[Premium-Rx] Racal 6217

[Michael O'Beirne]

Good evening team,

I entirely endorse Geoff's recent comments.  I have owned both the original 
RA217D and the long thin version, the RA1217, which is almost the same as 
the RA6217.  I have also used briefly the green military version in a solid 
Creeth transit case, the RA329B, which has an RTTY terminal unit as well.  I 
have some of the EMERs (the official army modifications).  If any one is 
interested please email me directly.

Both are beautifully and very solidly constructed and look very cute and 
pretty (particularly the RA217 IMHO).  In the end I traded them, though in 
the case of the semi-mint condition RA218, I regret that trade now.

The audio quality and frequency stability were stunning but you don't want 
big stations too close, and they are useless on wideband reception.  You 
must use the internal preselector.

SSB is a slight pain because it uses a single 3kHz filter, and for USB you 
have to read 1.5kHz up from the Veeder Root dial and down for LSB (or maybe 
it was the other way, but you see the problem, though no worse than on the 
R390 and without the wrist breaking tuning of the R390).

However, it should be possible to redesign the filtering for dedicated USB 
and LSB offset filters, as used in many other radios.  You will need 1.6MHz 
crystal filters which, I suspect, are hard to find in the USA (and no, I am 
not parting with mine!).

The Achilles heel was trying to emulate the famed and well-liked valved 
RA17L with germanium technology.  Given the technical knowledge at the time, 
Racal did a very good job, but as I say, they were let down by the bricks 
and straw available.

In a paper in Wireless World, Racal themselves accepted that the 217/1217 
series was inferior in terms of dynamic range to the RA17 series.  However, 
the tuning of the 217 series is more accurate and rather more stable, if a 
few Hz per hour is a serious matter.

However, the "squashed" and compact construction does not make life easy 
when it comes to repair, though there are plenty of signal access points 
using SMA connectors, and the manual is excellent in the array of tests and 
figures it gives, and the compactness is "giant" compared with SMD devices 
of current times.

As regards the alignment of the 40MHz and 37.5MHz bandpass filters, don't 
even think of it unless you have the right test gear and know what to do. 
There are 8 cascaded tuned circuits in each filter to align accurately.  The 
40MHz circuits are overcoupled and need to be set up for a square response 
about 1.3MHz wide at the -6dB points following the manual very carefully. 
If you simply tune for maximum smoke you will totally wreck the set.  Racal 
didn't do things by halves!  Basically you need decent sweep gear together 
with RF markers.  An ideal instrument is the R&S SWOB 4 Polyskop and a 
decent sig genie or perhaps a spectrum analyser with a tracking generator 
such as the Marconi TF2280 or the newer devices from HP and R&S.

That was the bad news.  The good news is that alignment of these filters is 
not often an issue unless some of the fixed capacitors have failed.

Racal and the UK military used a dedicated sweep genie that is a two man 
lift.  You don't want to go there!

I have often wondered whether with modern components such as FETs, ICs and 
DB diode mixers would it be possible to rebuild the front end and Wadley 
Loop and achieve a far superior performance.

There will always be the inbuilt problem of rf noise in the loop (deriving 
from the broad band of harmonics applied to the loop mixer) but it should be 
little worse than the noise given by most older PLL designs.

73s
Michael
G8MOB