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Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?
Greg Muir
Konrad,
If you are not extremely familiar with using a spectrum analyzer for the applications that you mention, here are some suggestions. 1. Do not connect a transmitter or any high RF level directly to the input of the spectrum analyzer. I have seen people do this several times not knowing the proper procedures when using an analyzer for RF signal analysis. The result can be very costly in repairs to the instrument. 2. Either built-in or external overload protectors are nice but they do have their limitations mostly from a maximum RF power level. Some external devices may be slow enough so as to allow a significant power level to pass on to the test equipment before activating protection. 3. If the situation permits, use an antenna connected to the spectrum analyzer. This can be done if you are not performing precise testing of power levels and such or not overly concerned with harmonic and spurious levels. 4. If you must connect to the output of a device under test to the analyzer input, utilize an in-line power attenuator to reduce the RF to a level lower than the maximum allowed for the spectrum analyzer. (Example: https://birdrf.com/Products/Test%20and%20Measurement/Attenuators.aspx). Calculate the attenuation required in relation to the RF power level you will be measuring. 5. If access to the transmission line is possible, use an indirect method of looking at the RF such as a signal sampler or something similar. These devices connect in-line and have a capacitive probe (sometimes adjustable to set the sampled signal level) with a sample port to connect the analyzer to. To see what is offered Google “RF signal sampler.” But you must be careful because some sampled signal levels may exceed the analyzer safe RF input level so use of an in-line attenuator between the sample port and analyzer may be required. I carry a field kit containing various attenuators with different attenuation and power levels. Much of my work involves dealing with large broadcast transmitters that have included RF signal sample ports on their transmission lines. But many of these ports will have several watts of power at the sample connector so it is standard practice to initially install attenuators in the line connecting the spectrum analyzer until the power level can be determined. Then any unneeded attenuators are removed to bring the signal up to the proper level required for testing. For off-line testing I also utilize RF terminations (dummy loads) anywhere from 50 watts to 35 kW. In this instance I again use in-line signal samplers and various attenuators to match the sampled RF to the spectrum analyzer. Since I start with an excessive amount of attenuation to begin with, I never worry about overloading the spectrum analyzer input nor any other device that I may be using in my tests. If you don’t know what RF level you are starting with it is much safer to start with a huge amount of attenuation then reducing it until you reach the proper level. I seldom if never use the method of connecting any high RF power device directly to the analyzer input through attenuators. Greg
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Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?
Tom Gardner
If you spent less than $21 on a working Tek 492, you are lucky :)
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The Minicircuits BLK-18-S is small enough to be fitted internally, and has a bandpass of 10-18000MHz. Internal fitting means it can't be forgotten and can't be knocked off, but different internal cables may change the overall frequency response. A DC block isn't a panacea, but it is a useful prophylactic. https://www.minicircuits.com/WebStore/dashboard.html?model=BLK-18-S%2B
On 20/10/19 05:40, Konrad Roeder -- WA4OSH wrote:
My primary interest in my new (used) Tek 492BP spectrum analyzer is to test ham radio transverters, linear amplifiers, filters and antennas with a return loss bridge. At my job, we're urged to always practice "Safe RF" to prevent damage to sensitive RF instruments. I'm not quite ready to buy a DC Block/Limiter that costs as much as what I spent on my Spec-An, but I still would rather blow a fuse than my beloved Tek 492.
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Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?
Konrad Roeder -- WA4OSH <konrad.roeder@...>
My primary interest in my new (used) Tek 492BP spectrum analyzer is to test ham radio transverters, linear amplifiers, filters and antennas with a return loss bridge. At my job, we're urged to always practice "Safe RF" to prevent damage to sensitive RF instruments. I'm not quite ready to buy a DC Block/Limiter that costs as much as what I spent on my Spec-An, but I still would rather blow a fuse than my beloved Tek 492.
