Post by thread:[OT]:Microwave Oven

Hello, I was working on a timer ckt on top of the microwave oven in the kitchen( only place with grounded outlet) when the wife needed to use it. My voltmeter was on top and it started giving me a reading of about a few tenths of a volt. The dvm lead was just lying over the top of the door. This caught my attention and I started to run the leads around the door seal. It reads when the leads are by it and no reading when I pull it away. Does this mean it is leaking? Regards, Robert Francisco -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

robertf wrote: >Hello, > >I was working on a timer ckt >on top of the microwave oven >in the kitchen( only place >with grounded outlet) when the >wife needed to use it. My >voltmeter was on top and it >started giving me a reading of >about a few tenths of a volt. >The dvm lead was just lying >over the top of the door. This >caught my attention and I >started to run the leads >around the door seal. It reads >when the leads are by it and >no reading when I pull it >away. Does this mean it is >leaking? > Probably not, I'd guess you were measuring the magnetic field of the power transformer. You meter has almost no chance of detecting the frequencies of the oven. {Quote hidden}> >Regards, > >Robert Francisco > >-- >http://www.piclist.com hint: To leave the PICList >.....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu > > > -- * | __O Thomas C. Sefranek tcsKILLspamcmcorp.com |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz ARRL Instructor, Technical Specialist, VE Contact. hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

{Quote hidden}> robertf wrote: > > >Hello, > > > >I was working on a timer ckt > >on top of the microwave oven > >in the kitchen( only place > >with grounded outlet) when the > >wife needed to use it. My > >voltmeter was on top and it > >started giving me a reading of > >about a few tenths of a volt. > >The dvm lead was just lying > >over the top of the door. This > >caught my attention and I > >started to run the leads > >around the door seal. It reads > >when the leads are by it and > >no reading when I pull it > >away. Does this mean it is > >leaking? > > Thomas C Sefranek wrote > Probably not, I'd guess you were measuring the magnetic field of the > power transformer. > You meter has almost no chance of detecting the frequencies of the oven. > > > Sorry to disagree. but any electrical non-linearities within the measurement system can cause the meter to register a microwave signal. The Microwave signal bathing the inside of a microwave oven consists of a 2450 MHz carrier pulsed at your line frequency 50 or 60 Hz. Old microwave ovens are particularly prone to leaky door seals And rusty self tapping screws, purely as part of the wearing out process. It is possible for the rectified Microwave leakage (Rust Bolt Effect) to be of sufficient power to register on the unconnected leads of a high input impedance dvm. If I was you I would play it safe and get your oven checked out for leakage. Regards Chris Carr -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

In message <005001c12cd5$b7e244c0$faba7ad5@dougal>, Chris Carr <nyedspam_OUTBTINTERNET.COM> writes >Sorry to disagree. but any electrical non-linearities within the measurement >system can cause the meter to register a microwave signal. The Microwave >signal bathing the inside of a microwave oven consists of a 2450 MHz carrier >pulsed at your line frequency 50 or 60 Hz. Old microwave ovens are >particularly prone to leaky door seals And rusty self tapping screws, purely >as part of the wearing out process. It is possible for the rectified >Microwave leakage (Rust Bolt Effect) to be of sufficient power to register >on the unconnected leads of a high input impedance dvm. I repair microwave ovens (amongst other items), leakage is EXTREMELY!!!!! rare - I've only ever seen two which leaked, both were the same Philips model with the door hinging downwards. However, both were still well within permitted UK limits (but not USA ones!). We are legally obliged to check every microwave we take apart, so I test a good many every year, and it's not a problem!. I would agree that it's more likely the large magnetic field from the transformer affecting your meter. >If I was you I would play it safe and get your oven checked out for leakage. If it will reassure you, get it tested, but it's unlikely to be leaking. -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : @spam@nigelgKILLspamlpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

