开云体育

John,

The capacitor you're talking of must have electrodes of some sort to define it. I agree that the energy is stored in an E-field, but it must still have a pysical definition, no?

Pete

Chuck,

It sure would, but so would aligning a perfect pool ball to continually bounce from one perfectly elastic collision to another & back.
But, is it useful, or even interesting?

Pete

You mention resonance, which implies stored energy. What physical
device are
you thinking of? I can't think of
any way to store energy without defining a physical device/mechanism
for the
storage medium.


The energy is stored in the FIELDS and a 'device' is not needed. Think
of a vacuum capacitor.
-John


Free space is
certainly large enough, but, at or near 0 deg K & very low density, it
seems
a poor candidate for energy storage.

Pete Rawson

Hi Guys,

Apologies for the hugely off topic question but as you guys are so into
RF (and its
been
a little quiet in last few hours ;) I was hoping someone might be able
to answer a
simple
question, well fairly simple, with caveats no doubt...

As free space has a characteristic impedance of some 376.7 Ohms (or
close to)...


Roughly:

Impedance depends on Mu (u) and Epsilon (e)[ and geometry. In free
space, geometry is constant. Since there is nothing in free space, u and
e are constant and independent of frequency, so impedance is constant
and independent of frequency.

Real space has gas molecules so there may be dispersion (variation of
index of refraction with wavelength) i.e.: impedance variation with
frequency.

-John

Pete wrote:

Mike,
Unless I'm badly informed (again), the characteristic impedance of free space simply reflects the physical constants
for permeability & permittivity of free space & nothing more glorious than that.
You mention resonance, which implies stored energy. What physical device are you thinking of? I can't think of
any way to store energy without defining a physical device/mechanism for the storage medium. Free space is
certainly large enough, but, at or near 0 deg K & very low density, it seems a poor candidate for energy storage.

Hmm? Let's see, place a pair of perfect mirrors in a relatively clean part
of free space, about 1 light year apart. Shine a laser at one mirror for
two years, and when the beam comes back, put your second perfect mirror
into the beam so it returns the light back to the first perfect mirror.

Wouldn't that count as storage of energy in free space?

-Chuck Harris

Hi, I'm looking for HP 495A TWTA service manual or schematics. I'm
working on a TWTA homebrew project and searching diagrams so 495A
could be a good start...

Thanks, Constantinos

At 11:35 AM 1/19/2007, Jerry Massengale wrote:

Greetings,

I spent 46 years as an electronic technician
without knowing free space had an impedance of 376.7 ohms. How did that happen?

Jerry

The permeability of free space (?0) is 400.pi nH/m

The permittivity of free space is 8.85pf/m

So if we take the square root of (permeability /
permittivity ) we get the intrinsic impedance of free space being 376.7 ohms.


These are both defined SI units. Any good text on
electromiagnetics (I usually use Kraus, John D,
Electromagnetics, 4th ed, McGram-Hill,
ISBN0-07-035621-1) should tell you about it. My
postgrad physics work is now 30 years old and I
think things have progressed a little since then.

John

[Non-text portions of this message have been removed]

Mike,

Unless I'm badly informed (again), the characteristic impedance of free space simply reflects the physical constants
for permeability & permittivity of free space & nothing more glorious than that.

You mention resonance, which implies stored energy. What physical device are you thinking of? I can't think of
any way to store energy without defining a physical device/mechanism for the storage medium. Free space is
certainly large enough, but, at or near 0 deg K & very low density, it seems a poor candidate for energy storage.

Pete Rawson

Hi,

I am looking for the Controller Assembly, A60, for this instrument; a
Hewlett-Packard 3586C Selective Level Meter, serial number 2511A019xx.
It is in the second slot from the right hand side of the instrument
when looking from the front. There should be a flat ribbon cable
connected to it on the top side. HP Part number should be
03586-66560. From the service manual, table 8-11, there seems to be
only one controller for all three models 3586A, 3586B and 3586C.

Also a Power Supply assembly, A80, would be nice, HP part number is
03586-66580.

Please specify ;
Controller Assembly 03586-66560
- the origin of the assembly; 3586A 3586B 3586C or unknown
- the serial number prefix; unknown or
- the status; working and tested, defective, unknown,
- complete, parts missing, unknown,
- asking price.

Power Supply 03586-66580
- the origin of the assembly; 3586A 3586B 3586C or unknown
- the serial number prefix; unknown or
- the status; working and tested, defective, unknown,
- complete, parts missing, unknown
- asking price.

Please contact me off-list.

Regards

Daniel Dufresne
Ville Saint-Laurent, Quebec, Canada
d22dufresne (at) yahoo (dot) ca

Greetings,

I spent 46 years as an electronic technician without knowing free space had an impedance of 376.7 ohms. How did that happen?

Jerry

Mike <erazmus@...> wrote:
Hi Guys,

Apologies for the hugely off topic question but as you guys are so into RF (and its been
a little quiet in last few hours ;) I was hoping someone might be able to answer a simple
question, well fairly simple, with caveats no doubt...

As free space has a characteristic impedance of some 376.7 Ohms (or close to)...

Does free space have any (equivalent) 'characteristic' frequency or resonant frequency(s),
no doubt derived from attenuation/gain factors from RF transmissions etc ?

And if so, can the responder hazard a guess as to why, in terms of equations from first principles
or observations from experiment, that such frequency or even such impedance exists and
practical consequences thereof ?

<cough> Thanks ;)


Regards from

Mike Massen
Network Power Systems
Lab +61 (0) 8 9444 8961
Mb +61 (0) 438 048961
Perth, Western Australia
* USA GMC, Opel and Australian VL/VK Commodore Fuse Rail that wont warp or melt, New model V 2.0
with engine bay illumination timer and relay holder options !
* RB30 Skyline/Nissan/VL Upgraded ignition driver now in long term economy trials
* Twin tyres for most sedans, trikes and motorcycle sidecars
* Industrial grade PolyVinyliDeneChloride (PVDC Copolymer) in bulk, the best
oxygen and water protective barrier you can find for circuit boards.
* Special Equipment for sale: 60KVA 3-phase UPS with large battery cabinet - $12,000
Web site under construction, Ebay and Oztion Auctions

Agilent have a document, "Choosing the Right Power Meter and Sensor".
Part of this document is called: "Understanding sensor technologies"

You can download this from:

At 12:35 AM 20/01/07, you wrote:

I spent 46 years as an electronic technician without knowing free space had an impedance of 376.7 ohms. How did that happen?

Hi Jerry,
I (also) wish I understood fully but, based on equations of primitivity/permeability of free space
and has been used practically (afaik) in design of some rather high gain antennas, have to find the
article but (iirc) was in UK wireless world some 9 years back. ie In general the 50 or 75 Ohm
impedance of coax needs to be matched to that of the antenna and this has a practical
exposure to free space of 376.7 ohms, so essentially the antenna does this matching, though this
issue seems to have been sidestepped many many times in anything other than Ba Eng courses :(
I also recall a lecturer in 1979 or 1980 harping on about it as an important property of space
and not to be ignored (at least as background info) for best understanding of RF principles at
the most basic and core physics levels but I could not find a rationale behind it for so long !
Suffice it say, my Ba Eng was not in RF but, in digital but have always had a casual interest
in the more sophisticated RF issues and recent experience has prompted my interest,
hence the question...

Regards

Mike Massen
ps: Interesting that your surname and mine are similar, curious where yours came from ?

Jerry

Mike <<mailto:erazmus%40iinet.net.au>erazmus@...> wrote:
Hi Guys,

Apologies for the hugely off topic question but as you guys are so into RF (and its been
a little quiet in last few hours ;) I was hoping someone might be able to answer a simple
question, well fairly simple, with caveats no doubt...

As free space has a characteristic impedance of some 376.7 Ohms (or close to)...

Does free space have any (equivalent) 'characteristic' frequency or resonant frequency(s),
no doubt derived from attenuation/gain factors from RF transmissions etc ?

And if so, can the responder hazard a guess as to why, in terms of equations from first principles
or observations from experiment, that such frequency or even such impedance exists and
practical consequences thereof ?

<cough> Thanks ;)

Regards from

Mike Massen
Network Power Systems
Lab +61 (0) 8 9444 8961
Mb +61 (0) 438 048961
Perth, Western Australia
* USA GMC, Opel and Australian VL/VK Commodore Fuse Rail that wont warp or melt, New model V 2.0
with engine bay illumination timer and relay holder options !
* RB30 Skyline/Nissan/VL Upgraded ignition driver now in long term economy trials
* Twin tyres for most sedans, trikes and motorcycle sidecars
* Industrial grade PolyVinyliDeneChloride (PVDC Copolymer) in bulk, the best
oxygen and water protective barrier you can find for circuit boards.
* Special Equipment for sale: 60KVA 3-phase UPS with large battery cabinet - $12,000
Web site under construction, Ebay and Oztion Auctions <>

Regards

Mike

* GMC/VK/VL Commodore & Calais FuseRail that wont warp or melt !
* High grade VL/Skyline milspec ignition driver electronics now in development
* Twin tyres for most sedans, trikes and motorcycle sidecars

Hi Guys,

Apologies for the hugely off topic question but as you guys are so into RF (and its been
a little quiet in last few hours ;) I was hoping someone might be able to answer a simple
question, well fairly simple, with caveats no doubt...

As free space has a characteristic impedance of some 376.7 Ohms (or close to)...

Does free space have any (equivalent) 'characteristic' frequency or resonant frequency(s),
no doubt derived from attenuation/gain factors from RF transmissions etc ?

And if so, can the responder hazard a guess as to why, in terms of equations from first principles
or observations from experiment, that such frequency or even such impedance exists and
practical consequences thereof ?

<cough> Thanks ;)




Regards from


Mike Massen
Network Power Systems
Lab +61 (0) 8 9444 8961
Mb +61 (0) 438 048961
Perth, Western Australia
* USA GMC, Opel and Australian VL/VK Commodore Fuse Rail that wont warp or melt, New model V 2.0
with engine bay illumination timer and relay holder options !
* RB30 Skyline/Nissan/VL Upgraded ignition driver now in long term economy trials
* Twin tyres for most sedans, trikes and motorcycle sidecars
* Industrial grade PolyVinyliDeneChloride (PVDC Copolymer) in bulk, the best
oxygen and water protective barrier you can find for circuit boards.
* Special Equipment for sale: 60KVA 3-phase UPS with large battery cabinet - $12,000
Web site under construction, Ebay and Oztion Auctions

Very new to power sensors and was wondering if someone had the time to
explain a few things with me. 1)When and why would you select one type
of sensor over the other? 2)Do both sensors work with the same
wattmeter? 3)Does the wattmeter need to be setup differently according
to the type of sensor used? I am a Ham and work with test equipment and
radios mainly below 1 Gig. Looking at buying HP, Boonton or Marconi
digital wattmeter. I am sure I have more questions but this
information would be of great help. Thank you……..Jim

Hi all, has anybody some service information, schematic of a HP117A VLF
comparator ?
Any help appreciated.

Regards
Antoon

Tks John
You're quite right , of course.- I actually want info on the 2650A for making up a 'modern equivalent' for phaselocking an older klystron generator- the 620B, which covers 10 GHz OK. But in parallel I'm also looking for info re the 8709 to see how I could use the 8690 (plus PI that covers 10GHz) as well. What ever I get first may make the other requirement redundant- will have to wait and see. For whatever reason I telescoped the two requirements--it's been a month or two since I last thought about either.
I think the 8690/8709 combo used special PIs that had factory mods done to interface to the BWO sweep cctry- I need to find out more on that aspect too.

I'm also looking for one or (maybe) two 5255A 12 GHz counter plugins. Both the EIP microwave counters I have don't have GPIB and I need a pair of counters with logging capability that I can use up around 10 GHz.
With a couple of 5245s on hand (and also in regular use!) I can use the BCD outputs to do the logging-but need the 5255As for the frequency coverage.

Meantime - how many pages has the 2650A handbook and are there any large foldouts? I can handle A4 scanning no problem-those large multi-page foldouts can present issues though.

Cheers
DaveB, Christchurch, NZ

i have found some very cheap sources of 30 pin and 36 pin
genuine cinch solder eyelet connectors "some ever are
genuine card extender types with terminals bent for card
extender applications.
i also have a cheap source that can supply pc cards
for the extenders.
in order to keep prices down id like to have a fairly
large initial run of the pc cards unless
their is great interest in the 36 pin and other sizes
of
extenders it will be just the 30 pin "15 pin double
sided extenders "contacts will not be gold plated but the
connectors will be "
if i can generate enough interest the price will be quite
low.
i woyuld probably just supply a board and connector to
the group and they can solder it on.
you cant troubleshoot boards in an 8640b without a 30
pin extender.
service manual says a 30 pin extender is supplied with
each new unit.
its like trying to find a 432a power meter with a
cable attached to it or a 428b with the probe "ha ha"
there probably is a need for other extenders for hp
scopes and spec analyzers
the double sided 15 pin card will work in older tek
stuff like 5245l counters and 310a wave analyzers
i had to do extensive work on my 310a and without an
extender had to struggle and probably replaced some
capacitors that were still in service limits.
get back to me shortly with your requests so i can
estimate how many boards and connectors i should order in
i think the 1740 scope is a good candidate for cheap
extenders.
im trying to keep this in the $20 range

Basically, you have to cannibalize

>another unit. I have a 3.7 to 4.2 and 5.9 to 6.5 GHz Communication
>Sweep Generator that died.

Hmmm, I might have one of those in the basement. What model number is
it?

I'll look & email you later.

> It turns out that HP left a loose screw in
>the RF output amp during assembly. The screw was provably NEVER
>tightened.... that was clear from a microphotograph I took I
complained
>bitterly, but they essentially said 'too bad'... it's out of warranty.

>They also said I should 'hurry up' and order the replacement module
for
>ONLY $1400 because the price was about to go up to $2000++. Since
then,
>I've tried to avoid their newer stuff.

Sadly, HP lost sight of the HP way. I know that many of us who were
very close to HP back in the 70's regret what happened. I know a lot
of the staff did too. But that's the way of the world I am afraid.

Well, I think HP got seduced by the Wall Street suits. They came out
with so many new products, they could not all succeed, and quality
suffered. Now they are producing almost disposable junk IMO.... And an
8620 produces just about as good microwaves as a current unrepairable
$$$$$ box.


>OTOH, I had a Tek RTD-710A fail. The replacement part was about $2500
>(an amplifier hybrid), but they said there had been a manufacturing
>problem. I took it to the local Tek office and they repaired and
>calibrated the unit and returned it to me shipping prepaid... at no
>charge... ZERO.

That sort of thing USED to happen at HP sometimes too. Sadly my last
experience with Tektronix was being laughed at when I asked about
parts for an AWG2000 series unit about two years ago. Luckily I
picked up a parts unit on the big auction for little money and saved
the day.

That's why I stick with the Tek 7000 and TM500 & TM5000 stuff. It's
mostly standard parts. What is special doesn't fail very often and there
are plenty of donor units about. The Tek 11000 was just not worth it
IMO and the new stuff is just not to my taste.

If you think HP had problems, try Keithley! I tried for ages
to get manuals for some gear with absolutely no luck at all, I gather
that they would not even provide service manuals where they had
signed contracts that required them to do so. In one case I know they
maintained the equipment free of charge for 13 years rather than
provide manuals.

John


I have some Keithley and like it. If they contracted to provide prints
and didn't do it, I'd send the stuff back or not pay the invoice. Almost
nothing any instrument maker sells is REALLY sole source. HP makes the
4140B which is just as good as many Keithley toys.

This no prints in the manual is silly. If anyone REALLY wants to reverse
engineer something, they will. Any protection is in special chips ar
PALs with security links blown. I've even seen the operating code in RAM
and when the BU battery fails, the code goes and you have to pay for a
reload. I've learnt the hard way to ask questions about such things
before buying something.

Damn lawyers and their suited Harvard Business School buddies. Ya gotta
remember, companies are in business for the benefit of their
stockholders and the mutual funds. It does not matter to those people if
someone makes instruments or sells turnips. It's only the next quarter's
profit that matters (and their bonuses, of course)

FWIW,
-John

At 05:53 PM 1/18/2007, you wrote:

My gosh! I wouldn't want one of those nowadays!

But I suppose that was what I used before the two rack 8620/9845
based versions. I do recall an automated spectrum analysis system
based on 141T's that took up a couple of racks, darned if I can
remember the controller though. Of course this was in the days when
we still had 524 series counters in racks because the powers that be
thought they were more reliable than 5245's. All the gear tended to
be in racks lined up along the wall and we worked on castored
trolley's that rolled between our individual benches and the test
gear.

The system is NOTHING like a 524 which is all tube. You could not give
me one of those.

My reminiscing, I used to have two of these in my house, saved on the
heating bill!

The system is mostly solid state (it has some BWOs (in the higher
frequency band PIs) and a couple of tubes in the power supply for them
and a CRT) and is largely ICs. In fact, it's a LOT more maintainable
since it has no unobtainable or $$$$$$$$$$ microwave hybrids or ASICs.

Have you tried to fix newer HP stuff?

Up until a couple of years ago I maintained all my own gear. My
"shack" collection included an 8505A (sorry I sold it now!) 141T
system (regret selling that too!) and a complete 8409C system. As
well as lots of other 1980's HP stuff. Fortunately much of the gear
was either acquired new ( 8620C's and plug-ins, 5345A & PI's, 8505A,
141T (2 complete systems) when I had a consulting practice, or came
from sources where I knew the entire history of the unit. In all
those years we replaced two output amplifiers in 8640B's and one 8555A mixer.

Basically, you have to cannibalize
another unit. I have a 3.7 to 4.2 and 5.9 to 6.5 GHz Communication
Sweep Generator that died.

Hmmm, I might have one of those in the basement. What model number is it?

It turns out that HP left a loose screw in
the RF output amp during assembly. The screw was provably NEVER
tightened.... that was clear from a microphotograph I took I complained
bitterly, but they essentially said 'too bad'... it's out of warranty.
They also said I should 'hurry up' and order the replacement module for
ONLY $1400 because the price was about to go up to $2000++. Since then,
I've tried to avoid their newer stuff.

Sadly, HP lost sight of the HP way. I know that many of us who were
very close to HP back in the 70's regret what happened. I know a lot
of the staff did too. But that's the way of the world I am afraid.

OTOH, I had a Tek RTD-710A fail. The replacement part was about $2500
(an amplifier hybrid), but they said there had been a manufacturing
problem. I took it to the local Tek office and they repaired and
calibrated the unit and returned it to me shipping prepaid... at no
charge... ZERO.

That sort of thing USED to happen at HP sometimes too. Sadly my last
experience with Tektronix was being laughed at when I asked about
parts for an AWG2000 series unit about two years ago. Luckily I
picked up a parts unit on the big auction for little money and saved
the day. If you think HP had problems, try Keithley! I tried for ages
to get manuals for some gear with absolutely no luck at all, I gather
that they would not even provide service manuals where they had
signed contracts that required them to do so. In one case I know they
maintained the equipment free of charge for 13 years rather than
provide manuals.

John

I've thought about changing from the 2100 to a 98xx or PC but rewriting
the SW is just not on my agenda. I mostly use a 8505A these days.

-John

At 07:56 PM 1/18/2007, Dave Brown wrote:

DaveB, NZ (Still after a 2650A synchroniser h'book or even the real
thing! - or anything to help get the 8690 + PI phaselocked around
10GHz)

Dave, my boy. I never realised you needed a handbook for a 2650A, I have the very thing, right here in front of me. It is 1964 printing with the modification data to use various other mixers. The 934A is the basic harmonic mixer used in these things (same as used in the 540A transfer oscillator as it happens).

But I am not sure that a DY-2650A is the right thing, they were intended for klystron oscillators, such as the 614, 616, 618, 620 and the 8614, 8616 units. These were all reflex klystron based. The DY-2650A takes the reflector voltage (2kV in the standard unit or up to 3kV with modification M18) and outputs the reflector voltage with error correction.

The Carcinotron (Backward Wave Oscillator) in the 8690's has different characteristics. They have an external FM input which is fairly consistently 6% of band deviation per volt of input (as I recall). I suspect you would be better off using an 8709 type synchroniser rather than a DY-2650A. The 8709's (used with the 8620 series and 8350 series sweepers) had a switch selection of sensitivity, again very much by recollection, and is pretty easy to modify if need be for other characteristics. Sadly, I don't appear to have the manuals for the 8709's any more.

The DY-2650A manual is available to a list member if they need it, provided they agree to have it scanned and the PDF sent to me for uploading.

John