Re: Test Equipment For Sale
Hi
?
In 75 I was playing with gun diodes and Klystrons?
at the age of 17 only test equipment where diode detectors on the end of a meter
and an oscilloscope I had rebuilt after someone had used it for spare parts ??
?
Paul
?
Well, in the early 70’s, to be able to do this
at home, was fun and rewarding. From some heavy math to a final product.
– Mike
?
Mike B. Feher, N4FS
89 Arnold
Blvd.
Howell NJ
07731
848-245-9115
?
?
Hi
?
yes a lot of filter work can be verified
using peak hold can be time consuming on a adjusting complicated filter
?
Regards Paul
?
In my early days of
designing filters, I used to use a broadband noise generator with a 141T
spectrum analyzer. Worked great in max hold after a few sweeps. Just had to
make sure the total in-band energy did not overload the front end. Was even
able to adjust the zeroes pretty accurately. Since I only built Elliptics, I
knew were the poles and zeroes were. 73 – Mike
?
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
848-245-9115
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Test Equipment For Sale
Paul - Yes - I am the author of th statement Quoting Paul Bicknell <paul@...>:
Hi Bruce I assume you are quoting the following
I think what they are trying to sayis they REALLY want a network
analyzer. SA +FG = S12 measurement
Because I did not as most amateurs would not understand network analysers
having never used one
In England as part of a two week satellite work experience program for
school children and a summer school for collage students
the practical demonstrations start of with the understanding of Dbs
followed by network analyser measuring throw loss and return loss
and also TDR measurements on fibber optic cables
These courses have even been rolled out to girls schools to educate them
that engineering is a profession they can do
and engineers no longer work with a greasy rag and go home stinking of oil
Personally I am sylph taught as never worked with RF test equipment as part
of my R & D work in the aerospace and automotive industry
Regards Paul
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Bruce
Sent: 25 April 2020 18:51
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
I think what they are trying to sayis they REALLY want a network
analyzer. SA +FG = S12 measurement (sorta)
Quoting Paul Bicknell <paul@...>:
Hi Dave I think you have it ! it is the tracking generator obsession As we have only had one person com back saying he requires it but shame it only goes to 1000 mhz I would think the minimum now days would be 2000 Mhz
for sat comes IF work Regards Paul -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Dave McGuire Sent: 25 April 2020 15:48 To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale On 4/25/20 5:59 AM, Paul Bicknell wrote: During the last year on a number of sites I have seen several requests
for people buying their fist spectrum analyser and all have spoken about
wanting a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment
and think a spectrum analyser is the only tool they require and unaware
of sweepers and Scalier analysers
I've wondered about this myself. I've always just assumed that the tracking generator obsession was from people who don't know about (or are intimidated by) network analyzers. -Dave Dave McGuire, AK4HZ New Kensington, PA
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Test Equipment For Sale
Well, in the early 70’s, to be able to do this at home, was fun and rewarding. From some heavy math to a final product. – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Paul Bicknell
Sent: Saturday, April 25, 2020 3:00 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale? Hi ? yes a lot of filter work can be verified using peak hold can be time consuming on a adjusting complicated filter ? Regards Paul ? In my early days of designing filters, I used to use a broadband noise generator with a 141T spectrum analyzer. Worked great in max hold after a few sweeps. Just had to make sure the total in-band energy did not overload the front end. Was even able to adjust the zeroes pretty accurately. Since I only built Elliptics, I knew were the poles and zeroes were. 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115
|
Re: Test Equipment For Sale
Hi
?
yes a lot of filter work can be verified
using peak hold can be time consuming on a adjusting complicated filter
?
Regards Paul
?
In my early days of
designing filters, I used to use a broadband noise generator with a 141T
spectrum analyzer. Worked great in max hold after a few sweeps. Just had to
make sure the total in-band energy did not overload the front end. Was even
able to adjust the zeroes pretty accurately. Since I only built Elliptics, I
knew were the poles and zeroes were. 73 – 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 Paul Bicknell
Sent: Saturday, April 25, 2020 2:24 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
?
Hi Jim
?
