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Author Topic: Television abandoning VHF  (Read 338 times)

Scott Helmke

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Television abandoning VHF
« on: June 17, 2021, 09:46:07 am »

Something I've noticed in the FCC digest is a steady trickle of DTV stations moving from VHF to UHF.  Would be great if wireless mic manufacturers had some really good products for the VHF band - we have some ULXD-V50 but it's never been as reliable as the UHF ULXD.
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drew gandy

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Re: Television abandoning VHF
« Reply #1 on: June 17, 2021, 01:37:37 pm »

Something I've noticed in the FCC digest is a steady trickle of DTV stations moving from VHF to UHF.  Would be great if wireless mic manufacturers had some really good products for the VHF band - we have some ULXD-V50 but it's never been as reliable as the UHF ULXD.

Aha! So it's not just me.  :D
Do you guys use VHF band paddles (log periodic) antennas with those?

We picked up a ULXD-V50 dual channel kit several years ago and just use it with the supplied whips. It's mostly been solid but I have noticed a little bit of trouble a few times. VHF obviously has a much higher noise floor to contend with. I wonder if directional antenna might be even more important for VHF than for UHF.

If I understand correctly, it's not just noise floor, antenna length (wavelength considerations) and interference intrusion because of the longer propagation distance, but, VHF has a more limited "throughput" capability on account of the allowed channel width/modulation intensity. My brain is tiny and I probably have some terms mixed up. That said, it seems that VHF is pretty complicated for high quality audio. Hence the tendency/recommendation to use VHF for intercom and other similar uses where the outcome is more forgiving and save the high quality bands for the VIP mics. 
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Philip Roberts

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Re: Television abandoning VHF
« Reply #2 on: June 17, 2021, 01:50:13 pm »

... we have some ULXD-V50 but it's never been as reliable as the UHF ULXD.

Could you expand a bit on how V50 compares to the UHF ULXD's?

Thanks

Philip
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Daniel Levi

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Re: Television abandoning VHF
« Reply #3 on: June 17, 2021, 02:18:36 pm »

Of course one of the big issues with VHF is antenna length, esp. on the transmitter.
If you look at the older systems a lot of them had long external antenna's (30cm+ on some) and I'm guessing the handheld ones that didn't a a lot of compromises had to be made, esp. as most of the time the antenna would be covered by someone's hand, contrast that with UHF systems  where the smaller size of the antenna allows it to be put where it is less likely to be covered, or if an external antenna is used then it don't need to be anywhere near as long and so a lot less cumbersome.

Naturally if Band II/III was to be where wireless systems ended up then you would expect the main players to plough a lot of money into it, wireless righty or wrongly is now essential to a lot of situations/performers and they expect decent reliable wireless equipment and any manufacturer that could not provide it would lose market share very quickly. At least the two main players, Shure and Sennheiser, have VHF experience even if it was mainly back in the day. 

Though just be glad they are not bringing back Band I wireless systems, I've seen pictures of the Beyer and Sennheiser ones, the aerial seemed so long that you might just have used a wired mic!

OT but I am guessing some/all of the mics on this performance were Band I (~30-50Mhz), wouldn't like to be too agile with them less I got repeatedly whipped by the antenna!
https://www.youtube.com/watch?v=8Tm6iO-mQfw     
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Scott Helmke

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Re: Television abandoning VHF
« Reply #4 on: June 17, 2021, 02:37:11 pm »

Aha! So it's not just me.  :D
Do you guys use VHF band paddles (log periodic) antennas with those?

We picked up a ULXD-V50 dual channel kit several years ago and just use it with the supplied whips. It's mostly been solid but I have noticed a little bit of trouble a few times. VHF obviously has a much higher noise floor to contend with. I wonder if directional antenna might be even more important for VHF than for UHF.

We used the log periodic antennas sometimes, otherwise just the whips.  I would guess that we just run into noise floor problems more than anything else. In one case where I went around with a spectrum analyzer the problem turned out to be a home brew "star drop" made from cheap eBay LED strings.  There's only one TV station in Chicago in the 7-13 band, but it seems like most venues have a high noise floor in that band - networking, LED systems, whatever.  Nobody has bothered to fix VHF noise problems because everything was up in UHF.
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Henry Cohen

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Re: Television abandoning VHF
« Reply #5 on: June 17, 2021, 08:31:56 pm »

The reasons VHF DTV and ULXD don't work as well UHF are essentially the same. Longer wavelengths need more than just bigger antennas; they need larger Freznel zones and transmitter antenna reactive near fields. These factors affect wideband DTV signals to a much greater degree (as compared to 'narrowband' LMR and LPAS). And then there's the higher RF noise floor previously mentioned.
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Henry Cohen

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Re: Television abandoning VHF
« Reply #5 on: June 17, 2021, 08:31:56 pm »


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