Re: LF: DREAM 9 ANTENNA

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Thanks for the good advice Mal.  I do hope you can find some time to give 9kHz a go as you'd be such a valuable contributor to any experiments. 

As a more general question, at what S/N should one expect to receive the ~11kHz Alpha beacon on a well optimised RX?

73s
Roger G3XBM

On 11 March 2010 16:41, mal hamilton <g3kevmal@talktalk.net> wrote:

Probably an inv L or T antenna as high as possible for TX  is the best solution for 9 kcs. Base load the antenna with the necessary inductance for resonance and if necessary add another small inductor in series to ground and adjust with taps up from ground to get a 1 : 1 match with the coax feed from the TX,  readjust the main inductor to maintain resonance if necessary.

This system has never failed me on 73, 137 and 500 kcs and this would be my approach on 9 kcs.

RX is a different matter and there are a variety of antennas suitable.

I can RX the Alpha signals around 12 kcs at good strength using my 500 kcs 1/4 wave inv L and weaker on the 40m loop both antennas not resonated for 9 kcs.

Obviously if resonated the signals would be very strong with these antennas.

9 kcs is a lot easier to get going than the other LF/MF bands because there is an abundance of LF generators and high power audio amplifiers about,

I would suggest modifying a audio amp output to 50 ohms with a suitable transformer then use existing station equipment for monitoring and measuring.

Suggested approach for making a large inductor to resonate antenna.

Get several slotted laundry baskets size diam 600mm, height about the same, stiff plastic material. Wind some wire on a few and connect in series with antenna and check for resonance, then add baskets as necessary to resonate at desired frequency These baskets fit into one another and look tidy.

Use the largest diam wire possible to achieve the desired inductance. If using a vy small inv L with lots of Henries required then go for the water butt coil former.

Do not forget some earth radials and rods.

I could probably manage about 4 inv L antennas in parallel, 500 kcs size, loaded against ground and would hope the signal would travel some hundreds of miles.

If only I had the time.

de mal/g3kev

 

 

 

 

 

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