Elecraft

OT: Bird Wattmeter "meter failures"

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Ken G Kopp

OT: Bird Wattmeter "meter failures"

An earlier posting brings this to mind ....

There is a seemingly little-known failure that frequently occurs to Bird
meter movements ... or more correctly ... to the connector at the sensor
casting end of the length of coax used to connect the (30 ua) meter to the
sensor.

Often a sharp "whack" on the housing will cause the meter to resume
working, often for long periods of time. The connector's internal
connection is made by inserting the (solid) center conductor of the coax
between turns of the coils of a tiny spring that's part of the center pin
assembly of the casting end's cable connector.

There's such a tiny amount of current flowing through the coax center
conductor and the spring "connection" that it seems to corrode easily, and
most assume the meter movement has failed. The resulting tiny disturbance
to the wire/spring junction is why the "slap" on the housing often brings
the meter back to life. Many of the expensive proprietary meters have been
needlessly replaced because of this.

73 - K0PP
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Bob K6UJ

Re: OT: Bird Wattmeter "meter failures"

Ken,

My bird has been acting as you described. I will check it out.
I guess the remedy is to clean the spring coils ?
Thanks for the info ?

73,
Bob
K6UJ

On 11/21/15 3:23 PM, Ken G Kopp wrote:

> An earlier posting brings this to mind ....
>
> There is a seemingly little-known failure that frequently occurs to Bird
> meter movements ... or more correctly ... to the connector at the sensor
> casting end of the length of coax used to connect the (30 ua) meter to the
> sensor.
>
> Often a sharp "whack" on the housing will cause the meter to resume
> working, often for long periods of time. The connector's internal
> connection is made by inserting the (solid) center conductor of the coax
> between turns of the coils of a tiny spring that's part of the center pin
> assembly of the casting end's cable connector.
>
> There's such a tiny amount of current flowing through the coax center
> conductor and the spring "connection" that it seems to corrode easily, and
> most assume the meter movement has failed. The resulting tiny disturbance
> to the wire/spring junction is why the "slap" on the housing often brings
> the meter back to life. Many of the expensive proprietary meters have been
> needlessly replaced because of this.
>
> 73 - K0PP
> ______________________________________________________________
> Elecraft mailing list
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>

Don Wilhelm-4

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Ken G Kopp

That brings to mind an adage advocated by my lab instructors in college
and has proven to be very worthwhile over the years - it is no less
applicable today.
"Technician (or Engineer), know your test equipment and especially know
its limitations".
That means always be prepared to verify your measurement equipment
readings by some other means rather than trusting the indication of any
one instrument.

In other words, if your test gear is telling you something that looks
"funny", verify the test equipment as a first order of business - use an
alternate measurement method to do a 'sanity check' and remember that
test equipment can fail just as well as the equipment under test.
Trust no piece of test equipment that cannot be verified for correct
operation.

As an example, I have a wattmeter that is supposedly good for HF as well
as VHF/UHF. The VHF part starts above 30 MHz. When I had problems
getting XV50 transverters to develop 20 watts as indicated on that
meter, I used an alternate power meter and discovered that wattmeter
took 36 watts to indicate 20 watts on its meter on 50 MHz. On 144, 220,
and 432 MHz it was accurate. So that condition is now plainly marked
with a sticker on that meter. Verify before believing the meter in use.

I know that such verification is not always within easy reach for the
average ham, but usually there are locals with test gear that can be
borrowed to give you a validation of whatever test equipment you are
using (test 3 and let the most common vote be the deciding factor). You
do not have to pay the cost of a calibration lab to do that kind of
verification of your test gear, but do be suspicious if you have not
validated your test equipment in some manner.

73,
Don W3FPR

On 11/21/2015 6:23 PM, Ken G Kopp wrote:

Merv Schweigert

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Bob K6UJ

Buy the new adapter that turns the bird connector into a BNC
then just use a BNC cable, wont have any future problems
with the crappy spring.

73 Merv K9FD/KH6

> Ken,
>
> My bird has been acting as you described. I will check it out.
> I guess the remedy is to clean the spring coils ?
> Thanks for the info ?
>
> 73,
> Bob
> K6UJ
>
>
>
>

Bob McGraw - K4TAX

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Bob K6UJ

And it may be related to a specific element as well. There is a carbon
pot inside the element that has been known to change and/or get dirty
just like any other pot that sits in one position for a long period of time.

