wavelength for FM is, using 100 MHz, 3 meters (one an use 1/4 wavelength to make a very effective antenna, which makes it 2.5 feet). AM at 1 MHz is 300 meters. The other is AM is more ubiquitous. One can get a signal from both the ground and the air. That's some of why AM can be received from a much further distance. In fact, I was reading an article from the 1970s speaking of how using trees as antennas worked well for low frequencies.

Even attenuating AM one still gets weaker stations bleeding in.

Of course, one can play with AM traps but it is more suited to reducing the strength of adjacent frequency stations which overpower weaker stations. But not on the same frequency.

Gabe

--- In ultralightdx@..., "farmerik" <farmerik@...> wrote:

I did receive the directional FM antenna ordered from Universal Radio, and tried it on my PL-390 because it has ETM.

On the fully extended whip, ETM locked onto 32 stations here about 5:20 PM local time and using the directional antenna I got 59. I turned the antenna about 90 degrees and got 57.

I wasn't sure if the PL-390 would like the 300 Ohm antenna connected without a matching transformer to the 1/8 th inch mini telephone plug, but it does seem to work well. Does anyone think a matching transformer to 50 or 75 Ohms would be significantly better?

The directional antenna is just near the ceiling in my radio room, only a couple feet higher than the top of the whip, not outside on a mast.

In switching from the 4 foot LW loop and putting the FM antenna in that spot, I damaged the end winding. I had been considering removing turns and using it for AM BCB. If I left some turns and grounded them at one end, does any one think it would shield AM signals from that side enough to help? [when an other station on the frequency is in the opposite direction?]

The reason I ask so many questions as I do is because I am disabled, and just trying things can take a lot of time and effort, so I'd like to only try things which people with more understanding of radio theory think could work.

-FARMERIK

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