Elecraft

Re: MFJ259

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g3ymc

Re: MFJ259

I don't have a 259 myself but some of my friends do. It is clearly a
useful bit of kit.

But I have repaired a couple! I agree about the build standard, not
that hot, and not made easy to repair either with most of the
components inaccessible underneath the board. In both cases they had
been damaged by the user applying the supply the wrong way round -
there is no idiot diode to prevent this. It takes out one of the 5V
regulators and also a LM324 quad op-amp. If you have one it is worth
adding a series diode in the supply to save you the hassle.

I would also make a plug for a noise bridge. I built the one by KI6WX
which appeared in QST in August 1989 (available to download from the
ARRL site). If you have a suitable portable rig to couple to it does
most of what the fancy analysers can do at a fraction of the cost.

73 Dave G3YMC

http://www.davesergeant.com

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David Cutter

Re: Re: MFJ259

I blew the front end while tuning an antenna near another that was energised.

David
G3UNA

>
> From: "Dave Sergeant" <[hidden email]>
> Date: 2007/03/14 Wed AM 10:04:57 GMT
> To: [hidden email]
> Subject: [Elecraft] Re: MFJ259
>
> I don't have a 259 myself but some of my friends do. It is clearly a
> useful bit of kit.
>
> But I have repaired a couple! I agree about the build standard, not
> that hot, and not made easy to repair either with most of the
> components inaccessible underneath the board. In both cases they had
> been damaged by the user applying the supply the wrong way round -
> there is no idiot diode to prevent this. It takes out one of the 5V
> regulators and also a LM324 quad op-amp. If you have one it is worth
> adding a series diode in the supply to save you the hassle.
>
> I would also make a plug for a noise bridge. I built the one by KI6WX
> which appeared in QST in August 1989 (available to download from the
> ARRL site). If you have a suitable portable rig to couple to it does
> most of what the fancy analysers can do at a fraction of the cost.
>
> 73 Dave G3YMC
>
>
> http://www.davesergeant.com
>
> _______________________________________________
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> Post to: [hidden email]
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>

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Geoffrey Mackenzie-Kennedy-2

Re: Re: MFJ259

In reply to this post by g3ymc

Dave G3YMC wrote:

> I would also make a plug for a noise bridge. I built the one by KI6WX
> which appeared in QST in August 1989 (available to download from the
> ARRL site). If you have a suitable portable rig to couple to it does
> most of what the fancy analysers can do at a fraction of the cost.

It should not be too difficult to design a fairly simple receiver drawing a
small amount of current to be enclosed with a noise bridge to make an 'easy
to carry' instrument. Top of head thinking.

73,
Geoff
GM4ESD

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Don Wilhelm-3

RE: Re: MFJ259

Those who have both an Elecraft N-Gen and a KX1 have everything needed
except the bridge elements to construct and use a relatively compact version
of that Improved Noise Bridge described by John Grebenkemper in that August
1989 QST article.

The N-gen is the noise source and the KX1 can serve as the detector - listen
for the null. Of course, it is easy to construct the noise generator, so
those with only a portable receiver like the KX1 can have an accurate
impedance meter once it is calibrated.

Detectors other than a receiver can also be used - an AD8307 based power
meter should work just fine and fit into a small case.

The 'disadvantage' of the noise bridge is there are two knobs to deal with,
but when a deep null is achieved one can read both the resistive and the
reactive component of the unknown impedance.

73,
Don W3FPR

> -----Original Message-----

> Dave G3YMC wrote:
>
> > I would also make a plug for a noise bridge. I built the one by KI6WX
> > which appeared in QST in August 1989 (available to download from the
> > ARRL site). If you have a suitable portable rig to couple to it does
> > most of what the fancy analysers can do at a fraction of the cost.
>
> It should not be too difficult to design a fairly simple receiver
> drawing a
> small amount of current to be enclosed with a noise bridge to
> make an 'easy
> to carry' instrument. Top of head thinking.
>
> 73,
> Geoff
> GM4ESD
>
>

--
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Checked by AVG Free Edition.
Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
4:51 PM

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Jack Smith-6

Re: Re: MFJ259

Don:

I've been giving the subject a bit of thought as well and a noise
bridge came to mind rather quickly. I have an old MFJ 202 noise bridge I
bought 25 years ago.

