Trantec aerial length

[sunray]

I had all of my Trantec S4 beltpacks (4xCH70, 4XCH38) out on hire a little while back, customer wanted these to match up with other kit, and checked them over on return.

 

I needed 2 during the week and randomly took 4 with me (3xCH70, 1xCH38) I found the range of the CH70 sets struggled to cover the 20m indoors.

 

I had the RX's on top of a L/S at 7ft (very normal for me) and the speakers were standing with packs in breast pockets facing L/S. CH38 body pack and CH70&38 HH's showed rock solid signals of 3 or 4 blobs and occasional aerial change. CH70 body packs kept dropping out, I tried all 4 frequencies and all 3 packs.

 

After the event I tested outdoors and found some similar results reaching 40-50m max, I know I've done better than this in the past but CH38 went to the end of the field. The strange question, all 8 aerials are the same length and a niggle in my head says they were different. Could anyone measure theirs for me please, I'm currently working on the thought the hirer did a bit of swappage and I now have all CH38 aerials.

Edited January 19, 2019 by sunray

[paulears]

A quarter wave for ch 38 is 11.6cm and ch 70 is 8.2cm, but that's from the PCB, not from the case grommet.

[sunray]

So Eventually I got to the botom of this and the hirer did manage to get them all mixed up, in fact he seemed very keen to assist.

 

What has now dawned on me is I am short of CH38 receiver aerials, due to buying second hand kit.

 

Does anyone have any spare? These are the Rubber dipoles for Trantec s4.16 CH38 with BNC plugs, ie: the standard aerials supplied with new kit.

 

I've now also posted this request in 'Wanted'

Edited March 21, 2019 by sunray

[graemeftv]

email sent to Roy

 

have loads of ant here for both transmitter and receivers

[Wolf124]

Paulears. What is the aerial length for ch65/66. The formula that I found elsewhere on here gives (300/frequency)/4 which gives an aerial length a little longer than those you give earlier. Is this just a 'ballpark' formula, if so, can you give the correct one please. I am making up some new aerials and want to make sure that I have it right!!! Thanks in advance. When you mention the length from the PCB, and not the case grommet, does that exclude the length of the screw section of the aerial?

[timsabre]

A quarter wave antenna is a quarter of the wavelength. The wavelength formula is V=f x w where V=300,000,000 (speed of light in m/s) , f is frequency in hz and w is wavelength in metres.

 

Your formula is right if you use frequency in MHz.

[paulears]

Channel 65 is just a bit longer - you need to be careful of the licensing situation and the interference. Probably OK if you're anywhere other than major cities. The actually length isn't remotely critical enough to need millimetre accuracy as some of the bands are quite wide. So bottom of 65 is 822MHz, and the top of 66 is 838 so 91mm to 89 is the length - Pick 90 and you're in the middle, but that's from the top of the antenna to the pub. So a few mm either way really doesn't matter.

[sandall]

Pub ???

 

(sorry, couldn't resist - feel free to remove)

 

 

Edited November 11, 2019 by sandall

[Wolf124]

Thanks all, just what I needed. Only thing remaining is the aerial measurement from where to where. Tip of the aerial (obviously) to tip of screw thread or shoulder where the screw threaded section ends? Not sure exactly where the pcb (pub!!) point is. Took one apart to have a look but still not sure. Edited November 11, 2019 by Wolf124

[timsabre]

All of the metal radiates, so it's measured from wherever the track starts on the pcb. Though as Paul says it is not all that critical

[cedd]

I length all of mine from the point the aerial leaves the body. The bodies on the Trantec mics are metal and grounded (well, to the battery -Ve anyway). My theory is therefore that until the point it leaves the body of the pack, the whole beltpack is essentially a coax. The threaded section extends in to the body some way hence why I make them longer. If you're using a plastic bodied beltpack then yes I'd take it from the pcb track or better still, just copy an original!

 

If you're making aerials for Trantec be very careful about where the aerial nips down on to. It's tempting (and easy) to make them nip on to the panel. If you look at the originals they extend in to the body of the pack and nip down on to the screw thread inside itself. If you nip it on to the body then overtightening can rip the pcb mounted socket off or at least loosen it.

 

 

 

[timsabre]

Yes should have said I was thinking of plastic bodied packs.

[Wolf124]

Thanks all for your help. Yes, I was aware of the dangers of using an oversize connector and ripping off the connector. As for copying an original, that was what started my enquiry as I have acquired many secondhand S5.3, S5.5 & S4.4 units which are wearing a motley selection of aerials of different lengths and types a wire from a rubber duck through to a piece of brown mains lead. I have collected all that I need to make new aerials (at about £2.00uk each) and now want to standardise with two/three lengths for channels 38, 65/6 & 70. It was just the overall length that was causing me concern. So now thanks to you all, I can make up some at 8.2cm, 9.0cm & 11.6cm from aerial tip to bottom of screw thread and be happy.

Paul - My PMSE licence only covers me from 830-832 on ch66 so 8.9cm should do me!! ,but who's to 1mm

Edited November 12, 2019 by Wolf124

[paulears]

I swap mine happily from that band to ch 70, and there's no issue with the length. I remember the Trance VHFs with helical antenna that got longer and longer with use as they got flexed and the turns opened up - some were amazingly longer than they should have been.

[cedd]

Remember as well that as the diameter of the antenna material gets thicker, the bandwidth of that antenna increases. Your pruning of the antennas and calculation of their length is assuming a wire with no real width. Certainly with mine (I use bicycle brake cable for added springiness) there's some decent thickness to the wire so the bandwidth is greater. We'll not get in to the velocity factors of the stainless steel I'm using versus copper or steel - I know they're not the same, but they work!