By the mid 1970's it was obvious that a new generation transceiver was
required. Vaccuum tube equipment was being replaced by solid state ra-
dios - especially for those that wanted to operate mobile. The solid
state equipment was obviously the way of the future. Drake answered this
challenge with the TR5 and TR7 transceivers. There also was an R7
receiver. This receeiver is not that common due to its intial expense
and the fact that those that have them tend to keep them.
Yes, there was a TR6. That was a 6 meter SSB transceiver circa 1970 in
much the same vein as an SB-110.
Yes, there was an 'A' model of the TR7. This is around a 1982 flavor.
What the 'A' model of the TR7 and R7 really was all about is that the
equipment contained standard such as noise blankers and crystal filters
that were options on the earlier model.
The TR7, as is common for most Drake equipment, is over built. This is
characteristic of most well made American equipment. While a TR7 may not
have all of the useless 'features' of foreign equipment, it is as reli-
able as a rock and solidly built. Drake made sure it was a quality piece
of radio and not intended to be disposable. An example - the TR7 gener-
ates 150 watts (250 in or so) output, yet the PA is capable of at least
225 out. At its nominal power rating, the final transistors are under
utilized. The transceiver is big and heavy at 17.5 lbs despite an
aluminium chassis. Glass epoxy boards are employed throughout the radio.
The receiver is dead quiet and almost immune to overload. A large part
of the reason for this is the lack of an RF amplifier and a strong pas-
sive DBM in the front end (ala Atlas 210). The TX SSB audio is rich and
clean. The AGC switches with the mode setting for near optimum tailor-
ing. The only item to be missed is an IF notch filter. You'd look at a
TR7 today perhaps with some distain if you didn't know any better.
A TR7 is a classic example of old ham gear easily overlooked since it is
'old tech'. Yet quite a few of the same amateurs will get very excited
over a Racal or other piece of 'commercial' equipment. At the end of
this document is a readers comment regarding the flexibility of the TR7
design for commercial applications. You see, Drake just didn't make ama-
teur gear.
A well working TR7 is a treat to use. Transmitted audio is excellent and
the receiver is a gem. The AGC is typical Drake - peerless. It can be
used for hours and hours without operator fatigue as the audio is clean
and near hiss free. The transmitter PA stages are constructed for heavy
use. The major downside of the radio is its current requirements. Nomi-
nal drain on receive is about 3 A, on transmit, it could run to about 22
to 25 A. Both of these figures are considered slightly excessive today.
The size of the radio rules out mobile operation in most of todays cars
and the red LED frequency display washes out in sunlight.
12.1 TR7A/TR7 DIFFERENCES
__________________________
The TR7A was an early 80's transceiver that had some subtle differences
to a TR7. Not that many were made and it is a bit of a collectors item.
Practically, it isn't all that much different to a TR7 except in the
following areas:
o Came with noise blanker
o Came with SSB, CW and AM filter
o Came with DR7
o Mic audio appears on back panel
o TR7A displayed on front panel.
o Some RX front end protection
12.2 TR7 MODS AND TECH
_______________________
I have encountered few mods for this radio. This could be caused by the
difficult nature of performing them or by the very fact that a stock TR7
is pretty good as it is. What makes this radio difficult to modify is
the plug in board modules. This is good. This means that a TR7 is un-
likely to be mucked with too severely. Your worst problem is likely to
be alignment if your 'new' TR7 is a little sour.
o Servicing
A TR7 is a robust transceiver that is almost impossible to kill. It
holds its alignment extremely well and generally is overbuilt and
'over designed'. Once brought up to specifications, it should stay
that way almost indefinitely.
However, should your TR7 require service, you are in a bit of a di-
lemma. To service a TR7 beyond the superficial, one needs a good
oscilloscope, volt meter, service manual and the extender boards.
The latter two are no longer available from Drake. A service manual
may be purchased from:
Antique Manuals, K7FG
1-800-807-6146
The telephone number is ... interesting.
