Question about using mobile HamStick on 75 meters
Michael Brown
that I have been having trouble with in terms of getting it to tune for
75 meters. I don't have any kind of load coil or matching system for
the antenna, it is just plugged directly into the 3/8x24 trunk lip mount
that I have. I have it on the back of my Olds 88. Every time I try to
tune it, the SWR reading is through the roof, I can't even get the meter
to calibrate in the range that I need it to in order to be able to check
the SWR of the antenna, that's how bad it is. I probably don't have the
best ground in the world on my trunk, that may be part of my problem.
Also, I have about 15 feet of RG-58/U coax leading from the mount to the
PL259 plug. Do I need more coax than just 15 feet for use on 75 Meters?
I have an MFJ 9475 75 meter mobile rig that I plan on using mobile, and
I would like to use this antenna with it. Does anyone have any
suggestions as to what I need to do in order to get this antenna tuned
using a trunk lip mount? Do I need some sort of antenna matcher? A
better ground? A matching load coil on the base? Any suggestions would
be greatly appreciated. Thanks!
Michael Brown KU4UV
W6RCecilA
> Does anyone have any suggestions as to what I need to do in
> order to get this antenna tuned using a trunk lip mount?
Check for continunity from the bottom to the top of the Hamstick.
Sometimes the wire used for the coil breaks. Did you try the
entire 80m band for an SWR dip? Try it with the stinger set
at different positions. Borrow an antenna analyzer to find
out exactly what is wrong. Make sure the coax braid has a
good connection to the chassis of the vehicle.
--
73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
Mark Keith
>
> I just recently purchased a mobile HamStick antenna for use on 75 meters
> that I have been having trouble with in terms of getting it to tune for
> 75 meters. I don't have any kind of load coil or matching system for
> the antenna, it is just plugged directly into the 3/8x24 trunk lip mount
> that I have. I have it on the back of my Olds 88. Every time I try to
> tune it, the SWR reading is through the roof, I can't even get the meter
> to calibrate in the range that I need it to in order to be able to check
> the SWR of the antenna, that's how bad it is. I probably don't have the
> best ground in the world on my trunk, that may be part of my problem.
> Also, I have about 15 feet of RG-58/U coax leading from the mount to the
> PL259 plug. Do I need more coax than just 15 feet for use on 75 Meters?
> I have an MFJ 9475 75 meter mobile rig that I plan on using mobile, and
> suggestions as to what I need to do in order to get this antenna tuned
> better ground? A matching load coil on the base? Any suggestions would
> be greatly appreciated. Thanks!
>
> Michael Brown KU4UV
You have to have a matching device. There is no way a ham stick on 75
will tune without one unless it has a matching coil built in at the
base,and you are lucky. You are talking quite a low feed impedance. You
have to convert this to 50 ohms to run to coax. You can use a small
tuner, or a tapped coil. You do have a loading coil. It's the whole
antenna nearly. The best ham sticks will maximize the windings at the
top. You want few windings at the bottom unless you wind the matching
coil into the antenna itself. Many do this. But you still will usually
need matching to fit youe car.
I use "fat" bugcatcher style hamsticks on 40 and 75. I make them myself
from old "hamsticks". Much more efficient than stock hamsticks with the
big coils I use. Also my coax is only 8 ft or so. Doesn't matter what it
is as long as you don't have common mode currents on the outer shield.
If you have a well grounded mount with metal under it, this usually
isn't much of a problem. Also ground your whole car together with copper
strap for the best setup. Most cars are pretty much that way already,
but it's a good idea to make sure. All this assumes your coax
connections etc., are good.MK
W6RCecilA
> You have to have a matching device. There is no way a ham stick on 75
> will tune without one unless it has a matching coil built in at the
The 'Q' of a Hamstick is pretty low on 75m. The ARRL Handbook
reports that a 75m mobile antenna with 'Q'=300 for the coil has
a 16ohm feedpoint impedance (SWR=3:1) which does require some
form of matching at the base. But a 'Q'=50 coil will exhibit
a feedpoint impedance of about 47 ohms and not require any
matching at the base. I suspect the 75m Hamstick coil 'Q'
is in the ballpark of 50 as it was 10-12dB down from the
bugcatchers and screwdrivers at the 75m mobile shootout.