However, I believe a broad band detector such as the AD8307 will fail.
The null condition is rather narrow frequency wise, and the noise
generator detector output is broad, so the different in total power at n
AD8307 detector between no null and perfect null will be tiny,
particularly if the bridge is constructed to have good balance, which
is, of course, the objective.

This is a case where one needs a narrow band tuned detector, I believe.
Or, a narrow band source.

Jack K8ZOA
www.cliftonlaboratories.com

Don Wilhelm wrote:

> Those who have both an Elecraft N-Gen and a KX1 have everything needed
> except the bridge elements to construct and use a relatively compact version
> of that Improved Noise Bridge described by John Grebenkemper in that August
> 1989 QST article.
>
> The N-gen is the noise source and the KX1 can serve as the detector - listen
> for the null. Of course, it is easy to construct the noise generator, so
> those with only a portable receiver like the KX1 can have an accurate
> impedance meter once it is calibrated.
>
> Detectors other than a receiver can also be used - an AD8307 based power
> meter should work just fine and fit into a small case.
>
> The 'disadvantage' of the noise bridge is there are two knobs to deal with,
> but when a deep null is achieved one can read both the resistive and the
> reactive component of the unknown impedance.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>
>
>> Dave G3YMC wrote:
>>
>>
>>> I would also make a plug for a noise bridge. I built the one by KI6WX
>>> which appeared in QST in August 1989 (available to download from the
>>> ARRL site). If you have a suitable portable rig to couple to it does
>>> most of what the fancy analysers can do at a fraction of the cost.
>>>
>> It should not be too difficult to design a fairly simple receiver
>> drawing a
>> small amount of current to be enclosed with a noise bridge to
>> make an 'easy
>> to carry' instrument. Top of head thinking.
>>
>> 73,
>> Geoff
>> GM4ESD
>>
>>
>>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
> 4:51 PM
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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>

Don Wilhelm-3

RE: Re: MFJ259

Jack,

How about putting a sharp tuned circuit between the detector output from the
bridge and the AD8307 - a single parallel tuned circuit with a variable cap
and a winding on a toroid can serve with high Q over a wide frequency range
(depending on the variable capacitor size) - not much different than tuning
the receiver. An input link on the toroid can match the 50 output of the
bridge and a third link can match the input impedance of the AD8307.

Of course the detector need not be so exotic if a narrow band signal source
is used (like a QRPp transmitter), and that can simplify not only the
bridge, but the detector too since more power is available.

Ideas and alternatives abound - all with tradeoffs for accuracy, ease of
construction, ease of use.

Yes, the number of knobs grows, and likely limits use at the top of a tower,
but half wavelengths (or multiples) of coax are handy in that situtation and
allow the measurements to be made on the ground - ideally by a ground crew
member and the antenna tuning done by the person at the tower top.