Yes filters that is exactly the thing I have used a
spectrum analyser with a tracking filter for and they where all below 100 Mhz
?
Regards Paul
?
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Re: Test Equipment For Sale
?
?
Hi Bruce ??I assume ?you are quoting the following
?
I think what they are trying to sayis they
REALLY want a network?
analyzer.? SA +FG = S12 measurement
?
?
Because I did not as most amateurs would not understand network
analysers having never used one
?
In England
as part of a two week satellite work experience program for school children and
a summer school for collage students ?
the practical demonstrations start of with the understanding
of Dbs ?followed by network analyser measuring throw loss and return loss
and also TDR measurements on fibber optic cables ?
?
These courses have even been rolled out to ?girls schools
to educate them that engineering is a profession they can do
and engineers no longer work with a greasy rag and go home stinking
of oil
?
Personally I am sylph taught as never worked with RF test equipment
as part of my R & D work in the aerospace and automotive industry
?
Regards Paul
?
toggle quoted message
Show quoted text
-----Original Message-----
From: [email protected]
[mailto:[email protected]]
On Behalf Of Bruce
Sent: 25 April 2020 18:51
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
?
I think what they are trying to sayis they REALLY want a network?
analyzer.? SA +FG = S12 measurement (sorta)
Quoting Paul Bicknell <paul@...>:
?
> Hi Dave
>?
> I think you have it !??? it is the tracking
generator obsession
>?
> As we have only had one person com back saying he requires it but
shame it
> only goes to 1000 mhz? I would think the minimum now days
would be 2000 Mhz
> for sat comes IF work
>?
> Regards Paul
>?
>?
>?
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]
On Behalf Of Dave McGuire
> Sent: 25 April 2020 15:48
> To: [email protected]
> Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For
Sale
>?
> On 4/25/20 5:59 AM, Paul Bicknell wrote:
>> During the last year on a number of sites I have seen several
requests
>> for people buying their fist spectrum analyser and all have
spoken about
>> wanting a tracking generator
>>?
>> I personally have only used an analyser with a tracking
generator a few
>> times in my life and that was 35 years ago a Marconi 110 Mhz
spectrum
>> analyser for setting up IF? filters
>>?
>> In my early days I started using swappers and diode detectors
or power
>> meters with an oscilloscope then moved onto Scaler analysers
>>?
>> Could it be the new people are not familiar with other test
equipment
>> and think a spectrum analyser is the only tool they require
and unaware
>> of sweepers and Scalier analysers
>?
>?? I've wondered about this myself.? I've always
just assumed that the
> tracking generator obsession was from people who don't know about
(or
> are intimidated by) network analyzers.
>?
>??????????????
-Dave
>?
> Dave McGuire, AK4HZ
> New Kensington,
PA
>?
>?
>?
>
?
?
?
?
?
?
?
?
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date:
08/14/18
Internal Virus Database is out of date.
|
Re: Test Equipment For Sale
In my early days of designing filters, I used to use a broadband noise generator with a 141T spectrum analyzer. Worked great in max hold after a few sweeps. Just had to make sure the total in-band energy did not overload the front end. Was even able to adjust the zeroes pretty accurately. Since I only built Elliptics, I knew were the poles and zeroes were. 73 – 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 Paul Bicknell
Sent: Saturday, April 25, 2020 2:24 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale ? Hi Jim ? Yes filters that is exactly the thing I have used a spectrum analyser with a tracking filter for and they where all below 100 Mhz ? Regards Paul ?