Mark Keith
I know mine with the fat coils, acts much the same as a bugcatcher as
far as matching required. I have them for all bands 80-10, and have to
use matching on every band if I want my radio to be happy. And 20-10 are
not using a fat coil. I've never been able to run a stick without some
form of matching. On 80-40 I couldn't imagine not having to have
matching. Would never work on my car. MK
--
http://web.wt.net/~nm5k
W6RCecilA
>
> W6RCecilA wrote:
> >
> > Mark Keith wrote:
> > > You have to have a matching device. There is no way a ham stick on 75
> > > will tune without one unless it has a matching coil built in at the
> > > base, ...
> >
> > The 'Q' of a Hamstick is pretty low on 75m. The ARRL Handbook
> > reports that a 75m mobile antenna with 'Q'=300 for the coil has
> > a 16ohm feedpoint impedance (SWR=3:1) which does require some
> > form of matching at the base. But a 'Q'=50 coil will exhibit
> > a feedpoint impedance of about 47 ohms and not require any
> > matching at the base. I suspect the 75m Hamstick coil 'Q'
> > is in the ballpark of 50 as it was 10-12dB down from the
> > bugcatchers and screwdrivers at the 75m mobile shootout.
> Will depend on the stick and how it's made. Some are better than others.
> I know mine with the fat coils, acts much the same as a bugcatcher as
> far as matching required. I have them for all bands 80-10, and have to
> use matching on every band if I want my radio to be happy. And 20-10 are
> not using a fat coil. I've never been able to run a stick without some
> form of matching. On 80-40 I couldn't imagine not having to have
> matching. Would never work on my car. MK
Mark, I would be willing to buy you a 75m hamstick, the kind that doesn't
have fat coils, if you will run tests on it and report back to us. Deal?
Mark Keith
>
>
> Mark, I would be willing to buy you a 75m hamstick, the kind that doesn't
> have fat coils, if you will run tests on it and report back to us. Deal?
> --
> 73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
Sure! I'll aways take free antennas. After the test, I'll butcher it up
into a real antenna. But I can already tell you that with my 40m stick,
with no fat coil, using a 3 ft stinger, must have matching to run. I bet
half the problem you refer to is from using little bitty useless
stingers. And the loss from the excess windings cause this effect.
I've never used one with a stubby stinger whip. The 40m ant is a 20m ham
stick with a 3 ft stinger to tune on 40m. 9 ft tall total. I bet the 80m
stock ham sticks are like 6 to 7 ft tall with a little stub tuning whip.
Not a good antenna... Also if I were to be able to get around matching
for small wound sticks, why do I still need it for 20-10 meters? Seems
on 10m I wouldn't need it, but I do if I want a perfect match. The only
way I can see to get around a matching device on a stick is to wind it
into the base of the stick. But they have to average it for the average
install. So might work, might not. Just depends on the car it's mounted
on. The 20m stick I use for 40m, has one of these matching coils in the
base for it's normal 20m use. But I never use it for 20m, as it will
exhibit the lousy performance you refer to from overkill windings and
stubby stinger. Most stock ham sticks leave alot to be desired. Not
enough whip in most cases. MK
Daveiq0
for his wisdom! Dave-KA4CNH
W6RCecilA
> But I can already tell you that with my 40m stick,
> with no fat coil, using a 3 ft stinger, must have matching to run.
What is the resonant frequency without base matching? I have been
talking about hamsticks resonated on the band for which they were
designed.
> The 40m ant is a 20m ham
> stick with a 3 ft stinger to tune on 40m. 9 ft tall total.
Now you tell us. I thought we were discussing stock hamsticks. Of course,
your reports make sense now. Did you tell us before that you were using
modified hamsticks? If so, I apologize because I missed it.
> I bet the 80m
> stock ham sticks are like 6 to 7 ft tall with a little stub tuning whip.
I think it's about 8ft and that's what I thought we were discussing. Did
I miss a post of yours about modified hamsticks? I did pretty well in
one of the 75m shootouts using a modified 40m hamstick.
> Not a good antenna... Also if I were to be able to get around matching
> for small wound sticks, why do I still need it for 20-10 meters? Seems
> on 10m I wouldn't need it, but I do if I want a perfect match.
A stock 10m hamstick used on 10m will exhibit close to a "perfect"
SWR, i.e. less than 2:1. The "coil" on a 10m hamstick is close to
nonexistent.
Mark Keith
> What is the resonant frequency without base matching? I have been
> talking about hamsticks resonated on the band for which they were
> designed.
About 7.240
All my sticks are resonant on the band used.
