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Weird behaviour with 9 volt battery connector and oscillator circuit

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In the process of constructing a wideband home brew rf signal generator,I noticed some very strange shinanagins with my pp3 9 volt
Battery connector.A simple colpitts oscillator followed by a buffer stage was constructed ugly style on a copper clad board.The current drawn by the buffer circuit was observed.In trying to match impedance of my next stage which will form a cascode amplifier.The emitter resistance of the buffer stage was varied to see how close I could get to the input impedance of the cascode stage ( common base amplifier which could be as low as 30 ohms.Without the buffer the colpitts oscillator signal has an output impedance of about 2.6k ohms.Definately too high to be of any use in a cascode circuit.Most commercial rf generators have an output impedance of 50 ohms which is what I was trying to achieve.As I lowered the emitter impedance down , I noticed the oscillator signal gave up at around 500 ohms.When I pressed hard against the pp3 battery connector I noticed the signal was restored,I could then lower the emitter resistance furthur until I achieved my 30 ohm target and drew around 30 ma of collector current in the buffer stage.Can anyone explain this weird behaviour as I have never noticed this before.

I was trying to keep the supply to the rf circuit as clean as possible,by utilising a battery supply instead of a mains psu.Also plenty of decoupling,rf choke use and good construction techniques,keeping all lead lengths as short as possible.
 

audioguru

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Obviously, the connector on your circuit or the connector on the battery was making a poor connection.
 
I knew the circuit should have functioned correctly, but the force I had to put on the connector was ridiculous.You had to be there to appreciate just how much.This is a cautionary tale for beginners, who think their circuit is not working when it is,if only for a little careful detective work.
 

alec_t

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This is a cautionary tale for beginners
Those little PP3 batteries actually consist of a stack of 6 cells. A cheapo battery's tolerances may be such that there is insufficient internal pressure to hold the cells in good contact with each other. Your applied external pressure may have 'cured' the problem for that particular battery. So advice to those beginners would be to use a good quality battery.
 

audioguru

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Name-brand Duracell 9V alkaline batteries have their cells welded together. Energizer, Varta and Cheap batteries have the cells simply touching together. Some manufacturers use AAAA cells and other manufacturers use rectangular "flat" cells.
Dave has a video:
 

dr pepper

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At Rf bad connections can act as diodes, something that could could have happened, do you have a cap across the power rails on the board, a 10u and 0.1u in parallel is a must for something like this, battery impedance tends to rise as they discharge and weird stuff happens, the cap keeps it down.
Might also be worth trying a couple of diffrent batteries.
I had a tv infra red remote that would only work on a bench psu, , it was an open electrolytic across the supply.
 

audioguru

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My first calculator had an LED display that used a lot of current. It was multiplexed then each segment had very high pulses of current. A super-heavy-duty battery lasted for only a couple of days. Then I learned about decoupling the rising impedance of the battery with a capacitor that the designers of the calculator did not know about and when I added a 47μF supply bypass capacitor the calculator worked brightly for weeks. I still have this calculator and it still works.
 
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