40meter Hamstick on Mazda Pickup ???
David Shively
I've been trying to set up for HF mobile operation and have run into
a slight problem. Tried several things and can't seem to get my
40m Hamstick to yield a good match on my Mazda pickup (same as Ford
Ranger).
First, I tried a bumper mount but this didn't work well and according to
the literature supplied with the antenna this is not the best point
to mount it. Ok, next I tried mounting the antenna up on the top
of the side-wall of the bed near the rear of the vehicle. This worked
a little bit better but still couldn't get less than a 2:1 VSWR.
I installed several straps of metal braid to various points on the
body of the vehicle to improve the RF ground but this has made no
noticable difference. I've checked the ARRL Antenna book and several
web-sites (e.g. www.k2bj.com) for pointers.
Has anyone had similar experience with the 40m Hamstick? The literature
mentions that in some cases a capacitor is needed at the feedpoint to
improve the match - anyone gone down that road? Also, the adjustable
coil
with the alligator clip feed is another option.
Any help or pointers to other web sites, info, etc. would be
appreciated.
Regards,
David Shively - AF4HH - Atlanta GA
Bob Lewis
cab, on the passenger side. I found all my hamsticks gave about a 2:1
SWR so I added a 2:1 UnUn in a water-tight box on the back side of
the mount. I got the info from Jerry Spevck's book "Building and
Using Baluns and Ununs. It now matches well on each of the bands.
David Shively <davids...@mindspring.com> wrote in message
news:38696F89...@mindspring.com...
Cortland Richmond
the SWR. You'll have to lengthen the stinger a bit.
Cortland,
ka...@saber.net
Bob Lewis
Cortland Richmond <Cortland...@usa.alcatel.com> wrote in
message news:386976B0...@usa.alcatel.com...
Aaron Jones
>That works [to match a Hamstick] but you need a different value
>of capacitor for each band.
The Hamstick is somewhat narrow on 40 and you may find that even with
a base cap it won't stay matched across the whole band.
My solution was to use an inexpensive tuner at the transmitter end to
make the rig happy. The coax run is so short that the loss is negligible.
I had presets for each band marked on my cheapie tuner. I kept it under the
front seat and pulled it out to adjust it when changing bands. Since that
time I got an auto-tuner that stays under the seat permanently...
W6RCecilA
> This worked
> a little bit better but still couldn't get less than a 2:1 VSWR.
It appears that your hamstick has a feedpoint impedance around 25 ohms.
If so, a parallel cap, parallel coil, or 2:1 UNUN will match it to
50 ohms.
--
73, Cecil, W6RCA http://www.mindspring.com/~w6rca
David Shively
Thanks for the info. Exactly what type of capacitor is necessary for
this type of application? (mica, ceramic, etc.) Also, what rating
is required in terms of voltage or power? Can I find this type of
cap at a local electronics store?
Thanks again,
David Shively - AF4HH
davids...@mindspring.com
Cortland Richmond wrote:
>
> Try a 470 pF cap from the feedpoint to ground and see if it doesn't lower
> the SWR. You'll have to lengthen the stinger a bit.
>
> Cortland,
> ka...@saber.net
>
> David Shively wrote:
>
> > Hi,
> >
> > I've been trying to set up for HF mobile operation and have run into
> > a slight problem. Tried several things and can't seem to get my
> > 40m Hamstick to yield a good match on my Mazda pickup (same as Ford
> > Ranger).
> >
> > First, I tried a bumper mount but this didn't work well and according to
> > the literature supplied with the antenna this is not the best point
> > to mount it. Ok, next I tried mounting the antenna up on the top
> > of the side-wall of the bed near the rear of the vehicle. This worked
> > a little bit better but still couldn't get less than a 2:1 VSWR.
