DC-supply for a preamp?

[Martin-2]

Elecrafters,
this might be a rig-killer and vy stupid, but....

Can i power a 6m masthead-preamp by feeding dc via choke and coupling
C's to the KXV3A's in/out sockets (where the elecraft preamp is supposed
to sit), or is this a big NONO?

Martin

--

73, DM4iM
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[W7GJ, Lance]

On 4/27/2010 2:32 PM, DM4iM wrote:
> Elecrafters,
> this might be a rig-killer and vy stupid, but....
>
> Can i power a 6m masthead-preamp by feeding dc via choke and coupling
> C's to the KXV3A's in/out sockets (where the elecraft preamp is supposed
> to sit), or is this a big NONO?
>
> Martin
>
Hello Martin,

I think you could do better by simply installing the PR6 at the K3 and using low
loss coax to the antenna.  Almost all the 6m EME stations around the world use a
good external preamp in the shack.  If your coax cable loss is 1 dB or less, you
will not gain anything by mounting the 6m preamp at the antenna.

You can model this for yourself in the EME CALCULATOR (accessed from the EME ECHO
MODE screen in the old WSJT Version 4). Because the EME CALCULATOR and EME ECHO
MODE were never re-written in the language used in more recent revisions of WSTJ,
that old version is still available:

http://www.physics.princeton.edu/pulsar/K1JT/WSJT498.EXE

I think you will find it much simpler to keep the preamp in the shack!  GL and VY
73, Lance

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
http://6meme.com/mailman/listinfo/magic_6meme.com
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[Cookie]

Lance, what kind of coax are you using that only has one dB loss at six meters?  7/8" Heliax would do it, but LMR-400 would not unless you could keep the run under 100 feet.
 Willis 'Cookie' Cooke
K5EWJ




________________________________
From: Lance Collister <[hidden email]>
To: DM4iM <[hidden email]>; Reflector Elecraft <[hidden email]>
Sent: Tue, April 27, 2010 11:25:52 AM
Subject: Re: [Elecraft] DC-supply for a preamp?

On 4/27/2010 2:32 PM, DM4iM wrote:
> Elecrafters,
> this might be a rig-killer and vy stupid, but....
>
> Can i power a 6m masthead-preamp by feeding dc via choke and coupling
> C's to the KXV3A's in/out sockets (where the elecraft preamp is supposed
> to sit), or is this a big NONO?
>
> Martin
>
Hello Martin,

I think you could do better by simply installing the PR6 at the K3 and using low
loss coax to the antenna.  Almost all the 6m EME stations around the world use a
good external preamp in the shack.  If your coax cable loss is 1 dB or less, you
will not gain anything by mounting the 6m preamp at the antenna.

You can model this for yourself in the EME CALCULATOR (accessed from the EME ECHO
MODE screen in the old WSJT Version 4). Because the EME CALCULATOR and EME ECHO
MODE were never re-written in the language used in more recent revisions of WSTJ,
that old version is still available:

http://www.physics.princeton.edu/pulsar/K1JT/WSJT498.EXE

I think you will find it much simpler to keep the preamp in the shack!  GL and VY
73, Lance

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]  URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
http://6meme.com/mailman/listinfo/magic_6meme.com
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[n7ws]

So use 7/8" Heliax :-)

--- On Tue, 4/27/10, WILLIS COOKE <[hidden email]> wrote:

> Date: Tuesday, April 27, 2010, 11:02 AM
> Lance, what kind of coax are you
> using that only has one dB loss at six meters?  7/8" Heliax
> would do it, but LMR-400 would not unless you could keep the
> run under 100 feet.
>  Willis 'Cookie' Cooke
> K5EWJ
>


     
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[Cookie]

That wouldn't quite reach the ground from my antenna but LMR600 has good specs.  How are the connectors to work with?  Do you need a flex jumper at the antenna to allow the rotor to work?  I am using 230 feet of RG-213 which has about 3.5 loss according to the specs.  It works, but I don't do Moon Bounce with it.
 Willis 'Cookie' Cooke
K5EWJ




________________________________
From: Ken Roberson <[hidden email]>
To: WILLIS COOKE <[hidden email]>
Sent: Tue, April 27, 2010 12:09:15 PM
Subject: Re: [Elecraft] DC-supply for a preamp?

