FREQ CHANGE BE AM-1A IN THE FIELD

RGORJANCE · Post by **RGORJANCE** » Wed Jul 20, 2016 8:47 am

Has anyone in the "brain trust" done a frequency change on a BE AM-1A in the field?

Off the top of my head, I know you have to change the exciter, and I think that is done with dip switches.

The PA modules are broad band and we have swapped these from time to time with the 1kw and 2.5kw rigs of different frequencies. Only changes are a few dip switch settings on the modules for different xmttrs.

Is there anything in the output section-----like freq determining caps that need to change? (on board output, not the optional tuning unit)

Fossil

kcbooboo · Post by **kcbooboo** » Wed Jul 20, 2016 11:18 am

According to the output matching network manual, there's one cap that can have 7 different values depending on the frequency band, from 3900 to 1300 pF. I presume this is the same assembly they install in the transmitters, although it uses N connectors for input/output, and is probably limited in power.

I was under the impression that there are frequency-dependent assemblies on the PA modules too, as the schematic shows multiple coil assemblies. I'm looking at an AM-6A manual and it has a combiner circuit as well. I'd suggest getting the manual from BE's web site; that info must be there somewhere but the manual is quite hard to follow.

Bob M.

Follow-up: I downloaded the AM-1A manual. On PDF page 144 there are seven "Frequency Kits" parts lists with dozens of parts listed for each range. Throughout the manual it says "...not changeable in the field..." pertaining to lots of adjustments.

RGORJANCE · Post by **RGORJANCE** » Wed Jul 20, 2016 3:03 pm

Thanks for pointing me right at the answer I was looking for. The reason I was able to swap PA module is that the our two stations are right in the same band/range of frequency determined components for the output network and the PA modules. Got lucky!

Appreciate your assist.

Thanks,

Fossil

Deep Thought · Post by **Deep Thought** » Wed Jul 20, 2016 10:21 pm

Yeah I wouldn't try it...a misstep will cause the PA to burn up. They are rather adamant that this not be done in the field.

An AM-1A is small enough to ship back to Quincy for them to do it. The cost to retune a 2.5E awhile back was around $4K so I would imagine a 1 would be about half that.

kkiddkkidd · Post by **kkiddkkidd** » Fri Jul 22, 2016 7:07 pm

The PA daughter boards can easily be changed to move the PA modules but as I understand, there is freq sensitive tuning in the combiner. BE recommended that a used tx be sent to them for freq change.

kkiddkkidd · Post by **kkiddkkidd** » Fri Jul 22, 2016 7:11 pm

And they estimated $3800 including new daughter boards for the AM1a...

Deep Thought · Post by **Deep Thought** » Fri Jul 22, 2016 11:24 pm

I'm beginning to think they use Dave Harry's rate card...no matter what it is, it costs $1800.

In BE's case it is $4k.

RGORJANCE · Post by **RGORJANCE** » Mon Jul 25, 2016 7:55 am

I just spoke with BE about this and found that there needs to be a whole lot of tweaking of special coils in the output. They also install all updates and they quoted over $3,000.00. Definitely not cost effective based on acquisition and update costs.

Pass on this one.

Appreciated all the comments. Thanks guys.

Fossil

kcbooboo · Post by **kcbooboo** » Mon Jul 25, 2016 10:34 am

Remember how it was in "the good old days" when your RCA BTA-1R transmitter was sent with coils and caps that would tune the entire AM BC band, and the manual had pages of instructions on where to set the taps and how to tune each stage? You didn't have to send it back to the factory; you could do it all yourself.

Now we have modern digital-age progress.

Bob M.

Deep Thought · Post by **Deep Thought** » Mon Jul 25, 2016 10:16 pm

The irony is that transmitter design is pushing 30 years old. It's just that fussy.

Shane · Post by **Shane** » Tue Jul 26, 2016 8:29 am

One of these outfits ought to change their name to AHASH: Always Have A Spare Handy. We had to do without our AM1a for a couple days after lightning (apparently) cooked a PA a few years back. But it was the first trouble major enough to actually require doing something that drastic (sending the whole module to Q).

I can't imagine needing to crate up a BTA to send it back to the factory!

br2600 · Post by **br2600** » Tue Oct 18, 2016 4:56 pm

I am a bit disappointed that BE takes the position "it has to be sent back to the factory". Harris gives you the information that you need to do a frequency change on a DX-10. Yes, you need a VNA to do it right, but it is possible.

Deep Thought · Post by **Deep Thought** » Tue Oct 18, 2016 6:58 pm

Oh they'll give you the info all right, and then tell you that if you screw it up they're going to charge you about what a new one costs to fix it. The problem is the "Class E" configuration doesn't leave any room for error, and there is plenty of opportunity for error in the combiner and matching network.

davedybas · Post by **davedybas** » Tue Oct 18, 2016 8:17 pm

Deep Thought is correct when he states that the Class E RF stage requires factory tuning. Class E doesn't tune like an old tube or other solid state stage. You can destroy the RF FET's real quickly when the RF stage isn't properly tuned. Send it to the factory and be done with it....

FREQ CHANGE BE AM-1A IN THE FIELD

FREQ CHANGE BE AM-1A IN THE FIELD

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