Yes. But only a very, *VERY* little. My dad worked for Litton Microwave for 11 or 12 years. Supposedly, you can run a small fluorescent tube around the door of an old microwave oven and the tube will grow if there's too much leakage. Douglas Wood Software Engineer RemoveMEdbwoodTakeThisOuTkc.rr.com Home of the EPICIS Development System for the PIC and SX http://epicis.piclist.com {Original Message removed}

In message <007901c12d15$acdb4960$spamBeGonecde51f18spamBeGonekc.rr.com>, Douglas Wood <TakeThisOuTdbwoodEraseMEspam_OUTKC.RR.COM> writes >Yes. But only a very, *VERY* little. My dad worked for Litton Microwave for >11 or 12 years. Supposedly, you can run a small fluorescent tube around the >door of an old microwave oven and the tube will grow if there's too much >leakage. That sounds unlikely, UK legislation requires leakage to be below 5mW at 5cm distance, USA regulations require below 0.5mW at 5cm - I wouldn't swear to the distance (although I think it's correct), but the power values are exact. All Microwaves are built to the USA standard anyway, almost always on our leakage tester (calibrated yearly, as required by UK regulations) on a scale of 1-5mW the needle never moves at all. BTW, the tester has a plastic cone on the front, which maintains the correct distance, you can remove this and test at zero distance - still no readings!. -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : RemoveMEnigelgTakeThisOuTlpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Your MW is not leaking, if it would be the DVM would go 'bananas'. The small leakage is normal. There is no such thing as 'perfect shielding' and with 700W inside it takes better than 1:1000 shielding to keep total radiation under 0.7W. That is very good shielding. The real leakage is probably 50mW or so. The DVM is sensitive and picks this up. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

In message <Pine.LNX.4.10.10108251305570.576-100000EraseME.....plp.plp.home.org>,> Peter L. Peres <EraseMEplpACTCOM.CO.IL> writes >Your MW is not leaking, if it would be the DVM would go 'bananas'. The >small leakage is normal. There is no such thing as 'perfect shielding' and >with 700W inside it takes better than 1:1000 shielding to keep total >radiation under 0.7W. That is very good shielding. The real leakage is >probably 50mW or so. The DVM is sensitive and picks this up. The permissible leakage is 5mW in the UK, and only 0.5mW in the USA, ovens are almost always (even 20 year old ones) well below 0.5mW. -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : RemoveMEnigelgEraseMEEraseMElpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Now this is starting to make sense. The units of measure (W/cm^2) (specified at a given distance) are what I'd expect. Let's take a 'real world' example. Assume a cube shaped microwave about 50cm on a side. A surface 5cm from it (at the measurement distance) would be a cube 60cm on a side. The total surface area of such a cube would be: 6 * 60cm * 60cm = 21600cm^2 At 5mw/cm^2 this would allow for a total (evenly distributed) leakage of 10.8 watts, or about 1.4% of the output of a 700 watt microwave. This makes sense. Even at 0.5mw/cm^2 we can have a leakage of 1.08 watts. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) {Original Message removed}

> leakage 0.5mW ERP isotropic point radiator? 0.5 mW/cm^2 at 5cm? 0.5mW/cm^2 at 5 cm with a good 1 meter total seam length around the door, taken as a swath only 1 cm wide totals 100cm x 0.5mW ~= 50mW total radiated (I am making some assumptions about the radiation starting as a line and spreading to a swath 1 cm wide exactly where the detector is). 0.5mW isotropic point radiator for an oven rated 700W that costs $150 is something I really want to see ;-). It means an attenuation of 7x10^2 / 5x10^-4 ~= 1.4x10^6 = 1,400,000 times. That would be just too neat to be achievable with a simple hinged door and some stamped steel and colored glass. Peter PS: If you set up 2.4GHz video links and have the equipment you will 'see' and cuss each and every MW in the neighbourhood (appear as mains noise bars on AM links). -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

