[Premium-Rx] Racal RA-6778C

[Thomas Adams]

At 09:01 AM 11/11/2006 -0600, you wrote:
>I am looking for any available reference sources on a Racal RA-6778C. Date
>of manufacture, specifications, capabilities, and performance reviews are
>all of particular interest. I have not been successful finding much on the
>internet. 
>
>Any & all help is greatly appreciated.
>
>Thanks
>
>Mark W. Stevens
>Taylor Ridge, Ill.
>


Howdy, Mark!

I have one of the radios, and a set of the manuals for the radio here.

You may have seen the review of it I wrote on EHam.

Date of manufacture is unknown with any real certainty; from date codes on
individual parts it looks like late 1970s - early 1980s vintage.

Re. specs... Here's a quick overview.


Frequency range = 10 KHz - 30 MHz, tuned in 10 Hz increments.

Frequency stability = +/- 1 part in 10 to the 7th using internal 5 MHz
reference oscillator. 

Modes = USB / LSB / CW / AM

Input impedance = 50 ohms

Noise figure = Does not exceed 12 DB over entire tuning range. May
 degrade below 100 KHz, but not exceeding 6 DB/octave.

Audio outputs:

- 600 ohms balanced line output; at least +3 DBm
- Phone outputs (2 jacks in parallel), minimum total output of 20 mw
  @ 5% max THD.

NOT in the manual;

- Internal speaker output: it's TERRIBLE, due to a very cheap speaker
  used by manufacturer. The amplifier is pretty good. It was only meant
  for a quick check of receiver operation by maintenance people, NOT for
  long term operator listening. Bear in mind that the radio was  meant 
  for REMOTE CONTROLLED operation, feeding a telephone line. I found it
  necessary to add a new screw terminal strip to the rear for external
  speaker output, with jumper positions on it to allow use of the internal
  speaker if desired. Never did power, response or distortion measurement
  on the audio amp, but it very nicely drives a 6, 8, or 10 inch external
  speaker (8 ohms) at comfortable listening levels.


Back to the book...

Frequency response:

- Line output = +/- 3 DB, 250 - 10,000 Hz
- Int. speaker = +/- 3 DB, 500 - 5000 Hz


IF outputs = Two post IF filtered, 100 KHz.

Remote control = serial async, character oriented, 9600 baud, MIL-STD-188C,
 type E format compatable.

(I never used the remote...  is all that another way of saying RS-232C?)


- Memories:

 Per the book, 90 memory channels (that's what mine has). I have heard from
 other owners tho that this is variable; some radios seen have less.


Hope that helps you on specs.



Now...  a couple of points from actual use of the radio.

CRITICAL MODS!!!

On my radio, the operating system EPROMS came with THE ERASER WINDOWS NOT
COVERED! I'd strongly suggest IMMEDIATELY adding some plastic electrical
tape over the windows ASAP, before stray sunlight turns the radio into a
very expensive door stop!

The memory battery is the DATA SENTRY type that's prone to leak & damage
the board. I replaced it with a NiCad pack that's connected to the board
by a long umbilical lead; the battery itself is attached to the rear panel
with Velcro.

The AC power switch is apparently prone to failure; I had mine fail by 
shorting across the AC line, causing some minor power supply damage. It
was, IMHO, never meant to be used day in, day out by an operator; this 
radio was meant to be nailed into a rack in a remote controlled site &
run 24 / 7. The switch is an oddball; start looking for a replacement
that will fit in the space NOW...  it's gonna let go eventually.


All in all I find the radio to be an EXCELLENT performer. My only gripe
is that the crystal oven for the time base oscillator takes some time to
come up to operating temperature and stabiliize (usually a half hour or
so...  remember, this radio was never meant to be turned off!).

If you want more information, feel free to write me off the list at
quixote2 at ix.netcom.com .



73's,

Tom "Mr. T." Adams, W9LBB
Sun Prairie, Wisconsin