73,
Don W3FPR

> -----Original Message-----

>
> Don:
>
> I've been giving the subject a bit of thought as well and a noise
> bridge came to mind rather quickly. I have an old MFJ 202 noise bridge I
> bought 25 years ago.
>
> However, I believe a broad band detector such as the AD8307 will fail.
> The null condition is rather narrow frequency wise, and the noise
> generator detector output is broad, so the different in total power at n
> AD8307 detector between no null and perfect null will be tiny,
> particularly if the bridge is constructed to have good balance, which
> is, of course, the objective.
>
> This is a case where one needs a narrow band tuned detector, I believe.
> Or, a narrow band source.
>
> Jack K8ZOA
> www.cliftonlaboratories.com
>
>
> Don Wilhelm wrote:
> > Those who have both an Elecraft N-Gen and a KX1 have everything needed
> > except the bridge elements to construct and use a relatively
> compact version
> > of that Improved Noise Bridge described by John Grebenkemper in
> that August
> > 1989 QST article.
> >
> > The N-gen is the noise source and the KX1 can serve as the
> detector - listen
> > for the null. Of course, it is easy to construct the noise
> generator, so
> > those with only a portable receiver like the KX1 can have an accurate
> > impedance meter once it is calibrated.
> >
> > Detectors other than a receiver can also be used - an AD8307 based power
> > meter should work just fine and fit into a small case.
> >
> > The 'disadvantage' of the noise bridge is there are two knobs
> to deal with,
> > but when a deep null is achieved one can read both the resistive and the
> > reactive component of the unknown impedance.
> >
> > 73,
> > Don W3FPR
> >
> >
> >> -----Original Message-----
> >>
> >
> >
> >> Dave G3YMC wrote:
> >>
> >>
> >>> I would also make a plug for a noise bridge. I built the one by KI6WX
> >>> which appeared in QST in August 1989 (available to download from the
> >>> ARRL site). If you have a suitable portable rig to couple to it does
> >>> most of what the fancy analysers can do at a fraction of the cost.
> >>>
> >> It should not be too difficult to design a fairly simple receiver
> >> drawing a
> >> small amount of current to be enclosed with a noise bridge to
> >> make an 'easy
> >> to carry' instrument. Top of head thinking.
> >>
> >> 73,
> >> Geoff
> >> GM4ESD
> >>
> >>
> >>
> > --
> > No virus found in this outgoing message.
> > Checked by AVG Free Edition.
> > Version: 7.5.446 / Virus Database: 268.18.11/721 - Release
> Date: 3/13/2007
> > 4:51 PM
> >
> > _______________________________________________
> > Elecraft mailing list
> > Post to: [hidden email]
> > You must be a subscriber to post to the list.
> > Subscriber Info (Addr. Change, sub, unsub etc.):
> > http://mailman.qth.net/mailman/listinfo/elecraft
> >
> > Help: http://mailman.qth.net/subscribers.htm
> > Elecraft web page: http://www.elecraft.com
> >
> >
> _______________________________________________
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> Post to: [hidden email]
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> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
> 3/13/2007 4:51 PM
>

Jim AB3CV

Re: Re: MFJ259

and the really cool thing about the 8307 is that it only draws 7.5ma and can
work with a single lithium cell.

a cr123 is good for about 1500maH. that would allow the 8307 to work for
about 200hrs.

pretty amazing.

73

jim ab3cv

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Jack Smith-6

Re: Re: MFJ259

In reply to this post by Don Wilhelm-3

Don:

My thought was a single conversion receiver with a high IF (45 MHz) with
a monolythic crystal filter, and an AD8307 as the IF amp and detector.
Use an NE602 or 612 oscillator/mixer. Throw in a 30 MHz LP filter to
knock down images. Local oscillator runs 45-75 MHz.

These filters are about 30 KHz wide, and not very expensive. Their
impedance is a good match for an AD8307 and the NE602.Use a PIC as a
frequency meter, maybe a huff-n-puff stabilization arrangement with the
PIC as well, or partial stabilization as used in the HP8640B signal
generator's PLL circuit.

If the objective is to come in at the $100 level or less, this approach
might make it. There's not a lot of budget for parts with that target price.

