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[Jens Palm Bacher]

It is interesting that some manufacturers seem to market active antenna as their recommended product for radio mic receive antenna. Is the correct application to make up for cable losses, not to compensate for rf path loss?

Are there any rules of thumb for how far to keep transmit and receive frequencies separated by in a spectrum band plan?

I also avoid broadband amplified antennas whenever possible. If i need to use long coax, i try to use antennas or amps with filtering, such as the Sennheiser A 12 AD or the AB 1036. It is interesting to see that Sennheiser have moved away from broadband amplifers in their 9000 series, and are going back to filtered antennas.

[Jason Glass]

It is interesting that some manufacturers seem to market active antenna as their recommended product for radio mic receive antenna. Is the correct application to make up for cable losses, not to compensate for rf path loss?

Are there any rules of thumb for how far to keep transmit and receive frequencies separated by in a spectrum band plan?

It is, indeed, only suitable to make up for cable losses and/or passive components like splitters, and is unnecessary for simpler systems.  The LPDA alone has +5dBi of gain, and if you use a helical, its gain is roughly 8-9 dBi (11-12 dBi gain minus 3dB polarization mismatch loss).  If you use high quality 3/8" low loss cable your losses are in the neighborhood of 3.5dB to 4.5dB per 100ft at the middle of the UHF-TV band (585MHz).

The question of band spacing is more difficult to answer.  Every urban area in the USA has different areas of the UHF-TV band available for use, so we are forced to be very flexible in our band planning.  You really just try to keep them as far apart as is practical and do your best to stick to it.  Unfortunately, someone almost always shows up late with a piece of gear that will only tune to a band where you don't want that type.  You just have to make it work as best you can.

Having a good spectrum analyzer helps very much to examine the spectrum at potential assignment frequencies to see if they have low enough noise, and to determine if predicted IMD products are really being transmitted by your equipment, although you are rolling the dice on what's happening inside the front ends of your receivers.  This is where expensive high-end gear helps, because its receiver channel filtering helps to reduce internal IMD products dramatically.

[Jay Rigby]

Scratch that, just realized you are using Parallels.

[Karl Winkler]

I can't stress enough the validity of this statement. Amplified antennas and other in line preamps cause far more problems than they solve 99% of the time. Their use has limited applications, and not has a band-aid for other inadequate system implementations.

Absolutely. Like audio gain structure, this concept can not be reiterated often enough!

[Ike Zimbel]

Here is an expansion on my videos about IAS and WB. 
It is divided into 2 - 12 minute videos.

Part 1

Part 2

Hi Pete,
I've been experimenting with this and one thing I'm finding pretty consistently is that it's very difficult to get the two programs to agree on even basic intermod calculations. In this instance, I did the initial coord in IAS (nothing too challenging, about 30 freq's, all Shure except 4 Lectro IFB's to avoid). Since I will be handing this show off to an A-2, I decided to re-enter it all in WWB-6 on the laptop included with the rig. Well, even though I had used the most restrictive IAS settings, WB didn't agree with about 1/3 of the frequencies I'd selected...so I did a re-calc in WB-6. Once it was happy, I punched those numbers back into IAS, and was quite surprised to have some of them be called out as 3rds...and so on, back-and-forth. It's working, RF wise, but I find this interesting. What I think is happening is that the results vary depending on where the calculations start, ie, in what order the frequencies are being calculated against each other.

[Pete Erskine]

Hi Pete,
I've been experimenting with this and one thing I'm finding pretty consistently is that it's very difficult to get the two programs to agree on even basic intermod calculations. In this instance, I did the initial coord in IAS (nothing too challenging, about 30 freq's, all Shure except 4 Lectro IFB's to avoid). Since I will be handing this show off to an A-2, I decided to re-enter it all in WWB-6 on the laptop included with the rig. Well, even though I had used the most restrictive IAS settings, WB didn't agree with about 1/3 of the frequencies I'd selected...so I did a re-calc in WB-6. Once it was happy, I punched those numbers back into IAS, and was quite surprised to have some of them be called out as 3rds...and so on, back-and-forth. It's working, RF wise, but I find this interesting. What I think is happening is that the results vary depending on where the calculations start, ie, in what order the frequencies are being calculated against each other.

IM calculations are like the lotto.  First a random number in the range is picked, then each additional freq is located working away from the first.  Every time you do a recalculate a random number starts the process.  So not only is it gambling but the actual calculation methods aren't exactly the same either.  Seems like the numbers chosen correctly by one program should test OK in another.  for this inconsistency I blame the calculation methods.

[ProSoundWeb Community]