Tell me more about what DC blocks, limiters and/or external attenuators you use on your instruments when making measurements. --Konrad
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Re: TDS544A major surgery - CRT issues
Harvey White
To the best of my knowledge. the displays are much the same, the difference being the LCD shutter feed from the MB. From what I know, the LCD shutter is "fastened" to the display with an intermediate gel, and one problem is that the gel goes odd, perhaps dries out. I know that there is at least one instance where the gel was rather laboriously scraped out, and the system was restored. If the CRTs are identical, you may wish to just simply replace the display boards.
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Not a quick answer, because I don't know (I have a 540 and a 640), wish I had a 544 or a 644 for just the color capability when running an external display, but that's the best I can do. Harvey
On 10/19/2019 8:11 PM, Ed Breya via Groups.Io wrote:
A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.
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TDS544A major surgery - CRT issues
Ed Breya
A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.
The 540 was just the guts with no can, but otherwise complete, and marked "won't start up" or something like that, so I figured typical PS trouble, and the display was likely OK. It turned out the PS and display were in fine shape, but the acquisition board indeed had the plague, so bad that it crashed the supply. I tried to clean it up as usual, but it did not recover enough. It all fires up, with a nice bright display, and passes the self-tests except for the dreaded acquisition failure. I have decided to go ahead with the display swap, and let the 540 be for the spare parts dept, but thought I'd check here for any advice before starting. The main issue is that the 544A has the color-shutter, while the 540 is straight monochrome. Is the same CRT/display unit used in both? I vaguely recall seeing online somewhere that the shutter may be glued to the CRT - that would spoil the whole deal. Does anyone know if this is the case? I'm up at the farm this weekend, so don't have access to all my usual tools and equipment, and I didn't think to bring all my notes and info from working on this before. The original shot display is still in the 544A (but unhooked), so I didn't even even experience removing it. I assume the front all has to come off, then the color-shutter and CRT out the front, and the rest out the middle after everything is opened up. If the shutter is bonded to the CRT, then the only other option is to leave the assembly in, and just replace the HV PS section - if it's compatible. Does anyone know if the CRTs are the same in this regard? I recall that before the 544A's display crapped out, the CRT seemed old and dim, so I'm hoping this new stuff will go right in. On the other hand, it's possible that the poor brightness on the old one was a symptom of the HV transformer going bad, so maybe it's in better shape than I thought. Anyway, just thought I'd ask if anybody happens to know quick answers to these questions. I've got both units here, ready to start once I clear some usable space and gather up some tools. I'd like to wrap it up tonight, one way or another - tomorrow will be occupied with the water tank and other outdoor projects. Ed
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Re: 7834 HT transformer rewind?
Chuck,
You are a cornucopia of knowledge! Thanks! -- Michael Lynch Dardanelle, AR
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Re: 130 LC meter
Bob Albert
I have spent lots of time and lost lots of sleep over this. I got up in the middle of the night last night and discovered that the problem appears to be a defective tube socket. Not the best news but I'll probably bite the bullet after a few more tests.
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I measure a variable resistance from one tube pin to ground, and see a spiky noise coming from the next stage. Bob
On Saturday, October 19, 2019, 01:05:56 AM PDT, Craig Sawyers <c.sawyers@...> wrote:
Have you checked the smoothing capacitor on the power supply? Mine was open circuit. Craig Is there anyone familiar with this unit? I have one that isn't working and have traced the problem
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Re: 7834 HT transformer rewind?
greenboxmaven
Has anyone investigated the compatability of transformers or cores from Tektronix televison studio equipment? I really don't care for the idea of trashing that gear, but I can't imagine any of the 480I archival and transfer studios wanting the vacuum tube versions of them. In addition to the transformers, the CRTs (IF they are not run to death) might be adaptable to replace smashed, missing, or dead ones, and the knobs are compatable with many older scopes. Maybe some conversations with broadcast engineers could locate a few to find out. Also, I heard years ago Conrac was the television division of Tektronix. Was this true? I do know there were gazillions of Tektronix wavefrom monitor/ 8 inch Conrac picture monitor combos in factory built rack trays used in TV studios.
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Bruce Gentry, KA2IVY
On 10/19/19 11:18 AM, Mlynch001 wrote:
David,
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Re: 7834 HT transformer rewind?
