I have recently acquired an antenna analyzer and have been getting my mobile
antenna ready for the summer (if we have one!). My procedure has been to
attach the analyzer to the base of the antenna or via 1/2 wavelength of coax
and tune the antenna to read j0 on complex impedance. This should then be
correctly resonant. I then look at the real (resistive) part of the
impedanceand use a transformer to match it. For example on 20M the antenna
reads 35 + j0 so I have a transformer toroidal transformer from 50 ohms to
35 ohms. This seems to work well.
Question is whether tuning for j0 is going to give a true resonance of the
antenna? Any other suggestions?
Dick

Richard Ferryman wrote:
I have recently acquired an antenna analyzer and have been getting my mobile
antenna ready for the summer (if we have one!). My procedure has been to
attach the analyzer to the base of the antenna or via 1/2 wavelength of coax
and tune the antenna to read j0 on complex impedance. This should then be
correctly resonant. I then look at the real (resistive) part of the
impedanceand use a transformer to match it. For example on 20M the antenna
reads 35 + j0 so I have a transformer toroidal transformer from 50 ohms to
35 ohms. This seems to work well.
Question is whether tuning for j0 is going to give a true resonance of the
antenna? Any other suggestions?
Dick

One presumes you then verified the transformer/antenna system was actually
50 + j0.



--
Jim Pennino

In article ,
"Richard Ferryman" wrote:

I have recently acquired an antenna analyzer and have been getting my mobile
antenna ready for the summer (if we have one!). My procedure has been to
attach the analyzer to the base of the antenna or via 1/2 wavelength of coax
and tune the antenna to read j0 on complex impedance. This should then be
correctly resonant. I then look at the real (resistive) part of the
impedanceand use a transformer to match it. For example on 20M the antenna
reads 35 + j0 so I have a transformer toroidal transformer from 50 ohms to
35 ohms. This seems to work well.
Question is whether tuning for j0 is going to give a true resonance of the
antenna? Any other suggestions?

Dick-

I think use of the 1/2 wavelength feed line, with you sitting inside the
closed vehicle, should give you a true resonance reading. Or at least
as close as you can get with the vehicle parked.

My concern is that your matching procedure may be sensitive to frequency
changes. In other words, whatever advantage you have at that one
frequency, may be lost at other frequencies across the band. This might
be especially true on 75 or 40 Meters.

Does your analyzer show SWR? If so, compare a plot of SWR across the
band between your method of matching vs just tuning the antenna for best
SWR at the center of the band.

Fred
K4DII

The resulting SWR plot (using Zplot to display plots) looks good on 20m and
gives a better SWR plot than just tuning for best SWR. Also I am getting
about 1dB better on field strength at about 30' from antenna. I suspect it
will be more difficult on the lower bands. My transformer is not perfect
but I am now getting 52 +j0 with it fitted. Using the 1/2 wave of coax
results in errors below about 13.9 MHz and above 14.5MHz but otherwise
matches the readings with the analyzer at the base of the antenna. Just
for fun I made up a full 1/4 wave whip on 20m and tried it out this
afternoon. Much better bandwidth and field strength but looked a bit
ridiculous (and dangerous) on my little Fiat :-)
Dick


"Fred McKenzie" wrote in message
...
In article ,
"Richard Ferryman" wrote:

I have recently acquired an antenna analyzer and have been getting my
mobile
antenna ready for the summer (if we have one!). My procedure has been to
attach the analyzer to the base of the antenna or via 1/2 wavelength of
coax
and tune the antenna to read j0 on complex impedance. This should then
be
correctly resonant. I then look at the real (resistive) part of the
impedanceand use a transformer to match it. For example on 20M the
antenna
reads 35 + j0 so I have a transformer toroidal transformer from 50 ohms
to
35 ohms. This seems to work well.
Question is whether tuning for j0 is going to give a true resonance of
the
antenna? Any other suggestions?

Dick-

I think use of the 1/2 wavelength feed line, with you sitting inside the
closed vehicle, should give you a true resonance reading. Or at least
as close as you can get with the vehicle parked.

My concern is that your matching procedure may be sensitive to frequency
changes. In other words, whatever advantage you have at that one
frequency, may be lost at other frequencies across the band. This might
be especially true on 75 or 40 Meters.

Does your analyzer show SWR? If so, compare a plot of SWR across the
band between your method of matching vs just tuning the antenna for best
SWR at the center of the band.

Fred
K4DII

The only people that worries about SWR is CB'rs.........

CB'rs only has one half of one megahertz to play with - hence antenna tune is critical.

If all you are going to play with is one frequency or one band - then I guess you are going in the right direction.

The missing information that my crystal ball is not clear on is the make and model of the vehicle and antenna.

With HF it is more important to have a large metal ground plane - large Suburban sized vehicle, that has all of its surfaces physically bonded together with a wide copper braid straps at all hinge points and corners - such as a pick up truck front walk away, hood, doors, cab, bed, exhaust, engine, transmission, exhaust, suspension etc..

It's more important to bond these surfaces together then it is to tune the antenna so it looks good on the analyzer.

At the same time, the ground conductivity changes as the vehicle moves down the road, so unless you plan to never move the vehicle again and operate from that one spot - the tune of the antenna will change with the earth as you travel down the road.

Hence it is not as critical to get a perfect match in a vehicle as it is using a home install that is not going to move once it is installed.

Can you see my point?

If you have a small plastic car - forget about trying to get a perfect match.

In message , Channel Jumper
writes

The only people that worries about SWR is CB'rs.........

