Andy's Postbag and random ebay links

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RogerClark
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Re: Andy's Postbag and random ebay links

Post by RogerClark » Wed Jan 31, 2018 10:23 pm

I have a SWR meter, which coincidently I took to pieces last week to try to improve its frequency range by replacing the 20 year old Schottky diodes with more modern ones.

Its basically like Andys schematic there is a PCB with a track that does a sort of zigzag across from one side to the other, to slighly increase the track length.
This track is connected to the input and output plug (centers)

On either side of this track are to slighly thinner tracks running in parallel, but a few mm apart.

Each track has a diode connected to it, which is connected via a switch to a meter.
(strangely one track has 2 diodes in parallel and the other only has one diode, but I presume this is to cope with the amount of forward power vs the reflected power which would be a lot less)

Anyway, this works OK up to about 144Mhz (2m band) but does not work on 432 Mhz (70cms band) even when I replaced the diodes with faster ones.


I have seen more modern designs, which now just use a direct piece of coax between the input and output connector, and have a ferrite ring around the coax, and the pickups are wound onto the ferrite ring

I think this is a more modern design

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BennehBoy
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Re: Andy's Postbag and random ebay links

Post by BennehBoy » Wed Jan 31, 2018 10:50 pm

The main problem with offroading is having the antenna knocked off the vehicle.... "why is nobody responding?!" :lol: :lol:
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BennehBoy
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Re: Andy's Postbag and random ebay links

Post by BennehBoy » Thu Feb 01, 2018 10:49 am

ahull wrote:
Wed Jan 31, 2018 9:16 am
I seem to recall building a couple of SWR meters out of surplus movements back in the days when CB was really popular round here. The schematic was pretty simple so far as I remember. Eventually they became so cheap that it wasn't worth building your own. On one occasion I managed to get a decent SWR on a carefully tuned sewing needle, just to prove a point. Needless to say the needle got a little hot, and didn't transmit that well, but neither did it blow up the output stage of the radio.

The more sophisticated versions contained op-amps and possibly a 555 timer?! but I can't think why... I'll need to do some googling.
My plan is to re-use much of the componentry from a cheapo (maplins) SWR meter but have the display and controls digitally operated via a bluepill/mini.

It's not super high on the list of priorities however :D
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ahull
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Re: Andy's Postbag and random ebay links

Post by ahull » Sat Feb 03, 2018 1:16 am

You may have spotted a couple of canary yellow £0.72p shipped from China, cheapest power banks available from the darkest recesses of ebay in the previous pictures. I finally got a chance to pop a couple of ex laptop 18650 cells in them, and they actually work. Blinky flashy lights, and no smoke(*).

Now I know what you are thinking, I can get an 18650 powerbank from the pound shop for .. well a pound obviously, so why would I bother with even cheaper ones, and the answer is, cos they were seventy two pence, about the cost of a Mars bar (other confectionery is available etc.), and 'cos I have a bunch of old laptop cells lying about that need a home, and laptop cells are usually a lot higher quality than the sort of thing you will get in a Poundland/Poundworld powerbank.

Incidentally my spell checker suggests Poundworld should actually be spelled roundworm..


(*) so far.. but you never know... they were only 72p :D

Image
The "brains" of a 72p powerbank.

NOTE: After I purchased these, I later found an even cheaper supplier. .. so I may order a couple of "Approximately £0.58" power banks. They work out cheaper than buying the bare charger board.
- Andy Hull -

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RogerClark
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Re: Andy's Postbag and random ebay links

Post by RogerClark » Sat Feb 03, 2018 5:50 am

Andy

I don't think they include the battery

See the description on the 72p version
Please note this is a DIY Power Bank Case Kit,You are required to assemble them yourself,and the battery is not included !
I bought something similar from another company and only received the cases, and No Batteries

After carefully checking the listing, they had put in some obscure text to the effect of "battery not included"

I'd be surprised if yours include batteries

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ahull
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Re: Andy's Postbag and random ebay links

Post by ahull » Sat Feb 03, 2018 11:20 am

@Roger, I know these doesn't include the battery (hence the low price), but I'm using them to allow me to use up some of the old laptop 18650 cells I have lying around.

Generally the cheap power banks that do include a cell, have some underpowered thing (around 800mAh or so is typical), whereas the laptop cells are typically >2000mAh and in my case, I got the old laptop batteries for free.
- Andy Hull -

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RogerClark
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Re: Andy's Postbag and random ebay links

Post by RogerClark » Sat Feb 03, 2018 8:26 pm

Andy..

Ok.

I don’t have a supply of laptop batteries, as I used up all the ones from my old laptops already.

I did manage to score a drill power pack the other day, from a recycling bin :D , but 2 or the 4 batteries in it were defective.

I was going to upgrade one of my NiCad cordless drills with it, as it’s an identical fitting to one of my old drills, which has dead nicads in it.

But the cells in the LiPo pack, as welded in, with 1.5cm wide straps on their terminals, and the only way I can think of to remove them, is to use a small disc cutter e.g. dremmel , to cut the straps.
I have ruined at least one pair of side cutters trying to remove batteries from other packs, so I don’t think cutting them out , that way, is an option.

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zoomx
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Re: Andy's Postbag and random ebay links

Post by zoomx » Tue Feb 06, 2018 10:49 am

I did the same but nowadays laptop batteries seems not to use 18650 anymore, they are too thin!

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Slammer
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Re: Andy's Postbag and random ebay links

Post by Slammer » Tue Feb 06, 2018 12:04 pm

This cheap Power Bank case is working well, but if you want something more check the TOMO M2/M3/M4 Power Bank cases, they are very capable devices.

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ahull
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Re: Andy's Postbag and random ebay links

Post by ahull » Tue Feb 06, 2018 3:35 pm

zoomx wrote:
Tue Feb 06, 2018 10:49 am
I did the same but nowadays laptop batteries seems not to use 18650 anymore, they are too thin!
This is true. A lot of the more modern laptops use pouch cells, however there are still loads of older laptops heading for the scrap pile that you can salvage 18650s from if you need them. Better in a power bank than in landfill I would suggest (although ultimately landfill is where the majority of them are likely to end up, since LiPos are tricky to recycle, and most users simply bin them in the general waste stream).

Recovering pouch cells is not really that much more tricky than recovering 18650s. They charge basically the same way, and so long as they are not subjected to extreme mechanical damage, or shorted out they are relatively safe and easy to use.
- Andy Hull -

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