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Antennas & RF

Can I use the SNA-600 with a block 470 receiver since the lowest frequency range of the SNA-600 is shown as 500 MHz?

The SNA600 will operate well below 500 MHz. It is marked 500MHz because we didn't make receivers below 500 MHz…

The SNA600 will operate well below 500 MHz. It is marked 500MHz because we didn't make receivers below 500 MHz until the great digital changeover of all the TV stations in 2009. The SNA-600 measures lower than a 2:1 SWR (Standing Wave Ratio) from 440 MHz to 600 MHz when the antenna arms are fully extended. Less than 2:1 SWR is considered a standard antenna range measurement. The marked range for fully extended is only down to 500 MHz but the antenna will operate much lower than that.

Posted 10 months agoby LectroAdmin
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Since the SRa is now using removable antennas, do I need to seal around the connectors to keep the SRa protected against rain?

The new stainless steel SMA female connector is pressed into the aluminum front panel and is an interference fit. Any…

The new stainless steel SMA female connector is pressed into the aluminum front panel and is an interference fit. Any possible panel to barrel gaps are filled by us with a Loctite gap filler. The antenna wire itself has an O-ring in the nut assembly that seals the wire antenna to the nut of the male connector so any water running down the antenna cannot enter the connector. Then the only possible water entry is if the SR is upside down or angled down and water runs into the inverted nut, around the threads, into gaps between the center insulator and the barrel and down into the unit. You can seal against this improbable occurrence with a small drop (dab) of Vaseline or other petroleum jelly inside the SMA connector applied right on the white insulator. The Vaseline will prevent leakage by this path totally, even if the unit is dropped into water and if the SR (and attached camera) are submerged, you've got bigger problems anyway. The Vaseline does not affect the RF at all. If the Vaseline gets dusty when the SMA is removed, just clean it with a cloth or Q-tip and some clean Vaseline.

Posted 10 months agoby LectroAdmin
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How can I prevent RF inter-modulation interference? Do I have to use a specific brand program for each type of wireless system?

This was a posting to RAMPS about "Calculating Intermod Frequencies". Here's a chance for a 40 page dissertation that I'm…

This was a posting to RAMPS about "Calculating Intermod Frequencies".

Here's a chance for a 40 page dissertation that I'm not going to take. In the interest of keeping it simple and easy to remember, I'll make some general statements that are 99% true, i.e., errors are 40 dB down and good enough for sound mixers. ;-)

Intermod is calculated in exactly the same way by all the programs and has little or nothing to do with i.f. frequencies.

Odd order intermod (3rd, 5th, etc.) is much more of a problem than even order intermod (2nd, 4th, etc.) because with odd orders it is possible to generate interference that is very close to the receiver frequency. This interference can therefore pass straight through the receiver front end filters. Of the odd orders, third order intermod is of greatest concern because the interference is always at a much higher level than 5th or 7th.

Second and 4th order are of lesser concern because the carriers that generate them cannot be close to the receiver frequency and will be filtered out by the front end. (Our IFB receiver is one of the few receivers for which this statement is not true. The IF is so low, 70 kHz (!!), that the image at 140 kHz from the operating frequency can be generated by 2nd order intermod.)

Intermod due to wireless transmitters getting into the receiver is not a factor if the transmitters are all, repeat ALL, 20 feet or more away from a good quality receiver. Intermod between a transmitter and a TV station does not follow the 20 foot rule for the TV station component obviously, or for two TV stations.

Intermod generation between transmitters is more of a problem in most situations particularly if the transmitters have standard output stages and are closer than 5 feet apart. The intermod frequencies are exactly the same as in receivers and any intermod program will catch them. I have seen fairly strong 5th and 7th order when transmitters are only a few feet apart.

A quick discussion of image frequencies is appropriate here since most programs also calculate images and this is where different brands do have differences. The knowledge of the i.f. frequency is critical in determining where the image frequencies will lie. A first low i.f frequency says the image frequency will be a small distance from the receiver operating frequency. Most modern receivers have a high first i.f. such as 244 MHz. This puts the image at 2 x i.f = 488 MHz away from the tuned frequency. Almost 500 MHz away means the front end filters can strongly suppress it. Generally, with modern i.f.'s, other wireless transmitters don't cause image problems. It's from other high power transmitters in the environment.

If the above is the Reader's Digest version of intermod stuff, here's the Cliff's notes:

  1. Third order intermod is the biggie.
  2. Any program will calculate third order.
  3. Third and higher order between transmitters is usually the main problem.
  4. You only need to worry about intermod if the transmitters are close to the receivers (less than 20 feet) or each other (less than 5 feet) or in other words, always.