In message <011a01c12e7c$7a7820c0$0100a8c0@piii500a>, Jim <RemoveMEjvpollspam_OUTKILLspamDALLAS.NET> writes > "That would be just too neat to be > achievable with a simple hinged door > and some stamped steel and colored > glass. > >Ever heard of, or seen, a "choke joint"? Personally I've always heard it called a 'choke seal'. We get a lot of people asking for their new ovens to be tested as they can see light through the door seal, or steam escapes. Another point to bear in mind is that you don't have 700W wildly trying to find it's way out of the cavity - most is absorbed by the load in the oven (which should never be used empty). -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : RemoveMEnigelgTakeThisOuTspamlpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

"The invention of the 'choke joint'." Excerpted from: www.ieee.org/organizations/history_center/oral_histories/transcripts/ ramsey1991.html ``Ramsey: ... Eventually we learned the art. That's one of the things we were learning. Initially, most of the laboratory waveguide work was being done by the three centimeter [10 GHz] group because the ten centimeter [3 GHz] group was still dominantly working with the coax lines. [snip] I remember for example just one of the problems. When one just wanted to fasten two waveguides together, one either butted them together and hoped they wouldn't spark, but you could see those little sparks at the joint. Or, else one had fingers inside where you put them together, but these tended to spark and destroy the impedance matching. Bryant: Spring fingers? Ramsey: Spring fingers, yes. Then we tried the trick of using a butt joint with a **choke**, which worked quite well. So we shifted over to that. As far as I know that was my invention, although Shep Roberts in the Radiation Lab joined in that work. '' ** End of excerpt ** Jim {Original Message removed}

On Sun, 26 Aug 2001 08:53:33 -0400 Bob Ammerman <EraseMERAMMERMANspamspamBeGonePRODIGY.NET> writes: > Now this is starting to make sense. The units of measure (W/cm^2) > (specified > at a given distance) are what I'd expect. > > Let's take a 'real world' example. > > Assume a cube shaped microwave about 50cm on a side. > How about we use a sphere instead, since the entire surface of the sphere is the same distance from the center. If you put a 1 watt isotropic radiator at the center of a 1 meter radius sphere, you'd have 1 watt spread over the surface area of the sphere or 79.577mW/m^2. Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/tagj. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Sat, 25 Aug 2001 06:58:18 +0100 Nigel Goodwin <RemoveMEnigelgKILLspamLPILSLEY.CO.UK> writes: {Quote hidden}> In message <007901c12d15$acdb4960$cde51f18STOPspamspam_OUTkc.rr.com>, Douglas Wood > <spamBeGonedbwoodSTOPspamEraseMEKC.RR.COM> writes > >Yes. But only a very, *VERY* little. My dad worked for Litton > Microwave for > >11 or 12 years. Supposedly, you can run a small fluorescent tube > around the > >door of an old microwave oven and the tube will grow if there's too > much > >leakage. > > That sounds unlikely, UK legislation requires leakage to be below > 5mW at > 5cm distance, USA regulations require below 0.5mW at 5cm - I > wouldn't > swear to the distance (although I think it's correct), but the power > values are exact. All Microwaves are built to the USA standard > anyway, > almost always on our leakage tester (calibrated yearly, as required > by > UK regulations) on a scale of 1-5mW the needle never moves at all. > These units don't make sense to me... Could it be mw/cm^2 or "power density?" Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/tagj. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> choke joint Yes but not 1:1.4E6 attenuation in one step. They usually have several impedance steps afair? In my non-extensive experience achieving >50 dB attenuation of nearly anything in 'one step' is no go (assuming it is not tuned). Untuned one-step attenuators seldom go beyond 30 dB assuming that they are to be reproducible and untuned. Even a simple cover joint with wire-clad gasket has two or three steps (depending on how you count). Apropos attenuation, any idea why a cellular phone works perfectly (S meter at 3 of 5 ?!) in a 4 x 2 x 2 meter welded steel safe with the door closed? Not all the seams are welded perfectly (this is not a submarine) but there are not enough bare wires to conduct the cellular signal inside at that level I think ?! Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Peter: "Yes but not 1:1.4E6 attenuation in one step. They usually have several impedance steps afair? In my non-extensive experience achieving >50 dB attenuation of nearly anything in 'one step' is no go (assuming it is not tuned). Untuned one-step attenuators seldom go beyond 30 dB assuming that they are to be reproducible and untuned." Two cases that work against any assumptions posted above: 1) I'm holding in my hand a Harris GSSD/PRD Instruments "Type X-101" , an X-band (10 GHz nominal) variable attenuator. Is is marked from 0 dB through to 60 dB. In my use of these and similar device made by HP I do not ever recall having 'trouble' with the higher attenuation values. Of course, this does not use a 'switchable resistor' bank either ... 2) The attenuator on any of the Hewlett Packard 608 series of sig gens - these are marked on the dial from +7 through to -127 dBm. It does this in a continuous, un-stepped fashion with one mechanism - I have repaired this model before and can testify to the fact that it is one 'piece' which serves to couple ever-progressively less energy as the movable 'piece' is pulled ever further from it's mating assembly. I can attest that this device operates as billed too. These *is* leakage from the oscillator portion of this instrument, but it is *not* from the attenuator. Testing a fully shielded radio apparatus like the GE Mastr Pro line presents no problem from the leakage, testing a Japanese made HT or a poorly shielded 'scanner ' is another story. Peter: "Even a simple cover joint with wire-clad gasket has two or three steps (depending on how you count). To what is this applicable? (Microwave oven or choke joint)? Jim {Original Message removed}