Jack

Don Wilhelm wrote:

> Jack,
>
> How about putting a sharp tuned circuit between the detector output from the
> bridge and the AD8307 - a single parallel tuned circuit with a variable cap
> and a winding on a toroid can serve with high Q over a wide frequency range
> (depending on the variable capacitor size) - not much different than tuning
> the receiver. An input link on the toroid can match the 50 output of the
> bridge and a third link can match the input impedance of the AD8307.
>
> Of course the detector need not be so exotic if a narrow band signal source
> is used (like a QRPp transmitter), and that can simplify not only the
> bridge, but the detector too since more power is available.
>
> Ideas and alternatives abound - all with tradeoffs for accuracy, ease of
> construction, ease of use.
>
> Yes, the number of knobs grows, and likely limits use at the top of a tower,
> but half wavelengths (or multiples) of coax are handy in that situtation and
> allow the measurements to be made on the ground - ideally by a ground crew
> member and the antenna tuning done by the person at the tower top.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>
>
>> Don:
>>
>> I've been giving the subject a bit of thought as well and a noise
>> bridge came to mind rather quickly. I have an old MFJ 202 noise bridge I
>> bought 25 years ago.
>>
>> However, I believe a broad band detector such as the AD8307 will fail.
>> The null condition is rather narrow frequency wise, and the noise
>> generator detector output is broad, so the different in total power at n
>> AD8307 detector between no null and perfect null will be tiny,
>> particularly if the bridge is constructed to have good balance, which
>> is, of course, the objective.
>>
>> This is a case where one needs a narrow band tuned detector, I believe.
>> Or, a narrow band source.
>>
>> Jack K8ZOA
>> www.cliftonlaboratories.com
>>
>>
>> Don Wilhelm wrote:
>>
>>> Those who have both an Elecraft N-Gen and a KX1 have everything needed
>>> except the bridge elements to construct and use a relatively
>>>
>> compact version
>>
>>> of that Improved Noise Bridge described by John Grebenkemper in
>>>
>> that August
>>
>>> 1989 QST article.
>>>
>>> The N-gen is the noise source and the KX1 can serve as the
>>>
>> detector - listen
>>
>>> for the null. Of course, it is easy to construct the noise
>>>
>> generator, so
>>
>>> those with only a portable receiver like the KX1 can have an accurate
>>> impedance meter once it is calibrated.
>>>
>>> Detectors other than a receiver can also be used - an AD8307 based power
>>> meter should work just fine and fit into a small case.
>>>
>>> The 'disadvantage' of the noise bridge is there are two knobs
>>>
>> to deal with,
>>
>>> but when a deep null is achieved one can read both the resistive and the
>>> reactive component of the unknown impedance.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>>
>>>
>>>> -----Original Message-----
>>>>
>>>>
>>>
>>>> Dave G3YMC wrote:
>>>>
>>>>
>>>>
>>>>> I would also make a plug for a noise bridge. I built the one by KI6WX
>>>>> which appeared in QST in August 1989 (available to download from the
>>>>> ARRL site). If you have a suitable portable rig to couple to it does
>>>>> most of what the fancy analysers can do at a fraction of the cost.
>>>>>
>>>>>
>>>> It should not be too difficult to design a fairly simple receiver
>>>> drawing a
>>>> small amount of current to be enclosed with a noise bridge to
>>>> make an 'easy
>>>> to carry' instrument. Top of head thinking.
>>>>
>>>> 73,
>>>> Geoff
>>>> GM4ESD
>>>>
>>>>
>>>>
>>>>
>>> --
>>> No virus found in this outgoing message.
>>> Checked by AVG Free Edition.
>>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release
>>>
>> Date: 3/13/2007
>>
>>> 4:51 PM
>>>
>>> _______________________________________________
>>> Elecraft mailing list
>>> Post to: [hidden email]
>>> You must be a subscriber to post to the list.
>>> Subscriber Info (Addr. Change, sub, unsub etc.):
>>> http://mailman.qth.net/mailman/listinfo/elecraft
>>>
>>> Help: http://mailman.qth.net/subscribers.htm
>>> Elecraft web page: http://www.elecraft.com
>>>
>>>
>>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>>
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>> --
>> No virus found in this incoming message.
>> Checked by AVG Free Edition.
>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
>> 3/13/2007 4:51 PM
>>
>>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
> 4:51 PM
>
>
>

Jack Smith-6

Re: Re: MFJ259

In reply to this post by Don Wilhelm-3

After thinking on it more, 30 KHz bandwidth is too wide to be useful for
a noise bridge detector, as it will not provide enough frequency
resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
measurement points, for example.

