Heh gotta love it; the oldest of all calibration methods... empirical analysis resolved to a pencil mark on the dashboard. Decades from now someone will wonder what that mark meant, (if your pet doesn't wind up straight in the tip the day after as you go tits-up) and if they have any sense at all, they'll leave it there until they learn enough to grok it's purpose. Wonder if this would make a good cage coffin for a very small ex parrot Glued up, coating of Orange oil for finish just need to add some felt lining now.
Have to run, I have some TEA both cooling down and some warming up to play with
Actually, when I first saw it I thought to myself
*That is a dandy little cricket cage; perfect for walkies...* It actually is quite in keeping with a number of traditional styles over the centuries.
For those who don't know,
keeping crickets as pets for their song or for luck has been a thing for thousands of years. Whoa, wait a minute. Before you Throw the bath water out, cycle the batteries to see if it is just a memory problem. Nicads develop a "memory" if they are discharged to the same voltage over and over. The memory is they begin to act as if the repeated discharge before recharge voltage is the new ground and they stop giving power.
The trick is to completely discharged them through a resistor to zero and then charge them completely, then wash and recycle. It takes several to many cycles of this to erase the memory in a nicad bank. Sure, they could be toast from use or age, but it won't hurt to try first. Read more about cycling nicad batteries in various radio control forums or solar panel forums.
Many people claim the memory effect only occurs in special circumstances, since it requires repeated discharging to the same depth.
OTOH, while discharging NiCd (and other) cells with a resistor is reasonable, with batteries it is suspect. The problem is that fully discharging a battery implies that the weakest cell or cells will be reverse charged, which will harm them.
I conjecture, without evidence, that effect is mistaken for a memory effect.
That is a much more concise explanation than the one I was just about to draft up; thank you for saving me a lot of time.
As Ni-xx cells age, through time or abuse, the chemistry and therefore the IR of individual cells changes. While trickle and/or shock-charging/desulfating techniques can in some cases rejuvenate a few
individual cells such that they have useful capacity again, it is very rare that they ever recover full capacity once they've gotten to this stage, and
almost NEVER do you recover an entire battery PACK to full capacity, or even a 25-50% level of useful capacity. As Ni-xx packs are not commonly balance-charged, that makes the likelihood of repeating the death scenario you describe above pretty much inevitable; therefore your least assache solution really is to just rebuild with new cells of same brand/part# so that capacity and IR all match reasonably closely.
Batteries (no matter the chemistry) are livestock; the worst abuse you can do to them is to not use them as a storage medium. Load them down, discharge them, recharge them regularly per manufacturer's recommendation and they will love you long time.
It will be a POS. Once you've lifted a "portable" real SA, or looked inside a "real" SA, you will begin to understand why.
I think the thing for me is that the HP SA’s are pretty good until they go wonky at which point they are murder.
Yes I had that 7L12 don’t forget which I had to excavate here: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg1849262/#msg1849262
I think a simplistic homebrew SA, while not suitable as a precision measurement device will allow useful things to be done. Such as filter sweeps, looking at TX harmonics, mixer products etc. Even if it only has 70-80dB of dynamic range and a 100Mhz span that’s good enough for stuff at HF.
I can build a 200Hz filter easily with crystals so RBW at 2nd IF can be quite tight too. Better than those Thurlby SA boxes.
My very first experience with a SA was in my Tech School daze; the WaveTek reps brought a SAM 450 and demonstrated it's SA output connected to one of the bench scopes. While in principle I agree with tggzzz; anything you make will likely be poop on a PCB, the SA function of the SAM was at least usable as a basic diag tool.
Since they regularly eBay in the $25-45 range, and there are multiple generations as well (though the digital tuning of later models may introduce noise that is problematic to the SA function) to choose from and
mod for other purposes, might be worth a few shekels to acquire one of them for your your tinkery time abuse.
Would probably save you a lot of assache and give you a much better starting point than reinventing the wheel from scratch. mnem
I have too much blood in my caffeine circulatory system right now.