|
Re: Test Equipment For Sale
Hi Jim
Yes filters that is exactly the thing I have used a spectrum analyser with a
tracking filter for and they where all below 100 Mhz
Regards Paul
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected][mailto: [email protected]] On Behalf Of Jim Shorney Sent: 25 April 2020 18:48 Cc: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale Paul, The Midnight SNA was a neat little kit I built a couple of years ago mainly because I needed something to test vintage IF crystal filters with. As such its top end of 60 MHz was more than adequate. It is an outgrowth of the PHSNA project. NanoVNA is all the rage these days, a fun little toy. I'm still figuring it out. My company manufactures low power VHF/UHF professional wireless intercom radios which have some pretty tight bandpass filters on the receivers and sometimes the transmitters. The SA + TG is how we align them both on the production line and in the service center. I also use if for checking the bandpass response of wideband powered antenna splitter/combiner boxen. Stuff that most hams/hobbyists don't usually see. 73 -Jim NU0C On Sat, 25 Apr 2020 17:33:28 +0100 "Paul Bicknell" <paul@...> wrote: Hi Jim
interesting about you using the tracking generator daily
Love to know how you use it in your daily job
Regarding Street credibility I think we all have it if we have HP test
equipment and I must admit I do have 6 HP spectrum analysers
But Midnight SNA and Nano VNA are both new to me
Regards Paul
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim Shorney
Sent: 25 April 2020 17:03
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
I have used HP tracking analyzers at work almost daily for many years. Last year I acquired one surplus that needed minor repair for a stupid low price. I also own a Midnight SNA and NanoVNA. And a vintage Eico sweep generator.
:)
Each tool has its own niche. Each is plenty good enough for most hobbyist
needs within those niches. The HP continues to be my favorite instrument and my go-to for sanity checks on the others. And yes, I do use the tracking
generator in radio service work. I likely would not have purchased this HP
if it did not have the TG.
And then there's always the street cred that comes with using a name brand
instrument.... :D
73
-Jim
NU0C
On Sat, 25 Apr 2020 10:59:31 +0100
"Paul Bicknell" <paul@...> wrote:
Hi all
During the last year on a number of sites I have seen several requests for people buying their fist spectrum analyser and all have spoken about
wanting a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment
and think a spectrum analyser is the only tool they require and unaware of
sweepers and Scalier analysers
Your comments please Regards Paul
----- No virus found in this message. Checked by AVG - www.avg.com Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18 Internal Virus Database is out of date.
|
Re: WTB HP 11852A or B 50/75 Ohm minimum loss pad
How good do they have to be?
How about?the Mini-Circuits UNMP-5075?? They have a ship from UK option.
Hi
I'm looking for a pair of the HP 11852A or B 50/75 Ohm minimum loss?pad adapters or their
equivalents. If there is someone that doesn't need them I'm willing to buy them. I'm located at Athens GREECE so will have to ship them with post if possible for economy... reasons :)
Thank you in advance
Sotiris Pdmt
|
Re: Test Equipment For Sale
I think what they are trying to sayis they REALLY want a network analyzer. SA +FG = S12 measurement (sorta) Quoting Paul Bicknell <paul@...>:
Hi Dave
I think you have it ! it is the tracking generator obsession
As we have only had one person com back saying he requires it but shame it
only goes to 1000 mhz I would think the minimum now days would be 2000 Mhz
for sat comes IF work
Regards Paul
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Dave McGuire
Sent: 25 April 2020 15:48
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
On 4/25/20 5:59 AM, Paul Bicknell wrote:
During the last year on a number of sites I have seen several requests
for people buying their fist spectrum analyser and all have spoken about
wanting a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment
and think a spectrum analyser is the only tool they require and unaware
of sweepers and Scalier analysers I've wondered about this myself. I've always just assumed that the
tracking generator obsession was from people who don't know about (or
are intimidated by) network analyzers.
-Dave
Dave McGuire, AK4HZ
New Kensington, PA
|
Re: Test Equipment For Sale
Paul, The Midnight SNA was a neat little kit I built a couple of years ago mainly because I needed something to test vintage IF crystal filters with. As such its top end of 60 MHz was more than adequate. It is an outgrowth of the PHSNA project. NanoVNA is all the rage these days, a fun little toy. I'm still figuring it out. My company manufactures low power VHF/UHF professional wireless intercom radios which have some pretty tight bandpass filters on the receivers and sometimes the transmitters. The SA + TG is how we align them both on the production line and in the service center. I also use if for checking the bandpass response of wideband powered antenna splitter/combiner boxen. Stuff that most hams/hobbyists don't usually see. 73 -Jim NU0C On Sat, 25 Apr 2020 17:33:28 +0100 "Paul Bicknell" <paul@...> wrote: Hi Jim
interesting about you using the tracking generator daily
Love to know how you use it in your daily job
Regarding Street credibility I think we all have it if we have HP test
equipment and I must admit I do have 6 HP spectrum analysers
But Midnight SNA and Nano VNA are both new to me
Regards Paul
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim Shorney
Sent: 25 April 2020 17:03
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale
I have used HP tracking analyzers at work almost daily for many years. Last
year I acquired one surplus that needed minor repair for a stupid low price.
