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Curious phenomenon with doublet on 80m

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k.igor

Curious phenomenon with doublet on 80m

Hello everybody,

Tonight I wanted to work station on 3504kHz but was not able to tune with K3
to transmit on that frequency. Here are the facts:

- The antenna is multi-band dipole, a.k.a Van Gorden or Doublet -
137ft dipole center fed with 450 Ohm ladder line.

- I do not use KAT3, it is installed but bypassed in this
configuration. I use MFJ-986 Differential-T tuner with built-in balun.

- I able to tune down to 1.1:1 on all frequencies above about 3505
with K3 and any other transceiver I tried. The optimal tuner settings at any
given frequency are the same for all transceivers (besides K3 I tried
Kenwood TS-930S and TS-570D with autotuner bypassed on both).

- My setting for tune power on K3 is 30W, on TS-570D - 30W, on
TS-930S - 50W

- On frequencies 3501 to 3505 with both Kenwood transceivers the
tuning is normal. With K3 the SWR is through the roof and there is no way I
can find resonance to see reasonable SWR.

- There is significant "hysteresis" to the phenomenon. When I move
down on frequency I am able to tune down to 3505 or so. When I see the
problem I have to return to about 3520 to see normal SWR again.

- The problem seem to be apparent only on this small part of the
band. I took time to go down from 3900 and was able to tune everywhere. Also
I didn't see any problem on low portion of 40m band.

Unfortunately, I don't have other antenna on 80m to compare. However, the
fact that I don't see any issues with the same setup with different
transceivers tells me that antenna and tuner probably are OK. I tried to
tune K3 with different power: from 10W to 50W - same behavior. I do not have
dummy load available at this moment, I will try tomorrow with dummy load.

Any thoughts?

73,

Igor, N1YX

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Don Wilhelm-4

Re: Curious phenomenon with doublet on 80m

Igor,

Double check to be certain the KAT3 is bypassed on that portion of the band.
Remember that the KAT3 segments the bands in order to provide greater
coverage after initially tuning with a given antenna.

73,
Don W3FPR

On 1/3/2011 1:30 AM, Igor Kosvin wrote:

> Hello everybody,
>
> Tonight I wanted to work station on 3504kHz but was not able to tune with K3
> to transmit on that frequency. Here are the facts:
>
> - The antenna is multi-band dipole, a.k.a Van Gorden or Doublet -
> 137ft dipole center fed with 450 Ohm ladder line.
>
> - I do not use KAT3, it is installed but bypassed in this
> configuration. I use MFJ-986 Differential-T tuner with built-in balun.
>
> - I able to tune down to 1.1:1 on all frequencies above about 3505
> with K3 and any other transceiver I tried. The optimal tuner settings at any
> given frequency are the same for all transceivers (besides K3 I tried
> Kenwood TS-930S and TS-570D with autotuner bypassed on both).
>
> - My setting for tune power on K3 is 30W, on TS-570D - 30W, on
> TS-930S - 50W
>
> - On frequencies 3501 to 3505 with both Kenwood transceivers the
> tuning is normal. With K3 the SWR is through the roof and there is no way I
> can find resonance to see reasonable SWR.
>
> - There is significant "hysteresis" to the phenomenon. When I move
> down on frequency I am able to tune down to 3505 or so. When I see the
> problem I have to return to about 3520 to see normal SWR again.
>
> - The problem seem to be apparent only on this small part of the
> band. I took time to go down from 3900 and was able to tune everywhere. Also
> I didn't see any problem on low portion of 40m band.
>
> Unfortunately, I don't have other antenna on 80m to compare. However, the
> fact that I don't see any issues with the same setup with different
> transceivers tells me that antenna and tuner probably are OK. I tried to
> tune K3 with different power: from 10W to 50W - same behavior. I do not have
> dummy load available at this moment, I will try tomorrow with dummy load.
>
>
>
> Any thoughts?
>
> 73,
>
> Igor, N1YX
>
> ______________________________________________________________
> 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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k.igor

Re: Curious phenomenon with doublet on 80m

In reply to this post by k.igor

Hi Chen,

I did connect dummy load tonight. With the dummy load the SWR at the
problematic region is fine, but I see different symptom. When I activate
tune everywhere else I see on the display: top line "1.0-1", bottom line "30
W". Which corresponds to my tuning power. Both lines are stable and the
power meter shows accurate 30W or so. At the problematic region the top line
alternates between "1.0-1" and "--" and the bottom line reading is very
unstable - the power jumps randomly from 18W to 48W, so is the reading of
wattmeter - it is also unstable. The returned power stays pretty low though.
The meter bars on K3 also unstable. The SWR shows one bar and it is blinking
fast. The RF is jumping randomly.
I do not have presently neither VNA nor Antenna Analyzer. I guess though
that use of dummy load pretty much exonerates antenna or tuner. The dummy
load is just one big resistor with very low reactance.

73,
Igor, N1YX

-----Original Message-----
From: Kok Chen [mailto:[hidden email]]
Sent: Monday, January 03, 2011 2:02 AM
To: Igor Kosvin
Subject: Re: [Elecraft] Curious phenomenon with doublet on 80m

Hi Igor,

You are correct that you should try to see if the K3 will work properly into
a dummy load at 3504 kHz.

Do you have an Antenna Analyzer or VNA?

If so, I would suggest tuning the MFJ to match the Kenwood rigs, then remove
the rigs from the tuner and use to antenna analyzer to look into the MFJ's
Tx connector instead of connecting the K3. The impedance that you read on
the analyzer might give a clue as to why the K3 can't work into it.

