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Author Topic: Boonton 103B Sweep Marker  (Read 4348 times)
ND9B
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Posts: 49




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« on: August 14, 2011, 08:08:12 AM »

I hope this is the proper forum for this topic. Anyone out there have this RF generator? I'm trying to use the sweep capability of this generator for aligning IF strips. My 103B has an "intensity marker" output on the back that I have connected to the "Z axis" input of my scope. This works, but only on the higher IF frequencies - 10.7 and 98 MHz. 262 and 455 KHz sweeps have no marker. I have a manual for the 103B, but it does not show an "intensity marker" output. There is also an extra circuit board in my 103B that does not show up in the manual. Evidently this extra board makes the "intensity marker" since it connects to the "intensity marker" BNC connector.

Should I be getting a marker on the lower sweep frequencies?

Bobby Dipole ND9B
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AC5UP
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« Reply #1 on: August 14, 2011, 08:59:21 AM »

I've had mixed results trying to get a nice passband sweep out of my function generator which does have sweep capability and a BNC output for the horizontal sawtooth. The classic setup is to run the 'scope as an X-Y display and let the generator draw the screen. It also took me a while to notice that on a Tex 2213A you select X-Y mode by setting the sweep rate to zero, then Channel 1 becomes X and Channel 2 becomes Y.

This is a very convenient feature when you know the trick as the vertical sensitivity attenuators still work, but otherwise it's frustrating.

Best advice I can think of for you is to try a slower than normal horizontal sweep rate on your 'scope. Might make for an odd viewing experience, but considering your setup does work at 10.7 and 98 MHz the chances are your 'scope sweep needs to be a much slower value (in terms of ratio) than what you're currently using at 455 kHz.

BTW: You've offered an excellent trivia question for the peanut gallery: Why would anyone need to sweep an IF at 262 kHz?
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ND9B
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« Reply #2 on: August 14, 2011, 09:37:25 AM »



BTW: You've offered an excellent trivia question for the peanut gallery: Why would anyone need to sweep an IF at 262 kHz?


Actually, the old mechanically tuned Delco car radios used an IF of 262 KHz on the AM band. (BTW, I retired from Delco.) Some of the newer ETR models use up conversion with an IF of 10.7 MHz FOR AM, believe it or not!

Bobby Dipole ND9B
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AC5UP
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« Reply #3 on: August 14, 2011, 10:00:37 AM »

Actually, the old mechanically tuned Delco car radios used an IF of 262 KHz on the AM band.

First thing I thought of as I have a minor stash of late 50's / early 60's Delco's with four tubes (Chevy, Cadillac had five tubes (?)) and a large Germanium transistor for the audio output. Not only were they permeability tuned with an IF at 262 kHz, but I understand the space-charge tubes ran 14 volts on the plate. No vibrator, no B+ inverter, and for years I thought the transistor on the back was an oscillator for an inverter. Couldn't imagine anything hollow-state running plate voltage that low, but the radio I had in a '61 Impala was definitely a skywave warrior and truly amazing at night...

Quote
(BTW, I retired from Delco.) Some of the newer ETR models use up conversion with an IF of 10.7 MHz FOR AM, believe it or not!

I also happen to have two Delco FM & AM Stereo radios (which is a very rare sight in a thrift shop, but that's where the last one came from) and I'm told they're one of the finer examples of AM receiver design Delco ever produced. I've had one of them hot wired onto a power supply with J-hooks and the like. Played well, and I have a back-burner plan to build a cabinet and turn it into a shelf radio with some serious moxie......
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WB2WIK
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« Reply #4 on: August 14, 2011, 10:17:50 AM »

Bobby, I worked for Boonton Electronics back then and the 102A and 103A (and the other suffix letters that followed) were my projects.

The 103A/B didn't have a sweep function as a factory standard feature.  I left BEC in early 1977 and don't know much about what happened after that, but I'm trying to even figure out how they'd make it sweep.  It was an analog LMO (VFO tuned by a rotary inductor) followed by binary dividers to cover the lower frequencies.  If I recall, the LMO tuning range was 65-130 MHz, and any frequencies covered below that were by division and mixing.  To make it "sweep" any kind of range down at 262 kHz, it would have to "sweep" 256 times more range at the LMO range, and since it wasn't designed to actually have a sweep function, I imagine it was modified to use the FM modulator for that (that was varactor modulation and could probably hit 100 kHz deviation or so...but if you divide that by 256, that would only be about 400 Hz).

I don't know what you have there but it sounds like a customization.  We made lots of products that were customized (by customer request) and those changes were not published nor even well documented anywhere outside the company.
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G3RZP
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« Reply #5 on: August 14, 2011, 10:36:35 AM »

I was told that 262 kHz as an IF in automobile receivers avoided certain spurious problems.

The straight sweeper with a linear display is a bit limited: adding a logarithmic video amplifier between detector and display makes it a lot more useful - typically 60 to 80dB of range is possible, while a linear display limits you to about 30dB - but is good for seeing passband ripple.
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ND9B
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« Reply #6 on: August 14, 2011, 11:28:02 AM »

Bobby, I worked for Boonton Electronics back then and the 102A and 103A (and the other suffix letters that followed) were my projects.

The 103A/B didn't have a sweep function as a factory standard feature.  I left BEC in early 1977 and don't know much about what happened after that, but I'm trying to even figure out how they'd make it sweep.  It was an analog LMO (VFO tuned by a rotary inductor) followed by binary dividers to cover the lower frequencies.  If I recall, the LMO tuning range was 65-130 MHz, and any frequencies covered below that were by division and mixing.  To make it "sweep" any kind of range down at 262 kHz, it would have to "sweep" 256 times more range at the LMO range, and since it wasn't designed to actually have a sweep function, I imagine it was modified to use the FM modulator for that (that was varactor modulation and could probably hit 100 kHz deviation or so...but if you divide that by 256, that would only be about 400 Hz).

I don't know what you have there but it sounds like a customization.  We made lots of products that were customized (by customer request) and those changes were not published nor even well documented anywhere outside the company.

Hi WB2WIK, there must have been a few ECOs on this model since you left. The actual sweeps are done with MC1648 oscillator chips one for each IF of 1.2 MHz, 10.7 MHz and 89 MHz. A single additional MC1648 is used for 262 KHz and 455 KHz. These are sweep using a 60 Hz ramp signal into varactors. In sweep mode the LMO is used as an adjustable marker.

My 103B has a board that generates an "intensity" marker. I actually have a second unit that is the same way. Neither one makes a marker on 262 KHz, 455 KHz and 1.2 MHz. I'm trying to find out if this is normal.

The 103B manual, I downloaded from the internet, does not show an "intensity" marker. I suspect it is for a variant model that uses a "blip" type marker. The manual refers to a "blip", but doesn't elaborate. It also doesn't indicate any IFs the marker doesn't work on.

Booby Dipole ND9B



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WB2WIK
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« Reply #7 on: August 14, 2011, 01:01:39 PM »

Hmmm.   I don't recall that at all, and may well have been added later in '77 or '78 or something.

Are you using a scope and outboard detector?

If so, maybe you could pump the divided/mixed LMO signal (CW) into the detector with a "T" connector, independently from the sweep output?
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