> >
Cortland Richmond
mica, glass, ceramic, polypropylene. Also, the value is not critical here. You
only need to reduce the SWR to what your rig can handle. 330-510 pF, somewhere
in that range, with about 470 being best, I'd think. Incidentally, you can also
use an _inductor_ instead of a a capacitor. You could wind, oh, ten turns of
hookup wire on a 35 mm film canister, for example, and parallel that with the
antenna feed point. You'd need to adjust the stinger downwards, in that case,
and see how your SWR looked at resonance then. Again, the value isn't all that
critical in this circuit.
Mike Pelgen
I used a pro-am similar to ham-stick 40 meter loaded whip on my Fairmont
wagon about 8yrs ago.
The antenna came with I think was a 250pf ceramic
capacitor across the base. The cap was only as big as
your little fingernail. If you get much bandwidth out of
this setup without a tuner, then you have some loss in
your system. Think I got about 50 khz 2:1 but it's been
a long time. Most hams would do well to read Walt
Maxwell's book "Reflections" published by the ARRL.
I am not endorsing the ARRL, but this book will dispel
many myths about HF antennas . I wish it were required
reading to get your ham license.
Happy Y2K
Mike WM9D Kokomo Indiana
David Shively wrote in message <38696F89...@mindspring.com>...
>Hi,
>
>I've been trying to set up for HF mobile operation and have run into
>a slight problem. Tried several things
TRON
but I have similar experiences with problems like the one you mentioned.
I have a question: Can you obtain a "dip" in VSWR? If you can it shows antenna
resonance.
If that is so you have some sort of reactance in the antenna SYSTEM.
Remember short antennas exhibit Capacitance (-)reactance. Long antennas exhibit
inductive (+)reactance.
The closer the antenna is to a -reactance (source?) such as the ground will also
induce a -reactance to the antenna.
I imagine your antenna is exhibiting a impedance change. To correct this problem
try playing with the coax length also try a matching section of different
impedance cable.
Remember to bond the hood, door and gate with finger stock.
I am sending you some info on Coax Matching transformers:
Some of the devices available seem to have almost magical properties. The
Q-section is one item that fits into that category.
What miracle does the Q-section perform? It has the ability to transform an
input impedance into a different output impedance!
This means there are a variety of uses for the Q-section , especially when
it comes to antenna matching.
One use is in the matching of two transmission lines which have different
impedance's. For example, let's say you have a length of low loss 75 ohm cable
that you want to use to feed your antenna. In order to match your 50 ohm to the
75 ohm , you'd need to insert a 1/4 wave section of transmission line between
the two. Using the formula shown below.
Another use is in the matching of a driven element of a beam. Let's say you have
a beam (split element type), with a feed point of 15 ohms. The square root of 15
(feed point) times 50 (normal coax cable) is 27.39 ohms. If you'd insert a 1/4
wave section of 27.39 ohm line, cut for the frequency of operation (between the
antenna and your cable) you'd end up with a perfect match.
To calculate the electrical length of the line you need to multiply the
velocity factor of the line by the free space length of 1/4 wave. For the
length in feet, this is (245.9/frequency in MHz) * velocity. For the length in
meters, this is (74.95/frequency in MHz) * velocity.
David Shively wrote:
> Hi,
>
> I've been trying to set up for HF mobile operation and have run into
W6RCecilA
> Most hams would do well to read Walt
> Maxwell's book "Reflections" published by the ARRL.
> I am not endorsing the ARRL, but this book will dispel
> many myths about HF antennas . I wish it were required
> reading to get your ham license.
Amazingly enough, the ARRL doesn't agree with Walt and stopped
publishing his book. Worldradio either has or is going to
publish a second edition of "Reflections".
Bob Lewis
reactance (only resistance) at resonance. How can the antenna be
resonant but contain a reactance causing high SWR?
The Hamstick at resonance presents a 25 ohm load which is why he gets
a 2:1 SWR at resonance with 50 ohm cable. Provide some type of match
between the 25 ohm antenna and the 50 ohm cable and the SWR will drop
to 1:1 at resonance. One way to do this is with a 2:1 Unun. This
will work on all bands so you only have to change the Hamstick, not
the matching device. Another way is to lengthen the antenna and then
place a capacitor from the base to ground. This requires a different
capacitor for each band (the Hamstick direction sheet had info on
values for each band as I recall). Another way to do it is to place a
coil at the base of the antenna and feed a tap on the coil. I believe
HamStick still sells a coil designed for this purpose. Again, the tap
must be changed for each band.
