Mobile Black box antenna

[MikeA]

Is touching the antenna a bad thing?
It was working great (Eclipse 4000) then I picked up the antenna off the floor and moved it to the mount I made now I get static at the end of the driveway (before it was about 1 block.
Yes, when I picked up the antenna the unit was on.

[JBullard]

Yoy could have upset the SWR and fried your output transistors.

First time I've heard of this with this unit, but used to be very common with the Ramseys

[MikeH]

MikeA wrote:

Is touching the antenna a bad thing?
It was working great (Eclipse 4000) then I picked up the antenna off the floor and moved it to the mount I made now I get static at the end of the driveway (before it was about 1 block.
Yes, when I picked up the antenna the unit was on.

Picking up the antenna won't cause any problems. What kind of mount did you make? It is possible that the mount is blocking the signal from the antenna.

MikeH

[JBullard]

Touching the antenna when the power is on, will definately change the SWR ratio, and cause much of the signal to be reflected back into the unit, overloading the final outputs of the transmitter.

This is what killed so many of the Ramseys.

one reason I like the EDM, designed to withstand a mismatch of 25:1

[Max-Paul]

MikeH wrote:

MikeA wrote:

Is touching the antenna a bad thing?
It was working great (Eclipse 4000) then I picked up the antenna off the floor and moved it to the mount I made now I get static at the end of the driveway (before it was about 1 block.
Yes, when I picked up the antenna the unit was on.

Picking up the antenna won't cause any problems. What kind of mount did you make? It is possible that the mount is blocking the signal from the antenna.

MikeH

MikeH,

Sorry to inform you, your comment could very well be made by a person who is ignorant of transmitters and how they work. I hold an Amateur Radio Lic (Advance). Worked on radios for the Air Force and hold a commercial Radio Telephone Lic to work on commercial radios. And as it has been pointed out by two others. There is a strong possibility that the finial transistor has be destroyed due to the high SWR reflecting power back into the transmitter. Why dont you spend a little time reading about SWR and why you want a 1:1 ratio. And what happens when your ratio rises. And depending on the type of antenna and mount and what it is mounted to. Could be directing the signal to a different quadrant. See ground planes and how they effect the radiation pattern.

MikeA,
Have to tried to put things back as before and see if the reception range returned? If you have and the range has not returned. Well you get to send your radio back into MBB and see if they can fix it and have it back in time for your show. Otherwise, looks like you will be in the market for a new transmitter. And I suppose you know better than touch the antenna or disconnect it while the transmitter is on.

[jstorms]

Wow! I would have never guessed that touching the antenna while the radio is on would be a bad thing. Learning something new everyday. I would be very sad if my E4000 died.

[Guest guest]

I know that the electricity your body generates (static electricity) can do some bad things if you're not grounded when you touch something.

Guess I've been very lucky, I touched my antenna on my MBB E-4000 many times with the unit on and it hasn't done anything to it.

But then again, I was GROUNDED when I touched it, wether or not that really made any difference I really don't know.

One thing I do know, if you mount the antenna to another metal plane and don't run a groud wire from that metal plate, transmission can be adversely affected. Most magentic mount antennas (like the one that comes with the the MBB E-4000) usually use a metal, grounded surface for best results. The magnet is actually part of the ground of the antenna, since automobiles are grounded, a magnetic antenna uses the vehicle body as a ground.

So when I put my magnetic antenna on a metal plate to hold it in place, I ran a ground wire from the plate to the center screw of a power outlet, as that metal screw screws into the metal box plate, which should be grounded.

So you could try that and see of your transmission improves as well.

If not, like the others have stated, you probably fried your output transistor(s) in the MBB E-4000 and will either need to send it in for repair or check with a local radio repair center (those that repair ham or CB radios) to see what it would cost to diagnose and repair.

If you take it to a local shop, you can get it fixed and back in your hands a lot sooner. May cost you a little money, but if you really need it back quick, this would be your best bet.

[Guest guest]

Max-Paul, maybe you could give us a little lesson here on the differences between a regular AM/FM radio receivers antenna as opposed to a transmitters antenna to educate everyone.

I know if you touch a regular radio antenna when it's getting lousy reception and you're not grounded, it seems to improve the reception. Seems this works in reverse with transmitters.

So maybe you can give us all a little comparison of the two and why one works one way, and the other works in a different manner.

This would probably help a lot of new and even some of us old timers around here that may not be aware of these differences. And the do's and don'ts with transmitter antennas.


