Radio mic antenna

[dco_uk]

So, im looking to add some further sets of anntena to our hire stock. We have Sennheiser ew500 g3 systems, with asa1 spliiters, racked on sets of 4.

 

We have some Sennheiser a2003 antenna to go with them. Now, as we all know, the a2003 has a silly price tag.

 

Does anybody have any experience with these? http://www.adamhall.com/index.php?set_language=en&cccpage=project_27&set_product_extid=LDWS100DA&searchterm=antenna

 

Would they be compatable? with our systems?

 

Thanks in advance

 

 

 

 

[ramdram]

An rf amp is an rf amp so yes in the sense of amplifying rf any rf amp covering the freqs you want would work...assuming the connectors were physically compatible or you cobbled on the correct connector. You could even use a TV rf amp designed for UHF bands.

 

However, what you might find is that the cheaper rf amps were not as "quiet" as the allegedly superior Sennheiser (and similar kit), ie the el cheapo kit introduced noise onto the audio signal.

 

Plus you might find that you got all sorts of spurious signals or intermod stuff. Ergo it is difficult to quantify or qualify an rf amp for your situation which would provide as clean reception as the specific aerials/amps designed and manufactured by the makers of your rms.

 

This is not to say the rf amp you mentioned won't work and it might be a case of buying/getting one on appro' one and doing listening tests.

[cedd]

Having recently done some response plots from a pair of cheaper (though not cheap!) log periodic paddles it's worth mentioning that they're not all created equal! Whilst they state a particular range and gain, don't assume it's anything like a flat top!

 

Excuse the fact it's only a phone picture - my spectrum analyser is actually just an additional function of a comms test set, so it's not that great.

 

To explain, I'm using a tracking generator (a source that sweeps frequency in sync with the spectrum analyser - bit like putting white noise into a sound system) fed into one of my two paddles. I'm then receiving at reasonably close range with my other paddle. This may sound messy, but it's the only easy way to do this. It's certainly not under lab conditions. It's worth mentioning though that as I'm using two aerials there is gain on both transmit and receive, which will be seen in this plot, so this is not the response of one aerial, it's effectively double the gain (assuming both aerials are identical).

 

http://i513.photobucket.com/albums/t335/ceddison/3071F1E7-22EF-4617-B0F6-B9B82DEC98C3-16588-00001D87B975A8B6.jpg

 

As I've managed to chop it off the screen, I can tell you that the RF scale is 10dB/div. This plot is 200MHz up to just over 1GHz (maximum for the test set). The stated bandwidth of the aerial is 450-900MHz.

 

As can be seen from the plot, there is a general downward trend below 450MHz, but it's worth noting that a lot of the dips up in the stated usable range of the aerial drop way below the out of band level - yet I guess many of us would never dream of using such an aerial outside of its' stated range, but would quite happily use it for anything within that range and never think twice about how much gain it's giving us.

 

 

The results above are very un-scientific, on a less-than-brilliant analyser, but it's enough to prove my point - not all LP's are created equal, nor can their response be considered anything like flat. I've never seen the response from a Sennheiser, but would guess that their R&D guys have made sure it behaves well on the likely frequencies it'll be used on.

 

Also to add, is a wideband antenna system really what you want? Look at all that gain you're putting on all the rubbish you don't want. I bought these two LP's so I could share them between my channel 70 and 38 racks, often both in use at the same time off of one pair of aerials. I'm discovering that their performance is less than ideal and I reckon it's because I'm allowing a lot of other noise into the antenna system and never filtering it until it gets to the receiver.

I'm about to start a redesign and am hoping to have a far more selective, narrowband system by the end of it.

[paulears]

That's quite interesting - especially some of those very deep an narrow notches.

 

I can speak from experience about the hazards of wideband amps - one that I used for a number of years failed miserably when a local mast appeared with a continuous output on a telemetry transmitter - the performance degraded significantly.

 

Cedd, is our RF expert, and I tend to always pay attention to his posts on the subject because his advice and comments are always sound. Many people treat paddles as directional aerial systems and just take them outside the performance area and point them inwards, when their polar diagram indicates some very prominent lobes. A dipole, in closer could easily be more effective than a LP at a distance. I'm also a firm believer of the train of thought that the reall problem to radio mics is not signal strength caused by distance, but dead spots that are in the same place for both aerials - which is why we so often go from full signal strength to no signal, rather than a noisy one!