I also own a Midnight SNA and NanoVNA. And a vintage Eico sweep generator.
:)
Each tool has its own niche. Each is plenty good enough for most hobbyist
needs within those niches. The HP continues to be my favorite instrument and
my go-to for sanity checks on the others. And yes, I do use the tracking
generator in radio service work. I likely would not have purchased this HP
if it did not have the TG.
And then there's always the street cred that comes with using a name brand
instrument.... :D
73
-Jim
NU0C
On Sat, 25 Apr 2020 10:59:31 +0100
"Paul Bicknell" <paul@...> wrote:
Hi all
During the last year on a number of sites I have seen several requests for
people buying their fist spectrum analyser and all have spoken about
wanting a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment and
think a spectrum analyser is the only tool they require and unaware of
sweepers and Scalier analysers
Your comments please Regards Paul
|
Re: Test Equipment For Sale
Paul,
Built-in tracking generators are rather nice.? When you are at a remote site in the winter in a blinding snow storm or somewhere else there really isn't time to be fudging around with multiple pieces of equipment to tune a frequency sensitive device or check its response.
Greg
|
Re: HP 4195A NiCad Battery replacement
It’s fairly simple.? If they are truly 2/3AA cells pick up a couple from the millions of distributors on the web, specify ones with tabs, solder the two interconnecting tabs together and? you have a battery.? If you want perfection take the cells over to your local Batteries & Bulbs store and have them assemble the pack and apply the customary shrink tube.? They might even have the 2/3AA NiCads in stock.? And there are other companies on the web who will build packs for you.
?
I nearly always build my own packs in-house for cheap and they look just like the OEMs.
?
Greg
|
Re: Hp 8660A extender cards
Hi John,
if still available, I would show interest in this nice extender package. Would be glad to hear back from you.
Thanks!
Chris
|
Tam, no problem, thanks for the suggestion anyway.
Looks like I'm going to have to wait for the CLIP docs. PS is dead-on, voltage is clean. Connectors reseatedseated. Unit is very clean. Amusingly, whoever owned it apparently sent to to Keysight for recal fairly regularly, stickers are on the box. Last recal 2017. Umm, so, just what were they paying for? A 5v source and about 20 seconds of button-pushing? This has got to be the easiest instrument to calibrate that I've ever seen.
Bill
|
Sorry Mate, I meant well. Wanted to make sure it does not get
forgotten.
Not my day today. Badly managed to hurt myself while shopping...
Tam
With best regards
Tam HANNA
Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at
On 2020. 04. 25. 18:12, Bill E wrote:
toggle quoted message
Show quoted text
Yes, the front-end gain calibration requires 5.000V. My fancy (and
calibrated) voltage standard is good to 50 times better than that.
:)
The interpolator calibration does NOT require an input, in fact,
you are explicitly told to be sure nothing is connected.
|
Re: Test Equipment For Sale
Hi Jim
interesting about you using the tracking generator daily
Love to know how you use it in your daily job
Regarding Street credibility I think we all have it if we have HP test
equipment and I must admit I do have 6 HP spectrum analysers
But Midnight SNA and Nano VNA are both new to me
Regards Paul
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected][mailto: [email protected]] On Behalf Of Jim Shorney Sent: 25 April 2020 17:03 To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] Test Equipment For Sale I have used HP tracking analyzers at work almost daily for many years. Last year I acquired one surplus that needed minor repair for a stupid low price. I also own a Midnight SNA and NanoVNA. And a vintage Eico sweep generator. :) Each tool has its own niche. Each is plenty good enough for most hobbyist needs within those niches. The HP continues to be my favorite instrument and my go-to for sanity checks on the others. And yes, I do use the tracking generator in radio service work. I likely would not have purchased this HP if it did not have the TG. And then there's always the street cred that comes with using a name brand instrument.... :D 73 -Jim NU0C On Sat, 25 Apr 2020 10:59:31 +0100 "Paul Bicknell" <paul@...> wrote: Hi all
During the last year on a number of sites I have seen several requests for
people buying their fist spectrum analyser and all have spoken about
wanting a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment and
think a spectrum analyser is the only tool they require and unaware of
sweepers and Scalier analysers
Your comments please Regards Paul
|
Yes, the front-end gain calibration requires 5.000V. My fancy (and calibrated) voltage standard is good to 50 times better than that. :)
The interpolator calibration does NOT require an input, in fact, you are explicitly told to be sure nothing is connected.