Hello,
I'm using About 65 ft LMR-600, and Elecraft 6M preamp,This
seems to work ok.

73 Ken K5DNL

--------------------------------------------------------------

--- On Tue, 4/27/10, WILLIS COOKE <[hidden email]> wrote:

> From: WILLIS COOKE <[hidden email]>
> Subject: Re: [Elecraft] DC-supply for a preamp?
> To: [hidden email], "DM4iM" <[hidden email]>, "Reflector Elecraft" <[hidden email]>
> Date: Tuesday, April 27, 2010, 12:02 PM
> Lance, what kind of coax are you
> using that only has one dB loss at six meters?  7/8" Heliax
> would do it, but LMR-400 would not unless you could keep the
> run under 100 feet.
>  Willis 'Cookie' Cooke
> K5EWJ
>
>
>
>
> ________________________________
> From: Lance Collister <[hidden email]>
> To: DM4iM <[hidden email]>;
> Reflector Elecraft <[hidden email]>
> Sent: Tue, April 27, 2010 11:25:52 AM
> Subject: Re: [Elecraft] DC-supply for a preamp?
>
> On 4/27/2010 2:32 PM, DM4iM wrote:
> > Elecrafters,
> > this might be a rig-killer and vy stupid, but....
> >
> > Can i power a 6m masthead-preamp by feeding dc via
> choke and coupling
> > C's to the KXV3A's in/out sockets (where the elecraft
> preamp is supposed
> > to sit), or is this a big NONO?
> >
> > Martin
> >
> Hello Martin,
>
> I think you could do better by simply installing the PR6 at
> the K3 and using low
> loss coax to the antenna.  Almost all the 6m EME stations
> around the world use a
> good external preamp in the shack.  If your coax cable
> loss is 1 dB or less, you
> will not gain anything by mounting the 6m preamp at the
> antenna.
>
> You can model this for yourself in the EME CALCULATOR
> (accessed from the EME ECHO
> MODE screen in the old WSJT Version 4). Because the EME
> CALCULATOR and EME ECHO
> MODE were never re-written in the language used in more
> recent revisions of WSTJ,
> that old version is still available:
>
> http://www.physics.princeton.edu/pulsar/K1JT/WSJT498.EXE
>
> I think you will find it much simpler to keep the preamp in
> the shack!  GL and VY
> 73, Lance
>
> --
> Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN,
> WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
> P.O. Box 73
> Frenchtown, MT  59834  USA
> QTH: DN27UB
> TEL: [phone]  URL: http://www.bigskyspaces.com/w7gj
> LIVE MESSENGER CHAT: [hidden email]
> 2m DXCC #11, 6m DXCC #815
>
> Interested in 6m EME?  Ask me about subscribing to the
> Magic Band EME email!
> http://6meme.com/mailman/listinfo/magic_6meme.com
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
>
>      
> ______________________________________________________________
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> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

     
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[W7GJ, Lance]

Hello Cookie,

I am using 200' of 1-5/8" Heliax, and used LMR600 for all my phasing lines.  The
10' flexible section around the rotor is LMR600UF. I think my total feedline loss
is less than 0.5 dB. Before I found the free piece of big Heliax, I used free 3/4"
CATV 75 ohm hardline, which also worked well at keeping the loss down.  7/8"
Heliax can also frequently be found in these short lengths.

If you can't find any used or end of spool pieces of hardline, new LMR600 has a
loss of 0.5 dB per 100', so it also is a readily available option.  With all these
options, and the fact that most people have 6m feedlines shorter than 200' long,
it really is getting pretty easy to achieve a feedline loss under 1.0 dB on 6m.