73
Bob, K4TAX

On 11/21/2015 6:27 PM, Robert Harmon wrote:
> Ken,
>
> My bird has been acting as you described. I will check it out.
> I guess the remedy is to clean the spring coils ?
> Thanks for the info ?

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Harlan Sherriff

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Ken G Kopp

I'm the supervisor of a metrology lab and that is one of the first things I ensure a new technician understands. And many times it isn't the test equipment that is at fault, nor the unit under test, but the methodology of using that test equipment. Not using the equipment "guard" correctly, induced voltages, improper test leads for the job.... and many many more.
Harlan NC3C

Sent from my Verizon Wireless 4G LTE smartphone

-------- Original message --------
From: Don Wilhelm <[hidden email]>
Date: 11/21/2015 7:28 PM (GMT-05:00)
To: [hidden email]
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

That brings to mind an adage advocated by my lab instructors in college
and has proven to be very worthwhile over the years - it is no less
applicable today.
"Technician (or Engineer), know your test equipment and especially know
its limitations".
That means always be prepared to verify your measurement equipment
readings by some other means rather than trusting the indication of any
one instrument.

In other words, if your test gear is telling you something that looks
"funny", verify the test equipment as a first order of business - use an
alternate measurement method to do a 'sanity check' and remember that
test equipment can fail just as well as the equipment under test.
Trust no piece of test equipment that cannot be verified for correct
operation.

As an example, I have a wattmeter that is supposedly good for HF as well
as VHF/UHF. The VHF part starts above 30 MHz. When I had problems
getting XV50 transverters to develop 20 watts as indicated on that
meter, I used an alternate power meter and discovered that wattmeter
took 36 watts to indicate 20 watts on its meter on 50 MHz. On 144, 220,
and 432 MHz it was accurate. So that condition is now plainly marked
with a sticker on that meter. Verify before believing the meter in use.

I know that such verification is not always within easy reach for the
average ham, but usually there are locals with test gear that can be
borrowed to give you a validation of whatever test equipment you are
using (test 3 and let the most common vote be the deciding factor). You
do not have to pay the cost of a calibration lab to do that kind of
verification of your test gear, but do be suspicious if you have not
validated your test equipment in some manner.

73,
Don W3FPR

On 11/21/2015 6:23 PM, Ken G Kopp wrote:

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Bob McGraw - K4TAX

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Bob McGraw - K4TAX

For that reason I shy away from buying Bird elements at a hamfest. As
my mother would frequently tell me; "don't touch that, you don't know
where its been".

73
Bob, K4TAX

On 11/21/2015 9:44 PM, Ron D'Eau Claire wrote:
> Banging on a slug it the quickest way to change the calibration.

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Don Wilhelm-4

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Harlan Sherriff

Harlan,

That is correct - improper test leads are often a 'culprit'.
For instance trying to measure an HF signal with a 'scope. The
'scope may b rated for 200 MHz, but if you try to us a "hunk of coax"
for a probe, the frequency rating may diminish to 2 MHz (OK, that is
just an example). You need to consider the whole measurement system. A
scope's frequency rating must also be coupled with the frequency rating
of the probe. The use of 10X probes is necessary to keep capacitance
loading of the circuit under test to a minimum. And those probes have a
frequency rating too. Take the entire setup of the test equipment into
consideration when doing measurements.
Make certain that every part of the test equipment being used is
suitable for the frequency involved. A simple coax probe may be OK for
AF frequencies, but it is not adequate when the frequency is increased.

A 'scope can show proper RF voltage amplitude, but the frequency rating
of the probe and the 'scope should be taken into consideration. For
instance, a 35 MHz scope will only show a signal that is 3 dB down at 35
MHz. I would suggest that valid RF voltage measurements be made at
1/10 of the 'scope's frequency rating (and that goes for the probe too).

Again I state, trust no measurement equipment until its accuracy has
been verified.

