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Sunday 26 March 2017

thoughts turn again to the magnetic loop antenna

With the Blackpool rally now 2 weeks away, my attention has again turned to the magnetic loop antenna I plan to build for 10-12 metres (though 12-metres may not be immediately possible due to lack of equipment for that band), sizes, capacitor values, even the feedline from the antenna to the radio is now being worked out.

The capacitor can probably be sourced from the Blackpool rally, the copper tube to make the main loop is available from Wickes as it is the cheapest I have seen it, Homebase don't sell it for some unknown reason and B&Q sell it for more than Wickes, I hope to get the tubing this Saturday for both the loop itself (copper) and the support (plastic), the coupling loop can be made out of RG58 or some other coax with the braid and centre shorted together, or the same copper tube as the main loop.

The design I had seen by Larry WD0AKX also incorporated a meter, though I plan my final build based on this design it will have an enclosure over the capacitor which will contain a motor on a gearbox to tune the loop with the capacitor and I will keep an SWR meter on the feeder, for initial tests though tuning will be done with the capacitor and a plastic tool to avoid stray capacitance from my hands, my final build will also be suited to 50 watts (maximum on the Intermediate) if I find a capacitor that can handle the resulting voltage but until I get my intermediate I would only transmit at up to 10 watts, for CB use I'd always be at 4 watts or 12 watts PEP for SSB on the midblock.

Naturally I also want both my CB and my 10-metre rig to both be connected so I don't have to go behind them to swap the coax over, this requires a switch, preferably one capable of dropping the output of the "disconnected" radio into a dummy load and the "connected" radio onto the antenna, such a switch does exist, my good dummy load is, however, rated only to 50 watts, though this would protect the finals of both radios, though the SS9900 does have a HI-SWR function that prevents TX if SWR exceeds a preset limit however I prefer the reassurance of a load always being there, as repair of the finals is something I have no time to do, this idea makes sense as the President Grant II does not have a high SWR safety cut out, much like many off the shelf CB radios.

Hopefully I can start gathering what I need to build the magnetic loop antenna this week save for the capacitor which I hope to get from Blackpool or Ripon if it comes to it.

73 de M6RSQ

Sunday 19 March 2017

Rescue Mission

As you may or may not be aware, I have a temporary mast setup consisting of a fibreglass mast, a TV antenna pole, and a 25kg cement parasol base, which at present is not set up with any antennas on it.
For a time, the parasol base, as it is heavy, and the near 2 metre antenna pole have both lived in a shed that is incorporated into the building for the storage of conventional dustbins, this arrangement suited me well until I received a letter from the district council along with a black and white photograph of the contents of both sheds, demanding the tenants in this block cease storage in these sheds and remove anything they have stored within by the 31st of this month, after that date the council would dispose of anything still left in these sheds and fit locks to prevent further use in this manner, I had to act and today I finally rescued my temporary mast base, both parts, from the council’s mercy.
With the pole and base both now safely within my flat, I am at a loss as to where to store these, so in the mean time I’ll look to put them under the bed until such times I can do something about storage outside again.
The securing of these sheds gave me an idea however, if they are to be permanently locked, with no bins stored in them as wheely bins are too big to store here, I could mount a plantpot mast containing a magnetic loop at the top and get on the air from home at last on 10-12 meters, even CB/11-metres, which I have not played with since I took my old car to Tan Hill.
Something good may come out of something bad.

73 de M6RSQ

Thursday 2 March 2017

ShackCam update

The shackcam is currently still down as I have yet to complete the hardware, however the Raspberry Pi Zero which I intend to use now has an update allowing me to make it easier to set up, it recently had WiFi added to it meaning one less device.

Externally the camera, when finished, will still appear the same, and should still function as intended, it just means now that all I need to complete the job is one power cable, one Pi Zero, the current version of the camera and the adaptor cable to connect the camera to the Pi Zero.

This comes as very welcome news because it means not only don't I need a WiFi dongle but I also do not need a USB-OTG lead, two purchases I no longer need to make.

Hopefully I will have this built after my planned 10-12m magloop.

73 de M6RSQ

Wednesday 1 March 2017

Remote magnetic loop antenna tuner

As you know, magnetic loop antennas require a tuning capacitor to tune across a range of frequencies,this is usually done manually by tuning the antenna with the capacitor, for maximum noise or strong signal and low SWR.

Manual tuning is not always ideal if the antenna is some distance away, a remote tuner is needed and this is usually two parts, a motor with a reduction gearbox and a remote control with electronics to control the motor.

I have found a suitable circuit that can do this and the majority of the parts and the motor can be obtained from the same place, there is a transistor in the circuit that has been discontinued so I have to find a suitable alternative, which I am working on now.

Obviously I have yet to buy a tuning capacitor to build my loop but I have an idea where I can obtain these and can test the controller before I connect the motor to a capacitor.

further research is needed but I should be able to begin construction by the end of the month.

73 de M6RSQ