GL and VY 73, Lance

On 4/27/2010 5:02 PM, WILLIS COOKE wrote:

> Lance, what kind of coax are you using that only has one dB loss at six
> meters? 7/8" Heliax would do it, but LMR-400 would not unless you could
> keep the run under 100 feet.
> Willis 'Cookie' Cooke
> K5EWJ
>
>
> ------------------------------------------------------------------------
> *From:* Lance Collister <[hidden email]>
> *To:* DM4iM <[hidden email]>; Reflector Elecraft
> <[hidden email]>
> *Sent:* Tue, April 27, 2010 11:25:52 AM
> *Subject:* Re: [Elecraft] DC-supply for a preamp?
>
> On 4/27/2010 2:32 PM, DM4iM wrote:
>  > Elecrafters,
>  > this might be a rig-killer and vy stupid, but....
>  >
>  > Can i power a 6m masthead-preamp by feeding dc via choke and coupling
>  > C's to the KXV3A's in/out sockets (where the elecraft preamp is supposed
>  > to sit), or is this a big NONO?
>  >
>  > Martin
>  >
> Hello Martin,
>
> I think you could do better by simply installing the PR6 at the K3 and
> using low
> loss coax to the antenna. Almost all the 6m EME stations around the
> world use a
> good external preamp in the shack. If your coax cable loss is 1 dB or
> less, you
> will not gain anything by mounting the 6m preamp at the antenna.
>
> You can model this for yourself in the EME CALCULATOR (accessed from the
> EME ECHO
> MODE screen in the old WSJT Version 4). Because the EME CALCULATOR and
> EME ECHO
> MODE were never re-written in the language used in more recent revisions
> of WSTJ,
> that old version is still available:
>
> http://www.physics.princeton.edu/pulsar/K1JT/WSJT498.EXE
>
> I think you will find it much simpler to keep the preamp in the shack!
> GL and VY
> 73, Lance
>
> --
> Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A,
> ZF2OC/ZF8, E51SIX)
> P.O. Box 73
> Frenchtown, MT 59834 USA
> QTH: DN27UB
> TEL: [phone] URL: http://www.bigskyspaces.com/w7gj
> LIVE MESSENGER CHAT: [hidden email] <mailto:[hidden email]>
> 2m DXCC #11, 6m DXCC #815
>
> Interested in 6m EME? Ask me about subscribing to the Magic Band EME email!
> http://6meme.com/mailman/listinfo/magic_6meme.com
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email] <mailto:[hidden email]>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
http://6meme.com/mailman/listinfo/magic_6meme.com
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[W7GJ, Lance]

Hello Cookie,

Wow - you must have a HUGE tower!  More power to you ;-)  Yes, I use LMR600UF
(Ultra Flex) around the rotor...you can't use cable with a solid center conductor
in an application requiring repeated flexing.  The special connectors work fine,
but you have to take some care and make sure you put them on properly.  I just
take my time when I have to put them on...it is worth it to have such low loss
cable!  I agree...you won't do much weak signal work with 3.5 dB loss ahead of the
preamp!  GL and VY 73, Lance

On 4/27/2010 5:37 PM, WILLIS COOKE wrote:
> That wouldn't quite reach the ground from my antenna but LMR600 has good specs.
> How are the connectors to work with?  Do you need a flex jumper at the antenna
> to allow the rotor to work?  I am using 230 feet of RG-213 which has about 3.5
> loss according to the specs.  It works, but I don't do Moon Bounce with it.
> Willis 'Cookie' Cooke K5EWJ
>
>
--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
http://6meme.com/mailman/listinfo/magic_6meme.com
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[Edward R Cole]

Martin,

I installed an ARR P50VDG preamp on the back side of my K3/10 using
preamp in/out connectors on the KVX3.
photo: http://www.kl7uw.com/K3-ARR-6mPreamp.jpg

I will control the power via the ACC jack when I get a VGA jack.  For
now it is on when the K3 is on.
Much easier and safer than using a bias tee  and remote switched
preamp.  I agree with Lance that you will not likely see any
improvement in sensitivity mounting the preamp at the antenna.  For
keeping loss down use LMR-400 coax for runs up to 100-feet, and
LDF4-50A Heliax for longer runs.  This keeps transmission losses down, too.