Since the original question was "Mathematical formula in finding Intermodulation free frequencies" here it is:
1.Find the difference between two transmitter frequencies. 
2.Subtract the difference from the lower frequency and add it to the higher frequency. Those will be the two interfering frequencies, so don't have a receiver on those frequencies.

Example: Transmitter A=525.000 MHz, transmitter B=550 MHz. Difference is 25 MHz. Don't have a system on 500.000 (525-25MHz) or on 575.000 (550+25MHz). Note that you can't screw up the math. Doing it wrong such as 525 +25 and 550-25 gives you the original starting frequencies. Also note that two systems don't have intermod problems. It takes two transmitters to generate garbage on a third frequency and you have to have a third system in order to have something to interfere with. TV stations do count as a transmitter, however, if the signal is strong at the receivers, i.e., equivalent to a wireless transmitter at 20 feet or less.

Well at least I managed to keep it to only one full page (if you use a small font).

Posted 10 months agoby LectroAdmin
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The best way is to use three 2-way splitters on 3 of the outputs from your 4 way multicoupler and run the last output as usual for a total of 7 outputs. You will have a 3 dB+ loss on the split lines. If you are working at relatively close distances (under 100 feet) and/or in a RF noisy environment, you will not notice any change in performance. The reason is that if you are close you have plenty of signal and a small loss won't be noticeable. If you are in an RF noisy environment, the splitter will drop the signal and the noise both by 3 dB and the signal to noise ratio at the input remain the same. This is true until the attenuated external noise is less than the front end input noise of the receiver. I would try the passive splitters and save the money. Plus, splitters are always handy things to have around even if you eventually get a UMC16B.

Posted 10 months agoby LectroAdmin
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If I have 7 dB of loss in my antenna cable does it actually affect range since any noise is attenuated the same amount as the desired signal?

This is one of those Zen "It depends" questions and answers. If you are in a high noise environment you…

This is one of those Zen "It depends" questions and answers. If you are in a high noise environment you will attenuate the signal and the noise the same amount and the signal to noise ratio at the input to the receiver will remain about the same. The performance of the system in the high noise environment will not change due to the 7 dB of attenuation.

If you are in a quiet environment, (the middle of Montana) then you will attenuate noise and signal the same 7 dB. The external noise is now attenuated to a lower value than the front end noise of the receiver. The front end noise of the receiver is now the determining noise floor and you've reduced the signal 7 dB so you get 7 dB less range than you would have gotten in the wilds of Montana.

Since RF is hard to see directly (magic), let's put it into audio terms that is maybe more familiar. If you have a good mic in a very noisy environment and the talent is screaming into it (rock venue), you can attenuate the mic signal 7 dB (pad), then turn up the gain 7 dB to compensate and the system signal to noise ratio will remain the same. 

If you insert the same 7 dB attenuation pad in the mic line while recording a very weak signal in a quiet room (one hand clapping in a Zen temple) then the input noise of the mic pre amp is the dominant noise source and the overall signal to noise ratio is decreased 7 dB as you have turn up the board gain to compensate for the 7 dB mic pad. The pre amp hiss is now the problem.

So as I said, it depends. In general it's not good to throw away 7 dB of signal from the antenna, but sometimes it doesn't hurt.

Posted 10 months agoby LectroAdmin
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Does Lectrosonics make an RF antenna amplifier that has a bandwidth wider than 50 MHz?

Yep, we do. We've had so many customers having problems when using other brand wide band RF amplifiers in their…

Yep, we do. We've had so many customers having problems when using other brand wide band RF amplifiers in their antenna systems that I caved in and set up some wide band versions of our distribution amps and amplifiers. They have a 230 MHz bandwidth and cover all our standard blocks. At least they still have a very high intercept point with low noise figures. The prices are the same as the narrower, 2 block wide units. The web site may not be changed yet but the sales crew have the details. The wide band version of the UHFM-50 is the UHFM-230. The UMC16A is the 50 MHz version and the UMC16B is the 230 MHz wide band version.

Posted 10 months agoby LectroAdmin
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When I operate my receivers near a portable recorder, I seem to be losing a lot of range. What's wrong?

Some digital recorders have high levels of radiated RF and some have moderate levels of radiated RF but all radiate…

Some digital recorders have high levels of radiated RF and some have moderate levels of radiated RF but all radiate some RF. In any case, if the RF is the same as the operating frequency of the receiver, the range will always be affected. In most cases that particular frequency will be unusable. Some older digital recorders were so bad and radiated on so many frequencies simultaneously that any selected frequency was unusable. The only reasonable solution was to put the recorder in a trash compactor and then engage the crush mode, preferably multiple times. Modern digital recorders are much better but again, all radiate some RF.

