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Topics - CPR

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Antennas / Random wire antennas and tuners
« on: May 17, 2018, 09:22:06 AM »
I got myself a Z Match Multi Tuner from QRP Guys. With 35$ its quite cheap, but winding the toroids is a pain in the butt.
First, a question about the functionality before I head over to the random wire antennas. I hope that's okay and won't be classified as offtopic.

Yesterday I tuned my triband vertical and decided to try out the tuner with the vertical to see if it does something.
When I switch to "TUNE" I can get the SWR down to 1.1. As soon I switch over to the "OPERATE" position the SWR jumps over 10.. I was using my Mini60s attached to the tuner going then to the antenna. I thought maybe the power of the mini60s is to weak to get a reading on operate, but I am not sure and pretty clueless if the tuner is maybe malfunctioning.

Another question is the random wire, assuming the tuner works, I thought about attaching the random wire and use it as an endfed antenna! Would be the cheap option for now, as my favourite endfed multiband is the mini from HyEndfed and with over 100 it's clearly over my budget at the moment.
Anyway, I found a good website about random wires:

Does anyone have any experience on the "best" length given: 
A standard recommendation (see QST, March 1936, p. 32, "An Unorthodox Antenna") is an 84' long end fed and a 17' long counterpoise (6.5' for 20m)

How do you layout the counterpoise at a random wire? Do you have to adjust the length of the counterpoise depending on the band tuned or does the tuner take over that part too? I don't understand what they mean with this 6.5' for 20m in the bracket.


Batteries & Solar / Salvaging old Notebook battery
« on: April 09, 2018, 08:21:43 AM »

I just found an old notebook battery in my cellar and decided to give it a try. I was able to salvage 8 x 18650 cells. 6 are still on 3.71V, 2 are on 2.1V unfortunately.
After googling I found out that those are 2600mAh cells. Pretty neat!

Is there a way to revive those cells on 2.1V or are they gone?

I think about a 3s2p battery bank with a built in BMS. Would give me 11.1V for the 817nd. I think thats quite good, I could use a step up converter to boost the voltage if necessary (or if it makes sense).

Batteries & Solar / USB Solar charger 5V to 12V
« on: March 19, 2018, 11:57:04 AM »

I was wondering if it's possible to use a 5V 2Amps solar charger to charge 12-14V batteries if using a step up converter. I own an Anker 14W solar charger with two usb ports, apparently they can deliver 1Amps each. Looking at those 12V portable solar chargers, they are way over my budget. Somewhere I read that you should charge batteries with 10% of their Ah specs. So let's assume I get a 12V / 7Ah SLAB and using a step up converter, I should charge it with 800mAh.

So, taking the real power of my solar charger, which is not 14W rather 10W (5V x 2Amps) I could deliver
P = U x I => I = P / U => I = 10W / 14V = 0.710A of charging current with 14 Volts assuming the stepup converter has no significant loss.

Is that realistically possible?

Another approach would be to see if the panels are delivering 5V or rather 12V and then transformed to 5V. Or, combining the two USB outputs to one giving me 2Amps at a time and increasing the charging current. I really like the idea of charging my batteries when in the field, but the 12V portable solar panels are really over my budget.


Radio Reviews, Questions and Comments. / Yaesu 817 vs 857 / 5W vs 100W
« on: March 02, 2018, 08:48:52 AM »
I want to get an all in one radio as soon I get my license.
I like that 817 a lot, its small and great for backpacking and camping obviously. Also, the small current drain is really appreciated. The only thing I am worried about is the 5W of power.
Hows the practical experience using 5W? Can you reach distant stations easily or is it really dependent on the atmospheric conditions?
Does the additional 95W make a huge difference that justify hauling double the weight and size on the radio + 1 x 2-3kg battery in the backpack?
I also read somewhere the 817 has a built in antenna tuner and the 857 doesnt.
Because I will most probably buy only one radio I dont want to regret my decision so I am asking on practical experience.

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