Recommend paddle antenna for SRas

[Christian Spaeth]

I am looking to buy a paddle antenna to get better range out of my Lectros in certain situations where I can't be close enough to the talent. I would like to get one antenna which I would connect to one SMA connector on each receiver. I know another mixer who uses a skeleton Lectro sharkfin like this and is very happy with it. I've read all the threads I found about shark fin/paddle antennas but I still don't feel like I know much about the subject (passive or active antenna? splitter? amp? what?).

Any hints or resources would be helpful. Basically I'm looking for cheaper alternatives to the Lectro active ALP antennas. Oh, and being in Germany, Euro resources for not-so-expensive antennas are very welcome!

[JT Mueller]

Have you checked out this article written by Mr. Trew?

http://www.trewaudio.com/audioflow/2012/02/16/3759/

[studiomprd]

The recommendations are the same as for any other receivers in the same frequency bands. The paddle antenna (aka sharkfin) is a Log Periodic Dipole Array (LPDA) and information is plentiful.

Of course, European wireless manufacturers manufacture them

Lots of good information available here (many previous antenna discussions) on jwsoundgroup, and <cap> web sites including FAQ's

Edited April 3, 2012 by studiomprd

[Raycom Ltd UK]

Log Periodic Dipole Antenna (LPDA)

'Array' actually, not 'Antenna', otherwise a good effort. B+

[studiomprd]

" B+ "

Oy! :'(

[David Waelder]

I made some antenna tests for the 695 Quarterly. The articles have the results of walk tests with sharkfins, 1/4-wave whips, dipoles, helicals, etc.

You can download copies of the Quarterly here:

http://695quarterly.com/previous-issues/

The pertinent issues would be:

Spring 2010, Fall 2010 and Winter 2011

The Summer 2011 issue has tests of transmitting antennas. (for Comteks, etc.)

And, while I'm promoting the Quarterly, the current issue, with part II of the interview with Courtney Goodin, is available here

http://695quarterly.com/

David

[pindrop]

I made some antenna tests for the 695 Quarterly. The articles have the results of walk tests with sharkfins, 1/4-wave whips, dipoles, helicals, etc.

You can download copies of the Quarterly here:

http://695quarterly....revious-issues/

The pertinent issues would be:

Spring 2010, Fall 2010 and Winter 2011

The Summer 2011 issue has tests of transmitting antennas. (for Comteks, etc.)

And, while I'm promoting the Quarterly, the current issue, with part II of the interview with Courtney Goodin, is available here

http://695quarterly.com/

David

Very interesting thanks.

[Raycom Ltd UK]

To answer the OP:

If you are using an SRA RX with whip antennas on top, the whip antenna is on an imperfect ground-plane (the RX body) and with other wiring around it will cause a net loss when compared to a dipole in free space, let's assume maybe 2dB, maybe considerably more if buried in a bag.

Now let's take a 'sharkfin' antenna, say the Lectro ALP500, this has a stated gain of 4dBd (4dB relative to a dipole), you already have a 6dB (4x power) advantage over the case above, but you need to factor in other losses, feeder loss, assuming RG58 (typical cable for this application) is about 0.5dB/m at 700MHz, also, if you are feeding two RX as you say from one antenna (one half of the diversity pair) then you will need a splitter, a two way splitter has a theoretical loss of 3dB (0.5 x power), but in the real world has a loss of 3.5 to 4dB. So see below for gain calc:

Antenna gain: 4dB

Feeder loss assuming 3.5m cable (including 0.5m jumper from splitter to RX): -2dB

Splitter loss: -3.5dB

Net loss: 1.5dB

You can see from the above that you are losing 1.5dB relative to a dipole assuming no other losses, but you are 0.5dB better than the assumed first case of 2dB loss, PLUS you would probably have a dB or more extra gain from having the antennas up higher on a pole (assuming mounted to a cart), so you will see a good benefit.