73,
Don W3FPR

On 11/21/2015 10:09 PM, hsherriff wrote:
> I'm the supervisor of a metrology lab and that is one of the first
> things I ensure a new technician understands. And many times it isn't
> the test equipment that is at fault, nor the unit under test, but the
> methodology of using that test equipment. Not using the equipment
> "guard" correctly, induced voltages, improper test leads for the
> job.... and many many more.
>
>

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Leroy

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Bob McGraw - K4TAX

The Bird wattmeter is a coarse and loose measurement device.
It is the most overrated power meter, especially in the amateur community.
The calibration is only possibly five percent at a single frequency,
usually the center frequency of the slug. Away from that frequency it
rapidly
goes way off , I have seen as much as 30% in the range of the slug.
It’s a very rugged meter, used to confirm a rough level of RF. It is better
at confirming a SWR, as the frequency error is the same in forward as in
reverse.
I have seen many new slugs that could not be calibrated to >10% over a
10Mhz range.
Accurate power meters have frequency calibration factors for each power
head sensor.,
in modern ones it is sometimes in a PROM in the sensor head.
I have told this story many, many times in the ham community.
Bird marketing may be the reason for the ridiculous reverence for them in
the ham community. You can drop one from the tower and it will probably
work as poorly as it ever did, one of their only strengths .

Leroy AB7CE , retired NIST calibrations standards technician.

-----Original Message-----
From: Ron D'Eau Claire
Sent: Saturday, November 21, 2015 8:44 PM
To: [hidden email]
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

If you want to rely on a piece of test equipment it MUST be serviced and
calibrated regularly. The Bird wattmeter I carried as a marine radio service
tech was calibrated annually without fail, or immediately after I dropped a
slug! Banging on a slug it the quickest way to change the calibration.
That's why they are kept in the spaces provide on the meter housing when not
in use.

All of the Birds I've seen in Ham's hands have calibration stickers many
years old.

73, Ron AC7AC

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Richard Fjeld-2

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Bob McGraw - K4TAX

I have found it necessary to apply some contact cleaner to a clean cloth
and wipe around the slug socket
and slug to restore conduction.

Dick, n0ce

On 11/21/2015 9:44 PM, Ron D'Eau Claire wrote:

> If you want to rely on a piece of test equipment it MUST be serviced and
> calibrated regularly. The Bird wattmeter I carried as a marine radio service
> tech was calibrated annually without fail, or immediately after I dropped a
> slug! Banging on a slug it the quickest way to change the calibration.
> That's why they are kept in the spaces provide on the meter housing when not
> in use.
>
> All of the Birds I've seen in Ham's hands have calibration stickers many
> years old.
>
> 73, Ron AC7AC
>
>
>

briancom

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Don Wilhelm-4

Good point Don. Would like to point out that some commercial scopes these days come with probes that are inadequate for the bandwidth of the scope they are connected to.
The scopes might be rated foe 100 MHz but with the supplied probes the system is lucky to make 50 MHz. Tektronix was an exception. Their bandwidth specs were met with factory probes. Unfortunately the only way to know is to test the entire systems response with a calibrated generator. One bargain sampling scope I bought was not such a bargain after buying several sets of probes to find ones meeting bandwidth specs. Even then the best match probe had to have its ground lead shortened a bit to flatten the response.

Developing a trust in ones test equipment takes effort and time.
73 de Brian K3KO
Sent from my iPad

> On Nov 21, 2015, at 10:58 PM, Don Wilhelm <[hidden email]> wrote:
>
> Harlan,
>
> That is correct - improper test leads are often a 'culprit'.
> For instance trying to measure an HF signal with a 'scope. The 'scope may b rated for 200 MHz, but if you try to us a "hunk of coax" for a probe, the frequency rating may diminish to 2 MHz (OK, that is just an example). You need to consider the whole measurement system. A scope's frequency rating must also be coupled with the frequency rating of the probe. The use of 10X probes is necessary to keep capacitance loading of the circuit under test to a minimum. And those probes have a frequency rating too. Take the entire setup of the test equipment into consideration when doing measurements.
> Make certain that every part of the test equipment being used is suitable for the frequency involved. A simple coax probe may be OK for AF frequencies, but it is not adequate when the frequency is increased.
>
> A 'scope can show proper RF voltage amplitude, but the frequency rating of the probe and the 'scope should be taken into consideration. For instance, a 35 MHz scope will only show a signal that is 3 dB down at 35 MHz. I would suggest that valid RF voltage measurements be made at 1/10 of the 'scope's frequency rating (and that goes for the probe too).
>
> Again I state, trust no measurement equipment until its accuracy has been verified.
>
> 73,
> Don W3FPR
>
>
>> On 11/21/2015 10:09 PM, hsherriff wrote:
>> I'm the supervisor of a metrology lab and that is one of the first things I ensure a new technician understands. And many times it isn't the test equipment that is at fault, nor the unit under test, but the methodology of using that test equipment. Not using the equipment "guard" correctly, induced voltages, improper test leads for the job.... and many many more.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
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N2TK