Peter: "Apropos attenuation, any idea why a cellular phone works perfectly (S meter at 3 of 5 ?!) in a 4 x 2 x 2 meter welded steel safe with the door closed? Not all the seams are welded perfectly (this is not a submarine) but there are not enough bare wires to conduct the cellular signal inside at that level I think ?!" I once tested a "screen room" where facilites had simply run a LAN connection into screen the room WITHOUT A FILTER. By placing my 2-way UHF ham transceiver next to this LAN wire I could bring up the UHF repeater that was on-site. All other facilities connections (AC power) were through filters. Standing in the *middle* of the SR - it was not possible to 'hit' the machine. I suspect that much of your 'leakage' in the safe was owing to poor contact around the door of the safe - that coupled with perhaps, a nearby cell site. All it would take is three or four inches (at that frequency) of even 'poor' metal to metal contact from the door to the body of the safe and you have an 'aperature' through which RF energy can propagate. Was there on-site "cell extender" (bascically two cell-band amps, appropriately duplexed, to create a bi-lateral amplifier like the dB Products "Prism" series) with one of the coverage antennas placed nearby the vault? I offer this as a possible reason - not knowing where your 'vault' was or the signal level outside the vault ... Jim {Original Message removed}

In message <KILLspam20010827.085759.-403285.0.haroldhallikainenspamBeGonejuno.com>,> Harold M Hallikainen <EraseMEharoldhallikainenEraseMEJUNO.COM> writes >> That sounds unlikely, UK legislation requires leakage to be below >> 5mW at >> 5cm distance, USA regulations require below 0.5mW at 5cm - I >> wouldn't >> swear to the distance (although I think it's correct), but the power >> values are exact. All Microwaves are built to the USA standard >> anyway, >> almost always on our leakage tester (calibrated yearly, as required >> by >> UK regulations) on a scale of 1-5mW the needle never moves at all. >> > > These units don't make sense to me... Could it be mw/cm^2 or "power >density?" Possibly? - I can't say I've ever paid much attention, you have to use an approved meter, calibrated yearly, and it has to read under 5mW (or 0.5mW in the USA). Presumably there's more to the specification, but it's not of any use in practice - unless you are manufacturing test equipment?. -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : @spam@nigelg@spam@spam_OUTlpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

A couple of points: A: A microwave leakage is specified in AU and UK as to be less than 5mW per cm2 at a distance of 5cm from the surface being tested. B: Most modern Microwaves have a 3 stage "filter" to stop leakage, I can not remember what they were or how they operated, as I did the theory 8 years ago when here in Perth AU you had to have a radiation permit to service a microwave oven. Regards, Kat. {Original Message removed}

