Using a sweep generator

[vinrads]

Hi,

I am thinking of buying a sig gen with sweep function.

I have no experience in using this type for IF alignment; interested in your thoughts. Mick.

[Herald1360]

You need to be able to sweep it over a suitable frequency range- for IF alignment something like +/- 20kHz or so on frequencies between about 50kHz and 1MHz, and +/- 500kHz or so at 10.7MHz should do for most jobs. The sweep rate needs to be fast enough (>10Hz or so) to give a reasonable refresh rate but not so fast (kHz) that the bandwidth of the IF you're tweaking starts to affect the response.

It'll need a suitable sweep output to drive a 'scope X input and you'll need a detector probe to feed the Y input. If the sweep input is external, you'll also need a suitable audio generator to drive that and the 'scope X input simultaneously.

[ronbryan]

You will also need a calibrated marker oscillator to show the centre frequency of the sweep and other points on the alignment waveform, as required by the IF strip's alignment specification.

Ron

[vinrads]

Thanks for the explanation Chris and Rob next question is which one to buy I was thinking around £300/ £400 spend any recommendations please, Mick.

[Bazz4CQJ]

If your needs for sweeping are limited to IF alignment, an alternative and probably less expensive approach might be to use a wobbulator. If you're not familiar with them, start on wiki for the basics, but there has been recent discussion on the forum of them. If you already have a scope, a few transistors may do the job for you.

- this is another project on my own (long) "To do" list
B

[KeithsTV]

The Philips PM5324 signal generator covers 100kHz to 110MHz with additional ranges from 400kHz to 500kHz and 10.3MHz to 11.1MHz for IF alignment and has a wobbulator function on the IF ranges and on the 75MHz to 110MHz range.

Keith

[Radio Wrangler]

Marconi TF2008 is another sig gen with sweep functions 10kHz to 520MHz

It's got comprehensive AM and FM facilities. You can do wide sweeps, or you can do precise narrow ones using the FM set wide. It's also good for a wide range of output level which not all sweepers are.

David

[WME_bill]

Sweep Generator. I am bemused by the gold plated approach. I suspect Mick "vinrads" is interested in aligning radios.
As this is a Vintage site, why not get an Advance 63 or the Taylor 62 signal generator. Both are intended for aligning radios and TV. Both cover the required ranges, both have a sweep oscillator and also a marker oscillator, with crystal calibration points. And they turn up quite often on ebay for under £50. The Philips PM5324 is the next generation, a fine transistorised machine, but goes usually for around £100.
A wobbulator is less flexible as it covers a much more restricted range of frequencies, often using harmonics, so the circuit has to be already roughly in tune. A Philips GM2877 has appeared recently on ebay. I have specifications etc for all these.

I hardly think you need a 0.1% accuracy for setting the 465 khz IF on a radio, and to check the sensitivity level within a few micro-volts. I usually just take whatever the tuning is there, peak it up and shape the response curve with the sweep facility.
You need an oscilloscope of course as well. Here again, a 100Mhz Tek 465 or a Digital storage is rather an overkill, when almost any 10Mhz or 20Mhz valve or transistor scope will do, and is much easier to "drive" if you are learning.
There is also the factor that an old simple signal generator or oscilloscope is vastly easier to keep going and to repair than a sophisticated Marconi or Tek or HP. If you are worried about the service manuals, I have copies of them all. wme_bill

[G6Tanuki]

Originally Posted by WME_bill

Sweep Generator. I am bemused by the gold plated approach. I suspect Mick "vinrads" is interested in aligning radios.

If you're aligning anything with "stagger-tuned" or overcoupled IF-transformers (as used in some medium/longwave radios for better audio quality) or high-quality FM tuners, communications-receivers with crystal-filters, or anything like a Racal RA17/117/217 with bandpass-couplers then you _will_ need a sweep-gen to do it properly.

Being able to see the full response-curve of the IF stages (which also needs a logarithmic-response detector) makes it so much easier than just "tuning for maximum smoke" at the detector, which may get you a sharp peak but doesn't give you any clue about the shape-factor.

[Station X]

I have an HP8601A. I chose it only because it was available at a reasonable price and would do what I wanted it to do.

I have used it to align the IFTs of comms receivers with switchable bandwidth. For a domestic receiver I just use a normal signal generator.