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Leroy

Leroy,
Totally agree with you. In the commercial RF generator business we used Bird's. But every 6 months we calibrated the unit with a calorimeter for the specific frequency of our generators. We would make a new meter face and also tape the slug to the particular meter so it couldn't be changed.
We bought a lot of slugs. It was not unusual for a brand new slug out of the box to be off >30%. Birds are good as a loose measurement device.

By the way, one year at Dayton I picked up a couple used Drake W-4 wattmeters. They were surprisingly accurate on 20M.
Today there are better choices in wattmeters for the shack.

73,
N2TK, Tony

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of lmarion
Sent: Saturday, November 21, 2015 11:35 PM
To: Ron D'Eau Claire <[hidden email]>; [hidden email]
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

The Bird wattmeter is a coarse and loose measurement device.
It is the most overrated power meter, especially in the amateur community.
The calibration is only possibly five percent at a single frequency, usually the center frequency of the slug. Away from that frequency it rapidly goes way off , I have seen as much as 30% in the range of the slug.
It’s a very rugged meter, used to confirm a rough level of RF. It is better at confirming a SWR, as the frequency error is the same in forward as in reverse.
I have seen many new slugs that could not be calibrated to >10% over a 10Mhz range.
Accurate power meters have frequency calibration factors for each power head sensor., in modern ones it is sometimes in a PROM in the sensor head.
I have told this story many, many times in the ham community.
Bird marketing may be the reason for the ridiculous reverence for them in the ham community. You can drop one from the tower and it will probably work as poorly as it ever did, one of their only strengths .

Leroy AB7CE , retired NIST calibrations standards technician.

-----Original Message-----
From: Ron D'Eau Claire
Sent: Saturday, November 21, 2015 8:44 PM
To: [hidden email]
Subject: Re: [Elecraft] OT: Bird Wattmeter "meter failures"

If you want to rely on a piece of test equipment it MUST be serviced and calibrated regularly. The Bird wattmeter I carried as a marine radio service tech was calibrated annually without fail, or immediately after I dropped a slug! Banging on a slug it the quickest way to change the calibration.
That's why they are kept in the spaces provide on the meter housing when not in use.

All of the Birds I've seen in Ham's hands have calibration stickers many years old.

73, Ron AC7AC

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Cortland Richmond-2

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Ken G Kopp

On 11/22/2015 6:34, Brian K3KO wrote
> ... some commercial scopes these days come with probes that are inadequate for the bandwidth of the scope they are connected to.

If you don't need to probe HV or more than about 1 KOhm, the probes, (or
indeed, the whole setup) used in Doug Smiths came up with for balanced
HF probing looks like a good alternative to"what came with" probes. from
1994: Balanced Scope Probe Extends High Frequency Measurements,
http://emcesd.com/pdf/cd94scr.pdf

Tek has good literature on probes; go to
http://info.tek.com/www-abcs-of-probes-primer.html (they'll need your
name, email, location and company -- IIRC, "self" might work) and look
at page 35.

Cortland KA5S
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Edward R Cole

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Ken G Kopp

My old 1976 Bird is that way... like an unruly child ... needs a slap
now an then to keep it on track! Actually, I don't condone physical
punishment of children. A word or a look can do much more...my Dad
was a master at that and I guess I picked up some from him. But
back to electronics:

I recently had a transverter customer call that it wasn't showing
anything on his Bird meter. The internal LED bar meter was showing
RF output which is driven by a simple diode. So there was RF at the
output of the unit but none at the meter. First thing I suggested
was trying a different coax jumper, then I suggested a different element.