The only current solution is to get the receiver antennas as far away from the recorder as possible. Increasing the separation by even a few additional inches may really pay off. We have some co-ax antennas that can be mounted on the straps of a bag system that will really help also. Things are easier on a cart setup since the antennas can be flown overhead to dramatically increase separation.

Posted 10 months agoby LectroAdmin
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How can I find how much RF loss there will be if I have to run a fairly long antenna cable?

The link shown below has loss numbers for just about every kind of coaxial cable that there is. The loss…

The link shown below has loss numbers for just about every kind of coaxial cable that there is. The loss is per 100 feet of cable so if you have only 50 feet of cable you will have half the loss and so forth. Note that the loss figures are different at different frequencies.The frequencies are across the top going from 1 Mhz to 5000 MHz. The types of cable are grouped together in families vertically on the left side.

Click here for chart on cable losses

Posted 10 months agoby LectroAdmin
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What is a coaxial dipole antenna and how can I easily make one?

Score the insulation of a 50 Ohm coax such as RG58 (RG174 is OK if it is less than 5…

Score the insulation of a 50 Ohm coax such as RG58 (RG174 is OK if it is less than 5 feet) one quarter wavelength from the end of the cable. Do it very gently and don't score or even scratch the stranded shield wires since they will easily break off. Remove the outer insulation. Pull the shield down so that it has some slack in it with a bulge near the remaining outer insulation of the coax. Poke an opening in the shield with a blunt tool near the remaining insulation. The hole should large enough to pull the center conductor with the inner insulation on it through the opening. Straighten the shield so that you have a quarter wavelength shield wire and a quarter wavelength center conductor. These are the two arms of your dipole. Fold the shield back along the outer insulation of the coax cable. The center conductor is left pointing in its original direction. Now cover the center conductor and the shield with a half wavelength or more of shrink tubing to make it look nice. This antenna works best if the center conductor and the folded back shield are both in the open air since both the folded back shield and the center conductor radiate.

Posted 10 months agoby LectroAdmin
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What do the different colors on the antennas mean?

The color of the antenna caps or bands correspond to the last digit of the block number of the system.…

The color of the antenna caps or bands correspond to the last digit of the block number of the system. The universal color code used for resistors was picked for the code.

BLOCK RANGE COLOR WHIP LENGTH
20

512.000 to 537.500

Black

4.98"

21

537.600 to 563.100

Brown 4.74"
22 563.200 to 588.700 Red 4.48"
23 588.800 to 614.300 Orange 4.24"
24 614.400 to 639.900 Yellow 4.01"
25 640.000 to 665.500 Green 3.81"
26 665.600 to 691.100 Blue 3.62"
27 691.200 to 716.700 Violet (Pink) 3.46"
28 716.800 to 742.300 Gray 3.31"
29 742.400 to 767.900 White 3.18"
30 768.000 to 793.500 Black (with label) 3.08"
31 793.600 to 819.100

Black (with label)

2.99"
32 819.200 to 844.700

Black (with label)

2.92
33 844.800 to 865.000

Black (with label)

2.87
Posted 10 months agoby LectroAdmin
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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.

Posted 10 months agoby LectroAdmin
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Will laying a piece of coaxial cable on a metal surface affect the RF signal? Will coiling coax cause additional cable loss?

Coiling coax or laying it on metal has little or no effect on loss. Even if the coax is terminated…
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.

Posted 10 months agoby LectroAdmin
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The whip antennas on small transmitters tend to bend over time, with some of the more flexible ones developing kinks and "S" curves.

As long as the bends are moderate, the bends don't affect the antenna much at all. The overall length and…

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.

Posted 10 months agoby LectroAdmin
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Will a dipole antenna give me more range than a 1/4 wave whip (or 1/4 wave ground plane) antenna?

Yes and no. If the 1/4 wave ground plane antenna is properly built and has the necessary good ground plane,…

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.

Posted 10 months agoby LectroAdmin
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Note: "vertically downward" (e.g., a beltpack upside-down)

When indoors, antenna orientation is not as critical as when the situation is line of sight outdoors. Indoors, the RF signal is bounced around so much that orientation is not as critical. In all cases though, you are safest using vertical transmitter antennas with vertical receiver antennas. 

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.

Posted 10 months agoby LectroAdmin
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What happens if I use 75 Ohm RG-59 cable instead of the recommended 50 Ohm cables for my antenna connections? Are lengths more than 3 feet OK?