Maybe make a new topic of Tranmitter Antennas Do's and Don'ts?


Just a suggestion, I'm tossing the ball in your court as I know you're very knowledgable with this kind of stuff.

[JBullard]

Orville,

In Mike A's case, I really doubt any damage was done by static electricty. More probably, by touching the antenna while the unit was on, changed the impedance characteristics of the antenna and resulted in a very high SWR which reflected back into the final output stage.

You never try to set (change) the SWR on a transmitter while it is transmitting.

[MikeA]

Thanks guys. Touching it caused something to happen but it is all good now.
Mobile Black Box got back to me quickly. All I needed to do was let the unit set for a bit to re set itself.
All is good now.

Now I have a new problem. I will make a new topic for my new issue.

[Max-Paul]

MikeA,
Glad to hear that they have built in some kind resettable safety for the transmitter.

Orville,
What I know now is more on the concept level. More or less you have to know what a sine wave looks like. And you got to be able to visualize a series of sine waves running along the antenna. And then you have to be able to understand that these sine waves have to end at the tip of the antenna. Yet if you touch the antenna, you become part of the antenna and now there is a chance that the wave wont end at the new antenna (thats you now) in the right phase of the wave. So, what ever is left over will bounce or reflect back towards the transmitter. This is really hard to take a complicated subject and try to break it down to layman terms. This reflected power seems to add to the outbound power and adds to the heat in the transistor to the point that the transmitter transistor over heats and destroys it's self.

So in a nutshell, the antenna must be the right length so that the sine wave ends at the tip of the antenna in the right phase. Adding a random length (your body) will leave a out of phase sine wave. Some people like to call this impedance which is what we measure. But it also has to do with the phase of the sine wave.

To help you see what I am talking about with the sine wave. Take a length of rope, about 20'. tie one end to something like the bottom of a chair on a smooth floor. Step back about 10' from the chair. Holding the loose end close to the floor and move your hand left and right rapidly. imagine a straight line between your chair leg and the middle of your hands travel. This is your antenna and the rope is the sine wave on the antenna. A tuned antenna is when your hand is in the middle of travel and at the chair the rope's first inch is pointing back to you. If not, then moving closer or further away will produce this effect. **Ok, maybe not really with a rope, but this is how you tune a wire antenna. An out of tune antenna would be like if someone was holding the rope at the chair end and it was moving at a different rate and you would feel a whipping motion at your hand. this is the reflected power that we are talking about. And it would effect your ability to keep a constant motion at your end. You would be forced to use more energy to try to over ride the reflected whip.

If someone has a better way to explain reflected power in layman terms. Please jump in and help.

I seriously suggest that you open your telescope antenna. I also suggest that you understand that what Oville says is part voodoo science. Example. The magnetic antenna that he speaks of. Cars are not grounded per say. A ground is a low resistance to earth ground. A car has carbon black in its tires on a concrete or asphalt path below those tires. This produces a very high resistance to earth ground. And did you all know that depending on where on the vehicle you mount an antenna, will effect the radiation pattern? Examples are if it is on the passangers rear bumper. Most of the RX & TX will be towards the front with more towards the drivers side. And with an antenna in the middle of the roof will send most front and back with some going to both sides.
Now for the bit about using a metal plate and connecting it to the screw on an outlet. Well lets say you use a steel 9" pie pan or use a top of a 55 gal can. You place the antenna in the middle of both. Both give a nice round radiation patter. But because this is part of the antenna. Both will need to be tuned to a different length. See the word (if I can spell it correctly) counterpoise. Meaning that the hot (center connector) and ground parts of the antenna have a certain ratio.

In short, most of you dont have the equipment to tune an antenna at this frequency and low power. Sorry a CB SWR meter is not going to cut it. You need a Bird Watt meter with the proper frequency and power slug. Or a similar piece of equipment. So I offer up this bit of advice. Use what the maker suggest. Quit trying to transmit 1 or miles away, just cause you can. But really your breaking the law. God I love bear bait. So, while you are attracting the FCC to you. They are not looking at me transmitting a block away.

[Guest guest]

Very interesting Max-Paul. I'm familair with SWR's and tuning CB antennas, never did it to what I'd call a "fixed" transmitter, like our FM tranmsitters, but being in the electronics industry from manufacturing to prototype labs for 40+ years, I do understand what you're saying about the antenna sine wave ratios.