This organization sells manuals for a considerable number of exam-
ples of old(er) gear and a lot of BoatAnchors. The current price of
the TR7 manual is about $34 US. Its not a bad deal.
A TR7 is not difficult to set up, but one must be aware of what to
tune and what not to touch. DO NOT align the first crystal filter
unless you are prepared to go at it with a sweep generator. Quite a
number of slugs, trimmers and trim pots are involved in an alignment
and not all of the adjustments are immediately accessible.
Especially in the case of a TR7, if it works, don't fix it.
o Set Up
The outlined procedures in the service manual are very well thought
out and are presented in a linear progression. Follow them. The
synthesizer set up is a bit tricky. Most important is to ensure that
the 40, 13.695 and 8.05 MHz oscillators are exactly on frequency. If
each one of these is within 100 Hz, then the readout, PBT and CLAR
will 'naturally' fall very close to spec. Proper test equipment is
essential to set up a TR7.
o All Band Transmit
Included with this article are additional TIF and TXT files outlin-
ing Drake synthesizer changes for full receive coverage and full
frequency coverage transmit.
o Digital Display
For a while the DR7 digital display was an option. A TR7 is signif-
icantly less without the DR7 display. If you are looking at a TR7 to
purchase, make sure that it does indeed at least have this option
installed. Of all the 'options' available for the TR7, it is un-
likely you'll ever find a loose DR7 unless someone is cutting up a
TR7 for parts.
o Early and Late Models
The very early model TR7 was sold without the DR7 board. It is un-
likely you will encounter one of these - few were made. ASK if it
has digital display before purchase!
The early model TR7 had a 3 transistor predriver on the PA heat
sink. Additionally, the adjustment for TX/RX frequency required you
to remove the DR7 and use extender boards. Very inconvenient.
The later model TR7 uses a 2 transistor predriver. You need to pull
the top cover and look at the circuit board closest to the front
panel. If you see a U shaped aluminium heat sink, it is the later
model. Additionally, this model TR7 had an access hole on the
motherboard for the TX/RX frequency adjustment.
AF/RF Gain Control
Is unavailable from Drake.
This is the same control as used on the SPR4, which was available,
although I don't know the current status. The one difference is that
the TR7 control has a double switch for both AC and DC. Depending on
what is gone on the TR7 control - anything but the switch, ba-
sically, you can graft the old control switch onto the replacement
control. This requires careful disassembly of the controls, but it
can and has been done.
As for replacement switches, about the best you can do is rummage
through someones surplus parts bin. These types of switches were
used in old AC/DC televisions and AM/FM radios.
o TR7 Mixing Scheme
The TR7 and TR7A is a dual conversion transceiver using a first IF
of 48 MHz and a second IF of 5.645 MHz. The same path is used in re-
verse on transmit. For the BFO, there is no 5.645 MHz crystal as
such, for it is synthesized from 2 crystal oscillators at 8.05 and
13.695. The first mixer is a DBM followed by a grounded gate post
amplifier in to a 48 MHz 4 pole crystal filter. On transmit, the 48
MHz transmit signal is routed through the 48 MHz filters, through
the post amplifier and into the DBM. The post amplifier has its in-
puts and outputs reversed through steering diodes. Output on trans-
mit is taken directly from the DBM into the 3 stage high gain PA
section (predriver, driver and PA functional blocks). ALC is
achieved on transmit by use of a diode attenuator in a previous low
level stage. In receive, there is a dedicated board for the IF fil-
ters followed by a 3 stage IF MOSFET amplifier employing forward
AGC. The crystal filters are treated all the same - there is no gain
compensation for bandwidth.
The primary reason for the mixing scheme is so full coverage from .5
to 30 MHz can be achieved with a 5 to 5.5 MHz VFO.