Interestingly he said received a beacon 60 miles away just fine -
hmm. That told me the internal coax and LO were working. Had him
check some other connections. Finally, I told him to connect the
antenna and try making contact with a nearby ham. He called me later
to say that he made the contact and got S7 report.

He then confessed that the Bird was unused for a couple years and
stored in his garage. I asked if he had a 2m FM radio that he could
use to test the meter and he said, yes. Haven't heard back but I'm
guessing he discovered the meter was not working. He had another
Bird meter to try, but it was also stored in the garage. He lives in
a humid climate on the Gulf of Mexico.

As Don put it know your test equipment and don't jump to conclusion
the radio has failed. I look at wires first. Oh and make sure the
PS is turned on! ;-) I drove two hours to a customer's house to
determine why his satellite TV quit...wife knocked the ac cord out of
the wall socket with vacuum behind the book shelf entertainment
center. Embarrassing!
I could only charge them my gas money even though I spent half a day traveling.

73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[hidden email]

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David Christ

Re: OT: Bird Wattmeter "meter failures" (scope probes)

In reply to this post by Cortland Richmond-2

Interesting article, but being a little dense at times, what is inside the box labeled combiner?

David K0LUM

> On Nov 22, 2015, at 6:10 AM, CR <[hidden email]> wrote:
>
> If you don't need to probe HV or more than about 1 KOhm, the probes, (or indeed, the whole setup) used in Doug Smiths came up with for balanced HF probing looks like a good alternative to"what came with" probes. from 1994: Balanced Scope Probe Extends High Frequency Measurements, http://emcesd.com/pdf/cd94scr.pdf

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Bob McGraw - K4TAX

Re: OT: Bird Wattmeter "meter failures"

In reply to this post by Leroy

Ron mentions various well taken points regarding the Bird 43 meter
series. This also applies to almost all watt meters as well, and that
is the power calibration is relative to a 50 ohm load only. Any other
load Z will introduce errors in the meter accuracy and indication.

At the same time, the ratio measurement for forward power and reflected
power will always be correct in that each value will be measured with
the same degree of error. Thus using this information, one can
accurately calculate the SWR using the forward power indicated and the
reflected power indicated. Where as, absolute values will not
necessarily be accurate under these conditions.

73
Bob, K4TAX

On 11/22/2015 11:38 AM, Ron D'Eau Claire wrote:
> Bird instruments specs a Bird 43 at plus or minus 5% of full scale. If you have a calibrated 1000 watt slug and meter it will read within 100 watts of the real power. What many people miss is that the possible 100 watt error is constant over the range of the meter, so measuring 500 watts the meter will indicate something between 400 and 600 watts and at 100 watts the reading can be off by a full 100%!

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Bob K6UJ

Re: OT: Bird Wattmeter "meter failures"

Thanks for all the info on diagnosing the intermittent problem with my
Bird 43 guys !
I discovered their was a poor connection where the RG58 from the meter
movement
connects to the element. As mentioned there is a tiny spring in the
connector on the end of the
cable. It didnt look dirty visually but I cleaned it with some contact
cleaner and now is fine.
It was mentioned to change over to a BNC connector to eliminate
problems. I assume we mean an
adapter from the bird element connection point to a BNC. Then add a BNC
on the end of the short
RG58 from the meter movement. Anyway it is working now, thanks guys !

73,
Bob
K6UJ

On 11/22/15 2:13 PM, Bob McGraw - K4TAX wrote:

> Ron mentions various well taken points regarding the Bird 43 meter
> series. This also applies to almost all watt meters as well, and that
> is the power calibration is relative to a 50 ohm load only. Any other
> load Z will introduce errors in the meter accuracy and indication.
>
> At the same time, the ratio measurement for forward power and
> reflected power will always be correct in that each value will be
> measured with the same degree of error. Thus using this information,
> one can accurately calculate the SWR using the forward power indicated
> and the reflected power indicated. Where as, absolute values will
> not necessarily be accurate under these conditions.
>
> 73
> Bob, K4TAX
>
> On 11/22/2015 11:38 AM, Ron D'Eau Claire wrote:
>> Bird instruments specs a Bird 43 at plus or minus 5% of full scale.
>> If you have a calibrated 1000 watt slug and meter it will read within
>> 100 watts of the real power. What many people miss is that the
>> possible 100 watt error is constant over the range of the meter, so
>> measuring 500 watts the meter will indicate something between 400 and
>> 600 watts and at 100 watts the reading can be off by a full 100%!
>
>
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Don Wilhelm-4

Re: OT: Bird Wattmeter "meter failures"

Another verification that *all* problems are not the fault of the DUT
(Device Under Test), and can often be a failure of the test equipment.
Do be prepared to check the test gear prior to taking measurements.