> Another point to bear in mind is that you don't have 700W wildly trying > to find it's way out of the cavity - most is absorbed by the load in the > oven (which should never be used empty). You wish ;-). Power distribution depends on the impedance ratios of the 'hole' and of the food. I suspect that running the oven with the door open will reduce its 'food' power by 50 to 80%. This because any MW still heating it will pass through it once instead of many times and the power distribution would correspnd to that of a 'hole' the size of the open door with the food obstructing part of it. Ok, I admit this is extreme. Peter -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestKILLspammitvma.mit.edu

> Peter: > "Even a simple cover joint with wire-clad gasket has two or > three steps (depending on how you count). > > To what is this applicable? (Microwave oven or choke joint)? > > Jim Both or none. I meant the cover joints normally used in RF proof equipment boxes, with a channel and an o-ring clad with wire (and sometimes flashing), as compared to oven doors. The simple box joints get it down by 40-55 dB in VHF/UHF in my experience, and they are more complex than the oven door joint. I believe what you say about the single-'step' continuously variable attenuators you mention, they can be very good, it's just that as you said, there are other factors (such as oscillator leakage) which prevent them from working perfectly in real life. There is also the small issue of the price tag of those parts and their 'wide' availability. It is trivial to design a T-pad attenuator with resistors for say 80 dB in one stage, but due to real life parasitics, radiative coupling, ground conduction, etc, etc it will do 80 dB only at DC. This is what I meant wrt 'not possible to attenuate in 1 stage'. The 30 dB I gave is a rule of thumb that comes from my experience with real life equipment and attenuators, in the sense that a 30 dB T, L or PI assymetrical attenuator calculated and implemented as designed will indeed attenuate 30 dB +/- 4 dB in the frequency band considered. Above that, the ifs become too many. If I'm not wrong the ARRL handbook also gives (or gave ?) a DIY attenuator schematic, and there too the first two stages are 26 dB, not a single 50 dB stage. Peter -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

>>Apropos attenuation, any idea why a cellular phone works perfectly (S >>meter at 3 of 5 ?!) in a 4 x 2 x 2 meter welded steel safe with the door >>closed? >>Peter > >Well, no, but I just gotta ask you how you know this :) Ever got a call while doing things inside the safe - well strongbox - at work? Peter -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-request.....TakeThisOuTmitvma.mit.edu

> Was there on-site "cell extender" (bascically two cell-band amps, > appropriately duplexed, to create a bi-lateral amplifier like the > dB Products "Prism" series) with one of the coverage antennas > placed nearby the vault? I offer this as a possible reason - not > knowing where your 'vault' was or the signal level outside the > vault ... > > Jim There are cellular towers all around me there, we are in 'downtown'. They put them on the roofs and move them all the time so I can't keep track but there was one definitely within 100 meters from where I was. There is no repeater that I know of there. It is hard to judge the field outside, we are in a well-covered city and the S meter stays at 5 (maximum) all the time while you are not in a basement or such. I haven't played with graphite sheet attenuators and such to estimate it. Peter -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestKILLspamspammitvma.mit.edu

At 10:26 PM 8/28/01 +0300, Peter L. Peres wrote: > >>Apropos attenuation, any idea why a cellular phone works perfectly (S > >>meter at 3 of 5 ?!) in a 4 x 2 x 2 meter welded steel safe with the door > >>closed? > >>Peter > > > >Well, no, but I just gotta ask you how you know this :) > >Ever got a call while doing things inside the safe - well strongbox - at >work? UHF signals are coming into the box on the skins of wires, conduits, etc. In one case, I saw a "safe" (room with a vault door) that had a hole above the ceiling that you could crawl through. It was where a jewelery shop was keeping it's goods at night. Things aren't always what they seem. (Neither was their alarm system) -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestRemoveMEmitvma.mit.edu