The synthesizer in the TR7 is a tracking synthesizer. The PTO at 5
to 5.5 MHz is used in the PLL with the divider chain to control a
VCO operating at 48 to 78 MHz. If the PTO drifts, then the
synthesizer will drift in step with it.
o RF Tightness
The radio cannot be aligned when extender boards are in use. Some
adjustments must be done with the cover plate off. For the other
adjustments, there are holes in the cover plate for access. These
can only be accurately adjusted with the cover plate in place. Make
sure the cover plate is screwed down snugly with all those screws -
not just a few.
Some boards have grounding fingers. While re-installing these
boards, make sure the fingers and tabs make chassis contact.
If the above is not adhered to, mediocre alignment and operation
will result. There will be RF leakage into the IF section of the
receiver. This will have a dramatic effect on S meter, AGC and
spurious responses.
o AUX 7 Programming
See the separate section covering this option in detail.
o The FA7 Fan
Some manufacturers do not provide for forced air cooling of their PA
stages. Ten Tec is a good example. Their PA stages can run so hot
that it really hurts to grab the heat sink. I've never seen one
'melt', but having them get that hot gives me the willies. Heat and
electronics do not happily co exist (ref TR4 above). While the
transistors may take it and good design compensates for it, thermal
run away is a concern. Its an ugly event to watch and once started,
the event is catastrophic and usually expensive.
The FA7 was an option on the TR7 for heavy duty cycle use. Experi-
ence has shown that without a fan, even on SSB, the PA gets inordi-
nately warm. Regardless of mode, some form of forced air cooling
should be employed. The requirement is to provide air circulation,
not necessarily air cooling. The fan should be set up to blow in,
not out. This is contrary to the FA7 direction, but seems to afford
much better cooling. I mount the fan so it blows in, under the
theory fans move more air on the blow side than the draw side. It
does seem to be noisier blowing in, though. I really do not think it
matters all that much, so long as you can get the temperature down
and the hot air out. If you mount it to draw, you should feel warm
air coming out and the top of the cabinet 'cool'.
The FA7 fan runs from 110 VAC and is meant to be run 'through' the
PS/7. If you have a PS/7, a 110 VAC 'muffin' fan will bolt right on.
If you use a generic power supply use a 12 volt version and power
the fan off the TX Vcc from the PA stage. 24 volt DC fans will push
a fair bit of air quietly and these are readily available surplus.
o Digital Operation
All Drakes with the exception of the TR5 use a free running VFO.
This may not be stable enough for RTTY as the long term drift is a
few hundred cycles. If you must use a Drake for digital operation,
your best bet is a TR5 or a TR7 with an RV75 remote VFO (not the
RV7).
I have no T/R switching times for any of the Drake equipment, but it
is reasonable to assume that none of it switches fast enough for
AMTOR.
* note readers comment on TR7 switching times
o Receiver Sensitivity Check
Properly aligned, the S Meter should rest just off zero, for the AGC
detector must be in the 'on' state slightly, otherwise the AGC will
pop. The calibrator should provide an S9 signal on 10 meters with no
antenna attached if the alignment is close. Without an antenna, a
properly operating TR7 should appear almost to be dead. If the RF
gain is rotated fully CCW, the S meter should rest at the S9 +80 db
mark - no higher or lower.
Since there is no preselector to peak, the calibrator test assumes
the S Meter is set up in accordance with the alignment instructions.
The other alternative 'sign of life' tests you can do is to scratch
the center pin of the SO/239 with a metallic anything. The S Meter
should respond and you should hear the scritch noises most plainly
in the speaker. You can also connect almost any antenna to the
SO/239 and you should hear an increase in background noise, however
slight - even on 10.
o 8.05 MHz Osc Won't Net
This oscillator is varicap controlled and is used in conjunction
with the 13.995 fixed oscillator to develop the BFO. In doing it
this way, there is little chance that there will be BFO leakage, or
what leakage there is, can be controlled.
