Do you have a sweep frequency Generator or Wobbulator?

[Mullard]

I am thinking of getting a sweep frequnency generator to realign TV IFs. I collect B&W micro-TVs (with CRTs) and I have a few US sets. These are easily converted to UK by changing the sound IF, but this leaves them with a less than ideal performance as the vision IF bandwidths are set for the 4.5Mhz US standard rather than our 6 Mhz. I have a couple of reasonable scopes and an FM/AM signal generator, but would like to add a sweep generator. I notice on eBay that there are a number for sale in the US and in Europe, but few in the UK.
I would be very interested in what others do for aligning TVs and in what equipment is used. I have considered making one and would be intersted in hearing from anyone who has done this. I am happy to have modern test equipment, and it occurs to me that a micro-processor controlled (or PC controlled) generator might be an option. Anyone got some thoughts on this?
John

[Colin]

John, I have a Heathkt HFW-1 TV Alignment Generator that I've never used. Not into TV's. I also have the Heathkit documentation for it in PDF format. PM me if you're interested. I'd just like to recover what I paid for it on eBay.

rgds
Colin

[XTC]

Originally Posted by Mullard

I am happy to have modern test equipment, and it occurs to me that a micro-processor controlled (or PC controlled) generator might be an option. Anyone got some thoughts on this?
John

If you want a microprocessor controlled sweeper/generator, this is a nice building block which saves a deal of work.

http://www.amqrp.org/kits/dds60/

But you've still got to write the code for the µcontroller, or develop (or find) a PC program to make it sweep. The problem with a µcontroller solution is that it needs quite a lot of memory as all the frequency steps in the range need the frequency word to be stored. It isn't feasible to work them out on the fly.

Having set up the control interface and display and got the DDS60 doing what you want and arranged other things like the markers and the sweep voltage for the scope, there are extras such as a PA and attenuator. Certainly I wouldn't have much faith in a home made wide-band attenuator. Commercial attenuators are available on ebay or at rallies.

It starts to add up to a lot of work and cost. So far I've got as far as getting a DDS60 up and working with a free PC program and I'm gathering the bits for the rest of the project, the keypads, the case, the LCD display etc.

It's a slow-burning project.

Pete.

[Marconi Man]

Basically you just need a wobbulator don't you?

What is all this talk of microprocessors and software?

Just do as we did in the Marconi spectrum analyser and use a sweep oscillator with a crystal oscillator plus mixer and filter and there it is - simple!

The voltage controlled oscillator doesn't need to be much more than a couple of transistors with a varactor diode to tune a tank circuit...
The crystal oscillator is just one fet feeding into a mixer ic and filtering the output...

A simple couple of days at most and a couple of quid.

John.

[XTC]

Just gotta see your design, the spec and the costings.

If it's a couple of days and a couple of quid - say 20 days even and £20, I'll swallow my pride and accept that a good engineer can do for a shilling what any damned fool can do for a tenner.

Pete.

[Mullard]

Well many thanks. I have 3 suggestions; buy a heathkit wobbulator, build a uProcessor controlled oscillator and write the scan/marker software, or produce an analogue varicap tuned oscillator and crystal controlled marker (could use the scope timebase with gain/DC shift to drive). They all look atttractive. The Heathkit is a quick solution and so I am tempted, the uProcessor controlled solution is right up my street, as I spent most of my working life in S/W development, and the analogue approach appeals as a quick, but homebuilt solution. I might go for all of them! finding time will be the biggest problem. I will let you know.
John

[Mullard]

Originally Posted by XTC

If you want a microprocessor controlled sweeper/generator, this is a nice building block which saves a deal of work.

http://www.amqrp.org/kits/dds60/

But you've still got to write the code for the µcontroller, or develop (or find) a PC program to make it sweep. The problem with a µcontroller solution is that it needs quite a lot of memory as all the frequency steps in the range need the frequency word to be stored. It isn't feasible to work them out on the fly.

Having set up the control interface and display and got the DDS60 doing what you want and arranged other things like the markers and the sweep voltage for the scope, there are extras such as a PA and attenuator. Certainly I wouldn't have much faith in a home made wide-band attenuator. Commercial attenuators are available on ebay or at rallies.

It starts to add up to a lot of work and cost. So far I've got as far as getting a DDS60 up and working with a free PC program and I'm gathering the bits for the rest of the project, the keypads, the case, the LCD display etc.

It's a slow-burning project.

Pete.

I have had a look at the DDS-60 and the AD9851 datasheet. It looks like the way to make the ideal sweep frequency generator. I am going to get the Heathkit wobbulator to give me something to use right away, but I am planning to experiment with the DDS-60.
I envisage using a PC to drive it with software that will allow and the parameters for the scan (start frequency, end frequency, marker positions, etc.) to be entered and to drive the DDS-60 from the parallel printer port (or via a USB adapter if no printer port available). Input from the tuned circuit being aligned would be fed back via a demodulator to an AtoD converter and plotted on the screen with the markers drawn on. The effect of tuning adjustments could then be seen as they are made to provdie the required response curve. A facility to store sweep profiles (set of parameters for a particualr purpose e.g. TV vision IF) would allow them to be recalled by name at a later time. The sweep rate does not have to be too high, and the accuracy of the AtoD converter is not too critical, and so this could be quite low cost.
I will write it in C# using Microsoft Visual Studio (Express Edition is a free download and well worth getting for anyone who is keen on developing their software skills). This is not going to be a quick project as I do not have enough spare time at the moment, but I should have more time after my autumn holiday.
John