Reference
pages:
b31
type 1-A, 2-A, 2-B
b32 type TR-4, TR-4C
Improving R-4C third mixer (temporary
text, because the first is lost).
R-4C (S/N 22000-up).
Got this receiver at very low price because a friend
didn't want to have it as it was some bad noise. We traced
it to the third mixer. It seems that 6EJ7 wasn't as good as the
previous 6HS6 for this type of mixer. LA7MI
discovered that a Philips EF184/6EJ7 didn't have
the same amount of white noise problem, but still it was
some desire to have it improved. This was described in '73' (June
79) by W5DA Howard J. Sartori, and solved
that sort of problem. The first direct fault was that the wire
from the IF coil were broken close to the solder
lug on the IF can, LA6VM Erling had the problem on his R-4C
first, so I could just follow his instructions.
How to build a proper mixer with a
pentode is old news. Below is shown how it was already
implemented
in 1936 for the German 80m CW/AM transceiver Torn.Fu.b1:
How to design proper mixer with a triode or a pentode may have
been forgotten,
but the principle was already known in the thirties, you could of
course use cathode injection,
but the conversion gain is very low, somewhat more complicated
with directly heated valves...
R-4C VFO leakage into the 1st IF
It was found impossible to use SB-620 Scanalyzer with R-4C, and I
was curious to find the reason.
Connected a high impedance probe (Mosfet buffer) to the input of
the first xtal filter and selective
voltmeter (Siemens D2008) to measure the levels.
I'll have to recalculate the figures later. -30dB = 50mV, here is
the preliminary list as found from some old paper
I wrote in december 82. Apart from the fact that R-4C has
6EJ7/EF184 and the predessors have 6HS6 as first
mixer it is likely that it is not so much difference between
Drake R-4 and R-4C (S/N 22000-up).
RX frequency | VFO kHz (4955-5455) | VFO Level at IF | IF level for CALIBRATOR |
28.0Mc/s 28.1 28.2 |
5455 5355 5255 |
-30dB -34 -36 |
-66dB ( =S9+10) as above as above |
28.3 28.4 28.5 |
5155 5055 4955 |
-38.5 -41 -43 |
-66dB ( =S9+10) as above as above |
21.0 | 5455 | -38 | -68dB ( =S9+ ) |
14.0 14.1 |
5455 5355 |
-41 -47 |
-67dB ( =S9 + 10) as above |
14.2 14.3 |
5255 5155 |
-49 -52 |
as above as above |
14.4 14.5 |
5055 4955 |
-54 -56dB |
as above as above |
7.0 | 5455 | -52 | -69dB (= S9) |
3.5 | 5455 | -54 | -62dB (= S9+20) |
1.5Mc/s | 5455 | -45 | -66dB (= S9+20) |
*) RX pre-selector is tuned for maximum
deflection for the calibrator signal.
With receiver tuned to 14.0MHz, with/without calibrator on, the
IF level for S9 deflection is -95dB (5642kHz).
For AM a spurious is measured at 5595kHz at
-81dB level (xtal oscillator)
For SSB a spurious occurs at 5645 at -95dB (xtal
oscillator)
With VFO level at 30-35dB above the strongest signal on the band
it should be proved that it is quite difficult
to use a scanalyzer (SB-620) connected to an output from 1st
mixer.
The following measurement of AGC voltage vs RF input (and S-meter
deflection) was measured on 14050kc/s
for Drake R-4C (87.05.18).
RF input voltage | S-meter deflection | AGC voltage | RF input voltage | S-meter deflection | AGC voltage |
0.1µV 0.3 |
S1 S3 |
-1.9 -2.6 |
30 100µV |
S9+20 S9+30 |
-10.2 -12.8V |
1.0 3.0 |
S5 S7 |
-3.6 ----- |
300µV 1mV |
S9+40 S9+50 |
-16.3V -22 |
5 | S9 | -5.8 | 3mV | S9+55 | -25V |
10 | S9+10 | -7.8 | 10mV | S9+60 | -28V |
So it seems to be just very useful for the
amateur who need deflection to justify the 59 report.
I made a s-meter converter trying to improve the s-meter
deflection using MPSA93 and uA741.
One of my attempts for better adjustment of S-meter deflection
and proper time-constant for the meter.
The first used 4N28, but it had too much drift over the time, so
I used MPS-A93 instead since they were
readily available. It is connected to the 6BA6/EF93 IF output
valve.
Drake (R4245) Multimode quadrature detector
(AM/SSB) (50kHz) with MC1496, see page c11
Circuit diagrams and list of the different
versions of R-4C is shown on http://bama.sbc.edu/drake.htm
Es stand in der CQ-DL, Band 2,
Testberichte
A really very interesting book from DARC showing
testreports by DL1BU for the following equipment:
Atlas 210/215, CRF320, Drake R-4C, Dressler D200, FT-221, FT-301,
FT-901,
IC-202S, IC-211, IC245E, IC-280E, IC402, IC-701, KDK FM 2015R,
KDK FM2016E,
LT470 (Braun), Multi 2700, REIS SE200XL-A, SB-104, SE301 (Braun),
TS-520, TS-820,
Vergleichtest FR101, FT-220, FT221, HG70D, IC201, Multi2000,
Multi2700
Drake R-4C 22000-up
Last update: 2004.01.19