[WME_bill]

Sweep generators.
I am very glad to see that G6Tanuki agrees with me upon using a sweep generator. It is so much easier not only with band-pass communication receivers and FM IF stages, but even for a good old MW receiver. And shows up how skewed a simple commercial receiver can be. Or even indicate a possible fault. But the Taylor and Advance both include a Sweep facility.
For StationX, I had not mentioned the HP8601, which is a lovely machine, and quite a different class, like the various Marconi generators. The last time I was offered the HP8601, he wanted well over £200, which I thought was a bit high, particularly as it had a minor fault, even though I had the manual, which the seller didn't. I was sorely tempted. You did well to get it. wme_bill

[dave cox]

I've used an HP3325A, and a working one should be within your stated budget. This would surely be in wme_bill's gold plated camp but it will do quite a bit more besides. One thing it can't do it reach the higher frequencies that some of the other instruments suggested can (IIRC up to 40MHz, but high enough for any IF?).

dc

[MotorBikeLes]

Many years ago I picked up a Cossor band 1 TV alignment generator, a model 1320. For FM work, it was on overtones, but I used it successfully. I also had a simple Xtal oscillator, then later a big professional one (don't remember the make). Later still I got a Cossor FM alignment generator (1324??) which was better. Not sure which scopes I used, but as said earlier, most will do the job. Then I picked up three Samwell and Hutton wobbulators which had their own CRT displays. I sold two and kept one, and it did just about anything I needed, including both FM and CTV. Sold most of this stuff 25 years ago, but I still have a NordMende SC384 Stereo FM alignment generator which I find meets my occasional present needs.
They are all different, but after a bit of use, they are easy and effective.
HINT. If you are doing FM radio, a little commutator electric motor (eg, out of an '80s or '90s CD player) is perfect for final setting of "a.m. minimum". Not all instructions mention this, but worth doing.
Les.

[Radio Wrangler]

There are lots of things that would do the job for you.

Once you've adjusted filters or IFs with a sweeper and a scope, you'll never go back. It makes life so much easier. True, a lot can be done without one, but seeing the shape makes understanding a lot easier too.

Don't worry about gold plated gear, it all comes down to what you find available and what the price is like. Sometimes better gear fetches lower prices because more people are scared of it.

I know the HP8601 that Graham uses well. They were originally part of a network analyser system, but are useful on their own. Two frequency ranges 0-110MHz and 0-11MHz. A good attenuator. Frequency is discriminator controlled, but is a bit drifty when you tune down to 465kHz, but it's fine with a marker.

DC mentioned the HP3325A function generator, which I know inside-out. A major chip in the fractional-N synthesiser went obsolete and I got given the job of re-designing the synthesiser around a new part. It's limited to 21MHz for sinewaves and can do square, triangle and ramp waves to lower frequencies. A step size of a milliHertz is probably ludicrous for our interests.
If you go shopping for one, it'll cost hundreds, but people find things like these being slung out or sold for peanuts if no-one knows what it can do.

The HP3335 is a more sig-gen like variant and goes higher in frequency.

I have an old Marconi TF2008 in the shack which does nice narrow sweeps for tweaking IFs and is a comprehensive sig gen. If I need stability or higher frequencies, then an HP8657 comes into play, but i don't use it to sweep, the top end of swept measurements are spectrum analysers with tracking generators or full-blodoed network analysers. I use an HP891E with built-in tracker. It does 100kHz to 1800MHz and can do sweeps down to a kHz or less.

I've seen high quality (real gold plated boards ) generators go sometimes for less than Radio/TV trade wobbulators.

It all depends what turns up, if it's something up market, then you may just have to force yourself to put up with all the convenience and performance.

Dead items needing fixing can be very good bargains. Years ago when the 2008 was a very posh bit of kit, I bought mine for £80, not working. After the tuning pointer wire was unjammed and put back on its pulley, all was well.

David

[Chaparal]

I use a Texscan (Jerrold) WB-713 sweeper, 0-950 MHz
with Jerrold detector.
Display is a Telonic 121 XY-Alignment scope.

Still searchimmg manuals for both.

If you look at different sweeper op manuals or Radio and TV service manuals,
you will find a lot of applications for use of a sweeper.

Peter

[G0HZU_JMR]

Originally Posted by Radio Wrangler

It all depends what turns up, if it's something up market, then you may just have to force yourself to put up with all the convenience and performance.
Dead items needing fixing can be very good bargains.

Agreed

I think patience is the key to finding bargains. There's so much surplus test gear out there that I generally consider anything less than lab grade (in its day) to be off the radar these days. It really does pay to be that patient and picky.

One lesson I learned very quickly as a student was that the signal generator is the item that will reward you most if you avoid the older drifty boat anchor models and buy a decent one with an accurate and stable output and easy to use 'touchy feely' controls. By contrast, things like scopes and meters and counters can be very old indeed and still give adequate performance on a repair bench.