Problems with Williams Sound PPA T27 Transmitter

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retiredtech
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Problems with Williams Sound PPA T27 Transmitter

Postby retiredtech » Mon Jul 01, 2019 3:37 pm

We have had the Williams Sound model PPA T17 wireless listening device for over 15 years and recently received the newer T27 model. At our recent stake conference I received numerous complaints that the signal was breaking up, especially at a distance of around 120 feet. We never had any issue with the previous older T17 transmitter.
In order to isolate this problem I set an uncalibrated RF field strength meter at 50 feet from both the T17 and T27 transmitters. I then preset the no signal value at the field strength meter at a value of 385. I then activated the T27 transmitter. The FS meter moved to a value of 400. I then disconnected the T27 and activated the old T17 transmitter. The value at the FS meter moved up to 560. This indicates the power out of the T27 is significantly less than that of the older T17. Both used the default "rubber ducky" antennas. Before I ask for a replacement of the T27 are any of you having a similar issue?

Richard True, STS
Taylorsville Stake

russellhltn
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby russellhltn » Mon Jul 01, 2019 3:58 pm

You might try swapping the antenna. The new one may have a broken connection inside rendering it a poor performer.
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retiredtech
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby retiredtech » Tue Jul 02, 2019 10:45 am

First, there is nothing wrong with the antenna. Both check out ok.
I decided to move to another building in the stake and obtain another T27 transmitter for comparison.......

Set up another test with equipment and RF Field Strength meter at 20' apart. Set the FS reading at 266 with no RF from any of the 3 units. I then tested the frequency of each unit. The T17 transmitter was at 72.9000 Mhz. The new T27 was 72.9002 Mhz. The spare T27 was 72.8993. Results of the test with each unit turned on separately for 3 minutes to stabilize are:

Original T17: FS at 428 When antenna was changed from 6 3/8" unit to the 9 1/4" of the newer T27 the FS was now 448
New T27: FS at 361
Spare T27: FS at 361

So there is no difference between the new T27 units. However, there is still an increase in RF field strength of the older T17 unit and especially if I use the newer longer rubber ducky antenna. So the decision is: I will use the older T17 transmitter with the newer longer antenna for the next stake conference. As a standby I will have a 1/2 wave vertical antenna cut for 73 Mhz to give me more gain out across the cultural hall and chapel. So keep your old T17 units if you have one as they seem to have more power output.

Richard True STS

russellhltn
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby russellhltn » Tue Jul 02, 2019 12:30 pm

RF Field Strength:
T17: 8000 µV/m at 30 m Max., 20 mW typical
T27: Does not exceed 80mV/m @ 3m

*Effective July 11, 2016, the FCC has mandated tighter emissions limits on auditory assistance transmitters (72-76 MHz) manufactured or imported after this date to help avoid interference with and/or degradation of other airborne signals (All products manufactured prior to July 11, 2016, are compliant). Williams Sound FM transmitters – PPA T46, PPA T27 and PPA T45 (all models) – all have received a Grant of Certification from the FCC and are fully compliant/approved under this new mandate.

A bit of a applies to oranges comparison there (30m vs. 3m), but I suspect that's the underlying issue with what you're experiencing. I did a quick search, but didn't find the FCC regulation to figure out what the change was.
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retiredtech
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby retiredtech » Tue Jul 02, 2019 2:18 pm

I understand the specs on the transmitters and the tighter limits specified by the FCC. I assume these specs, 80mV/m @3m, would apply to the output design setting of the RF amplifier in the transmitter. So if I put a higher gain antenna on the transmitter and increase the ERP would I still be in specs set by the FCC?

Richard True STS

russellhltn
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby russellhltn » Tue Jul 02, 2019 2:53 pm

I doubt it. I notice the specs are stated as a field strength measurement rather than output power. I know many part 15 devices can't be modified and still be "legal".

However, you could place the device at a higher elevation to get above the "ground clutter" and get a better line-of-sight to all the users.
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retiredtech
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby retiredtech » Tue Jul 02, 2019 4:51 pm

OK, here is the answer. Go to the williams sound web site and look at their antennas for the T27. A coaxial dipole antenna at 80" should give significant gain to the T27 transmitter. Here is their url: https://www.williamssound.com/accessories.

Richard True STS

russellhltn
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Re: Problems with Williams Sound PPA T27 Transmitter

Postby russellhltn » Tue Jul 02, 2019 5:14 pm

And if you don't want to go with something wall mount, the 39" telescoping antenna should work much better. (Although, there's a higher likelihood of getting broken.) There's a reason those flexible style antennas are called "dummy loads" by some.
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