|
Re: Test Equipment For Sale
I have used HP tracking analyzers at work almost daily for many years. Last year I acquired one surplus that needed minor repair for a stupid low price. I also own a Midnight SNA and NanoVNA. And a vintage Eico sweep generator. :) Each tool has its own niche. Each is plenty good enough for most hobbyist needs within those niches. The HP continues to be my favorite instrument and my go-to for sanity checks on the others. And yes, I do use the tracking generator in radio service work. I likely would not have purchased this HP if it did not have the TG. And then there's always the street cred that comes with using a name brand instrument.... :D 73 -Jim NU0C On Sat, 25 Apr 2020 10:59:31 +0100 "Paul Bicknell" <paul@...> wrote: Hi all
During the last year on a number of sites I have seen several requests for
people buying their fist spectrum analyser and all have spoken about wanting
a tracking generator
I personally have only used an analyser with a tracking generator a few
times in my life and that was 35 years ago a Marconi 110 Mhz spectrum
analyser for setting up IF filters
In my early days I started using swappers and diode detectors or power
meters with an oscilloscope then moved onto Scaler analysers
Could it be the new people are not familiar with other test equipment and
think a spectrum analyser is the only tool they require and unaware of
sweepers and Scalier analysers
Your comments please Regards Paul
|
On 25/04/20 16:30, Bill E wrote: The 'not working - for parts' 53310 I bought just showed up. It indeed won't pass the interpolator calibration, says can't set the interp gain or offset, and I get a DAC failure, value 255. I have the CLIP level schematics coming, but any clues? Given the 255 value, it would seem to be a problem with whichever DAC is involved, not the interps themselves. BTW, it seems to work just fine using whatever cal values it had when last calibrated. Looking at my 10 MHz GPS standard, it's well within frequency specs, historgram is nice, etc. Opt 031 works fine also, shows a pretty analysis of a 1Ghz signal.
It does pass the front-end gain/offset tests, and those recalibrate with no problem..
So, any ideas? I'd start with the obvious things. ?- check the PSU rails for voltage and ripple. ?- reseat connectors ?- just generally eyeball the relevant circuits
|
Hello,
AFAIK, one of these tests requires a precision external voltage.
Tam
With best regards
Tam HANNA
Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at
On 2020. 04. 25. 17:30, Bill E wrote:
toggle quoted message
Show quoted text
The 'not working - for parts' 53310 I bought just showed up. It
indeed won't pass the interpolator calibration, says can't set the
interp gain or offset, and I get a DAC failure, value 255. I have
the CLIP level schematics coming, but any clues? Given the 255
value, it would seem to be a problem with whichever DAC is
involved, not the interps themselves. BTW, it seems to work just
fine using whatever cal values it had when last calibrated.
Looking at my 10 MHz GPS standard, it's well within frequency
specs, historgram is nice, etc. Opt 031 works fine also, shows a
pretty analysis of a 1Ghz signal.
It does pass the front-end gain/offset tests, and those
recalibrate with no problem..
So, any ideas? BTW, the other unit, no 031 option, in working
condition seems to have been lost by the wonderfully-incompetent
USPS. Third package they've lost in 7 months. Hopefully, they'll
find it. I should be able to cobble together a fully-working 031
optioned unit from the two.
Bill
|
Paul Bicknell
Jim Shorney