> > The 40m ant is a 20m ham
> > stick with a 3 ft stinger to tune on 40m. 9 ft tall total.
>
> Now you tell us. I thought we were discussing stock hamsticks. Of course,
> your reports make sense now. Did you tell us before that you were using
> modified hamsticks? If so, I apologize because I missed it.
I've been saying that for months. But it just stands to reason, if the
other guy has a high SRW, and no coax problems, he needs a matching
device. Not much else it can be.
>
> > I bet the 80m
> > stock ham sticks are like 6 to 7 ft tall with a little stub tuning whip.
>
> I think it's about 8ft and that's what I thought we were discussing. Did
> I miss a post of yours about modified hamsticks? I did pretty well in
> one of the 75m shootouts using a modified 40m hamstick.
Well, it's hard to say for sure, because there are so many varieties. I
assume his was a "hamstick" brand.
>
> > Not a good antenna... Also if I were to be able to get around matching
> > for small wound sticks, why do I still need it for 20-10 meters? Seems
> > on 10m I wouldn't need it, but I do if I want a perfect match.
>
> A stock 10m hamstick used on 10m will exhibit close to a "perfect"
> SWR, i.e. less than 2:1. The "coil" on a 10m hamstick is close to
> nonexistent.
It's pretty good generally, but I still use matching to have a wider
usable bandwidth.
But, I don't think I've ever been able to run below 20m without it. And
on 20m my stick is fairly normal. No "fat" coils.
I don't doubt you could find a stick to have the poor Q that you refer
to, but I would never run something like that. If an antenna is so
poorly designed to not need matching on 75m, I wouldn't bother with it.
I've never had one that was that bad here yet, So you may be right, they
could be out there, but not at my house. :> MK
grif...@my-deja.com
and 20 meters. Experiment number 1. I ran a 40
meter Hamstick on the drivers side rear bumper of
my 1998 Chev pick up, it has a fiber glass
topper. The ham sick was mounted on a three foot
standred antenna extension making the antenna
about 12' off the ground. I used a smiple gum drop
type mount. I worked very hard to make sure I had
a good ground.
With no base matching the antenna tuned up using
the singer on 40 meters and gave me 60khz of band
withth at 2:1 swr. I was happy. On day about two
months later I took the truck throug the car wash.
I removed the antenna but could not unscrew the 3
foot extension. I thought it would be Okay. I had
to send the boy drying off my truck back in for
the extension and what was left of the mount.
Experiment #2. I decided to make my own mount
becasue I was going to install a screwdriver type
antenna. I did and put extensive work into it so
that I could run all types of antennas. In side of
my special mount I installed a torid matching coil
used on the screwdrivers antennas thinking it
works on them why not a hamstisck.
I now have a twenty-four extension made of copper
3/4" pipe and my specaial mount. My Hamstick tuned
up with matching caps from the base to the ground,
about 900 pf. with out adjusting or cutting the
stinger. Guess what, my band width was better at
2:1 is was about 80Khz wide. The antenna work very
well.
With my quick disconnect I installed the 20 meter
Hamsick. Doing nothing it came in at about 13Mhz.
I tried a different matching cap 75pf and cut the
stinger, torid still built into the base. This
antenna now is flat at 14Mhz and 2:1 at 14.35,
beleave it or not. Band width is only advertised
as 175Khz. So I left every thing the way it was an
put the 40 meter back on. Now I am low in
frequency. 1.2 at around 7.05 Mhz. Leaving all
matching the same I cut the stinger to about 36
inches doing this in several cuts, then adjusting
the stinger in the antenna I cover 7.16 to 7.26 at
2:1 on both ends for 100khz of band width
advertised as 60Khz. I don't do anything execpt
change the ant. of the quick connect. I stay
within the bandwidth and don't use a tunner. The
rig is a TT Scout 555.
Whats the difference. Two things I think.
1. There is a lot more metal in a pick-up truck
then any car now on the road. A big plus for
running mobile in a pick-up.
2. The toried from Don Johnson's book "Everything
you Forgot about going Mobile." or close to
that is an exclent broad band matching device.
And yes I have loaded a 40 meter Hamsick up with
no matching on my truck, with 60Khz of bandwidth,
but my truck has way more metal than any car on
the road. So if you are in a small car, all of
them are small now, match it at the base or get a
tuner. I don't bleave in paying with very many
knobs while trying to drive and am very happy with
my Hamsticks. Happy enough not to install a
screwdriver type antenna.
Jim, WA7NDD
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.