Ramsey Electronics FZ-146 Manual de instrucciones descargar pdf (Pagina 24)

P-IBM • 24

ONCE!

"Great!" I said to myself, wondering what was so wrong with the FX-146

that I had built so carefully while writing its instruction manual. Now I know

that the P-IBM Packet Modem and the Baycom software surely DO work.

Still, I had to KNOW why the prototype FX-146 worked better than "my

baby".

What can be wrong? There's only 3 receiver adjustments in ham history's

EASIEST- EVER VHF rig to build. I re-checked the trimmer cap in the PLL

and found it to be WWV-perfect. No need to play with the VCO coil,

because I knew the PLL was solidly locked. I tinkered (uselessly) with the

receiver quadrature coil.

So, I dutifully practiced what I always preach and re-checked almost ALL of

FX- 146's parts. I was NOT happy to find them all fine. I really WANTED to

find a mistake in my own FX-146 transceiver. The bad news for me at the

moment was that there were NO mistakes. Then, I remembered a last-

minute revision in the FX-146 book requested by Ramsey. That revision

sought better clarity for adjusting the modulation control. The goal is proper

deviation rather than loudest audio. After receiving that revision from

Ramsey engineers, I verified their point for myself with quick tests. But, I

forgot to set the modulation control to its ideal level. In fact, I found it in its

HIGHEST setting, which results in the excessive deviation we don't want.

So, sheepishly, I backed the FX-146's modulation trimmer back down to

proper FM deviation level. Just as quickly, my computer screen became

filled with more worldwide Christmas messages, local news and other

packet stuff.

But, WHY or HOW can a "transmit" adjustment help a "receive" problem?

The answer lies in understanding the VCO: if the modulation is set way too

high, the receiver mode of the radio can be bothered by just enough "stuff"

from the IC microphone amp to interfere with proper data demodulation. It

just takes one "pop" or touch of distortion to demolish a data packet.

Add it all up, and you see exactly what we mean. A guy adds a newly-built

modem and unfamiliar software to his favorite computer and FM

transceiver. Nothing works right. Gradually, he discovers that he was (1)

using the wrong cable; (2) that the serial port in one computer is not set up

properly, and (3) that one transceiver's modulation was not set properly. In

the meantime, the P-IBM and Baycom software were working just fine all

along. And there was really nothing "wrong" with the computer or the radio;

they just weren't set up right by the human in charge.

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Ramsey Electronics FZ-146 Manual de instrucciones Pagina 24