Tecktronix 492P Spectrum Analyser - Page 1
Forum section: electronics / testgear

author: eurofox
author_rank: Unknown
timestamp: August 21, 2014, 07:51:02 am
content: Hi,Could you share your experience with this SA?Is it a good idea to spend money on it?eurofox

author: skipjackrc4
author_rank: Regular Contributor
timestamp: August 21, 2014, 05:57:01 pm
content: I don't have one, but I've used them in the past. If memory serves, they're a pretty capable piece of gear, but the interface on them is pretty awful. Nonsensical shift key combinations and a hybrid digital/analog CRT (at least it seems like it). If the price is good, then go for it. Otherwise, I'd look for an HP 8566. Better interface, better specs, LCD replacement screens available.

author: Orange
author_rank: Frequent Contributor
timestamp: August 21, 2014, 07:32:56 pm
content: Quote from: skipjackrc4 on August 21, 2014, 05:57:01 pmInterface awful ?, Shift key ?The 492P does not even have a shift key, The analyzer has a three knob set-up; Attenuator, Span, Frequency. The B/W is automatically set. Ditto for sweep time....So basically a child could use it. All settings can be adjusted also in manual mode.I have one, and it is one of the best analyzers together with the 494 that Tek ever made.Make sure you get the full loaded version, that is Option 1,2 and 3. These are the Digital memory, The pre-selector, and the Phase lock. I would not consider a 492 analyzer without those options.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: August 21, 2014, 07:49:59 pm
content: Quote from: Orange on August 21, 2014, 07:32:56 pmMy mistake. I was thinking of the 494, which has 2 shift keys. I agree that it's a good analyzer.

author: G0HZU
author_rank: Super Contributor
timestamp: August 21, 2014, 08:12:41 pm
content: The trouble is, when it came to spectrum analyser design, HP and Advantest etc were miles ahead of Tektronix in those days. So the best from Tek was still grim compared to the very best analysers from HP or from Japan.Therefore, I wouldn't recommend the 492 to anyone unless you 'need' a fair chunk of the 21GHz frequency range it offers and you are on a tight budget and can live with ropey accuracy, ropey linearity, limited log range and fairly poor phase noise.QuoteYes, the 8566 is in a completely different class but I expect the 492 will be a lot cheaper. However, I wouldn't really recommend the 8566 either unless the massive 22GHz frequency range it offers is really 'needed'. This is because the 8566 is still fairly expensive to buy used and also they are getting quite fragile these days. The 8566 is also huge and heavy and makes a lot of fan noise.But the RF performance of the 8566 is way ahead of the 492

author: eurofox
author_rank: Unknown
timestamp: August 21, 2014, 08:18:14 pm
content: Thanks your guy's for the inputI have Rigol SA815 with TG but is a little short on frequency, the Tek 492P reach the 20Ghz is is available for a low price.eurofox

author: G0HZU
author_rank: Super Contributor
timestamp: August 21, 2014, 08:36:13 pm
content: In that case it might be worth considering provided you also keep the 815.Otherwise you will be in for a shock when you see how crude the 492 is after using the modern interface + features found with the 815. Things like the log accuracy, frequency stability and display range will be notably worse than the 815.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: August 22, 2014, 01:48:23 am
content: Quote from: G0HZU on August 21, 2014, 08:12:41 pmFragile in what way? I'm currently in the market for a microwave SA, and it's at the top of my list. And I DO need the 22 GHz range.

author: bingo600
author_rank: Super Contributor
timestamp: August 22, 2014, 07:56:48 am
content: I got a 492P w. opt 1,2,3 for $300Haven't used it much , but i couldn't say no at that price.I primarily use my HP8594E , but was looking for some higher BW.I see the 492P as a "i'm not blind up there" , but nothing more for now.Still have to get some time to play with it seriously , but my E4432B stops at 3Ghz.John Miles has some neat info.http://www.ko4bb.com/Test_Equipment/Tek7L18-492-494_compared.phphttp://www.ke5fx.com/gpib.htmhttp://www.ke5fx.com/49x_notes.pdfEdit: Just saw this: If someone has a 492 wo. gpib.Rather cool.http://www.circuitben.net/node/4/Bingo

