I'm building a wobbulator !!! - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: July 07, 2013, 06:05:08 pm
content: This will catch a few out , it's a piece of equipment used by us radio hams , for tuning IF stages, or for repairing and setting up coils, it would also be useful in your Electronics Dens . Unless your scientists then it would be Electronics Labs, quite easy to build very useful. not to sure who the presenter of this is, excellent accent.This is a better one

author: PA4TIM
author_rank: Super Contributor
timestamp: July 07, 2013, 09:22:27 pm
content: Do you mean you want one too , or build one too. ?I'm made several (at the moment a 25MHz t- 2 GHz version (in 10 rangeshttp://www.pa4tim.nl/?p=2662) and had some commercial wobbulators (only one left:http://www.pa4tim.nl/?p=520 ) and a couple of VNAs. Theya are real handy if you know how to use them. And that is harder as building one.http://www.pa4tim.nl/?p=1371this was one of the first. It uses a noise source and a seperate signal generator so you can use it at high frequencys too.http://www.pa4tim.nl/?p=1546this was a lot of wotk.

author: Unknown
author_rank: Unknown
timestamp: July 08, 2013, 06:01:43 am
content: Quote from: PA4TIM on July 07, 2013, 09:22:27 pmI want to build one, I'm looking at a circuit at the moment, I want to build one with a good bandwidth, your 25Mhz to 2Ghz looks an interesting, I think a simple one to start with would be a good idea, to gain confidence.Paul M0BSW

author: PA4TIM
author_rank: Super Contributor
timestamp: July 08, 2013, 12:31:30 pm
content: You need a sawtooth to drive the X of the scope and to tune a VCO.If you have scope with a sawtooth output, like the Tek tube scopes (535/545/547) you van use a voltage divider to bring down the amplitude (that is around 100V)Them make some VCO and use the sawtooth from the scope itself.Important is that you must keep the VCO output amplitude constant over the sweep.The filter must be terminated at both in the right impedance ( that is not always 50 Ohm) because a different termination pulls the filter of frequency.To detect you can use the SNA priniple and use a tuned receiver and only listen at the transmit frequency. In that case harmonics or f.i. RFI from BC, telephones, mains etc do not polute the measurement. That is a lot of work. Basicly that is a SA with TG.Wobbulators use diode detectors. That is much more simple and handy in case of a filter in a radio. You can inject the signal somewhere before the filter or even mixer en detect it after it. In that case you use a high impedance setup ( a diode detector can be made close to 50 Ohm but that is not easy.Important is a marker function or a very well defined sweep ( so you know f.i. That the screen shows 1 MHz /div. It is very very easy to make a perfect filtershape at the wrong frequency. So i alway combine adjustments in radio filters with a TRMS meter at the audio output to check if the filter is at the right frequency and check if the 3dB points are too. Then the wobbulator can make the passband smooth and the skirts as steep as possible.

author: Unknown
author_rank: Unknown
timestamp: July 08, 2013, 12:44:57 pm
content: Quote from: PA4TIM on July 08, 2013, 12:31:30 pmBrilliant this is really good help, going to print this off, as I'm bound to forget parts, thank you