hello

i would love to hear some opinions on what you guys think is the best sweep signal generator....

here are the qualities im looking for.
* easy to use
* least complicated and not alot of un-necessary functions
* high build quality and high reliability
* will be used for tube hf communications receivers with a top end of 50 MC's
* doesnt need to be fm capable

thanks very much
73s
dave

Just an opinion but if you aren't doing FM broadcast alignment, you shouldn't need a sweep gen. Below 50MC is almost entirely AM and only the very high end (usually mil grade) receivers require any sweeping of IF stages. Even then, a tech can usually use FM instead of sweeping. With over 50 years in the radios and 30 years of sweep work while at HP, I never found use for a sweeper in AM radio work.

IF stages usually have a circuit Q of less than 10; all that means is that simple modulated signal is all that's needed for alignment; they don't require sweeping until you get to the special or variable bandwidth circuits.

There are an awful lot of great sig gens out there. The HP 8640 is fantastic but it won't cover IF alignments. Unless you are doing the really ancient superhet radios, you will need to have a generator that goes down to 450KC with AM; it's very important. You can get away with a lower grade sig gen as long as you have a freq counter and a variable audio source.

Pete

AA KENT
hello

your right
for the most part, i wont need a sweep generator: but i do have a handfull of high end military receivers with complicated variable bandwidth circuts that would benefit from a swept alignment. i have read several articles by hams that say that the manuals only recommend a standard alignment with these rigs, but when a swept alignment is performed, they really come alive.

dave

About the best bang for the buck IMHO for a signal generator capable of sweeping IF's in high end comm receivers would be the HP 3336C, or the HP 3325A function generator. These will cover just about any IF you'll encounter, and although they look complex they are not complicated at all to set up for sweeping and give you accurate points of frequency reference - push the right buttons and they will do the signal generator end of the job without any messing around. These generators are a little expensive, but the $50 jobs don't cut the mustard stabilty wise for sweeping a high end radio, and you end up buying a lot of other inaccurate crud like marker generators in the struggle to try to make them work, and just end up spending more to end up getting less. You are well better off getting a good quality non-sweeping signal generator and peaking the IF's rather than trying to perform sweeps with a crappy sweep generator that has no points of reference.

-Mark-

I agree- mil receivers with selectable bandwidths do need to be swept. You don't necessarily need to sweep though; some sig gens will have a DC FM mode which can be driven with a sawtooth ramp. Also, you can use a sig gen with a roughly calibrated FM mode instead of a sweeper; a high persistance scope helps here. It's this FM mode that I use very successfully for my selectable bandwidth alignments.

Pete

To me, the most convenient aspect of using any of the generators mentioned are their frequency management attributes. With the 3336 generator, you enter the start frequency, stop frequency, and the amount of time you want the generator to take to sweep from start to stop. I presume the 3325 is very similar. With the 8640 you need to know the frequency deviation per volt of applied ramp signal. I have an 8640 but never used it as a sweeper per se. On the scope's screen, it's own scales eliminate the need markers. Markers are so necessary when using older "free running" sweep oscillators, so you have an idea of where you are, frequency wise.

Here is a 30Kc wide sweep of a BC348's IF strip. Each vertical division across the screen is 3Kc wide, and each horizontal division is 10db. You can easily determine that the peak is at 917 Kc, the frequency of the receiver's crystal filter, and the total dynamic range of the sweep is 70db.



As Pete mentioned, sweeping this type of receiver borders on a total waste of time, but nevertheless, its interesting sometimes, to actually see the performance of these old receivers. Another common method Pete mentioned, of aligning the I.F. on older receivers, is to measure the receivers audio output using a modulated signal generator. you simply connect your VTVM across the speaker's voice coil, or use a metered, switched load like the GR-1840 audio power meter.

Fooled around at work once trying to make a regular sig gen sweep. Unit had an FM feature and selectable FM deviation. So I tried feeding a sawtooth wave into the ext. modulation input and then adjusted the FM deviation range and RF freq. Was able to get an RF sweep that way and it seemed to have potential to use sweeping an IF, etc. but then with that method, there was no easy way to get markers in the trace as a reference for center freq, etc. Maybe an old Wavetek 2001 sweep gen. might show up as cheap surplus sometime. Good for RF sweep but maybe not 455 IF sweeping. Has built-in markers and ext. marker input, I believe. Analog tuned and 70s vintage unit.

If you set up the generator properly, run a couple simple tests and take good notes, you can easily sweep I.F. strips, using 10, 20, and 30Kc sweeps, and won't need any markers.

Try this to get started.

To determine the amplitude of the ramp you need for each sweep width, hook up a DC supply to the generator's external input. with the supply's output initially at "0". Adjust the generators frequency for what would be your "start" frequency (450, 445, or 440Kc depending on the sweep width). Set the Modulation level control to mid range, and the deviation range control to accommodate the desired deviation.

Connect the generators RF out to a counter and adjust the generator output to get reliable readings.

Adjust the power supply output as you watch the counter. Apply enough DC to get the generator to move 10Kc, and note the DC Voltage. Make your "start" frequency adjustments, and do the same for 20Kc, and 30Kc shifts, adjusting the deviation "range" control if necessary, and note any changes.

Once the tests are done and you have your data, you know the amplitude of the ramp, and deviation "range" settings needed for a 10, 20, or 30Kc sweep. Now you will have 1, 2, and 3Kc shift per division, and don't need any markers.

So, to set up a particular sweep, set the generator "start" frequency and modulation controls per your notes. Use a scope to set up your ramp for the proper amplitude, per your notes, at maybe 30 cycles or so, connect it to the generator and you're set.

I was able to get sweeping to work somewhat with my Marconi 2019A using the FM deviation, but for all practicality I found it too hard to use, especially when I wanted to change things up with the settings. Things on the 3336C or 3325A are so much easier, especially when you incorporate the Z axis marker- this gives another piece of insurance that the setup from the signal generator is correct. I have yet to see anything that works as impressively for lower frequency IF's.

-Mark-

I've managed to drive my HP 8660 signal generator with a sawtooth and sweep 455KHz IFs, but I just got an HP8601A, which was made to be a sweeper in the 0.1 to 100 MHz range. It looks like it will do fine with any scope, but I've just gotten it repaired and so have no bench experience with it. You can look up the specs on the web and see if it suits your needs.
It wasn't expensive- $150, and looks like it can be maintained easily(except for a couple of hybrid RF amplifiers).
Ed W2EMN

Ed,

Seems to me there are a couple guys who've used them and say they aren't all that accurate, and need to be used with the 8600 marker generator, so you know when you're on frequency.



I've used the 8660 a number of times since it has a built in sweep function, why do you use a ramp to modulate it?

I recall that George fellow a couple years back extensively evaluated an 8601A for sweeping the 10.7 MHz IF on FM radios, and I've seen them used for IF's on comm receivers. They look to work OK on the sweep end but here again was the marker problem, and what I saw on the lower frequency IF's didn't look nearly as easy to interpret as what a 3336C or 3325A will do, the accuracy and stability is just no match. It's not at all hard to come across a good working 3325A for $150-200, a big plus being it's a piece of equipment that has multiple uses other than just an IF sweeper.

I have one of those mechanical "odometer" dial frequency displays like the 8601A has on my HP spectrum analyzer. Along with the marker generator you'll want to verify the 8601A's center frequency output with a counter also, as those dials don't seem to be the most trustworthy things on the planet.

-Mark-

For the 3336C



I take it that Mhz is a typo

Carl

Hi oldlongwave. I would look for something digital, that has the option of sweeping or a jack where sweep can be applied. There are lots of good gens out there, and since this is a hobby, almost any of them will do. I used to own an 8640B, and was quite happy with it. Now I own a Fluke 6071A, and a Polarad-SMPC. I would never go back to anything else. If you can find a Fluke 6071A for a reasonable price, a strongly suggest purchasing it. It's an incredible machine. The Polarad much the same. Both machines have memory, so you can program band edges in it for each band your aligning, they both will sweep and have variable audio insertion (+ much more).

Good luck on your search!

I think you guys are right about the frequency readout of the 8601A- it can't compare with a synthesized generator. However, it's got an output for a frequency counter if needed. I've found the "odometer" to be very accurate within the limits of its resolution.
But the other reason I got the generator is that it has a calibrated attenuator so that I can do alignments and sensitivity tests without hauling out the 8660.
And in response to the last question- it's an 8660A with the thumb wheel switches, so it doesn't have a sweep function.
Ed W2EMN

howdy

thanks for all of your great and detailed responses. you guys have given me alot to think about.

i dont know if i mentioned that i would be using such a critter on military communications receivers no newer than @ 1955, so stabillity is very important....but probably not as important as if used for some of the high end receivers produced later.

also i have extremely little space available for a test bench so a compact and self contained unit is also key (one that would have all functions necessary for sweeping a 50s vintage receiver built in)

and of coarse simplicity and ease of use are important because i am just a beginner right now and now where near as educated as you all are.

thanks again
73s
dave

LMAO - that statement coming from a weiner!

Just a layman's terms way of saying, "Hats off," to the guys who waste money on things like this at weiner-fests in hopes of sweep aligning thier R 390A with it



-Mark-