CB'rs only has one half of one megahertz to play with - hence antenna
tune is critical.

If all you are going to play with is one frequency or one band - then I
guess you are going in the right direction.

The missing information that my crystal ball is not clear on is the make
and model of the vehicle and antenna.

With HF it is more important to have a large metal ground plane - large
Suburban sized vehicle, that has all of its surfaces physically bonded
together with a wide copper braid straps at all hinge points and corners
- such as a pick up truck front walk away, hood, doors, cab, bed,
exhaust, engine, transmission, exhaust, suspension etc..

It's more important to bond these surfaces together then it is to tune
the antenna so it looks good on the analyzer.

At the same time, the ground conductivity changes as the vehicle moves
down the road, so unless you plan to never move the vehicle again and
operate from that one spot - the tune of the antenna will change with
the earth as you travel down the road.

Hence it is not as critical to get a perfect match in a vehicle as it is
using a home install that is not going to move once it is installed.

Can you see my point?

If you have a small plastic car - forget about trying to get a perfect
match.

I've never been aware of the antenna tuning changing as you drive along
over ground where the conductivity changes. However, especially on the
lower HF bands, being over an area of high ground conductivity certainly
enhances RF signal level (both TX and RF).
--
Ian

On 3/16/2014 9:43 AM, Ian Jackson wrote:
In message , Channel Jumper
writes

The only people that worries about SWR is CB'rs.........

CB'rs only has one half of one megahertz to play with - hence antenna
tune is critical.

If all you are going to play with is one frequency or one band - then I
guess you are going in the right direction.

The missing information that my crystal ball is not clear on is the make
and model of the vehicle and antenna.

With HF it is more important to have a large metal ground plane - large
Suburban sized vehicle, that has all of its surfaces physically bonded
together with a wide copper braid straps at all hinge points and corners
- such as a pick up truck front walk away, hood, doors, cab, bed,
exhaust, engine, transmission, exhaust, suspension etc..

It's more important to bond these surfaces together then it is to tune
the antenna so it looks good on the analyzer.

At the same time, the ground conductivity changes as the vehicle moves
down the road, so unless you plan to never move the vehicle again and
operate from that one spot - the tune of the antenna will change with
the earth as you travel down the road.

Hence it is not as critical to get a perfect match in a vehicle as it is
using a home install that is not going to move once it is installed.

Can you see my point?

If you have a small plastic car - forget about trying to get a perfect
match.

I've never been aware of the antenna tuning changing as you drive along
over ground where the conductivity changes. However, especially on the
lower HF bands, being over an area of high ground conductivity certainly
enhances RF signal level (both TX and RF).

It doesn't (not who was posting the crap). Any change in ground
conductivity is so minor compared to everything else it will have no
discernible effect on the antenna tuning.

The antenna moving back and forth in the wind will have a much greater
effect.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

My vehicle is tiny - 12 feet by 5 feet approximately - it will never provide
a perfect ground plane. I use to have a Land Rover Discovery which was
better. When stationary I used to use a set of battery jumper leads to
connect the vehicle to the nearest wire fence or metal handrail. Could give
a full 6dB improvement on 80M or 3dB on 20M. Best ever was when parked on
a quayside next to a derelict steel hulled tugboat. Connected my jumper
leads to the hull, tuned up the antenna and gained two whole S-points. I
also noticed that on the higher bands such as 20M there was a definite gain
when close to the sea or wetlands but that is probably reflection. I have
never monitored the matching whilst mobile but guess it changed dramatically
when passing trucks, buildings, bridges etc. At best all one can do is
compromise.
Dick

"Channel Jumper" wrote in message
...

The only people that worries about SWR is CB'rs.........

CB'rs only has one half of one megahertz to play with - hence antenna
tune is critical.

If all you are going to play with is one frequency or one band - then I
guess you are going in the right direction.

The missing information that my crystal ball is not clear on is the make
and model of the vehicle and antenna.

With HF it is more important to have a large metal ground plane - large
Suburban sized vehicle, that has all of its surfaces physically bonded
together with a wide copper braid straps at all hinge points and corners
- such as a pick up truck front walk away, hood, doors, cab, bed,
exhaust, engine, transmission, exhaust, suspension etc..

It's more important to bond these surfaces together then it is to tune
the antenna so it looks good on the analyzer.

At the same time, the ground conductivity changes as the vehicle moves
down the road, so unless you plan to never move the vehicle again and
operate from that one spot - the tune of the antenna will change with
the earth as you travel down the road.

Hence it is not as critical to get a perfect match in a vehicle as it is
using a home install that is not going to move once it is installed.

Can you see my point?

If you have a small plastic car - forget about trying to get a perfect
match.




--
Channel Jumper

In article ,
"Richard Ferryman" wrote:

I have
never monitored the matching whilst mobile but guess it changed dramatically
when passing trucks, buildings, bridges etc. At best all one can do is
compromise.

Dick-

I've noticed some reduction in signals when going under an overpass, but
not as much as you might expect. The effect may be different for
different bands.

I accept the fact that I have a compromise antenna when mobile. Since I
don't have a remotely tuned screwdriver antenna, I stop the car and
change the antenna to change bands.

My current setup has a Hustler fold-over mast with an assortment of HF
resonators, mounted low on the side of the car. I use an LDG tuner.
The tuner works well on most bands, but only matches about 200 KHz on 75
Meters.

Your idea of using a matching transformer is interesting. If I have to
change resonators, I could change transformers at the same time. But I
doubt it would eliminate the need for the tuner.

Fred
K4DII