There is a trimmer adjustment to net the 8.05 MHz crystal, but what
the manual fails to tell you is that this adjustment is also af-
fected by the trim pots for the injection frequencies for the BFO.
If you try to set this trimmer up and it just won't trim, try an
arbitrary setting of the trimmer screw and see if, say, on LSB you
can get it to the proper frequency with the trim pot for that mode.
o Receiver AGC Set Up Notes
Aside from alignment, set up in this area has considerable affect on
the receivers sensitivity and AGC 'personality'. Also important is
the 10 volt regulator adjustment, for it too will have an effect on
oscillator alignment, AGC and sensitivity. Tests indicate that at 9
volts, the receiver and AGC setup is quite 'mushy'. For all prac-
tical purposes, the 10 volt regulator adjust is the one adjustment
that will determine how 'crisp' the radio is.
Adjust the 10 volt regulator from measurements taken on the
motherboard.
o Transmitter Output Check
A TR7 should produce 150 watts output on 80 meters if set up prop-
erly. Current draw will be 22 amps at 13.6 volts. Use no smaller
power cable than #12 for short runs and #10 for 15 feet or more.
You should be able to disconnect the transmitter load and key the
transmitter to full output. Properly set up ALC will limit the out-
put 'power' to 20 watts or so.
If you pull the blue wire from the ALC board (the one between the
shielded cable and the red wire on the LHS), the PA stage will run
wide open and I've measured over 225 watts output on 80 meters. Not
recommended as a normal practice, but this is a good test of final
transistor health. Set to its nominal 150 watt output, a TR7 is
definitely loafing along.
o Won't Transmit
The TR7 has a separate pin on the power connector for +13 volts to
the PA. Out of the 4 pin power connector pins, 2 are ground and one
pin each is for the radio proper and the PA. Ensure that the PA
stage does have 13 volts. The transceiver will make all the right
noises (relay closure, etc), but won't generate any RF.
This is a common oversite. Its comparable to not having plate volt-
age for the PA stage in the TR4.
o Accessory Filters
The TR7 filters are not interchangeable with the R4C filters. The
R4C accessory filters are 5695 kHz and the TR7 are 5645 kHz. The
factory supplied SSB filter is a 'fidelity' filter. Your transmitted
audio with a properly set up radio and a microphone should sound
like FM broadcast. The skirt roll off is just a little 'soft'. You
need to go to a 1.8 kHz filter to get much RX improvement. The stock
SSB filter is quite good in receive.
The TR7 always transmits through the SSB crystal filter supplied
with the radio. You can put the other 3 filters where ever you want,
but don't mess with this filter in this position.
o AM Filter
An AM filter is almost impossible to find. You can fake an AM 'fil-
ter' by putting a 390 ohm resistor through the input and output pins
of any blank crystal filter position. It actually isn't bad. What is
determining the selectivity is the 48 MHz first IF filter.
o Transmit Power
Pay particular attention to the SWR balance trimmer, C1901. ALC
action is affected adversely by an improper null. This null trimmer
also affects the watt meter calibration, so if you change the
trimmer setting, R2001 and R2002 will need adjustment also. Essen-
tially, the FOR output is used for ALC and the REV output is used
for shutdown. This is independant of the watt meter setting. When
you set up the ALC null, use a high impedance analogue meter, a non
metallic alignment tool and a good 50 ohm load.
There are 2 control settings that affect the ALC. The obvious one is
the 'ALC' control on the ALC board in the bottom of the transceiver.
The other setting control is the gain pot on the predriver. This
control sets the gain by setting the feedback on one of the driver
stages (old driver board) or the current in the preamp stage (newer
driver board). Properly set, you should have just enough ALC on 10
and as expected, a controllable abundance on 80 meters. Improper set
up of the ALC usually means no ALC or will make the mic gain setting
overly sensitive and the ALC clamp early on the lower bands. There
is additional ALC/drive compensation from the band switch for the
10 and 15 meter bands. Extra resistors are switched in on these band
settings to provide more drive/higher ALC threshold to provide gain
compensation. These resistors have only a very minor effect on drive
compensation. If you are having upper band drive problems, these
resistors should not be the first suspects.