[mackerr]

An rf amp is an rf amp so yes in the sense of amplifying rf any rf amp covering the freqs you want would work...assuming the connectors were physically compatible or you cobbled on the correct connector. You could even use a TV rf amp designed for UHF bands.

 

However, what you might find is that the cheaper rf amps were not as "quiet" as the allegedly superior Sennheiser (and similar kit), ie the el cheapo kit introduced noise onto the audio signal.

 

Plus you might find that you got all sorts of spurious signals or intermod stuff. Ergo it is difficult to quantify or qualify an rf amp for your situation which would provide as clean reception as the specific aerials/amps designed and manufactured by the makers of your rms.

 

This is not to say the rf amp you mentioned won't work and it might be a case of buying/getting one on appro' one and doing listening tests.

 

The question wasn't about RF amps, it was about LPDA (paddle) antennas. Whenever possible RF amps should be avoided as they are a point of non-linierity where intermod products can be generated. They should only be used to make up for losses in long cable runs.

 

Like any transducer, antennas have a frequency response. In Cedd's example only the really big dip in the middle in inside the area of interest, and we don't know what caused it. It would be interesting to see a comparison between a LPDA, a 1/4 wave whip, and a helical, all receiving from a whip transmitter antenna. Preferably outdoors away from large metal objects.

 

The antenna design used in paddles is pretty simple. I would not expect there to be significant differences between paddles from different manufacturers other than possible gain differences based on antenna size and number of elements.

 

There are some new designs that are interesting. They are flat panels based on fractal antenna design like that used in cell phones. They are both vertically and horizontally polarized (although some call them circular polarized they are not), and being flat, present their narrow axis to the audience when used at the side of the stage.

 

http://www.kaltmancreationsllc.com/rf-test-equipment-html/invisiblewaves-html/cpa-antenna-html/

 

http://clairglobal.com/fractal-cf1090/

 

Lectrosonics has a nifty little tunable dipole, the SNA600. Scroll to the bottom of the page:

 

http://www.lectrosonics.com/Antennas/

 

Mac

[ramdram]

The device cited by the OP is an rf amp...with 13dB gain. I read the question as, "will this rf amp, with aerial, be as good as (a) Sennheiser?"

 

Unless the OP does an A-B test then how would the difference (if any?) be compared with any degree of accuracy? Cedd mentioned there are LPs and LPs and he is not wrong there. In my view LPs are always second best because they are neither one thing or another; we only had one on our station, on a rotator, for measuring local VHF stations..and those frequencies are, relatively speaking, quite close together. Obviously it wasn't much good for anything else.

 

(Personally I prefer the rxs to have their own aerials, and not being fed from a single aerial via an rf buffer amp (or with a few dBs of gain). I presume the OP is, because of his own particular venue(s), unable to get enough gain from the "back of the box" rx aerials and needs some amplication.

 

We could have done the BR thing and veered slightly off topic and suggested the OP forget all about rf amp/aerial kit and sited his rxs much closer to the stage or space, which is probably the best option for most venues...but not in this situation perhaps.

 

The kit you linked to (thanks btw, always useful to keep abreast of stuff) appears to be mainly rx/tx stuff with a 50ohm connectors...and more expensive than the kit the OP linked to.)

[mackerr]

The device cited by the OP is an rf amp...with 13dB gain. I read the question as, "will this rf amp, with aerial, be as good as (a) Sennheiser?"

 

When I click on that link it takes me to a "Paddle" antenna with 13dB of gain wrt an ideal zero gain whip. There is no mention in the sparse information on the page of it having an active RF amp built in, although this is not uncommon.

 

The OP also asks how they compare to a Sennheiser A-2003 antenna, which is a passive directional antenna.

 

As with any RF mic setup, the receivers should be situated as close to the transmitters as possible, to shorten antenna cable runs whether individual antennas, or single antennas with distribution are used. Signal loss through the air follows inverse square law and getting your antennas close should be the first choice to minimize loss. Once you are close, antenna choice, with an awareness of coverage patterns, nulls, and lobes, should be next. As always, low loss antenna cable should be used. If proper location, antenna, and cable does not get you good reception, an RF amp is unlikely to be any better. An amp should only be used to make up cable losses from very long antenna cables.

 

Mac

[ramdram]

You could be right Mac, I possibly...probably, inferred wrongly that with 13dB of gain and the £££ it was powered. I would have said a LP gain would be around half that stated and that on a good day. My bad as they say.

 

Edit to add the Senny LP claims 3dB of gain so if the other LP is NOT powered and claims 13dB of gain then I am even more intrigued/puzzled, ** laughs out loud **.