Chuck Harris <cfharris@...>
The 7834 transformer is an all-in-one transformer, and as
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such it has all of the power supply windings, and the EHT on a single core. It is a cornucopia of wire sizes, taps, tapes, and wedges. The winding machine would have to be started and stopped two dozen times before the entire winding would be finished. There are many in the 7000 series that are similarly done, among them the 7904, 7934... The "A" scopes went back to the separate Power and EHT style of design. -Chuck Harris Mlynch001 wrote:
David,
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Re: 7834 HT transformer rewind?
David,
I would be interested in a quote for the HV transformer of the Type 576 as well. The winding specs are readily available, unfortunately, the ferrite cores are not. There are very likely some buyers for a "factory built" replacement HV transformer for the 576 as well. Just throwing that out there, as this subject has already been thoroughly discussed in another thread. -- Michael Lynch Dardanelle, AR
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Re: 130 LC meter
Jack Wills
My Tek 130 had several Sprague Black Beauty capacitors in the oscillator
circuit All were bad. I've had enough trouble (and been shocked enough) with these caps that I replace them on sight. On Sat, Oct 19, 2019 at 1:05 AM Craig Sawyers <c.sawyers@...> wrote: Have you checked the smoothing capacitor on the power supply? Mine was
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Re: 7834 HT transformer rewind?
That is good news to hear , some years ago I went to a company that said they could wind a 549 transformer , in todays money it cost about the same -- but it didnt work when I got it ?? . I was never able to discover why
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Brian
On Saturday, 19 October 2019, 13:14:02 BST, David C. Partridge <david.partridge@...> wrote:
I may have located a company in UK that can handle the rewinding of these transformers. It won't be dagger cheap - they gave me a ball-park figure of about GBP100 plus tax and delivery, but that was without seeing the winding specification which I have just emailed to them. I'll let you know when they say once they've had a chance to look at the document. David | | Virus-free. www.avg.com |
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7834 HT transformer rewind?
I may have located a company in UK that can handle the rewinding of these
transformers. It won't be dagger cheap - they gave me a ball-park figure of about GBP100 plus tax and delivery, but that was without seeing the winding specification which I have just emailed to them. I'll let you know when they say once they've had a chance to look at the document. David
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Re: 130 LC meter
Craig Sawyers <c.sawyers@...>
Have you checked the smoothing capacitor on the power supply? Mine was open circuit.
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Craig
Is there anyone familiar with this unit? I have one that isn't working and have traced the problem
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130 LC meter
Bob Albert
Is there anyone familiar with this unit? I have one that isn't working and have traced the problem to the variable oscillator not oscillating.
It's plate voltage is too low but everything seems good otherwise. Too low for enough gain to oscillate. The tubes are good and the transformer resonates. There is less than one volt on the plate of V4A.
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260-2500-00 Encoder
There was some announcement a year or so ago that somebody has several of
those in stock. Don't know who it was and if there are still some available bue I need one for my recently acquired CG5011 that arrived with a broken inner shaft, Variable control. If somebody has this one I will be happy to pay a reasonable price and shipping from anywhere on on Earth. A front panel with that encoder intact from an otherwise damaged CG5010/5011 would also do as well as non-working CG5010/5011 at a reasonable price. --- ****************************************************************** * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
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Re: Chart Recorder and Its Replacement
Pax Electronica
I did some testing on the terminals that supposedly provide the START signal. It turns out to be just a relay that closes when the recording starts and opens again when the scan is finished. The resistance goes from infinity to zero at START and goes infinity again at STOP, at least in theory. In reality, the instrument has other stepper motors going on and off. When that happens, the relay seems to be unable to hold down and goes open momentarily. The interruption is short enough so that a small capacitance could solve the problem, but is that what we supposed to do? Or is it an indication of some other problems, such as power supply going weak?