For proper transmitter ALC action it is essential for the PA driver
and final stages to be in good condition. 150 watts output should be
easily attained on 40 and 80 meters.
o External Speakers
Unlike the '4 line, the TR7 employs an LM380 audio power stage. This
IC is load tolerant and 8 ohm speakers may be used without problem.
o Microphone
Later series TR7 provided for both high and low impedance microphnes
through the use of different pins on the connector.
High impedance mics may be connected to pin 4. Input Z is about
750K, but this port is much less sensitive than pin 1. High Z mics
are expected to be high output (> 100 mv).
The above is a factory change on the later series TR7. Early models
had a jumper on the circuit board for microphone impedance.
o PA Driver Stage
At least 2 different sets of boards were used in the driver stage
next to the power amplifier. Early TR7s used 3 transistors; the late
model board used 2 transistors. In this board, the last transistor
is an MRF476. The final amplifier board seems to have remained much
the same, but the components around the PA input and output trans-
formers were different.
The board with the MRF476 predriver most likely was changed because
it was much cheaper to make. This in itself is not a fault, but the
way it was executed presents some problems that will be dealt with
in a separate area. On this board the driver is an MPS-H20. I've
used the MRF237 as a replacement because the transistor is biased
for about 20 ma - about .3 watt. In my mind this is a little heavy
for a TO92 transistor. The MRF237 may also be used as replacements
for the SRF2331. These transistors are somewhat unique - the case is
the emitter and the collector and emitter pins are interposed. If
you orient the transistor so the base (center lead is furthest away
from you) is in the centre and the transistor is held by the leads
underneath, the emitter is the left hand lead, NOT on the right
where you would expect a TO5 to be. The case in question is a TO39.
If it is necessary to change any of the transistors in this area,
you must use heat sink compound on the mounting bases. Most folks
use far too much of this stuff. The purpose of this compound is to
ensure a good thermal contact between the transistor and the heat
sink by filling in the (natural) pits in the metal faces. Thats all
its used for. Too much is just as bad as none - its a metal filler
only. Do not over goop this stuff!
o Late Model Driver Boards
The problem with the later model board is the bias network on the
MRF476. Its bias level is such that the transistor will go into
thermal runaway or may latch up by itself. The 270 ohm resistor from
base to ground is not enough to prevent this. The 300 ohm resistor
and 1N4005 diode is an acceptable method of providing bias, but with
the grounded emitter, there is no way to guarantee thermal stability
around the transistor. You'll notice this if all of a sudden the
transmitter output drops or, on the lower bands, the ALC is gone and
more mic gain is required. You let up on the mic for a few minutes
and all is well. If you were to feel the heatsink on the MRF476, it
will be very, very hot. It may also be possible that the predriver
board 'eats' MRF476s. You find its bad - usually leaky and low gain
- replace it, and soon the new one dies an inglorious death also.
The cure is to lift the emitter off ground with a resistor. Make a
tight bundle of 3 - 1.8 ohm 1/8 watt resistors in parallel. Cut the
emitter lead of the MRF476 about where the lead changes width. Re-
move the stub from the circuit board and put this resistor network
between the emitter and where the the stub went into the circuit
board. Removing the stub can be interesting for its soldered on both
sides of the board.
