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Monday 31 January 2022

Fun with fitting roof bar mounts for antennas

I've fitted roof bars to my car and mounted the two antennas to them, the bars are coated in plastic and their mounting hardware is powder coated, however the bolts holding the fitting kit parts to the car showed continuity to the bodywork, the CB antenna at the very least needs bonding, which I have done using a piece of 27A DC rated cable, but this may be posing a problem itself so I will need a braided strap, while DC continuity is all well and good there could be reactance in the copper cable used, so a braided battery strap is needed instead.

This would be run from the bolts on the CB mount. then one of the bolts holding the roofbar mount fixing plate onto the mounting points on the car.

Using the wire, which is stranded, I got two low-SWR points either side of the CB allocations (SWR remains high within the band) once the mount was bonded, with the wire at the full spool length (2-meters or so) the SWR was much lower but it really needs bonding.

The 2/70 colinear antenna is offset from the centre towards the driver's side of the car, early tests on the VNA suggested that on 2-meters this antenna is working fine so I do not know where the antenna is getting its ground from on that band, I've not checked this on 70cm as yet.

As the VNA battery ran out during tests today I tried to power it from the car charger, this created a ground loop because the car electrical system has its negative grounded to the body as well as is the case in many modern vehicles.

Tomorrow I will pick up a braided earth strap of suitable length and try this on the car to bond the CB antenna as I suspect this copper DC cable I've used may not be working as expected.

73 de M0WNU/26CT730

Sunday 9 January 2022

New year and a catch up and eBay goodies

So we enter 2022, a new year and let's start as I mean to go on, so I did in the end buy the Yaesu FT991A after the tax refund I had but yet to get it on HF due to lack of suitable antenna so that's a work in progress.

I took the time to rebuild my desktop computer, as it was woefully outdated and could not process video fast enough. it is now much improved with the original hard disk being used for storage and the machine booting from a solid state drive, a 4K video renders at about the time the video takes to play back rather than many hours, 1080p videos are also quicker also and do not take hours to do.

I also had to rewire the CB antenna magmount after damaging the coax during a trip to the car wash, it is working fine and the SWR is low, one meter suggested almost perfect but other meters suggested that meter may have been a bit optimistic.

And of course, eBay goodies, I won an auction yesterday on what looked like a well used Midland 38, though it appeared not to have a microphone but the one from my existing Midland should work, as Knights sell these as replacements and suggest them for 38s, I am also watching another Midland radio and will bid on it as long as the price does not go too high and I will report back if I win it or not.

For a radio ham and tinkerer like myself it is no great loss if I buy CBs that do not work as I can attempt to repair them, old kit like this can often have failing electrolytic capacitors which should be replaced at the first opportunity, these are easy to spot, other parts like the PLL chips are a little harder to come by for some of the 80s classics as the usual ones used in those are long discontinued, the Midland 38 is a 1990s set so would not use the LC7136/7. prime suspects for other failures in radios like that is adjusted coils done by "screwdriver experts" who do not have a clue what they're doing, turn things with screwdrivers and break ferrite cores in inductors, though more often than not they set the deviation far too high thinking this results in higher power (it doesn't, it makes the radio sound crap and bleedover adjacent channels). so one tatty Midland 38 in the bag, another less tatty one if I win it could be here.

A commenter on my YouTube channel suggested I buy a K-Po power mic, I won't ever do this because I feel these don't really help matters at all, my desk mic is a power mic but has an awful capsule in it, a speech processor mic perhaps will, the most I'd want in a CB mic is a roger bleep but even then that's pushing it, the same commenter told me that Knights can wire the mics to whatever radio desired, however I prefer to do this myself as I generally prefer to wire my own CB mic plugs.

And on the subject of YouTube  I have a video to make which requires I put the antenna up so I best crack on with that.

73 de M0WNU/26CT730 (or just the red squirrel on the CB, and maybe later this year or next year my spouse will be heard on air once again too)