If the device were to be used only to measure components, and not
connected to an antenna, lots of circuit simplification is possible in a
bridge generator / detector approach, i.e., a knock off of the classic
GR916 RF bridge with an integrated source and detector. Like Boonton did
with the 250A RX Meter, for example.

However, as soon as you connect the unknown port to an antenna, simple
detectors are out as the null will be submerged in trash unless the
detector receiver has excellent selectivity and that means frequency
stability as well.

Jack

>
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Don Wilhelm-3

RE: Re: MFJ259

Jack,

Yes, connecting a measureing instrument directly to an antenna can be
troublesome if there are strong broadcast stations in the area or other
sources of signals that can fool the instrument.

Zack Lau addressed that situation in a Technical Correspondence article in
QST a while ago - his answer was to measure the antenna indirectly with an L
network - the L network provides selectivity - adjust the L network to
provide a 50 ohm match, then remove it from the antenna, terminate what was
the measurement side with 50 ohms and measure the side previously connected
to the antenna.

Sounds like a sane way to approach it to me.

73,
Don W3FPR

> -----Original Message-----
> From: Jack Smith [mailto:[hidden email]]
> Sent: Wednesday, March 14, 2007 4:38 PM
> To: [hidden email]
> Cc: Elecraft reflector
> Subject: Re: [Elecraft] Re: MFJ259
>
>
> After thinking on it more, 30 KHz bandwidth is too wide to be useful for
> a noise bridge detector, as it will not provide enough frequency
> resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
> measurement points, for example.
>
> If the device were to be used only to measure components, and not
> connected to an antenna, lots of circuit simplification is possible in a
> bridge generator / detector approach, i.e., a knock off of the classic
> GR916 RF bridge with an integrated source and detector. Like Boonton did
> with the 250A RX Meter, for example.
>
> However, as soon as you connect the unknown port to an antenna, simple
> detectors are out as the null will be submerged in trash unless the
> detector receiver has excellent selectivity and that means frequency
> stability as well.
>
> Jack
>
> >
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
> 3/13/2007 4:51 PM
>

Jack Smith-6

Re: Re: MFJ259

Don:

I have little or no problem putting an HP8752B VNA on my antenna
feedline, or my N2PK VNA. Both have narrow band receive (adjustable down
to 10 Hz in the 8752B) and hit the antenna with a reasonably hefty
signal, 0 dBm or so. Consequently, unless you have a very strong signal
inbound, measurements can be made without much trouble.

The subject needs further though and library research, on the theory
that an hour in the library can be worth a month in the lab.

Jack

Don Wilhelm wrote:

> Jack,
>
> Yes, connecting a measureing instrument directly to an antenna can be
> troublesome if there are strong broadcast stations in the area or other
> sources of signals that can fool the instrument.
>
> Zack Lau addressed that situation in a Technical Correspondence article in
> QST a while ago - his answer was to measure the antenna indirectly with an L
> network - the L network provides selectivity - adjust the L network to
> provide a 50 ohm match, then remove it from the antenna, terminate what was
> the measurement side with 50 ohms and measure the side previously connected
> to the antenna.
>
> Sounds like a sane way to approach it to me.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>> From: Jack Smith [mailto:[hidden email]]
>> Sent: Wednesday, March 14, 2007 4:38 PM
>> To: [hidden email]
>> Cc: Elecraft reflector
>> Subject: Re: [Elecraft] Re: MFJ259
>>
>>
>> After thinking on it more, 30 KHz bandwidth is too wide to be useful for
>> a noise bridge detector, as it will not provide enough frequency
>> resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
>> measurement points, for example.
>>
>> If the device were to be used only to measure components, and not
>> connected to an antenna, lots of circuit simplification is possible in a
>> bridge generator / detector approach, i.e., a knock off of the classic
>> GR916 RF bridge with an integrated source and detector. Like Boonton did
>> with the 250A RX Meter, for example.
>>
>> However, as soon as you connect the unknown port to an antenna, simple
>> detectors are out as the null will be submerged in trash unless the
>> detector receiver has excellent selectivity and that means frequency
>> stability as well.
>>
>> Jack
>>
>>
>> --
>> No virus found in this incoming message.
>> Checked by AVG Free Edition.
>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
>> 3/13/2007 4:51 PM
>>
>>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
> 4:51 PM
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