Vy 73
Chen, W7AY

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k.igor

Re: Curious phenomenon with doublet on 80m

In reply to this post by Don Wilhelm-4

Hi Don,
Yes, the KAT3 is bypassed as far as I can see. The ATU on display is not
lit. I toggled with long hold of ATU TUNE and the last I see is Bypassed and
the ATU goes off. I also don't see any ATU activity (relays etc.) when I
press TUNE.
73,

Igor, N1YX

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Monday, January 03, 2011 8:34 AM
To: Igor Kosvin
Cc: [hidden email]
Subject: Re: [Elecraft] Curious phenomenon with doublet on 80m

Igor,

Double check to be certain the KAT3 is bypassed on that portion of the band.
Remember that the KAT3 segments the bands in order to provide greater
coverage after initially tuning with a given antenna.

73,
Don W3FPR

On 1/3/2011 1:30 AM, Igor Kosvin wrote:
> Hello everybody,
>
> Tonight I wanted to work station on 3504kHz but was not able to tune with
K3
> to transmit on that frequency. Here are the facts:
>
> - The antenna is multi-band dipole, a.k.a Van Gorden or Doublet -
> 137ft dipole center fed with 450 Ohm ladder line.
>
> - I do not use KAT3, it is installed but bypassed in this
> configuration. I use MFJ-986 Differential-T tuner with built-in balun.
>
> - I able to tune down to 1.1:1 on all frequencies above about
3505
> with K3 and any other transceiver I tried. The optimal tuner settings at
any
> given frequency are the same for all transceivers (besides K3 I tried
> Kenwood TS-930S and TS-570D with autotuner bypassed on both).
>
> - My setting for tune power on K3 is 30W, on TS-570D - 30W, on
> TS-930S - 50W
>
> - On frequencies 3501 to 3505 with both Kenwood transceivers the
> tuning is normal. With K3 the SWR is through the roof and there is no way
I
> can find resonance to see reasonable SWR.
>
> - There is significant "hysteresis" to the phenomenon. When I
move
> down on frequency I am able to tune down to 3505 or so. When I see the
> problem I have to return to about 3520 to see normal SWR again.
>
> - The problem seem to be apparent only on this small part of the
> band. I took time to go down from 3900 and was able to tune everywhere.
Also
> I didn't see any problem on low portion of 40m band.
>
> Unfortunately, I don't have other antenna on 80m to compare. However, the
> fact that I don't see any issues with the same setup with different
> transceivers tells me that antenna and tuner probably are OK. I tried to
> tune K3 with different power: from 10W to 50W - same behavior. I do not
have

> dummy load available at this moment, I will try tomorrow with dummy load.
>
>
>
> Any thoughts?
>
> 73,
>
> Igor, N1YX
>
> ______________________________________________________________
> 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
>

Cady, Fred

Re: Curious phenomenon with doublet on 80m

In reply to this post by k.igor

Hi,
I had a similar problem last year in ARRL SS where the power output
jumped around. Gary suggested doing the power calibration again. I had
little trouble getting it done in the Utility but doing it manually got
things settled down again. I'm not sure that this fixed whatever the
problem was (why did the calibration have to be done again) but it fixed
the symptoms as it hasn't done it again. Well maybe it did it a bit once
or twice at C6AKX this year.
Dunno. Try it.
73,
Fred KE7X

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Igor Kosvin
Sent: Monday, January 03, 2011 4:24 PM
To: 'Kok Chen'
Cc: [hidden email]
Subject: Re: [Elecraft] Curious phenomenon with doublet on 80m

Hi Chen,

I did connect dummy load tonight. With the dummy load the SWR at the
problematic region is fine, but I see different symptom. When I activate
tune everywhere else I see on the display: top line "1.0-1", bottom line
"30 W". Which corresponds to my tuning power. Both lines are stable and
the power meter shows accurate 30W or so. At the problematic region the
top line alternates between "1.0-1" and "--" and the bottom line reading
is very unstable - the power jumps randomly from 18W to 48W, so is the
reading of wattmeter - it is also unstable. The returned power stays
pretty low though.
The meter bars on K3 also unstable. The SWR shows one bar and it is
blinking fast. The RF is jumping randomly.
I do not have presently neither VNA nor Antenna Analyzer. I guess though
that use of dummy load pretty much exonerates antenna or tuner. The
dummy load is just one big resistor with very low reactance.

73,
Igor, N1YX

-----Original Message-----
From: Kok Chen [mailto:[hidden email]]
Sent: Monday, January 03, 2011 2:02 AM
To: Igor Kosvin
Subject: Re: [Elecraft] Curious phenomenon with doublet on 80m

Hi Igor,

You are correct that you should try to see if the K3 will work properly
into a dummy load at 3504 kHz.

Do you have an Antenna Analyzer or VNA?

If so, I would suggest tuning the MFJ to match the Kenwood rigs, then
remove the rigs from the tuner and use to antenna analyzer to look into
the MFJ's Tx connector instead of connecting the K3. The impedance that
you read on the analyzer might give a clue as to why the K3 can't work
into it.

Vy 73
Chen, W7AY

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______________________________________________________________
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Tony Estep

Re: Curious phenomenon with doublet on 80m

>
> With the dummy load the SWR at the
> problematic region is fine, but....at the problematic region the
> top line alternates between "1.0-1" and "--" and the bottom line reading
> is very unstable - the power jumps randomly...
>

Sounds like there's a lookup table in memory with a piece of bad data in it.
If so, there must be a way to re-write it....Maybe a way to re-init the ATU.

Tony KT0NY

>
>
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