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

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

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

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

Magnetic loop antennas–a follow up

As I have mentioned previously I have a desire to build a magnetic loop antenna for HF use, primarily with my CRT SS9900 on 10 metres, though something that could cover 12 through to 10 metres meaning will work on CB as well as I still have a keen interest in that side of things despite holding an amateur radio foundation licence and hoping to go for my intermediate exam very soon, as alluded to in my last post.

My antenna situation as you know is very poor right now, made worse due to the fact I live in a first-floor flat, though I have a CB antenna in the attic it functions very poorly with high SWR readings and the need of a tuner to prevent damage to rigs connected to it, though this antenna works on 10-meters as well the tuner does not and to get the SWR to safe levels requires it be tuned with both sides turned all the way up to 10 (the unit is a Euro-CB EM-110 and is really suited to 11 metres rather than 10 metres), 2 metres is currently done with an antenna on a biscuit tin, also poor but it does work.

This is where the magnetic loop comes in, and I saw a YouTube video showing a design made out of copper tubing, with a power meter on the larger loop itself, a variant of this design was also on YouTube by an English member of Charlie Tango (of which I am a member with the callsign 26CT730) for CB use, with the right capacitor and correct dimensions I should be able to build a loop to this design (without a power meter fitted to the loop itself as I intend to fit the loop with a remote tuning system utilising a stepper motor and gearbox) and be able to start using 10 metres, despite the poor conditions at this time on that band I am eager to give it a go, also as I have not played with 11 meters since I scrapped my old car this would be a good opportunity as I understand CB is alive and well and there are regular nets held now, even on the midblock using AM and SSB since those modes became available to UK CB operators in 2014, but naturally I am keen to give 10 metres a go, whether I get a working magloop before or after I get my intermediate remains to be seen however I intend to make sure I get on 10 metres regardless, I have invested in equipment for that band I may as well use it.

I know I can get copper and plastic tube locally but for a suitable tuning capacitor I may have to look to rallies to do so, the requirements are that the tuning capacitor will work happily up to 4kV (though I suspect 50 watts is far below this but I like the idea of a safety margin).

The antenna will be connected with a suitable SWR meter in line almost permanently, my Zetagi Mod. 203W is perfect for this as it covers a frequency range of 26-30MHz for TX power measurement and 3-200MHz for SWR measurement.

I will post more on this subject as it progresses

 

73 de M6RSQ

Upcoming rallies–planning

As you know since I was licenced in 2015 I have attended whatever rallies I could, notably these have been the Blackpool rally at the Norbreck Castle Hotel and the National Hamfest, though in December I was also at the Bishop Auckland rally in Spennymoor, this year that is to be improved on and plans are already underway.

It comes as no surprise that the first rally I will be at this year is indeed Blackpool on the 9th April again at the Norbreck Castle Hotel, only a couple of weeks later I plan to be in attendance at the Ripon rally as I missed it the last two years, of course I will also be at the National Hamfest again this year, as well as the Bishop Auckland rally in December.

one of my main aims is to get hold of a suitable tuning capacitor for building a magnetic loop, for this I will take my multimeter with me as that can measure capacitance, if I can also find some other materials suited to building a magloop that will be even better as I am very keen to get on 10-meters (and HF in general) and if I can source the parts at rallies that will be excellent, of course I need to know how much power I can get away at putting through a tuning capacitor, so I shall ask of course.

Hopefully I can complete my aim at either Blackpool or Ripon.

 

I’ll post an update once I have attended the first rally, of course that is Blackpool.

 

On closing I hope to take my intermediate exam soon, wish me luck

 

73 de M6RSQ

APRS map display on tablet

I found that it is possible to connect a tablet to the Yaesu FTM-400 to display the data on a map (in a similar manner to aprs.fi), this only uses the data cable that the radio is supplied with and a USB-OTG adaptor.

APRSDroid isn't reported to work with this in this manner, so a different app and approach is needed, after a little bit of searching on Google (other search engines are available) I found a suitable app that reportedly works with the FTM-400, and needed only two setting changed, both in "DATA" in the main menu.

Before venturing down to the car to test this out I tested my tablet (a Huawei MediaPad T1, the 4G and WiFi model supplied by EE) with the USB-OTG adaptor I had spare and the data cable supplied with the FTM-400XDE, the tablet operated as it should have, I then went to the car to connect the radio and tablet together and it worked again as it should have, each station received by the radio was displayed on the tablet, and if it contained location data it would also appear on a map, exactly as intended.

Now I know this works I have to solve a second problem, running the tablet like this with the USB-OTG adaptor plugged in means it cannot be charged, I need to find a way to allow the tablet to charge and at the same time run the interface between radio and tablet to display the APRS data on a map, at the moment my efforts to figure this out have come to nothing, replacing my car's stock head unit with one that runs Android is a possibility but these are usually double-din and are expensive so I have ruled this out, modifying an OTG cable may also be possible but I have not found any schematics that do this, safely or otherwise, of course I shall investigate this

My third problem is a mount for the tablet so it won't get in the way of anything while the car is under normal operating conditions, though for obvious reasons I'd not look at this while driving, of course I have to figure this out owing to the car's lack of useful space and where the data cable will need to run, this is now a work in progress,

Now I have it working I'll see how it pans out

73 de M6RSQ