author: G0HZU
author_rank: Super Contributor
timestamp: August 22, 2014, 12:25:54 pm
content: Quote from: skipjackrc4 on August 22, 2014, 01:48:23 amSome of the 8566 models are now over 30 years old and they are starting to show fairly common failures.I have one here and I've had to replace several dead capacitors in it in the few years I've owned it. This is a common failure on certain cards inside the analyser and causes various symptoms including onscreen error messages and winking on/off of one or both of the red status LEDs.I also had to remove/clean/reseat the cards in both the display and RF unit to get it reliable. The other known weakness is the CRT of course. These can go dim and also suffer focus issues.Despite all this it is a wonderful spectrum analyser. Mine has been reliable for a year or so since I replaced the dead caps etc but the CRT is showing early signs of ageing.I don't use it very much unless I need the higher frequencies because the RF performance isn't that great in terms of phase noise or front end linearity. However, the amplitude flatness and input VSWR (with 10dB attenuation) is extremely good on the 2.5GHz range.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: August 22, 2014, 02:17:12 pm
content: Quote from: G0HZU on August 22, 2014, 12:25:54 pmNothing too serious then. Caps can be replaced, and there are LCD replacement screens available. Even after $500 for a new screen, their performance is better in most ways than any modern equipment that costs even close to the 8566 price.

author: G0HZU
author_rank: Super Contributor
timestamp: August 22, 2014, 02:44:22 pm
content: I'm not sure I'd want to put a VGA LCD screen into mine if/when the CRT finally dies.The CRT display driver has 1000 x 1000 display data points inside the graticule area which is very impressive and it would be a shame to lose this performance with a VGA LCD. Have you seen a demo of the LCD screen and compared it to the CRT?I think that if my CRT fails then I'll just buy another display unit with a known working CRT

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 22, 2014, 02:53:07 pm
content: There appears to be reasonable success using a CRT restorer on the CRTs. Not a real fix, but it will squeeze another year or two out of it.

author: David Hess
author_rank: Super Contributor
timestamp: August 22, 2014, 03:13:59 pm
content: Quote from: skipjackrc4 on August 21, 2014, 05:57:01 pmTektronix was using vector CRTs for digital displays at around this time which is what gave them that interesting look. The 2440 series of DSOs worked the same way. On the plus side, horizontal and vertical resolution was often 10 bits so the displays were 1024 x 1024 if you neglect trace width. That gives them an unusually "smooth" look.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: August 24, 2014, 05:06:56 pm
content: Quote from: David Hess on August 22, 2014, 03:13:59 pmAh, that makes sense.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2014, 07:57:09 pm
content: Quote from: skipjackrc4 on August 24, 2014, 05:06:56 pmThis is also why they used their LCD color shutter technology in later oscilloscopes. Monochrome CRTs have higher potential resolution than color CRTs which use a shadow mask so their TDS series of oscilloscopes used this configuration for high resolution color when other manufacturers were stuck with monochrome or low resolution color. HP also developed some high resolution monochrome raster CRTs at one point but I do not know how many of their products used them.As far as the earlier vector CRTs, Tektronix already had the infrastructure and design knowledge so it made sense to use them even in raster applications and their high resolution was an advantage anyway. Some of their combination analog and digital oscilloscopes like the 7854 could generate a combination of raster and vector display. One of the 7000 series spectrum analyzer plug-ins had digital storage which used the vector CRT in the same way as their later dedicated spectrum analyzers.

author: nctnico
author_rank: Super Contributor
timestamp: August 24, 2014, 08:00:58 pm
content: Interestingly the TDS5xx/6xx/7xx series only uses half the vertical resolution of the display even with the LCD shutter technology. On a CRT you don't see it but as soon as you fit a TFT screen you'll notice that in some modes only half the lines in the display are used.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2014, 08:08:24 pm
content: That might be a problem with how the LCD demodulates the analog video signal. Good LCD monitors use synchronous demodulation when driven from a VGA source to prevent aliasing and the TDS video may be odd enough (Isn't the TDS frame rate some odd value?) to cause problems with that.