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Re: 465B fan question
Robert Simpson
Received and installed a new Thermister and 15Ohm resistor. The fan does start up better but there is still a problem. Watching it carefully, I see that the fan shaft has about 1/32 inch forward and back movement. When the shaft is in (relative to the front of the scope), it starts fine. But when is is out (toward the back of the scope), it doesn't start, although will continue to spin if I manually start it. Maybe a warn thrust washer or weak magnet. I don't see how to get at the thrust washed due to all the wring in the inside (front of scope ) part of the fan housing. Any thoughts?
Bob
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Re: 175 Curve Tracer Rear 9-Pin Connector
Hi :
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It seem the data for ebay item were missing after I post them . Add the ebay ID for easier find them . RegardTony CheungOCT 19 2019
On Saturday, October 19, 2019, 02:29:09 AM GMT+8, Yiu On Tony C via Groups.Io <tonycheung_hk@...> wrote:
Hi : Cable connector for the rear of 575 connection is a Amphenol 165-13 ( male ) , for the rear of 175 connection is a Amphenol 165-14 ( female ) , all those connection pin are occupied ( 9 connections ). original design do not have shielding at all , but it is recommended due to 58 years ago design may not consider such issue. Also can find the connectors available at ebay : Amphenol 165-13 Circular Connector 16513 | eBay eBay item number:351435448017 | | | | $66.77 | | | | | | | Amphenol 165-13 Circular Connector 16513 | eBay Amphenol 165-13 Circular Connector 16513 - New No Box. Circular Connector. 9 Pin Male. | | | Amphenol 123-166-1826 165-Series / 165-14 Circular Connector Mil-Spec. b1 | eBay eBay item number:173917828823 | | | | $38.40 | | | | | | | Amphenol 123-166-1826 165-Series / 165-14 Circular Connector Mil-Spec. b... Our sales team Works diligently to price everything competitive. Or if you buy a part and it doesn't fit your ne... | | | Rebuild Tek Cable for Tektronix 575 to 175 interconnection | eBay eBay item number:264306657081 | | | | $200.00 | | | | | | | Rebuild Tek Cable for Tektronix 575 to 175 interconnection | eBay It is a new build item for Tektronix 575 to 175 interconnection, which is no longer available anywhere. | | | Above information may help ? RegardTony CheungOCT 19 2019 On Friday, October 18, 2019, 05:34:26 PM GMT+8, Craig Sawyers <c.sawyers@...> wrote: I have a 175. It is pins Craig Does anyone know for certain if the 9-Pin connector on the rear of the 175 curve tracer is pins or
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Re: 175 Curve Tracer Rear 9-Pin Connector
Hi :
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Cable connector for the rear of 575 connection is a Amphenol 165-13 ( male ) , for the rear of 175 connection is a Amphenol 165-14 ( female ) , all those connection pin are occupied ( 9 connections ). original design do not have shielding at all , but it is recommended due to 58 years ago design may not consider such issue. Also can find the connectors available at ebay : Amphenol 165-13 Circular Connector 16513 | eBay | | | | $66.77 | | | | | | | Amphenol 165-13 Circular Connector 16513 | eBay Amphenol 165-13 Circular Connector 16513 - New No Box. Circular Connector. 9 Pin Male. | | | Amphenol 123-166-1826 165-Series / 165-14 Circular Connector Mil-Spec. b1 | eBay | | | | $38.40 | | | | | | | Amphenol 123-166-1826 165-Series / 165-14 Circular Connector Mil-Spec. b... Our sales team Works diligently to price everything competitive. Or if you buy a part and it doesn't fit your ne... | | | Rebuild Tek Cable for Tektronix 575 to 175 interconnection | eBay | | | | $200.00 | | | | | | | Rebuild Tek Cable for Tektronix 575 to 175 interconnection | eBay It is a new build item for Tektronix 575 to 175 interconnection, which is no longer available anywhere. | | | Above information may help ? RegardTony CheungOCT 19 2019
On Friday, October 18, 2019, 05:34:26 PM GMT+8, Craig Sawyers <c.sawyers@...> wrote:
I have a 175. It is pins Craig Does anyone know for certain if the 9-Pin connector on the rear of the 175 curve tracer is pins or
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