73, Ed - KL7UW
I run 80-feet of LMR-400 to my 3-element 6m yagi at 55-feet on the tower.
http://www.kl7uw.com/6m.htm

------------------------------

Message: 2
Date: Tue, 27 Apr 2010 16:25:52 +0000
From: Lance Collister <[hidden email]>
Subject: Re: [Elecraft] DC-supply for a preamp?
To: DM4iM <[hidden email]>, Reflector Elecraft
         <[hidden email]>
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 4/27/2010 2:32 PM, DM4iM wrote:
 > Elecrafters,
 > this might be a rig-killer and vy stupid, but....
 >
 > Can i power a 6m masthead-preamp by feeding dc via choke and coupling
 > C's to the KXV3A's in/out sockets (where the elecraft preamp is supposed
 > to sit), or is this a big NONO?
 >
 > Martin
 >
Hello Martin,

I think you could do better by simply installing the PR6 at the K3
and using low
loss coax to the antenna.  Almost all the 6m EME stations around the
world use a
good external preamp in the shack.  If your coax cable loss is 1 dB
or less, you
will not gain anything by mounting the 6m preamp at the antenna.

You can model this for yourself in the EME CALCULATOR (accessed from
the EME ECHO
MODE screen in the old WSJT Version 4). Because the EME CALCULATOR
and EME ECHO
MODE were never re-written in the language used in more recent
revisions of WSTJ,
that old version is still available:

http://www.physics.princeton.edu/pulsar/K1JT/WSJT498.EXE

I think you will find it much simpler to keep the preamp in the
shack!  GL and VY
73, Lance

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A,
ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
http://6meme.com/mailman/listinfo/magic_6meme.com


73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010
DUBUS Magazine USA Rep [hidden email]
======================================

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[Martin-2]

Hello all,
thank you for all the info about losses in a coax cable,
but the original question was if this is a good or a bad idea.
Lots of qsb, so it disappeared in the noise. :-)

I've been thinking about it myself, my conclusion is: no good idea.
Even if the K3 passes the supply voltage to it's antenna jack, bad
things can happen if you forget to switch the supply off, when you
change antennas, switch to your dummyload, you name it.
So it is a big NONO.

Martin

--

73 , DM4iM
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[Bob McGraw - K4TAX]

I seem to recall that several companies make "bias T" devices that allow RF
to pass but block DC in one direction.  Thus these are suitable for feeding
DC to a antenna mounted preamp.  Then the challenge of switching the preamp
out of line for transmit is next.

For my EME applications I have made my own bias T.   I apply DC to the bias
T that switches the preamp in line and supplies power to same.  For transmit
I remove the DC from the bias T thus turning off the preamp and switching it
out of line.

Personally, two feedlines, one for RX and one for TX  and a separate DC
control cable is the more reliable system, specially when running high
"legal limit" power.  I've vaporized more than one preamp PCB and other
components in the past not to mention the more likely probability of a relay
failure on the top side.

My rule is "the less stuff in the RF path, they better the reliability".
Low loss feedline is the best approach.

73
Bob, K4TAX


----- Original Message -----
From: "DM4iM" <[hidden email]>
To: "Reflector Elecraft" <[hidden email]>
Sent: Wednesday, April 28, 2010 6:18 AM
Subject: Re: [Elecraft] DC-supply for a preamp?