Jim AB3CV

Re: Re: MFJ259

is this an application where a direct conversion (QSD) might work better?
certainly easy to hit a narrow bandwidth.

jim ab3cv

----- Original Message -----
From: "Jack Smith" <[hidden email]>
To: <[hidden email]>
Cc: "Elecraft reflector" <[hidden email]>
Sent: Wednesday, March 14, 2007 6:14 PM
Subject: Re: [Elecraft] Re: MFJ259

Don:

I have little or no problem putting an HP8752B VNA on my antenna
feedline, or my N2PK VNA. Both have narrow band receive (adjustable down
to 10 Hz in the 8752B) and hit the antenna with a reasonably hefty
signal, 0 dBm or so. Consequently, unless you have a very strong signal
inbound, measurements can be made without much trouble.

The subject needs further though and library research, on the theory
that an hour in the library can be worth a month in the lab.

Jack

Don Wilhelm wrote:

> Jack,
>
> Yes, connecting a measureing instrument directly to an antenna can be
> troublesome if there are strong broadcast stations in the area or other
> sources of signals that can fool the instrument.
>
> Zack Lau addressed that situation in a Technical Correspondence article in
> QST a while ago - his answer was to measure the antenna indirectly with an
> L
> network - the L network provides selectivity - adjust the L network to
> provide a 50 ohm match, then remove it from the antenna, terminate what
> was
> the measurement side with 50 ohms and measure the side previously
> connected
> to the antenna.
>
> Sounds like a sane way to approach it to me.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>> From: Jack Smith [mailto:[hidden email]]
>> Sent: Wednesday, March 14, 2007 4:38 PM
>> To: [hidden email]
>> Cc: Elecraft reflector
>> Subject: Re: [Elecraft] Re: MFJ259
>>
>>
>> After thinking on it more, 30 KHz bandwidth is too wide to be useful for
>> a noise bridge detector, as it will not provide enough frequency
>> resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
>> measurement points, for example.
>>
>> If the device were to be used only to measure components, and not
>> connected to an antenna, lots of circuit simplification is possible in a
>> bridge generator / detector approach, i.e., a knock off of the classic
>> GR916 RF bridge with an integrated source and detector. Like Boonton did
>> with the 250A RX Meter, for example.
>>
>> However, as soon as you connect the unknown port to an antenna, simple
>> detectors are out as the null will be submerged in trash unless the
>> detector receiver has excellent selectivity and that means frequency
>> stability as well.
>>
>> Jack
>>
>>
>> --
>> No virus found in this incoming message.
>> Checked by AVG Free Edition.
>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
>> 3/13/2007 4:51 PM
>>
>>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
> 4:51 PM
>
> _______________________________________________
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>

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--
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
4:51 PM

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Jack Smith-6

Re: Re: MFJ259

Yes, that's the basis of the N2PK VNA and it is worth looking at in a
modified version, with I and Q detection.

The new DDS chips have simultaneous I & Q outputs, which makes that part
of the design easier (N2PK design uses two AD9851's to generate
quadrature output.) The newer chips are, however, on the small side.

