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Unexpected use for a P3

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Chuck Guenther

Unexpected use for a P3

I've been spending the winter on 160 meters with my Cushcraft MA160V
top-loaded vertical antenna. This antenna has been surprisingly effective
for such a short (approx. 36 feet) vertical. I have a decent, though by
no means
exceptional, ground system. The usable bandwidth is on the order of 20 KHz,
and I carefully tuned it for a center frequency of 1820 KHz, positioning
me for
CW DX fun on Top Band.

Since I obtained the P3 last Fall, I've noticed that I can see the
rolloff characteristics
of my antenna simply by looking at the display with band noise.

We had considerable freezing rain and sleet, followed by snow here in
St. Louis
in the past couple of days. The top loading elements (coil and top-hat
capacitance)
have a thick coating of ice on them. The other night, I turned on my K3
and P3 and
was prepared for listening for DX at sunset when I noticed the P3 was
indicating a
frequency response rolloff far below what was normal. In fact my
antenna had made
a QSY right out of the band to a new center frequency of roughly 1770
KHz! Even at
the 1800 KHz band edge my SWR was about 5.5:1.

Having used this and other top-loaded verticals, I had experienced
shifts of 15-20 KHz
due to icy conditions previously. But never a 50 KHz shift!

I tried using my MFJ-259B Antenna Analyzer to check the resonant
frequency and
bandwidth of my antenna, only to discover the lower limit of the
analyzer is 1800 KHz.

Now, I'm waiting for some of the ice to melt or evaporate from my
antenna so I can use it
again. So I'm watching band noise on my P3, waiting for the resonant
frequency to
come back up. Already today, it has moved up about 10 KHz (even though
the temperature
remains below freezing).

I just thought I'd point out this aspect of the P3 (or other panadaptor
frequency displays) for
indicating the frequency response characteristics of high-Q antennas.

73,
Chuck Guenther NI0C

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Jim Sheldon

Re: Unexpected use for a P3

Very interesting. My Butternut HF2V with a homebrew copy of their 160 meter base loading coil is pretty high Q as well and after reading Chuck's post, I just got done checking mine the same way.

The K3's tuner will match this vertical from 1800 up through about 1840 before it goes out of range. Using Chuck's technique of the P3 and band noise with the internal tuner bypassed, it's pretty easy to see the peak in band noise at the resonant frequency. The display shows it best when the span is set pretty wide. You can actually see the SWR curve as a peak in the noise around the resonant point, rolling off fairly sharply either side of it.

To get an accurate look at it, you have to put the ATU in BYPASS mode to make sure you are seeing the true antenna impedance and not the last point the tuner matched it at.

Jim - W0EB

> I've been spending the winter on 160 meters with my Cushcraft MA160V
> top-loaded vertical antenna. This antenna has been surprisingly
> effective
> for such a short (approx. 36 feet) vertical. I have a decent,
> though by
> no means
> exceptional, ground system. The usable bandwidth is on the order
> of 20 KHz,
> and I carefully tuned it for a center frequency of 1820 KHz,
> positioning
> me for
> CW DX fun on Top Band.
>
> Since I obtained the P3 last Fall, I've noticed that I can see the
> rolloff characteristics
> of my antenna simply by looking at the display with band noise.
>
> We had considerable freezing rain and sleet, followed by snow here
> in
> St. Louis
> in the past couple of days. The top loading elements (coil and top-
> hat
> capacitance)
> have a thick coating of ice on them. The other night, I turned on
> my K3
> and P3 and
> was prepared for listening for DX at sunset when I noticed the P3
> was
> indicating a
> frequency response rolloff far below what was normal. In fact my
> antenna had made
> a QSY right out of the band to a new center frequency of roughly
> 1770
> KHz! Even at
> the 1800 KHz band edge my SWR was about 5.5:1.
>
> Having used this and other top-loaded verticals, I had experienced
> shifts of 15-20 KHz
> due to icy conditions previously. But never a 50 KHz shift!
>
> I tried using my MFJ-259B Antenna Analyzer to check the resonant
> frequency and
> bandwidth of my antenna, only to discover the lower limit of the
> analyzer is 1800 KHz.
>
> Now, I'm waiting for some of the ice to melt or evaporate from my
> antenna so I can use it
> again. So I'm watching band noise on my P3, waiting for the
> resonant
> frequency to
> come back up. Already today, it has moved up about 10 KHz (even
> though
> the temperature
> remains below freezing).
>
> I just thought I'd point out this aspect of the P3 (or other
> panadaptor
> frequency displays) for
> indicating the frequency response characteristics of high-Q
> antennas.
>
> 73,
> Chuck Guenther NI0C
>
>
> ______________________________________________________________
> 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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Chuck Guenther