Now, looking at active systems, you could have an amplified antenna such as the Lectro ALP650, it's worth noting that directly at the antenna, before any feeder or other losses is the ideal place for the gain (rather than an inline amp) you can jumper this for 5dB or 8 dB gain which would offset the losses in the feeder and the splitter and get you back to the 4dB antenna gain position (net 6dB relative to first case of whip antennas on RX).

A couple of important points relating to active (amplified systems):

1: NEVER use more gain than you need to make up for the feeder and other losses between the antenna output and RX input terminals. Using more gain will not improve range, it will actually work against the RX which will be designed to have a specific internal gain structure to provide the best possible sensitivity and intermodulation performance, overloading the RX front end will compromise the intermodulation performance of the RX and reduce the amount of usable channels and make it more susceptible to overload (blocking) by other local RF signals.

2: The weakest link effect - Always use a good quality amplifier in active systems or the performance of the whole system will suffer. As an RF designer one of my pet hates is having designed a receiver that is good as you can only to have someone stick a cheap amplifier in front of it thus rendering a $2000 RX no better than a $10 FM radio! Bottom line is that the RF performance of the whole system is only as good as the worst link in the chain.

Also remember that active antennas tend to be wideband, so, unlike the filtered input of the RX are more susceptible to out of band signals (for example a cellphone going off in your pocket next to the antenna whilst recording an end of lens shot with a weak wireless mic signal).

Personally I would always use a passive system where I can unless I really need the extra range as the design performance of the RX is preserved and uncertainties are minimised (though once you go above 2 way splitters the splitter losses start racking up rendering active systems more attractive).

One last point about choice of antenna with gain, there are two main choices, 'Yagi' or 'Log Periodic' (ALP500 is the latter), Yagis tend to have more gain, but are more directional and have lots of 'ripple' (nulls, sometimes very deep) in their gain pattern so are best suited to fixed point to point links, log periodics have a good front to back ratio and a very smooth pattern so if talent is moving around in front of the antenna they are much less likely to enter a deep null and drop out.

I hope this is helpful.

[soundslikejustin]

I hope this is helpful.

Extraordinarily.

[Christian Spaeth]

I hope this is helpful.

Thank you very much indeed, great information pressed into one post. Thank you JT, too, I haven't read the Trew article but will - their site is offline at the moment.

Focussing on passive LPDA antennas, does anybody have specific recommendations? Would it make sense at all to use just one or is a pair necessary to get actual improvement over not using them?

[Raycom Ltd UK]

Thank you very much indeed, great information pressed into one post. Thank you JT, too, I haven't read the Trew article but will - their site is offline at the moment.

Focussing on passive LPDA antennas, does anybody have specific recommendations? Would it make sense at all to use just one or is a pair necessary to get actual improvement over not using them?

You need a pair for diversity reception, if you use just one antenna you will suffer from much worse dropout due to multipath reflections that would negate any benefit of any extra gain.

If your question was whether you could use just one LPDA with just a dipole, this is not advised as the diversity circuitry in receivers normally works better when both antenna inputs have a roughly similar nominal input level, you would also get worse dropouts as you were near the range limit.

[studiomprd]

" passive LPDA antennas, does anybody have specific recommendations? "

I'm guessing you mean make/model ?? electronically, as receptors of RF energy, they are pretty much similar, but there are differences in materials, construction, mounting options, etc. as well as any perceived value of brand names.

The "skeleton" or rod models are better in windy situations.

[taylormadeaudio]

Hey Christian,

I'd just reiterate what's been said here earlier, that active antennas can bite you in the ass if they're not used properly -- there is a huge misconception regarding the benefits of using active antennas (which I'm sure you've already found if you've read other threads on the subject here on JWSound)... if you do wind up going with powered antennas, just do the math -- make sure you're as close to unity gain as possible. The "amplification" is really only beneficial in compensating for signal loss do to long antenna cable runs and/or passive splitting. There are formulas and other information one can use to properly calculate loss based on # of splits, cable type, length, etc.