Jack

Jim Miller wrote:

> is this an application where a direct conversion (QSD) might work better?
> certainly easy to hit a narrow bandwidth.
>
> jim ab3cv
>
> ----- Original Message -----
> From: "Jack Smith" <[hidden email]>
> To: <[hidden email]>
> Cc: "Elecraft reflector" <[hidden email]>
> Sent: Wednesday, March 14, 2007 6:14 PM
> Subject: Re: [Elecraft] Re: MFJ259
>
>
> Don:
>
> I have little or no problem putting an HP8752B VNA on my antenna
> feedline, or my N2PK VNA. Both have narrow band receive (adjustable down
> to 10 Hz in the 8752B) and hit the antenna with a reasonably hefty
> signal, 0 dBm or so. Consequently, unless you have a very strong signal
> inbound, measurements can be made without much trouble.
>
> The subject needs further though and library research, on the theory
> that an hour in the library can be worth a month in the lab.
>
> Jack
>
> Don Wilhelm wrote:
>
>> Jack,
>>
>> Yes, connecting a measureing instrument directly to an antenna can be
>> troublesome if there are strong broadcast stations in the area or other
>> sources of signals that can fool the instrument.
>>
>> Zack Lau addressed that situation in a Technical Correspondence article in
>> QST a while ago - his answer was to measure the antenna indirectly with an
>> L
>> network - the L network provides selectivity - adjust the L network to
>> provide a 50 ohm match, then remove it from the antenna, terminate what
>> was
>> the measurement side with 50 ohms and measure the side previously
>> connected
>> to the antenna.
>>
>> Sounds like a sane way to approach it to me.
>>
>> 73,
>> Don W3FPR
>>
>>
>>
>>> -----Original Message-----
>>> From: Jack Smith [mailto:[hidden email]]
>>> Sent: Wednesday, March 14, 2007 4:38 PM
>>> To: [hidden email]
>>> Cc: Elecraft reflector
>>> Subject: Re: [Elecraft] Re: MFJ259
>>>
>>>
>>> After thinking on it more, 30 KHz bandwidth is too wide to be useful for
>>> a noise bridge detector, as it will not provide enough frequency
>>> resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
>>> measurement points, for example.
>>>
>>> If the device were to be used only to measure components, and not
>>> connected to an antenna, lots of circuit simplification is possible in a
>>> bridge generator / detector approach, i.e., a knock off of the classic
>>> GR916 RF bridge with an integrated source and detector. Like Boonton did
>>> with the 250A RX Meter, for example.
>>>
>>> However, as soon as you connect the unknown port to an antenna, simple
>>> detectors are out as the null will be submerged in trash unless the
>>> detector receiver has excellent selectivity and that means frequency
>>> stability as well.
>>>
>>> Jack
>>>
>>>
>>> --
>>> No virus found in this incoming message.
>>> Checked by AVG Free Edition.
>>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date:
>>> 3/13/2007 4:51 PM
>>>
>>>
>>>
>> --
>> No virus found in this outgoing message.
>> Checked by AVG Free Edition.
>> Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007
>> 4:51 PM
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
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>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
>>
>
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>
>
>
>

Vic K2VCO

Re: Re: MFJ259

In reply to this post by Don Wilhelm-3

Don Wilhelm wrote:

Ron D'Eau Claire-2

RE: Re: MFJ259

If the L-net brings the system to resonance (X=0) then whatever reactance
the L-net introduces must be equal to the reactance present at the antenna
but opposite in sign!

For example, if the antenna shows j-500 ohms, the L-net must show j+500
ohms. So if you want to know what the antenna shows based on measuring the
L-net, you must reverse the sign!

Ron AC7AC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Vic K2VCO
Sent: Wednesday, March 14, 2007 5:10 PM
To: Elecraft Reflector
Subject: Re: [Elecraft] Re: MFJ259

Don Wilhelm wrote:

> Jack,
>
> Yes, connecting a measureing instrument directly to an antenna can be
> troublesome if there are strong broadcast stations in the area or
> other sources of signals that can fool the instrument.
>
> Zack Lau addressed that situation in a Technical Correspondence
> article in QST a while ago - his answer was to measure the antenna
> indirectly with an L network - the L network provides selectivity -
> adjust the L network to provide a 50 ohm match, then remove it from
> the antenna, terminate what was the measurement side with 50 ohms and
> measure the side previously connected to the antenna.
>
> Sounds like a sane way to approach it to me.

