Exciter shopping

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radiowave911
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Exciter shopping

Post by radiowave911 » Wed Jul 17, 2019 4:51 pm

Our NCE is shopping for an exciter to use as our backup. We have a QEI Quantum FM solid-state transmitter that was recently upgraded when we did a power increase. The exciter recently went out on us, and we pressed into service our very old LPB exciter, which lasted a day (we knew at some point it was going to go, it wasn't a matter of if - it was a matter of when). We now have a loaner QEI exciter in service as of about an hour ago. We are looking for a new exciter to be used as our backup. Looking for something that will accept a composite input, and have up to about a 50 watt output. It does not have to be frequency agile, or have a lot of bells and whistles. We do not have a specific price point we are trying to stay under - but being a high school, we would like to keep costs down, but have decent reliability.

Suggestions?
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TPT
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Re: Exciter shopping

Post by TPT » Wed Jul 17, 2019 5:23 pm

Look for a used Continental 802B or BE FX-50 (both available new, but pricey).New: Armstrong or Bext, both around 30 watts. Another option Ecreso 100 watt exciter. Avoid BW broadcast.

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Re: Exciter shopping

Post by DaveSt » Wed Jul 17, 2019 11:34 pm

Personally, I am not a fan of the FX-50. You could add the GatesAir Flexiva Compact which has a 50W version to your list. Not cheap, but very good. You might be lucky and find something used.

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Re: Exciter shopping

Post by TPT » Thu Jul 18, 2019 6:29 am

The FX-50 is forgiving to a bad match--if this would be used to drive the QEI. Have one driving the final on an old Harris 3.5K--the solid state IPA died, the FX 50 delivers just enough to get the required 3 kw TPO.

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Re: Exciter shopping

Post by RodeoJack » Thu Jul 18, 2019 10:01 am

TPT wrote:
Wed Jul 17, 2019 5:23 pm
... Avoid BW broadcast.
Just out of curiosity, why do you feel this way?

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Re: Exciter shopping

Post by radio_guru » Thu Jul 18, 2019 10:05 am

The Harris THE-1 would also fit the bill. Add a LPF and it's good to go for being a fully qualified transmitter. And it sounds pretty good after a recapping. But not as good as a FX50.

Keep in mind, from a FCC standpoint, exciters are not type certified transmitters. They don't have harmonic or out of band emission filters. I recall reading over the years a number of Class D stations using donated exciters for their TX's and eventually cited for spurious emissions. OOOPS...

Exciters as a general rule of thumb don't need to be filtered much. They drive downstream amplifiers which are filtered as a matter of course. So when repurposing an old exciter to drive an antenna, put a LPF on it and then proof the thing to be sure the station is not taking out something up spectrum.

Same thing for LPFM's, which has it's own set of rules on TX's.

RG

TPT
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Re: Exciter shopping

Post by TPT » Thu Jul 18, 2019 10:31 am

The Continental 802A/B usually have an external (to the PA amp) filter. The more modern exciter/transmitters also have harmonic filtering.

Have two tenants on my one tower that tried using BW products for translators. One had to send their 300 watt back twice to get a working unit. The other had a bad spur, replaced with another unit. Can't say I am impressed.

Another tenant has the Flexiva transmitter driving a translator on 103.5--with a class A (albeit operating at 750 watts) antenna only about 20 feet above the translator antenna. No reflected, no spurs I've noticed. This is a kilowatt transmitter, the exciter in the Flexiva line that I've seen at another installation looks similar in construction. As suggested, expensive, but probably worth the price.

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Re: Exciter shopping

Post by ChuckG » Thu Jul 18, 2019 10:56 pm

Is this driving an amplifier, or direct to antenna?

I have several stations with the RVR/Armstrong/Bext exciters, from 30W up to 100W...they've been solid as a rock.
Usually a couple on Ebay under 1K. That's probably the least expensive option that's still decent.
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Re: Exciter shopping

Post by kkiddkkidd » Fri Jul 19, 2019 5:52 am

ChuckG wrote:
Thu Jul 18, 2019 10:56 pm
Is this driving an amplifier, or direct to antenna?

I have several stations with the RVR/Armstrong/Bext exciters, from 30W up to 100W...they've been solid as a rock.
Usually a couple on Ebay under 1K. That's probably the least expensive option that's still decent.
I have a few actual RVR's scattered around and they seem to work well. I understand that they have greatly improved their US tech service but it was maddening early on. The importers and US tech support of the Italian equipment was thru a Miami located, south American distributor. The techs spoke neither English nor Italian. And their translators just barely spoke English. I doubt that their Italian was much better.

One of my clients has a 2200w RVR that had infant problems and I spent 15 minutes just trying to get them to understand my email address. Troubleshooting was impossible. It was returned for repair and was repaired and back in just a few days and is still running fine several years later.
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Re: Exciter shopping

Post by TPT » Fri Jul 19, 2019 6:04 am

Many of the Bext and Armstrong products are re-branded RVR equipment. Some of the older products (both exciters and STL transmitters--essentially the same design--had synthesizer problems. Also, you have to watch the fans, especially in dirty environments. If the fan dies, the power supplies cook. I would usually replace the fan with better quality EBM-Papbst units.

Newer models were wired with a current sense leg off the fan. If the fan stopped, the power supply shut down. Got fooled by this & thought the power supply failed--then I jeeped in a tiny CPU fan and up it came. Good feature--as long as you know it is there.

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