The car ground I guess I should have stated, thinking CB ground plane antenna here I guess, requires a good ground to the car body from the battery ground of the vehicle. And so, guess I mistakenly thought, at least from your description, we shouldn't tie the antenna mounting plate to any ground from a "fixed" transmitter like the FM Transmitters we use in our shows, unless the manufacturer would state otherwise.

So I am going to remove mine! Just thought it would be the same for one of these "fixed" transmitters as it would be for a CB, apparently I was off the mark on that, but fixed transmitters are a fairly new thing to me, I worked more on RX/TX type stuff in the manufacturing business, things like aircraft radio, CB radio, missile telemetry, satelite telemetry, basically PC board construction and sometimes helped the techs and engineers with testing on occasion when needed.

But, I'm not trying to transmit any great distances, but on and under certain weather conditions, my transmitter does go further than it should at times, but it is usually broken and staticy, so I'd think that's what and how the signal should be, even though the signal can be picked up, it's not a constant crystal clear signal like being near or next to the display. So I'm thinking I should be good.

So far been transmitting this way since 10/1 when my show officially started, and haven't seen any guys in black vehicles or black suits cruising by or knocking on my door. With the exception of my black SUV parked out front. LOL

This is why, when I can, I'm planning on the purchase of an EDM unit where I have better control of the power, as opposed to what I have now, and can't really adjust the power output to keep it constantly at the FCC part 15 guidelines.

[Max-Paul]

Orville,

If everything is done right, a wire going to the ground wire of your house electrical system would not be needed. A good example that comes to mind is this. I have a 2 meter ham radio (144-148Mhz). I made an antenna that is based on the SO-239 connector (think CB female UHF connector). I solder an 19" wire to the pin and in each of the 4 mounting holes I solder another 19" wire in each hole. Now bend those 4 wires down in a 45 degree angle. Attach coax and a string to the hot wire. Thumb tack to ceiling. And other end of coax to transceiver. I used this while in an apartment in TX with my Walkie Talkie when I was a new ham. Beat the heck out of my rubber duckie any day. But the point is I used string on the hot wire and if I had not bend the 4 wires down in a 45 degree angle. My SWR would have been sky high. Not all ground planes are 90 degrees to the hot element. Although I am sure you are familiar With the pole or tower mounted ground plane antennas. Cause the ground plane is grounded to earth and the reaction this causes, the ground plane element are parallel to the earth. Two different antennas, with two different situations, one floating above earth and one actually grounded to the earth. Then one should also learn about beams and what makes them able to focus the radiation pattern in a direction. Notice How I didnt say single direction. Nothing is perfect and a beam antenna will have side lobes. Once you understand beam antennas and how they work, then you also understand how the antenna on a car works and how this also can be applied to an antenna on or in a house works.

Unfortunately a lot of people what a quick answer. I hope that between this post and the one before. Some will start to understand there is no such thing as a quick and easy answer. There are so many issues that effect the end result. BTW I think what happened with your attaching a wire to your plate and now getting better reception is one of two or two things that caused this. The ground wires in your house have acted as reflectors or directors and have focused your signal to where you wanted it. Or your counterpoise has tuned your antenna.

BTW not just for Orville.

[Guest guest]

Thanks Max-Paul! I can always count on your for a great explaination of things. I ungrounded the antenna and then my LED sign I use went kaput, it would only show the bottom line of LED's. I thought the sign had gone belly up, found out later, the now ungrounded antenna mounted about 6" on an metal L bracket and near the power input side of the LED sign (BetaBrite Sign, older model) when the transmitter was on, the LED sign wouldn't work, turn off transmitter sign worked fine! Weird!

Just strange it didn't affect the sign when I had the L bracket grounded the antenna sits on!

Took me a little time to figure this one out.

Never had problems with the two before, but the antenna wasn't near the sign last year, this year, being in an apartment and the antenna and sign sharing the same space, well the FM transmissions were disabling the information sign!

No, I didn't re-ground the L bracket, instead I flipped the board the antenna L bracket is mounted to under the sign 180 degrees, placing the antenna on the opposite side of the sign, away from the power input jack. Sign started working again just fine, and the transmitter working right alongside it.

Thinking if anyone uses a BetaBrite sign and an FM transmitter in the same location, better tell them not to put the antenna near the side with the BetaBrite power jack or your sign may do as mine and you'll think it's really messed up and in need of repair or replacement!

Funny thing with it, is I could press on the display window and the sign would work, making me think it was the sign, I accidentally found out the antenna was creating the problem when I'd turn off the transmitter sign worked, on, sign didn't, several off and ons later, I finally realized I needed to move my antenna! LOL