~tt

[LarryF]

If you can, use passive antennas. The amplified antennas are for making up losses due to very long cable runs and downstream splitters. The amplified antenna does have everything in one package (antenna and amplifier) and is very useful in a fixed installation where you will always have a fixed cable and splitter loss. A passive antenna plus an equivalent in line amplifier is more flexible for work where the antenna arrangement changes from job to job. Use the amplifier when you must and leave it packed away when the cable runs are short.

Best,

Larry F

Lectro

[Jan McL]

Your posts made my day, Ray/Larry.

Thanks!

[Solid Goldberger]

Seriously great thread. This should be pinned.

E.

[David Sanderson]

If your looking for specific models I have been VEARY happy with the professional wireless antenas. There LPDA is very nice and competitively priced it can be found at:

I also love there helical antenna, if you are looking for a passive antena for transmitters at a long distance it really can not be beat. It can be found here: http://www.professio...helical/#s8089l

[Bob]

So what if on my Lectro i use one passive shark fin for one antenna and one whip for the other?

Or one passive shark fin and one dipole?

Do the antennas always have to match?

[LarryF]

No. However, the smart squelch algorithm does assume you have equal antennas on average. Two LPDA's are better than one LPDA + one dipole. One LPDA + one dipole are better than two dipoles. Two dipoles are better than one LPDA. One LPDA is better than one dipole. One dipole is better than a coat hanger. One coat hanger is better than nothing.

A whip and a dipole in the same position are roughly equivalent so you can substitute the word whip for dipole above. The dipole has the advantage of not needing a ground plane (usually the receiver) very close. Generally the dipole can be placed in a better position giving them an undeserved reputation for having more gain. But who cares about theory, if they usually work better.

Best Regards,

Larry Fisher

Lectrosonics

So what if on my Lectro i use one passive shark fin for one antenna and one whip for the other?

Or one passive shark fin and one dipole?

Do the antennas always have to match?

[taylormadeaudio]

Thanks Larry for such an informative and humorous post -- almost made me shoot coffee out my nose.

~tt

[old school]

I think you should not read with any liquid in your mouth Tom. You keep doing spit takes. That can't be good for the gear.;~)

CrewC

[Raycom Ltd UK]

No. However, the smart squelch algorithm does assume you have equal antennas on average. Two LPDA's are better than one LPDA + one dipole. One LPDA + one dipole are better than two dipoles. Two dipoles are better than one LPDA. One LPDA is better than one dipole. One dipole is better than a coat hanger. One coat hanger is better than nothing.

A whip and a dipole in the same position are roughly equivalent so you can substitute the word whip for dipole above. The dipole has the advantage of not needing a ground plane (usually the receiver) very close. Generally the dipole can be placed in a better position giving them an undeserved reputation for having more gain. But who cares about theory, if they usually work better.

Best Regards,

Larry Fisher

Lectrosonics

You forgot to mention a piece of wet string in an earthed dustbin!

[LarryF]

Yeah, but everybody has tried that.

LEF

You forgot to mention a piece of wet string in an earthed dustbin!

[Bob]

A whip and a dipole in the same position are roughly equivalent so you can substitute the word whip for dipole above. The dipole has the advantage of not needing a ground plane (usually the receiver) very close. Generally the dipole can be placed in a better position giving them an undeserved reputation for having more gain.

So I hope this doesn't sound like a stupid question but other than being able to move the antenna away from the receiver is there any other advantage in using a dipole vs a whip?

[Raycom Ltd UK]

So I hope this doesn't sound like a stupid question but other than being able to move the antenna away from the receiver is there any other advantage in using a dipole vs a whip?

A dipole has its own ground plane that is tuned rather than a random piece of metal (normally the RX body) and generally is located in a better position for line of sight to the talent (unless you plug a dipole into your RX then drop it in your bag which would just be, err, silly!). Also a whip connected directly to your RX is more likely to pick up spurious signals and their harmonics induced in the RX case by the clocks and oscillators within. So it is always a better choice than a whip on the RX unless you are really close to the talent in which case you probably won't notice and, as Larry says, a coat hanger will probably do the job