> Hello all,
> thank you for all the info about losses in a coax cable,
> but the original question was if this is a good or a bad idea.
> Lots of qsb, so it disappeared in the noise. :-)
>
> I've been thinking about it myself, my conclusion is: no good idea.
> Even if the K3 passes the supply voltage to it's antenna jack, bad
> things can happen if you forget to switch the supply off, when you
> change antennas, switch to your dummyload, you name it.
> So it is a big NONO.
>
> Martin
>
> --
>
> 73 , DM4iM
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Cookie]

Martin, it is a common idea.  The antenna tuners and remote relays that use only the coax use the idea.  The big danger is connecting the injection port incorrectly and putting the 12 volts on your transceiver.  I have a dead TS-850 waiting for repair because I connected the injection port backwards for my MFJ Antenna Tuner.  I have been holding off on this note because I hoped for official work from Elecraft, but I have seen none, so here is your "Take it for what it cost free advise".  The comments about putting the amp at the transceiver have merit.  Personally, I don't have an external preamp and I have about 3 db loss in my cable, but I make some nice 6 meter contacts.  The people with more equipment no doubt hear better than I.
 Willis 'Cookie' Cooke
K5EWJ




________________________________
From: DM4iM <[hidden email]>
To: Reflector Elecraft <[hidden email]>
Sent: Wed, April 28, 2010 6:18:37 AM
Subject: Re: [Elecraft] DC-supply for a preamp?

Hello all,
thank you for all the info about losses in a coax cable,
but the original question was if this is a good or a bad idea.
Lots of qsb, so it disappeared in the noise. :-)

I've been thinking about it myself, my conclusion is: no good idea.
Even if the K3 passes the supply voltage to it's antenna jack, bad
things can happen if you forget to switch the supply off, when you
change antennas, switch to your dummyload, you name it.
So it is a big NONO.

Martin

--

73 , DM4iM
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[W7GJ, Lance]

This will be my last comment on this thread, which seems to be digressing from the
original inquiry.  However, when I see information like the one below, I feel it
needs to be addressed, so inexperienced readers do not get a wrong impression and
experience equipment failure as a result.

The biggest reason I can think of for running the preamp voltage up the receive
cable is to AVOID what K4TAX recommends below.  Running a separate unshielded
power line up a tower to a preamp is a sure way to generate voltage spikes which
will destroy a sensitive preamplifier.  Of course such spikes can be caused by
induction of nearby lightning but the most common problem is simply switching
transients from the relay control lines also run up the tower.  Using bias T's to
send the voltage to the preamp via a shielded coaxial cable is the safest way to
provide a stable controlled DC voltage to a preamp.

The bottom line for K3 users is to keep the coaxial loss low and keep the preamp
attached to the K3.  If you are operating higher frequencies where your feed  line
loss will degrade front end performance and you MUST mount a preamp and relays at
the antenna, use shielded cable to provide voltage to the preamp.

GL and VY 73, Lance

On 4/28/2010 11:42 AM, Bob McGraw - K4TAX wrote:

> I seem to recall that several companies make "bias T" devices that allow RF
> to pass but block DC in one direction.  Thus these are suitable for feeding
> DC to a antenna mounted preamp.  Then the challenge of switching the preamp
> out of line for transmit is next.
>
> For my EME applications I have made my own bias T.   I apply DC to the bias
> T that switches the preamp in line and supplies power to same.  For transmit
> I remove the DC from the bias T thus turning off the preamp and switching it
> out of line.
>
> Personally, two feedlines, one for RX and one for TX  and a separate DC
> control cable is the more reliable system, specially when running high
> "legal limit" power.  I've vaporized more than one preamp PCB and other
> components in the past not to mention the more likely probability of a relay
> failure on the top side.
>
> My rule is "the less stuff in the RF path, they better the reliability".
> Low loss feedline is the best approach.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "DM4iM"<[hidden email]>
> To: "Reflector Elecraft"<[hidden email]>
> Sent: Wednesday, April 28, 2010 6:18 AM
> Subject: Re: [Elecraft] DC-supply for a preamp?
>
>
>> Hello all,
>> thank you for all the info about losses in a coax cable,
>> but the original question was if this is a good or a bad idea.
>> Lots of qsb, so it disappeared in the noise. :-)
>>
>> I've been thinking about it myself, my conclusion is: no good idea.
>> Even if the K3 passes the supply voltage to it's antenna jack, bad
>> things can happen if you forget to switch the supply off, when you
>> change antennas, switch to your dummyload, you name it.
>> So it is a big NONO.
>>
>> Martin
>>

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

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