The RG-59 will work for even longer runs than 3 feet. Assume operation at 600 MHz and 70% velocity factor…
The RG-59 will work for even longer runs than 3 feet. Assume operation at 600 MHz and 70% velocity factor for the RG-59. You do get some mismatch, but you will get it at any point beyond a 1/8 wavelength which is only 1.7 inches (!). At a 1/4 wavelength, 3.4", you get the worst mismatch but that will still give you 88% of your power. At a 1/2 wavelength, the 75 Ohm cable will look like a perfect 50 Ohm match (!), since whatever impedance is at one end is transformed to the exact same impedance at the other end. At 3/4 wavelength it looks like the 1/4 wavelength case, 88%, and at 1 wavelength it looks like the 1/2 wavelength case or a perfect match again. This just repeats for each additional 1/4 or half wavelength of cable. Added to this small mismatch, you will have the cable loss which is actually lower for RG-59 than for RG-58, since RG-59 is physically larger. You can use RG-59 for up to 15 feet or so where I wouldn't recommend RG-58 beyond 10 feet. 


You will see some mismatch to input or output filters but it isn't severe. Basically under the worst mismatch 1/4 wavelength, the 50 Ohm source or load is transformed into 100 Ohms. Antennas and filters will shift some but it isn't horrible. (RF is weird stuff.)

Posted 10 months agoby LectroAdmin
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Antenna gains are sometimes specified as Gd and sometimes as Gi. What do these gain terms mean?

Antenna gain is specified in some different ways that are confusing. The first is Gain referenced to an isotropic radiator…

Antenna gain is specified in some different ways that are confusing. The first is Gain referenced to an isotropic radiator (G subscript i) which is an antenna that radiates omni directionally and equally in all directions. A dipole antenna in this specification has a gain of about 3 dB Gi. However,an isotropic radiator doesn't exist in the real world. Any efficient antenna has more gain than an isotropic radiator. Even a simple 1/4 wave whip antenna has a gain of 3dB Gi. Since it radiates its power only above the ground plane, or into half free space it has a Gi of 3 dB. 

The other way of specifying the gain of an antenna is referenced to a dipole (or G sub d ). Obviously a dipole has a gain of 0 dB or unity referenced to Gd. The dipole is just referenced to a dipole. 

As an example, our ALP600 log periodic antenna has a gain of 4 dB Gd or 4 dB better than a dipole. If we wanted bigger, more impressive numbers, we would just rate it at 7db Gi. 

The ALP600 is more directional than a dipole of course, in fact 4 dB more directional. Gain is always proportional to directionality. Most of the directionality is in the vertical plane or up and down. The horizontal plane, left to right, which concerns you, is +- 60 degrees or 120 degrees total for a gain equal or better than a dipole.

Posted 10 months agoby LectroAdmin
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If I use dipole antennas in a bag system, meaning they have to be close together, how should I orient them, vertically or horizontally?

Here's what I think I know about antenna orientation. If you are outdoors with the transmitter in the normal position…

Here's what I think I know about antenna orientation. If you are outdoors with the transmitter in the normal position with the transmitter antenna vertical, then you will get the best antenna strength ON THE AVERAGE with the dipole antenna arms also vertical. Inside where you have lots of reflections and the antenna signals are coming from all over, then vertical or horizontal polarizations are about the same. So vertical polarization is still, the safest orientation. There are two exceptions to this. If the transmitter antenna is horizontal, then the dipole arms should also be horizontal. Or if you can't separate the two dipole antennas by ideally at least a 1/2 wavelength (8 inches) to get good space diversity, then you can go to polarization diversity by rotating one antenna 90 degrees to the other. My advice is, if you can get the antennas 8 inches apart or more, then go with the vertical polarization.

Posted 10 months agoby LectroAdmin
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Can I use two antennas with the Venue receiver's frequency diversity operation or is the extra antenna useless?

The Venue receiver will do both antenna and frequency diversity simultaneously. The reduction in drop outs and noise ups should…

The Venue receiver will do both antenna and frequency diversity simultaneously. The reduction in drop outs and noise ups should be just as dramatic as the reduction going from single antenna reception to regular diversity reception. Definitely use two antennas. An antenna port is a terrible thing to waste.

Posted 10 months agoby LectroAdmin
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Will an RF antenna amplifier or splitter give me an increase in wireless range or sensitivity?

Usually it won't. Our receivers' front ends are very quiet and within a few dB of the theoretical limits for…

Usually it won't. Our receivers' front ends are very quiet and within a few dB of the theoretical limits for noise. The range limitations are usually due to other interfering noise sources in the environment. Additional gain before the receiver will not increase range but will lead to increased RF intermodulation and RF overload. The only time you want gain before a well designed receiver is to neutralize cable and/or splitter losses. In this case, the gain must go before the cable or splitter loss and it must be a high quality amplifier such as our IFM50. Putting the gain after the loss is too late since the signal to noise ratio is now poor and gain won't improve it. An analogy for RF is the same as for music; lots of amplification can't overcome poor source material.

Posted 10 months agoby LectroAdmin
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