Yes, raising the emitter will decrease the gain. The degenerative
feedback also makes the MRF476 easier to drive, so the net result is
a wash. This one change for this specific board type is highly re-
commended, especially if you're thaving problems with MRF476 longev-
ity.
o PA Stage
Co incident with the different driver boards, Drake changed the PA
stage around the ferrite transformers. These changes look like they
were done to improve stability, and the differences are minor.
o PA Stage Bias Setting
There isn't any. There is no bias adjustment for any of the stages
in this amplifier chain. If your final or driver transistors have
suffered catastrophic failure, before installing replacements and
after removal of the transistors, measure the base voltage on trans-
mit. Nominal reading is about .6 volts. If higher than .7 volts,
further inspection of the bias supply is in order. Failure to do so
will likely cause the new set to be compromised immediately upon
use.
o PA Transistors
MRF421MP will replace the SRF2337 final transistors. The MP indi-
cates Matched Pair, so order one of these or two MRF421 and ask them
to be beta matched. At this power and current level, it is wise to
have current balance in this stage.
MRF475/2SC2092 will replace the SRF2338 driver transistors. The col-
lector is the mounting tab, so don't forget the insulating wafer.
MRF476/2SC2166 will replace the TO220 predriver. The driver board
changed over the years. The collector is the mounting tab, but its
board placement is isolated from the circuit board. Do not use tab
isolation hardware. The collector choke makes collector contact
through the bolt.
The cost of all of the above is about $90 from RF Parts. One final
transistor alone is over $63 from Drake.
The TR7 will shut down 50% at a 4:1 SWR. This provides more than
adequate protection. However, the transmitter draws considerable
current from a 13 volt supply. The supply should be rated at 30 AMP
ICAS minimum. Marginal supplies and DC power cords will not provide
enough current under load and likely will drop in and out under full
carrier condition jeopardizing the PA. It is important that a stiff
high current supply be employed with the TR7.
o ALC Time Constant
On the ALC board, the ALC decay time constant is over 1 second. This
can be decreased to about 1/2 this value without any ill effects and
will allow the ALC to track voice input a little better. Change
R1618, a 1 meg resistor, to 470K.
o VOX - Transmit Generator Board
The VOX requires about 50 mv of microphone input to trigger reliably
from pin 1 on the mic connector. On the TR7, it takes a very high
setting on the VOX Gain control to make the VOX trip. This is in
contrast to the mic gain, where not much is needed at all. C304, a
.01 uF capacitor coupling the voltage doubler has a reactance of 15K
at 1 kHz. Its value is much too low, especially when the applied mic
input signal is divided in half by C320, another .01 (transient sup-
pression). Change C304 to a .1 uF. The improvement is such that it
will take barely adequate VOX gain to 'acceptable'.
I recommend this change for those SSB operators that would like to
operate VOX on their TR7's but haven't for lack of VOX gain.
13.0 AUX7
__________
You can make the all band transmit mod by just cutting one trace for the
TX band inhibit line. The other, official way of getting additional
bands is through the AUX7. This was an option board on the TR7 series
that allowed one to operate the TR7 either crystal controlled or allow
one to buy program modules for any .5 MHz segment. Special program mod-
ules were ordered for transmit. Use of an AUX7 is a nice touch, for by
just rotating 2 switches, you can get to any band you want without mod-
ifying the transceiver. The option modules were all the same - you 'pro-
grammed' the modules by cutting off the appropriate pins from a chart.
Drake no longer provides the AUX7 optional band modules, but you can
make your own from a 14 pin DIP header and a batch of 1N4148 diodes.
Each of these modules will consume less than 13 diodes, depending upon
the frequency. Yes, its a lot of diodes. Typically, you'll need 7 or 8
diodes per module. You must use the diodes, for the band modules are ma-
trixed.
The AUX7 is not easy to install or gain access to for it involves open-
ing the TR7. The front panel will flip down, but to do this, you need to
extract the band switch shaft. If you are not careful, you can rip the
wafer rotors out when you extract or reinsert the shaft. This will cause
REAL trouble and given the age of the unit and replacement parts avail-
ability (don't count on it!),
The AUX7 band module has a separate pin for TX enable. Obviously, this
pin must be enabled for any of the WARC amateur bands you need or want
to enable. The band switch must be set to the appropriate filter range.
