Frequently Asked Questions - Wireless
The MM400B has a better seal between the battery compartment and the electronics compartment. You will notice a new line of screws in the middle of the cover. We were getting occasional leakage between compartments. The battery door now has a spring battery contact because the old solid door was putting too much pressure on the battery. The new spring door controls that pressure. The chain that was used to retain the battery door on most of the MM400A's was recently replaced with a stainless wire lanyard that is much stronger. That lanyard is carried over to the MM400B also.
The biggest change is a new off-on switch. The only way to turn off the older MM400A was to unscrew the battery door a turn or two. This could introduce moisture under wet conditions when all the user wanted to do was to shut the unit off. We added an easy to find, magnetic on-off switch on the side of the unit. The magnet activates a tiny reed switch on the inside of the case. Since this does not penetrate the case, the unit is just as weather proof as always. If you don't like the on-off feature the switch can be removed and the unit will stay on at all times. It can also be reprogrammed to become a mute switch. If this mode is programmed, the unit can still be turned off with the switch. You simply activate the switch three times to turn the unit off.
The MM400C replaced the SMA connected antenna with a permanet antenna for much better water sealing. About the same time as the C changeover, we went to a darker finish that tarnishes less.
The UCR201, UCR211 and UCR411A (but not the UCR411 -- no room for the code) are equipped with a Pong game. To activate, hold down the UP button while powering on.
The Venue has the Whack-A-Mic game. To activate that, hold down button 1 while powering on.
The R400 doesn't have a game yet but we are thinking Asteroids, because all it requires is a rotation control and a fire button. Stay tuned.
The blocks are a holdover from our early UM200 systems before we put in microprocessors. The frequency switches directly controlled a parallel input PLL (frequency chip). Since we had 256 possible switch settings using two 16 position switches and we were making 100kHz steps, we defined a block as 25.6 Mhz in size. Block 0 would have gone from 0Hz to 25.5 Mhz, Block 1 from 25.6 to 51.2 MHz and so forth. So the beginning frequency in any of these blocks would have been the block number times 25.6 MHz and the last frequency in that block would 25.5 MHz above that.
So, in a sense our blocks were pretty arbitrary and have little to do with the world outside Lectrosonics. As far as the outside world, you can call the sales department at Lectrosonics (800 821-1121), give them your location(s), what other wireless gear you have and they will make a good recommendation. If they mess up and you are using our recommended gear, we then have the responsibility to get you out of trouble. Our dealers are pretty good at frequency selection since they live in the neighborhood.
The other valuable resource is the RAMPS group since you can probably find someone that is operating in your area and can tell you what works. (See info on RAMPS in FAQ#021-WIRELESS)
I assumed that you were speaking about our gear since you mentioned blocks. If you are interested in other brand equipment, call their offices and get advice for your area. The other manufacturers are generally quite helpful and if they aren't then try some one else.
As far as the question of whether the antenna should be above the transmitter or below it, the only rule I'd follow is the higher the antenna the better. Higher, upside down is better than lower, right side up. Usually, right side up does get the antenna a little higher.
Yes and no. If the 1/4 wave ground plane antenna is properly built and has the necessary good ground plane, it has exactly the same gain or range as a dipole antenna. The 1/4 wave whip antennas on receivers and transmitters are just mounted to a connector for convenience and do not have the large ground plane that they should have. They are not good examples of a properly built 1/4 wave ground plane antenna.
However, the dipole antenna does not need a ground plane since the two arms of the dipole balance each other perfectly and no ground plane is needed. Generally a good dipole will work much better than the typical receiver whip antenna. The drawback to a dipole antenna is that it is twice as big as the small 1/4 wave whip antenna and correspondingly much more difficult to place on a person. In addition, the dipole antenna not only doesn't need a ground plane, it shouldn't be near a ground plane such as a transmitter case, a receiver housing or a camera body.
If you can find the room for the dipole it is generally a better choice; not because it is a better antenna but because the usual whip antennas don't have good ground planes due to space restrictions.
As long as the bends are moderate, the bends don't affect the antenna much at all. The overall length and distance to the ground plane establishes the capacitance of the antenna and the length establishes the inductance. Neither of these vary much with small bends in the wire. The capacitance and inductance establish the resonate frequency of the antenna which is the most critical factor. If the wire gets very close to metal (or the ground plane) then the capacitance to ground increases greatly. If the wire makes a loop or folds back on itself then the inductance will also increase a lot. Either of these would lower the resonance below the "cut" frequency and the antenna would not work as well.
The cable in our antennas can be dekinked by bending it with your fingers and you can do this hundreds if not thousands of times without breaking the wire.
Coiling coax or laying it on metal has little or no effect on loss. Even if the coax is terminated poorly, all fields are internally contained in the coax. The only time you will have currents on the coax is from the antenna at the end radiating back to the shield. Coax is a truly balanced cable in that the currents on the center conductor and on the shield are exactly the same and in opposite directions. This is true at least to the limits of shielding and copper resistance.
Since the magnetic and electric fields are self contained, the outside world doesn't "see" any current flow and coiling the cable or even wrapping it around a piece of iron makes little or no difference. The prohibition against coiling coax has been around for a long time. I know that, because many years ago I read an article that disabused "yours truly" of that firm belief.
The worst thing about a coiled cable is that the signal has to go through a longer piece of cable and has a little more loss than a straight shot. A one foot diameter coil is harmless for the coax that we all use.
However, coiling cables in a very small coil deforms or even damages the cable, and will mess up the cable impedance.
Yes, in its simplest form it is just a wire that is twice the length of a 1/4 wave whip. However, it doesn't work very well with a standard 50 Ohm antenna output or input. A half wave antenna has a very high input impedance (5000 Ohms or so) and requires an additional matching circuit to work well. Basically, a 1/2 wave antenna is a dipole antenna that is end fed rather than the more common center feed.
Our SNA600 dipole antenna is a good example of a center fed dipole. It is a 1/2 dipole that has two 1/4 wavelength arms with a center feed where voltages are low and currents are high. The impedance of a center fed dipole is close to 50 Ohms and easily matched with striplines in the antenna body.
Since the two dipole antennas are equivalent, there is no advantage of one over the other as far as gain goes. Neither antenna requires a ground plane.
In comparison to a 1/4 wave antenna, the gain is also exactly the same. For an explanation (See FAQ#056-WIRELESS). So in specific answer to your question, a wire twice as long as our normal antennas would not work well at all.