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As an alternative to the inverted L, ground system and auto-tuner I have been experimenting with the end fed half wave antenna (EFHW), sometimes known as the “Little Dutch Girl”. Feeding a half wave length of wire at the far end rather than in the middle as per the classic dipole means that the impedance at the feed point will be high. Around the order of 2500 ohms at resonance.
A 1:49 matching transformer is used to match the output of the transmitter and feedline to the antenna. These are conventionally made by winding transformers on a ferrite core with a 1:7 turns ratio.
In my small garden even with an inverted configuration as shown the lowest frequency I can fit half a wavelength in is 7MHz for the 40 meter amateur band. I have used an additional 2 meters of length to add a loading coil and a 1.5m length of wire to add a capability at 3.65MHz in the 80m amateur band.
I experimented with a commercial transformer, but ended up replacing most of the parts with more heavy duty components.
Here’s my 1:49 transformer based around 2 X FT240-43 ferrite cores:
In theory should be good for around 400W RMS or 1kW PEP.
And here’s the unit mounted at the bottom of the garden.
and the loading coil mounted on a former for the 80m band.
Spiderbeam 12m pole is up at the bottom of garden with Inverted L antenna, sloping back down to the house. Some encouraging results so far on 40m and 80m with US,European and North African contacts on 40m and daytime 80m signals being received at the Hack Green SDR. Clearly hiding the antenna in a tree hasn’t made much of a difference
Irritatingly I have managed to disable my K2 transceiver on Tx by shorting the VRFDetect line to 12V on the AuxIO sokcet when making up a RS232c lead for rig control and being a bit clumsy with a scope probe. Oh Well. I have had to send off to Elecraft for a new programmed MCU chip, as the A/D input is damaged and its taking an age to come!
I have been planning a return to HF operation, so the question of stealthy (small) backyard antennas comes up. The available space is the typical ‘not much’, roughly 55ft by 30ft
Plan A is an inverted L, fed via an auto ATU at the far end of the garden, with the horizontal section of the “L” coming back towards the house. So far A CG3000 auto-tuner has been obtained on ebay, and a 12m “Spiderbeam” telescopic fibreglass pole. Every plan should have a sketch, so here’s mine:
So the ATU will not tune easily a length of wire close to 1/2 a wavelength or multiples pf half a wavelength. I reckon the wire length will be around 23m. I have to keep away from 21m which is a half wavelength at 7.1MHz and multiples at 14.2 and 21.3MHz (!)
I plan to run radials under the lawn and along the bottom part of the wooden fencing.