While that is not practical in most cases, do be suspicious of your
measurements until you have taken steps sufficient to validate your test
setup.
I do not know how to tell you how to validate your test setup in detail,
because that will vary depending on the equipment used, but what I am
saying is that you should not trust the indication of any measurement
device at face value. Verify that the measurement device is giving
proper indications as the fist order of business - or at least second
order when measurements begin to "look funny".

73,
Don W3FPR

On 11/22/2015 5:46 PM, Robert Harmon wrote:

> Thanks for all the info on diagnosing the intermittent problem with my
> Bird 43 guys !
> I discovered their was a poor connection where the RG58 from the meter
> movement
> connects to the element. As mentioned there is a tiny spring in the
> connector on the end of the
> cable. It didnt look dirty visually but I cleaned it with some
> contact cleaner and now is fine.
> It was mentioned to change over to a BNC connector to eliminate
> problems. I assume we mean an
> adapter from the bird element connection point to a BNC. Then add a
> BNC on the end of the short
> RG58 from the meter movement. Anyway it is working now, thanks guys !
>
> 73,
> Bob
> K6UJ
>
>
>
> On 11/22/15 2:13 PM, Bob McGraw - K4TAX wrote:
>> Ron mentions various well taken points regarding the Bird 43 meter
>> series. This also applies to almost all watt meters as well, and
>> that is the power calibration is relative to a 50 ohm load only. Any
>> other load Z will introduce errors in the meter accuracy and indication.
>>
>> At the same time, the ratio measurement for forward power and
>> reflected power will always be correct in that each value will be
>> measured with the same degree of error. Thus using this
>> information, one can accurately calculate the SWR using the forward
>> power indicated and the reflected power indicated. Where as, absolute
>> values will not necessarily be accurate under these conditions.
>>
>> 73
>> Bob, K4TAX
>>
>> On 11/22/2015 11:38 AM, Ron D'Eau Claire wrote:
>>> Bird instruments specs a Bird 43 at plus or minus 5% of full scale.
>>> If you have a calibrated 1000 watt slug and meter it will read
>>> within 100 watts of the real power. What many people miss is that
>>> the possible 100 watt error is constant over the range of the meter,
>>> so measuring 500 watts the meter will indicate something between 400
>>> and 600 watts and at 100 watts the reading can be off by a full 100%!
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
>
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Al Gulseth-2

Re: OT: Bird Wattmeter "meter failures" (scope probes)

In reply to this post by David Christ

David,

As no one else appears to have replied, I'll take a stab at it. Basically,
a "combiner" is a transformerish arrangement which isolates the ports from
each other to keep them from interfering while maintaining the correct
impedance. They can be pretty simple and inexpensive, with basic versions
requiring just a couple of small ferrite cores (of the correct mix for the
frequency range involved) with tapped or bifiliar windings and a terminating
resistor or so. The following articles explain things far better than I can:

AN10-006 Understanding Power Splitters - Mini Circuits
www.minicircuits.com/app/AN10-006.pdf
‎
Magic T combiners splitters and how they work - W8JI.com
www.w8ji.com/combiner_and_splitters.htm

Hope this helps.

73, Al

On Sun November 22 2015 8:16:28 am David Christ wrote:

> Interesting article, but being a little dense at times, what is inside the
> box labeled combiner?
>
> David K0LUM
>
> > On Nov 22, 2015, at 6:10 AM, CR <[hidden email]> wrote:
> >
> > If you don't need to probe HV or more than about 1 KOhm, the probes, (or
> > indeed, the whole setup) used in Doug Smiths came up with for balanced HF
> > probing looks like a good alternative to"what came with" probes. from
> > 1994: Balanced Scope Probe Extends High Frequency Measurements,
> > http://emcesd.com/pdf/cd94scr.pdf
>
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