Michael Young
papers section. Start at www.arrl.org and look for the tech stuff. Strange;
the ARRL books were among the few Maxwell cited as presenting accurate
information.
Michael.
K9ZC
W6RCecilA <Cecil....@IEEE.org> wrote in message
news:386C07AF...@IEEE.org...
W6RCecilA
> Strange;
> the ARRL books were among the few Maxwell cited as presenting accurate
> information.
That's because Walt wrote a lot of the material. However, to the best
of my knowledge, all of Walt's contributions have been purged from the
ARRL publications. It's a pity. His explainations of reflections on
transmission lines are the most understandable that I have ever seen.
Ka9p
a 2:1 SWR at resonance with 50 ohm cable >>
I've measured 12 ohms (probably +/- 12 :) with a Palomar noise bridge on that
antenna. What I finally did was put a 4 foot extension at the base of the
antenna (I've used both a helically wound section from the base of an SGC whip,
and the base section of a ten meter ProAm, with similar results - both just
screw right in). The antenna gets taller (duh- you can tie it over a bit and
still get the benefit) but gets noticeably more efficient as reported from the
other end - the coil also is cooler after extended periods of transmission, I
imagine because the current is less - the SWR at resonance drops to about
1.4:1, giving an SWR 2:1 bandwidth of about 120 khz. I mention this only
because after spending alot of time matching and tuning HamSticks and the like
this summer manually, with caps, and with autotuners, I ended up proving what
everyone already knows - higher, longer, better :) Dropping the SWR makes you
feel better, but moving the other guy's S-meter is what it's alll about, IMHO.
Good luck, 73 and Happy Y2K Scott KA9P
Bob Lewis
gets
> a 2:1 SWR at resonance with 50 ohm cable >>
>
> I've measured 12 ohms (probably +/- 12 :) with a Palomar noise
bridge
I haven't measured it but if it were 12 ohms, the SWR would be
approx. 4:1. Since I read 2:1 I assumed it was 25 ohms. Since a 2:1
Unun brought the SWR very near 1:1 that looked like a correct
assumption. I wonder how much the impedance varies with vehicle type
and location? It probably has some impact.
Ka9p
and location? It probably has some impact. >>
Bob- No doubt it does, I got 12 ( like I said +/- 12, tongue in cheek :) pretty
much up in the clear - I'm sure you're right, you can introduce all sorts of
reactance by moving the antenna around the car and the SWR could look better -
I can see that when the antenna is tied over or flexes back and forth. My
point was only that on 40 and 75 the hamstick just isn't very efficient -
getting a low SWR isn't going to make it radiate any better-if you do something
to improve the antenna properties, it moves the match in the right direction
and actually improves performance. But they sure are convenient. Scott
Bob Lewis
improve performance, it only makes the transmitter happy and reduces
feed-line loss (which is minimal in a mobile installation anyway).
I'd never put a HamStick up against a Bug Catcher for performance.
I'd never put a Bug Catcher up against a 3 element yagi either :-)
It's all a matter of trade-offs and where you choose to make them
(that's antennas in general for most of us I think).
Aaron Jones
>I'd never put a HamStick up against a Bug Catcher for performance.
On the lower bands the Bug Catcher has the advantage because of efficiency.
But from 17 meters and up, all bets are off. The Hamstick has the advantage
in that it is light and can be mounted high up on the trunk or roof (luggage
rack) of a vehicle. The Bug Catcher in most cases because of it's weight and
size must be on the bumper, and thus lower and near more body metal. Add to
that the fact that the Hamstick becomes more efficient on the higher bands
and the difference may not be that great if at all. I suspect that a 10
meter Hamstick on the luggage rack would outperform a bumper mounted Bug
Catcher most of the time...