Very low power recommendation

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Re: Very low power recommendation

Post by kcbooboo »

Bird (part of TxRx) and Narda make coaxial attenuators in various power ratings. A 6-10dB attenuator rated for a few hundred watts will have no problem reducing a 50-300w transmitter down to 10w TPO. Probably will take up less room than 100ft of coax. I use a 30dB 50w attenuator with two-way radios as it reduces watts to milliwatts, making it very convenient for test equipment that can't deal with more than a watt of input signal.

I've never had google ignore "-ebay", however have you ever noticed that at the top of the results page they always tell you "About xx,yyy,zzz results found" yet at the bottom there are only two more pages of results? I think they just have a random number generator producing that top number because it's never right and always in the millions. And when you DO go to the 2nd or 3rd page, the results count reduces to something like 80. Also, it seems that google only gives you what you asked for in the first 10 results; anything after that is just whatever they can use to fill the page and show you how good they are at satisfying searches. Also, since google searches are a revenue-based service, in order to earn that revenue they have to include completely unrelated results in every search. That could be one reason why ebay results show up even though you've requested they not be.

Bob M.

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Re: Very low power recommendation

Post by TPT »

I have a Bird 25 watt attenuator. Use it with a BE STX kilowatt--the built in exciter is not reliable, so I run about 5 watts through the attenuator from an Armstrong exciter to get the 250 milliwatts needed to drive the transmitter. Luckily BE has BNC's in and out to allow this.

Back to the original question--apparently 6 watts is needed for the ten watts ERP for this Class D station. I renew my suggestion for the Armstrong since mine is quite comfortable at that low level. The Bext branded RVR models would also work well. The Armstrong was my primary exciter for a number of years on a Harris FM10K, before that transmitter was retired in favor of a Nautel 10.

Weakness on the Armstrongs and the RVR's are the fans. The FMX-30B (and the very similar Armstrong STL transmitters)--the older models, would overheat and fail when the fan failed. The newer generation Amstrong STL transmitters have a sensing circuit that shuts down the transmitter if the fan stops drawing current. Would not be surprised if the same change has been made with the FMX-30B.

Other than that, this would be a good choice for the 10 watt station.

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Bill DeFelice
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Re: Very low power recommendation

Post by Bill DeFelice »

Ray wrote:
Mon Mar 04, 2019 5:52 pm
There was a BW TX-5 V2 5 watt transmitter on ebay last week. I've used a BW TX-50 as a standby. It has a simple 4 band processor included,
The only problem is the display seems to go bad with time. Has a good remote interface.
I had a couple of TX-5 original versions and that was the problem. I still have one never used except for testing so, I hope, the display is still good.
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Re: Very low power recommendation

Post by RodeoJack »

I second the BW equipment. They've gone to a new display, so that issue has been dealt with.

For the money, I'm not sure you can beat the feature set in the V3 versions. As noted, they are fully web-enabled, are able to email out RF and modulation-related alarms (assuming power is available), and include a reasonable multi-band processor that, while not on par with an Omnia One, is much better than the wideband limiters in the early Crowns. If you're using them as translators, FSK ID keying is included.

The equipment is cleared by the FCC. You might recall that, a few years ago, the commission tried to nail SCMS for selling non-certified transmitters. SCMS successfully defended the alleged violation and the FCC backed off.

With few exceptions, I've had very little trouble with these rigs. I have roughly 20 of them in translator and LP service, and use them at my 3-screen drive-in theatre. Other than the early displays, I've found their higher-powered versions don't much like intermod. They'll pop a PA deck if forced to deal with large amounts of RF back down the pipe. For that matter though, those cases would have been moot if the installation had included a look with a spec-an.

SCMS and Progressive audio will do some service on these, if you aren't so-inclined. Otherwise, you have to send them to the UK for major fixing. That alone suggests you have something on the shelf to back them up. BW's service turnaround is pretty fast though, and I've found their pricing to be quite reasonable.

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Re: Very low power recommendation

Post by ChuckG »

The problem I had with BW, and I believe I posted it here a while back, was absolute indifference when I needed replacement parts.

Had two 300W units pop their Meanwell power supplies. These units were barely 3 years old.
BW no longer had stock and told my to "buy new transmitters".
I was able to find the supplies directly from Meanwell....BW couldn't be bothered to re-stock, or even pass along the manufacturer info. They just saw it as a sales opportunity.
Not impressed, not at any price.
Chuck Gennaro
Central Wisconsin

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Re: Very low power recommendation

Post by W2XJ »

I would find a part 73 accepted transmitter and use an attenuator. One way or another there will be heat dissipated. The attenuator will also provide better isolation from the antenna.

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Re: Very low power recommendation

Post by W2XJ »

I kind of agree but an attenuator is cleaner and more precise.


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Re: Very low power recommendation

Post by radio_guru »

I agree, get an FX 50, a 6dB 50W-100W attenuator and set it for 25W for 6.25W to the coax. Then put in a low pass filter, proof it, set power against a cal'd Bird 43 to the coax, and you're set.

You could do the same with just about any modern day TX...even a DIGIT. But you need a filter which drops off starting at 110Mhz. The out of band phase noise on that thing is horrendous.

The key is to meet FCC type acceptance...which requires nothing more than a proof of performance report showing emission purity and power.


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