If it is set to a range that does not match the module programming, the
SETBAND light will come on.
When you set up the DIP header with the 1N4148 diodes, use the following
programming chart. The pin numbers are as if it were an IC. Make sure
you do not wire it backwards! This is a very common mistake:
PIN USE PIN USE
=== ========== === ==========
1 Select 5V 8 Range B2
2 Range A0 9 Range B3
3 Range A1 10 TX enable
4 Range A2 11 Band A
5 Range A3 12 Band B
6 Range B0 13 Band C
7 Range B1 14 Band D
Essentially the AUX7 programming is divided into 2 halves - BAND and
RANGE. BAND sets the band as if it were coming from the band switch.
RANGE sets the .5 MHz offset as if you were to hit the UP/DOWN buttons
on the front panel. The BAND programming is compared against the BCD
band switch wafer. If there is no match against these two, the SETBAND
light comes on. This is used to tell the operator that the band switch
setting does not correspond to the programming and the band switch
should be rotated until the light extinguishes.
13.1 BAND PROGRAMMING
______________________
Band programming is done in BCD to indicate the band switch setting
through the SETBAND indicator. If this is not programmed, the unit will
not transmit. If pin 10 is not made high, the unit will not transmit.
Band Range BA BB BC BD
========== == == == ==
1.5 - 2.0 - x - -
2 - 3 x x - -
3 - 4.5 - - x -
4.5 - 7 x - x -
7 - 10 - x x -
10 - 15 x x x -
15 - 22 - - - x
22 - 30 x - - x
The band range pins BA to BD correspond to the previous 14 pin chart.
This programming sets the band switch data/SETBAND light. If this is not
programmed, the unit will receive, but it will not transmit, even if pin
10 is high.
13.2 SYNTHESIZER PROGRAMMING
_____________________________
The synthesizer requires programming in order to set the correct 1/2 MHz
range. This requires some calculation. The pins A0 to B3 comprise a 1
byte field to indicate the correct .5 MHz chunk. You simply cannot as-
sume that 18 MHz is the 36th 1/2 MHz chunk and program '0011,0110', for
there is a modulus to be accounted for.
The formula is 86 - (f*2), where f is in MHz at 500 kHz settings. To set
the synthesizer to 27.0 MHz, you would calculate 86-(27*2) = 32 =
0011,0010.
0 0 1 1, 0 0 1 0 PIN
| | | | ===
| | | |___ A0 2
| | |_________ A3 5
| |____________ B0 6
|__________________ B3 9
To program this 27.0 matrix, you would connect diodes from pin 1 to pins
3,6,7 for the synthesizer, diodes to pins 11 and 14 for the band switch,
and a diode to pin 10 to enable transmit. (but we'd NEVER do that, would
we?).
The TR7 has 2 master oscillators that are selected by the band switch,
NOT the frequency programming. Although it is not obligitory for recep-
tion, you should also program the band switch data so the SETBAND light
will come on. A common error is to do the diode programming, fire it up
and the synthesizer won't lock. This is usually caused by the band
switch in the wrong position. The band programming and the SETBAND light
is designed to prevent this.
13.3 CRYSTAL CONTROL
_____________________
Crystal control on the TR7 is independant of the programming matrix.,
The PTO tunes up and is offset 50 kHz, so finding the right crystal is f
+ 5.05 - f(MHz). To crystal control to 7.055 MHz, you'd order a crystal
for 7.055 + 5.05 - 7 or 5.105 MHz. For bands that are on a .5 MHz bound-
ary, you'd subtract an extra .5 to put the crystal within the 5 to 5.5
MHz range. The above crystal would put you on 3.555 MHz on 80 meters
(3.5 + 5.105 - 5.05).
Since crystal control is related to a specific band, you should program
the AUX7 as documented above. This is not mandatory.
I do not have specs on the crystal, but an educated guess would be
HC/25U, 20 pf, series, fundamental.
|