In message <RemoveMEPine.LNX.4.10.10108282151280.619-100000spamBeGoneplp.plp.home.org>,> Peter L. Peres <spamBeGoneplp@spam@spam_OUTACTCOM.CO.IL> writes >> Another point to bear in mind is that you don't have 700W wildly trying >> to find it's way out of the cavity - most is absorbed by the load in the >> oven (which should never be used empty). > >You wish ;-). Power distribution depends on the impedance ratios of the >'hole' and of the food. I suspect that running the oven with the door open >will reduce its 'food' power by 50 to 80%. This because any MW still >heating it will pass through it once instead of many times and the power >distribution would correspnd to that of a 'hole' the size of the open door >with the food obstructing part of it. Ok, I admit this is extreme. Well the power rating of a microwave oven is measured by the temperature rise of a certain quantity of water (with a specified salinity, and starting temperature within a defined range) with the oven on full power for a certain time (usually 87 seconds for 2 x 500ml containers). So a 700w oven is rated as 700w into the load, the actual RF output of the magnetron isn't considered. I'm sure I don't need to mention that a microwave won't work with the door open, and requires at least three safety switches bypassing to allow it to do so!. -- Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : TakeThisOuTnigelgspamlpilsley.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.co.uk | | Chesterfield | Official site for Shin Ki and New Spirit | | England | Ju Jitsu | \--------------------------------------------------------------/ -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseMEmitvma.mit.edu

Peter: "Both or none. I meant the cover joints normally used in RF proof equipment boxes, with a channel and an o-ring clad with wire (and sometimes flashing), as compared to oven doors. The simple box joints get it down by 40-55 dB in VHF/UHF in my experience, and they are more complex than the oven door joint." I've had extensive experience sweeping and tuning both commercial and amatuer band duplexers at between 50 MHz and 1300 MHz. I've also designed, modeled and built duplexers for use in this same range of frequencies. (A 'duplexer' allows the simultaneous use of an antenna on two different frequencies - most normally one frequency is receive and the other is transmit. The duplexer supplies the much needed islolation between the two thereby allowing simultaneous, concurrent operation as required in a "repeater".) These duplexers exhibit attentuation values from 40 dB (the simpler designs) to greater than 95 dB attenuation (the better-built commerical designs by the likes of dB Products and Collins). It requires a great deal of skill and the proper equipment using double-shielded (or "Super-flex" Heliax) at times to assure one is not simply seeing coaxial cable leakage (at 150 MHz and up) as opposed to DUT (device under test) 'leakage'. Some of this product uses construction techniques *far* simpler than you describe (i.e. an aluminum cylinder with a tight-fitting cast end-cap fitted with coupling loops and pop riveted in place, *no* gaskets, no finger stock, etc.) - with much better isolation and shielding results than you describe. It makes me wonder - what it is you were using to make these measurements? Were the contacting 'metal' surfaces painted? Were you using double- shielded coaxial cable on your test/measurement instruments? Jim -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

David VanHorn wrote: > >Ever got a call while doing things inside the safe - well strongbox - at > >work? > > UHF signals are coming into the box on the skins of wires, conduits, etc. > In one case, I saw a "safe" (room with a vault door) that had a hole above > the ceiling that you could crawl through. It was where a jewelery shop was > keeping it's goods at night. > > Things aren't always what they seem. > (Neither was their alarm system) Ha ha! We once looked at renting a business premises that had been a Bank for many years. It had a huge impressive steel strongroom door with enormous lock, looked great to the customers. It was like a small room, but the entire strongroom was just double brick wall and the wall to the next shop was the same double brick wall!! Maybe 2 minutes for any meathead with a sledgehammer. Was most amusing. The door must have been worth a lot of money though. :o) -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>but the entire strongroom was just double brick >wall and the wall to the next shop was the same double >brick wall!! Maybe 2 minutes for any meathead with a >sledgehammer. Was most amusing. The door must have been >worth a lot of money though. :o) Sounds like it was sold to the bank by a cellphone aerial salesman. ;)) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads