I have a couple of complete sets of the RadLab books. They are available for sale if any one is interested. Thanks & have a great Thanksgiving - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
848-245-9115
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of saipan59 Sent: Thursday, November 22, 2018 10:39 AM To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] Rad Lab was NOT in Tuxedo Park! MIT [with a grin] ...And it pains me to see an educational thread corrupted by posting a New Topic, when you meant to post a Reply... I also have several of the original RadLab books. The one titled "Waveforms" is like a foundation text on pulse circuits and such. Pete
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Interesting point. I have not worked with thermistor heads since ages but I always wondered how the screws work on the HP478 and HP8478? 73 de
Harke
On Thursday, November 22, 2018, 4:58:38 PM GMT+1, Paul Bicknell <paul@...> wrote:
Hi Jeff??
good to talk to you again regarding the 478
and rebalancing the head using the screws
I have found that the temperature? compensation
isn’t as good after you have to rebalance using the screws
?
By the way never opened the 478? to
find out how the screws work
Paul B
?
From:
[email protected]
[mailto: [email protected] ]
On Behalf Of Jeff Kruth via
Groups.Io
Sent: 22 November 2018 15:38
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
Really? Because HP used
the same idea in the 478A & 8478A heads, they were 200 ohms series under AC
bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they
were approx 3-4K ohms. I would have thought G-M would have used a similar
method.
The big thing with the
HP heads was the balance between the ref thermistor pair and the measurement
thermistor pair. If the measurement pair was damaged by excess RF power, the
"rest" resistance was too different from the temperature reference
pair (say 7K instead of 4 K). SO you could no longer balance them with the
screws.
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time,
paul@... writes:
Regarding the TFT
?Marconi? power meter ?they had 2? thermisters? at 100
ohm each
?And connected so
that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was
easily tested as the 2 large pins on the convector should read 200 ohm
?
From:
[email protected]
[mailto: [email protected]
] On Behalf Of RFI-EMI-GUY
Sent:
20 November 2018 05:12
To:
[email protected]
Subject:
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with
homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT
hermocouple. It is an ancient beast. They got bought up by Marconi down the
line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Hi Jeff??
good to talk to you again regarding the 478
and rebalancing the head using the screws
I have found that the temperature? compensation
isn’t as good after you have to rebalance using the screws
?
By the way never opened the 478? to
find out how the screws work
Paul B
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Jeff Kruth via
Groups.Io
Sent: 22 November 2018 15:38
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
Really? Because HP used
the same idea in the 478A & 8478A heads, they were 200 ohms series under AC
bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they
were approx 3-4K ohms. I would have thought G-M would have used a similar
method.
The big thing with the
HP heads was the balance between the ref thermistor pair and the measurement
thermistor pair. If the measurement pair was damaged by excess RF power, the
"rest" resistance was too different from the temperature reference
pair (say 7K instead of 4 K). SO you could no longer balance them with the
screws.
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time,
paul@... writes:
Regarding the TFT
?Marconi? power meter ?they had 2? thermisters? at 100
ohm each
?And connected so
that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was
easily tested as the 2 large pins on the convector should read 200 ohm
?
From:
[email protected]
[mailto: [email protected]
] On Behalf Of RFI-EMI-GUY
Sent:
20 November 2018 05:12
To:
[email protected]
Subject:
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with
homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT
hermocouple. It is an ancient beast. They got bought up by Marconi down the
line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Rad Lab was NOT in Tuxedo Park! MIT
[with a grin]
...And it pains me to see an educational thread corrupted by posting a New Topic, when you meant to post a Reply...
I also have several of the original RadLab books. The one titled "Waveforms" is like a foundation text on pulse circuits and such.
Pete
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Really? Because HP used the same idea in the 478A & 8478A heads, they were 200 ohms series under AC bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they were approx 3-4K ohms. I would have thought G-M would have used a similar method.
The big thing with the HP heads was the balance between the ref thermistor pair and the measurement thermistor pair. If the measurement pair was damaged by excess RF power, the "rest" resistance was too different from the temperature reference pair (say 7K instead of 4 K). SO you could no longer balance them with the screws.
J.Kruth
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time, paul@... writes:
Regarding the TFT ?Marconi? power meter ?they had 2? thermisters? at 100 ohm each
?And connected so that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was easily tested as the 2 large pins on the convector should read 200 ohm
?
From: [email protected] [mailto: [email protected] ] On Behalf Of RFI-EMI-GUY
Sent: 20 November 2018 05:12
To: [email protected]
Subject: Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT hermocouple. It is an ancient beast. They got bought up by Marconi down the line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
The reference is "Tuxedo Park" by Jennet Conant, a marvelous book! I use this as well as others when I talk about electrotechnology and the importance of WWII to my students.? However the facts as presented were incomplete/incorrect.
For those not aware of it, the Rad Lab existed in Tuxedo Park, NY as a personal project of Alfred Loomis before WW II.?
No. Loomis, made rich by the electrification of America, pulled out of the stock market before the crash and used part of his considerable fortune to establish a personal research lab in a mansion purchased from a now-broke millionaire, so that he could pursue his true love: science.
Loomis was also involved in building the cyclotron at Berkeley.?Yes, He was friends with Lawrence and funded him.
Luis Alvarez made an off hand comment to Loomis one evening that if they couldn't get copper they could use aluminum.? Alvarez was blow away the next morning when Loomis told him it was not possible to build the magnets with aluminum wire for any of the designs being discussed.? Loomis had stayed up all night making the calculations.
No, it was a few days later, and the reason was that the cost savings was not sufficient to justify the increased size. (pp 143-144 in "Tuxedo Park").
Loomis invented LORAN in the shower after a conversation with a Brit who was visiting.? They wanted to name it after him, but he declined so they came up with a phrase to match the acronym.? Bowen had given Loomis the patents for Gee, the British system, which he adapted to a longer wave system. He did add the master/slave idea.
Loomis closed the Rad Lab at the end of the war because he didn't think the government should be involved in research except in exigent circumstances such as war.
Loomis closed his personal lab at Tuxedo Park after he moved to MIT to help run the Rad Lab there. He never re-opened it after the war, he had moved on.? His personal lab did research long before the war. He never sought fame, only putting his name on the first patent in a field, like ultrasonics, or brain wave research. He left the follow-up work for others. He did not have any misgivings about the govt in research.
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
On 11/22/18 1:51 AM, Robert G8RPI via Groups.Io wrote: Because the Keysight 432A power meter and thermistor sensor technology is based on the highly precise DC-substitution method, the sensors are used as transfer standards, traveling between the user’s primary lab and the NIST measurement services laboratory. Are the diode sensors for lower levels good and linear so a transfer from a 432A sensor gives a good cal on the nanowatt ranges?
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Hi regarding the HP power meters
HP 430?? was the first of the
microwave power meters ?its coaxial thermistor mount HP
477 ?10 mhz to 10 Ghz?
The HP 430 sold for $300? in 1967??
and? the ?HP 477 sold for $75? in 1967??
I did all my early microwave experiments
with the? 430 ?and then progressed onto a 431
?
The improved system using a second thermistor
in the coaxial thermistor mount for temperature compensation HP 431 ?&
HP 478 and a wider dynamic range
The HP 431 sold for $475? in 1967??
and? the ?HP 478 sold for $155? in 1967??
?
Currently looking for wave guide power sensors
above 50 ghz
?
Regards Paul B?
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Robert G8RPI via
Groups.Io
Sent: 22 November 2018 07:52
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
The GM / Marconi TfT deivces are thermocouple arrays. Bismuth /nichrome
couples bad as a electrical generation device but can be made to match 50R.
The resistor thermocouple types were common in RF ammeters and some power
meters. The early?Marconi TF144 signal generator models used them for the
output meter.
The classic thermistor detector is the HP 478A that was first used?with
the 431A power meter around 1961 and still made today at $5000 a pop. The
analogue ?432B power meter was discontinued a few years ago with a final
price of over $10,000 but the pair can be picked up for a few hundred dollars
used. They built a new digital meter for the 478A the N432A at $10,000. but
none if these appear in the Keysight power meter guide tables.
So why is this "old tech" still made? the answer is in the guide:
"Not discussed is the Keysight family of thermistor sensors and the
associated Keysight 432A power meter. This venerable technology now is used
almost exclusively for the
standardization and traceability of power measurements from the U.S. National
Institute of Standards and Technology and other international standards
agencies. Because the Keysight 432A power meter and thermistor sensor
technology is based on the highly precise DC-substitution method, the sensors
are used as transfer standards, traveling between the user’s primary lab
and the NIST measurement services laboratory.
Users interested in such metrology power-transfer processes may request
Keysight’s AN 64-1, 5965-6630E and AN 64-4, 5965-8167E application
notes."
Basically you can use a head with any 431/432/N432 meter and a accurate
DC?DVM to get transfer accuracy to?a national standard. The
"meter" is just a servo to balance the bridge and the accuracy is at
the DC voltage. They do special variants of the head?with larger blocking
capacitors for low frequency work.
?
Robert G8RPI.
?
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Rad Lab was NOT in Tuxedo Park! MIT
Mixing two stories. Loomis tested first Maggie in Tuxedo Park.
Rad Lab was at MIT.
Please review your history!? I teach this stuff and it pains me to see it corrupted.
Jeff Kruth
Technical Historian
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Regarding the TFT ?Marconi?
power meter ?they had 2? thermisters? at 100 ohm each
?And connected so that DC they added up
to 200 ohm but presented a 50? to an AC signal
?
The power sensor was easily tested as the
2 large pins on the convector should read 200 ohm
?
?
I have such an animal here a GM 460B with that TFT hermocouple. It is
an ancient beast. They got bought up by Marconi down the line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Warning to buy equipment on Ebay on auctions using GSP (global shipping programme)
This happens to me occasionally (I buy a lot of gear from the US). In one case they told me the item can't be exported (it was a standard RAID controller that is sold all across the world). Another time the item exceeded the allowed size and was 'destroyed' (i.e. sold off by Pittney Bowes) while I was refunded.
Overall, GSP is OK. From the side of an European buyer it means shipping costs are often very reasonable, and most of the time the item arrives on time. I also know what an item is going to cost me, including customs, which is an advantage.Occasionally however, Pittney Bowes (who operate GSP for ebay) screw up, and if one of their monkeys doesn't understand what a part is for they may select the wrong sitem category or believe it's something hyper-special secret gizmo no-one else than the US is allowed to own.
If they blocked that 8593E it appears the person who dealt with your package in Pittney Bowes was a moron. Unfortunately there's nothing you can do, but if you buy another 8593E then it very likely will just be sent to you as the first one should have been.
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Thanks for the Rad Lab link. It appears that all the volumes are available in PDF format. I'm downloading them all now. Having read a history of the Rad Lab and a biography of the man responsible, Alfred Loomis, it should be a lot of fun to read.
For those not aware of it, the Rad Lab existed in Tuxedo Park, NY as a personal project of Alfred Loomis before WW II. Loomis was also involved in building the cyclotron at Berkeley. Lui Alvarez made an off hand comment to Loomis one evening that if they couldn't get copper they could use aluminum. Alvarez was blow away the next morning when Loomis told him it was not possible to build the magnets with aluminum wire for any of the designs being discussed. Loomis had stayed up all night making the calculations.
Loomis invented LORAN in the shower after a conversation with a Brit who was visiting. They wanted to name it after him, but he declined so they came up with a phrase to match the acronym.
Loomis closed the Rad Lab at the end of the war because he didn't think the government should be involved in research except in exigent circumstances such as war.
|
Re: Warning to buy equipment on Ebay on auctions using GSP (global shipping programme)
Battery fitted inside equipment is exempt ? David ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Robert G8RPI via Groups.Io
Sent: 22 November 2018 12:58
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Warning to buy equipment on Ebay on auctions using GSP (global shipping programme) ? Ahh the GSP "police"
There are two main reasons why GSP may say something is restricted
1/ it's hazardous to ship e.g. batteries chemicals. The rules on batteries are complex, but a internally installed memory back-up lithium is NOT grounds to classify as hazardous.?The 8593E does have?a battery?marking on them which may have triggered?the stop?However the "safe" option for the GSP is not to ship if in doubt. Obviously shipping back to seller is impossible.
The second reason is "military" or other classified equipment i.e. items controlled by ITAR or EAR (google them)
There is no reason why these should not be returned to the seller.
Robert G8RPI.
|
Re: Warning to buy equipment on Ebay on auctions using GSP (global shipping programme)
Ahh the GSP "police" There are two main reasons why GSP may say something is restricted 1/ it's hazardous to ship e.g. batteries chemicals. The rules on batteries are complex, but a internally installed memory back-up lithium is NOT grounds to classify as hazardous.?The 8593E does have?a battery?marking on them which may have triggered?the stop?However the "safe" option for the GSP is not to ship if in doubt. Obviously shipping back to seller is impossible. The second reason is "military" or other classified equipment i.e. items controlled by ITAR or EAR (google them) There is no reason why these should not be returned to the seller. Robert G8RPI.
|
Re: Warning to buy equipment on Ebay on auctions using GSP (global shipping programme)
Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 22 Nov 2018 at 09:27, Peter Hansen < oz1lpr@...> wrote:
I just bought a HP 8593E on ebay. It was going through the Global Shipping Programme (GSP). For no good reason they said it is restricted unit and it cannot be exported to Denmark.
The seller will also not get it back. The message to was unit must be destroyed.
Both me and the seller was refunded but what is going on.
I heard many of?that type of equipement is restriced and will be destroyed if exported.
Does anyone else have had same?problems ?. ??
Or is it the Global shipping programme that has gotten something wrong ?
regards Peter??
Someone I know had a lithium ion battery distroyed. The seller should never have shipped such an item in the first place, and the seller lost his money.
It seems the GSP was kind to the seller in this case, but there are some items that can't be shipped. There are severe restions on Lithium ion batteries, especially if they need to go on a plane. Some thing are also covered by ITAR (International Traffic in Arms Regulations).?
The GSP has ****ed up with me, but both me and the seller got a refund. But that was because they sent a tiger figurine rather than a cal kit. Items do get mixed up. I would suggest sticking the name and address of the sender and recipricant on the actual item, which will reduce the chances of a screwup.
--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892
Tel 01621-680100 / +44 1621-680100
|
Warning to buy equipment on Ebay on auctions using GSP (global shipping programme)
I just bought a HP 8593E on ebay. It was going through the Global Shipping Programme (GSP). For no good reason they said it is restricted unit and it cannot be exported to Denmark.
The seller will also not get it back. The message to was unit must be destroyed.
Both me and the seller was refunded but what is going on.
I heard many of?that type of equipement is restriced and will be destroyed if exported.
Does anyone else have had same?problems ?. ??
Or is it the Global shipping programme that has gotten something wrong ?
regards Peter??
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
The GM / Marconi TfT deivces are thermocouple arrays. Bismuth /nichrome couples bad as a electrical generation device but can be made to match 50R. The resistor thermocouple types were common in RF ammeters and some power meters. The early?Marconi TF144 signal generator models used them for the output meter. The classic thermistor detector is the HP 478A that was first used?with the 431A power meter around 1961 and still made today at $5000 a pop. The analogue ?432B power meter was discontinued a few years ago with a final price of over $10,000 but the pair can be picked up for a few hundred dollars used. They built a new digital meter for the 478A the N432A at $10,000. but none if these appear in the Keysight power meter guide tables. So why is this "old tech" still made? the answer is in the guide: "Not discussed is the Keysight family of thermistor sensors and the associated Keysight 432A power meter. This venerable technology now is used almost exclusively for the standardization and traceability of power measurements from the U.S. National Institute of Standards and Technology and other international standards agencies. Because the Keysight 432A power meter and thermistor sensor technology is based on the highly precise DC-substitution method, the sensors are used as transfer standards, traveling between the user’s primary lab and the NIST measurement services laboratory. Users interested in such metrology power-transfer processes may request Keysight’s AN 64-1, 5965-6630E and AN 64-4, 5965-8167E application notes." Basically you can use a head with any 431/432/N432 meter and a accurate DC?DVM to get transfer accuracy to?a national standard. The "meter" is just a servo to balance the bridge and the accuracy is at the DC voltage. They do special variants of the head?with larger blocking capacitors for low frequency work. ? Robert G8RPI.
?
|
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
(It appears that my list of the RadLab books came from:
This link no longer works but:
Does and I did get volume 11 from there.
At MIT, I find a page about the series, but not the texts of the volumes:
)
In the second above, page 81 mention is made of “bolometers”, being
implemented with thermistors and bolometer, these having negative and
positive temperature coefficients. It goes on to describe bridge circuits and
the characteristics of the measurement elements. There's a copy of the Rad Lab series on ko4bb.com: -- john, KE5FX
|
Re: Tips on repairing the stick attenuator in the HP86603A
Part number would be 86603- 60074  Never had to fix on so can't help further Robert G8RPI.
|
Re: Tips on repairing the stick attenuator in the HP86603A
Perhaps a picture would be useful too.
Daun
Daun E. Yeagley II, N8ASB
On 11/21/2018 12:19 PM, Glenn Little
wrote:
toggle quoted message
Show quoted text
I guess a part number for the attenuator in question would help.
Everyone does not have 86603A manuals to check the part number.
The o-ring failures are quite common.
The attenuators with o-rings are used in a number of instruments.
Without the attenuator part number, who would know that your
attenuator is of a different design.
Glenn
On 11/21/2018 10:13 AM, Jeff Kruth
via Groups.Io wrote:
I had asked if anyone
was familiar with this type of atten. NOT the 8495
style, but a long stick. I guess no one reads. NO O
rings.
Jeff
In a message dated 11/20/2018 7:02:42 PM Eastern Standard
Time, glennmaillist@...
writes:
Here is a video on repairing one of these
attenuators:
The O-Rings are 2mm od x 1 mm id x 0.5mm thick.
Theses are used in watch making.
Hope this helps
Glenn
On 11/20/2018 6:31 PM, g lowrey wrote:
> Hey Jeff. Have you measured one to check the size? I
have several
> sources that might be able to supply them -
> 73,
> Bo L.
>
> On 11/20/18, Jeff Kruth via Groups.Io <kmec= [email protected]>
wrote:
>> Hi All!
>> Dont ask why, but I am resurrecting several HP
8660D generators with the
>> HP86603A plugin. The attenuators are "sticky", get
stuck in a certain
>> position. If you have experience with this exact
type of stick attenuator
>> (long silver block) with the 3 - 40 dB, 20 dB,
& 10 dB sections and can
>> advise how to make a reliable repair, I would love
to hear about it. Several
>> that I cleaned the solenoid shafts on seemed to be
working only to stick
>> again. I do not know how to search the archives as
well, can someone
>> advise?Thanks!73Jeff Kruth
>>
>>
>>
>>
>
>
>
--
-----------------------------------------------------------------------
Glenn Little? ? ? ? ? ? ? ? ARRL Technical Specialist? QCWA?
LM 28417
Amateur Callsign:? WB4UIV? ? ? ? ? ? wb4uiv@...? ?
AMSAT LM 2178
QTH:? Goose Creek, SC USA (EM92xx)? USSVI LM? NRA LM? SBE
ARRL TAPR
"It is not the class of license that the Amateur holds but
the class
of the Amateur that holds the license"
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Paul Bicknell
David C. Partridge