Re: Unexpected use for a P3

Thanks, Jim. In addition to a wide span (I use 128 KHz), a low value of
scale (30-40 dB) and the maximum value of averaging time also
improve the display of the antenna characteristics.

73,
Chuck Guenther NI0C

On 2/2/2011 3:10 PM, Jim Sheldon wrote:
> 
> The display shows it best when the span is set pretty wide. You can
> actually see the SWR curve as a peak in the noise around the resonant
> point, rolling off fairly sharply either side of it.
> Jim - W0EB
>
>

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N5GE

Re: Unexpected use for a P3

In reply to this post by Chuck Guenther

Yes!

I discovered a couple of weeks ago that the P3 can also be used to see the
approximate settings on my Palstar AT5K tuner by adjusting the inductance and
capacitance for maximum band noise on the P3.

In fact when experimenting I found that if I tuned my 80m half sloper with the
K3 set to 1.825Mhz I could actually see the center point of the match moving
from side to side in the P3 display when the total P3 span was set to 200Khz.

I'm sure as time goes by we will find many other uses for the P3. It is indeed
a very useful piece of equipment.

73,

Tom Childers
Radio Amateur N5GE
Licensed since 1976
QCWA Life Member 35102
ARRL Life Member
Retired Professional
C# Software developer
http://www.n5ge.net

On Wed, 02 Feb 2011 14:44:59 -0600, Chuck Guenther <[hidden email]> wrote:

>I've been spending the winter on 160 meters with my Cushcraft MA160V
>top-loaded vertical antenna. This antenna has been surprisingly effective
>for such a short (approx. 36 feet) vertical. I have a decent, though by
>no means
>exceptional, ground system. The usable bandwidth is on the order of 20 KHz,
>and I carefully tuned it for a center frequency of 1820 KHz, positioning
>me for
>CW DX fun on Top Band.
>
>Since I obtained the P3 last Fall, I've noticed that I can see the
>rolloff characteristics
>of my antenna simply by looking at the display with band noise.
>
>We had considerable freezing rain and sleet, followed by snow here in
>St. Louis
>in the past couple of days. The top loading elements (coil and top-hat
>capacitance)
>have a thick coating of ice on them. The other night, I turned on my K3
>and P3 and
>was prepared for listening for DX at sunset when I noticed the P3 was
>indicating a
>frequency response rolloff far below what was normal. In fact my
>antenna had made
>a QSY right out of the band to a new center frequency of roughly 1770
>KHz! Even at
>the 1800 KHz band edge my SWR was about 5.5:1.
>
>Having used this and other top-loaded verticals, I had experienced
>shifts of 15-20 KHz
>due to icy conditions previously. But never a 50 KHz shift!
>
>I tried using my MFJ-259B Antenna Analyzer to check the resonant
>frequency and
>bandwidth of my antenna, only to discover the lower limit of the
>analyzer is 1800 KHz.
>
>Now, I'm waiting for some of the ice to melt or evaporate from my
>antenna so I can use it
>again. So I'm watching band noise on my P3, waiting for the resonant
>frequency to
>come back up. Already today, it has moved up about 10 KHz (even though
>the temperature
>remains below freezing).
>
>I just thought I'd point out this aspect of the P3 (or other panadaptor
>frequency displays) for
>indicating the frequency response characteristics of high-Q antennas.
>
>73,
>Chuck Guenther NI0C
>
>
>
>
>______________________________________________________________
>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

Amateur Radio Operator N5GE