Sunday, 11 March 2012

Pop, pop, pop rivets!

OK, so not pop rivets, as yet. Planning the mobile installation, ive decided that a 'cage', in effect, is needed in the boot within which to mount the radio and ancilliaries. This is to prevent anything else in the boot from banging into them. The intention is to fabricate a L shaped frame from sheet aluminium or steel, and bolt this to the wheel arch and the floor of the boot. Within this, a shelf/frame will be fitted. The radio, tuner, fusebox, junction box, interfaces etc, will bolt to the frame or the inside of the cage. A DC socket will be provided as well.

This is where the pop rivets come in. They will be used to attach the framework. To attach the cage to the car, ordinary machine screws will be used, but the car bodywork will have 'nutserts' installed. These are rivet in threaded tubes, and provide a secure and simple mounting.

The tool and inserts to do the nutserts is on order. The pop riveter i'll pick up from ASK when next that way out. The only other thing i might need is a bending brake, to form the bends and flanges of the cage.

The 2.5mm2 DC cable has been routed along the left hand sill, but has not yet been fed through the firewall into the engine bay. This will be done when i have the necessary crimps and fuseholders to attach to the battery.

I had intended mounting everything on the left hand side of the boot, as this seems intuitive. But its not to be, as the spare wheel carrier goes right over to the left! On the right however, there is a 9" space between the wheel arch and the carrier cover board, just enough for the cage. It means i have to route the DC cable around the inside of the boot to the right hand side, but the signal and control cables (head cable, mic cable etc) can run up the right hand sill. Mounting on the right makes perfect sense, in a country who drive on the left, as it means the antenna will be mounted on the right of the tailgate, away from pedestrians, bikes and low branches. Its also, on my car, diametrically opposite the fuel filler cap!

I have to finish the HF mounting. This will need bolting to the car, then continuity testing to make sure the ground path is good, before final paint spray to match the car body, and laquering. Ground strapping will also be needed on the hinges of the tailgate.

I have installed the first Panorama M8 mount, roof center, for VHF/UHF. It currently got the 5/8th 2m whip on it, and working fine. But, I installed it with the view of the equipment being mounted on the left, so the coax routes down the left hand pillar. I'll need to correct this over to the right (which will also mean it doesnt cross over the washer tubing to the rear window!) but that means yet again dropping the headlining. I might wait to do that when i have the next mounts ready for the roof! I'll post the pictures of that install job in the next update.

As regards mounting the control head, i searched every possible location in the car, and short of getting a new stereo with DIN sized fitting, so i can mount it to the blanking plate, the only sensible place is to the right of the steering wheel, where the rig was in the old car! I havent decided on the speaker location yet.

Wednesday, 7 March 2012

Sams Valve Radio - Almost

Work started again today on Sams single valve regenerative set. Up to now this was dogged with troubles as it just simply didnt seem to work. Well, i sought advice from the chaps at G-QRP club, always a helpful bunch, and received loads of info back. It seemed the first task was to up the HT voltage.
So, I went out today and bought 10 PP3's from which to build a 90v B+ battery. Well, they only had six on the shelf, but the assistant was stocking the batteries up. She at first didnt think there were any more, but i spotted a box at the bottom of her trolly. A box of ten. So i bought the whole box. The end batteries, where the connections to the pack are, have had shrouded 4mm sockets soldered on, and then the whole lot taped over, so as to prevent any contact with the terminals. As new, it measured 98.8v! The smaller pack is the present heater battery, 6v, although reading a bit low, using 4x AA's. In the future i'll change this for four C or D cells.

This is the view of the front panel, the big knob, which incidentally isnt big enough with a 600pF variable capacitor, is the tuning, and very delicate it is too! The bare shaft is the regeneration control pot. The 6K7G pentode valve can be seen behind the panel. A bandspread capacitor may well have to be fitted.

It can easily be seen that there is very little to the radio underneath! The view from above shows the main components, the big 600pF air spaced variable, the valve, and the audio transformer. The ferrite rod antenna has had its main winding progressively reduced to bring the tuning onto the MW band at a sensible spot and now has only about 55 turns out of the original 80, the smaller winding is the 20t tickler coil.

In its present state, its possible to find a couple of stations during the day. I think the big problems now are that even with the transformer, the audio output into low impedence phones is poor, and the tuning is far, far too coarse.

Tuesday, 6 March 2012

Mobile mounts agogo

Ive taken the MB-400 mount off. As it turns out, its not that distorting the boot lid, it seems the boots not a perfect fit anyway! Ive decided permanent through body mounts are the way to go. Im not bothered by drilling the car, lets face it by the time i sell it it will be knackered. So, im building a mount to bolt to the tailgate by the number plate, using a right angle section of steel plate. Below this will be fitted to the car a cable gland, to take the RG-58 into the car. Im priming the mount,a nd when im next near A.S.K i'll get some matching touch-up paint, it will look like it was made for the car, which of course it is!

Tomorrow, if alls well, i'll go through the rigmorole of removing the internal panels and lowering the roof lining, in order to drill the roof and fit a Panorama M8 mount for VHF/UHF.

Theres no rush with any of the mobile install, as i havent received the seperation kit yet. But i might as well get the antenna mounts sorted and run the power cable if i can.

Talking of cable, i managed today to run the spare coax feed (from the broken 2m Slim-jim) up the side of the house and into the loft. I'll mount a BNC patch box somewhere up there, and then can try different antennas on it. The first i think will be a 10m dipole!

Friday, 2 March 2012

Mobile HF

The Sharman MB-400 mount is nice, strong and well made. Thats all you can say for it! Its four 4mm 3mm grub screws i doubt will hold out long, and the nice black paint coating is non-conductive - theres no ground path through the whole thing!

The 105ADT 3/8th mount didnt fit the 16mm hole in the MB-400. So, so carefull grinding, cutting and o-ring selection, and ive modified it to fit. Its attached to the car, but i feel that additional work will be required to create a usable ground path, probably straps from the mount to the bodywork.

Im going to test the antennas on it later using the MFJ-259B, and see what the whips are like, at the very least i'll be able to positively identify which is which. I still think a through roof mount is going to be best, although the whips are very long!