I'm not sure of the reasoning, but he also said that if you do this, you
need to reverse the sign of the reactance that you get when you measure
the network.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco _______________________________________________
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Don Wilhelm-3

RE: Re: MFJ259

Yes, that is true - the laws of reciprocity apply, and a conjugate match is
indicated here - but OTOH, the MFJ259 does not display the sign of the
reactance directly, one must check above and below the frequency of interest
to determine the sign - some other analyzers do display the sign of the
reactance..

73,
Don W3FPR

> -----Original Message-----
>
> If the L-net brings the system to resonance (X=0) then whatever reactance
> the L-net introduces must be equal to the reactance present at the antenna
> but opposite in sign!
>
> For example, if the antenna shows j-500 ohms, the L-net must show j+500
> ohms. So if you want to know what the antenna shows based on measuring the
> L-net, you must reverse the sign!
>
> Ron AC7AC
>
> -----Original Message-----
>
> Don Wilhelm wrote:
> > Jack,
> >
> > Yes, connecting a measureing instrument directly to an antenna can be
> > troublesome if there are strong broadcast stations in the area or
> > other sources of signals that can fool the instrument.
> >
> > Zack Lau addressed that situation in a Technical Correspondence
> > article in QST a while ago - his answer was to measure the antenna
> > indirectly with an L network - the L network provides selectivity -
> > adjust the L network to provide a 50 ohm match, then remove it from
> > the antenna, terminate what was the measurement side with 50 ohms and
> > measure the side previously connected to the antenna.
> >
> > Sounds like a sane way to approach it to me.
>
> I'm not sure of the reasoning, but he also said that if you do this, you
> need to reverse the sign of the reactance that you get when you measure
> the network.
> --
> 73,
> Vic, K2VCO
> Fresno CA
>

Marteinn Sverrisson

RE: Re: MFJ259

In reply to this post by g3ymc

As Don indicated, one can use indirect measurements to measure
the R and X components of an antenna,

If you have a KAT100, you already have all what is needed to make
a good antenna analyzer.
Just push TUNE and let the KAT100 find a match, then
read out the L and C values from the KAT.

I have not worked out how to read out the L and C from the KAT100,
but it should be easy to make a simple program which reads them and
the frequency and displays the actual R and X, with sign.

I have used the KAT100 to measure the SWR of an antenna, just connect
a 50 Ohm dummy load and push TUNE, then connect the antenna,
and set the output level to 1 og 2 Watts, and key the K2 in CW mode,
the SWR leads will show the antenna SWR (the range from 1:1 to 1:5),

just my $0.02

73
Matti
--
Marteinn Sverrisson TF3MA
Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is
270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma
Iceland
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Marteinn Sverrisson

RE: Re: MFJ259

In reply to this post by g3ymc

I read the KAT100 manual :-)

This is how you do:
Push TUNE and let the KAT100 find a good tune, preferable 1:1.

To read the L, C and NET( Cin/Cout) just push MENU and select ATU,
then scroll until you see Lxx.x uH and Cx.xx pF and NETx 1=Cin, 2=Cout,
note the frequency and you have all you need to work out the
actual antenna parameters, well these are the complementary values,
needed to get a 50 Ohm match.

If you have a computer connected to your K2, it is trivial to make
a small program which reads the ATU parameters and FREQ and
calculates the actual R, X for the antenna.

You can even let the program scan the band(s) (you can use CW on
all bands, except 60m) and get a graph of the antenna parameters.

But remember you can not transmit outside the hambands....

Possibly I will try this out, writing a small TCL program,

but I have the VK5JST aerial analyzer which works well,
it took only abt a week, to get the kit from VK land to TF,
total cost incl post abt U$100.

73, matti

--
Marteinn Sverrisson TF3MA
Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is
270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma
Iceland
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