The
H
F
-
T
r
a
n
s
c
e
i
v
e
r
H
H
F
F
-
-
T
T
r
r
a
a
n
n
s
s
c
c
e
e
i
i
v
v
e
e
r
r
Kenwood TS-830
Survival Guide
PART I
edited by
Olaf Rettkowski DL9AI
2
VERSION
Kenwood TS-830 Survival Guide, ed. Olaf Rettkowski
, DL9AI, ver.1.2, 03 Dec 2002
REFERENCE
This is a collection of material found on the net. For reference and further information visit
the following sites and/or see the following papers:
http://myweb.tiscali.co.uk/martin.atwsm/TS830S.html , Martin, G1XGX
http://www.vcnet.com/measures/830.html
, Richard L. Measures, AG6K
http://www.eham.net
http://www.mods.dk
http://groups.yahoo.com/group/Amateur-repairs
http://www.kenwood.net
Kenwood TS-830S Operating Manual
Kenwood TS-830S Service Manual
3
1 Preface .........................................................................................................................6
2 Read first ! ...................................................................................................................6
3 History of this document ............................................................................................7
4 To-Do list .....................................................................................................................7
5 General Description....................................................................................................7
6 Problems and known Fixes ........................................................................................8
6.1 Excessive delay in relay control signal to external amplifier--which causes hot
switching in the amplifier's RF relays
..........................................................................8
6.2 Frequency drift..............................................................................................................8
6.3 Frequency drift during warm-up...................................................................................9
6.4 TS-830S Frequency Drift - "FIX" switch.....................................................................9
6.5 Frequency jumping .......................................................................................................9
6.6 Intermittent shift in display and operating frequency.................................................10
6.7 Intermittent ALC on transmit .....................................................................................11
6.7.1 Problem 1: Intermittent ALC indication [TX] on only one band ...............................11
6.7.2 Problem 2: Intermittent ALC on transmit...................................................................11
6.8 Lack of crispness in receive audio..............................................................................11
6.9 Lack of crispness in transmit audio ............................................................................12
6.10 No power output on most bands .................................................................................12
6.11 Noisy or intermittent front panel control potentiometers [pots].................................12
6.12 On the AF-AVR Unit, the 4-pole relay contacts which switch the bias to the finals
may fail after extensive use.
.......................................................................................12
6.13 Peak-distortion in the RX audio .................................................................................13
6.14 Poor, transmit, SSB carrier-suppression after alignment............................................13
6.15 Power-output falls off when the key is held down .....................................................13
6.16 Premature 12V pilot lamp burnout .............................................................................13
6.17 Rapid jumps in VFO frequency..................................................................................14
6.18 Receive [RX] signals intermittently drop roughly 40 db............................................14
6.19 Receiver AGC-overshoot, causing receive audio-distortion on voice-peaks and
concurrent S-meter overshoot.....................................................................................14
6.20 Television interference with the radio transmitting into a 50 Ohm, shielded
termination
..................................................................................................................14
6.21 Receive suffers or goes out after QRO modification..................................................15
6.22 Transmitter "talkback"................................................................................................15
7 Problems and Hints from Newsgroups ...................................................................16
7.1 Beware of high voltage!!!...........................................................................................16
7.2 No sidetone when keying CW, VOX doesn't work on CW........................................16
7.3 Resistor replacement after grid-to-cathode short of the 6146 tubes...........................16
7.4 Difference between 6146B und 6146W tubes ............................................................16
7.5 Slow power drop-off...................................................................................................17
7.5.1 Slow power drop-off: Answer 1 .................................................................................17
4
7.5.2 Slow power drop-off: Answer 2 .................................................................................17
7.5.3 Slow power drop-off: Answer 3 .................................................................................17
7.5.4 Slow power drop-off: Answer 4 .................................................................................18
7.6 Low power output.......................................................................................................18
7.6.1 Low power output: Answer 1 .....................................................................................18
7.6.2 Low power output: Answer 2 .....................................................................................18
7.6.3 Low power output: Answer 3 .....................................................................................18
7.7 Intermittend drop of power output .............................................................................19
7.8 Problem peaking Drive control ..................................................................................19
7.9 Intermittent loss of drive to final ................................................................................19
7.10 No dip on the plate current and no or small output ....................................................20
7.11 Reducing power output to QRP-like levels, No.1 ......................................................20
7.12 Reducing power output to QRP-like levels, No.2 ......................................................20
7.13 Increasing power output / QRO-modification, No.1 ..................................................21
7.14 Increasing power output / QRO-modification, No.2 ..................................................21
7.15 Intermittent loss of audio............................................................................................22
7.16 Final tubes replacement and neutralization ................................................................22
7.17 Low power output on 160 m only ..............................................................................22
7.18 Crystals for FIX band selection..................................................................................23
7.19 Changed DRIVE setting after final tubes replacement is normal ..............................23
7.20 Difference between TS-830 and TS-830 "gold label"................................................23
7.21 Microphone impedance matching ..............................................................................23
7.22 Problem with TS-830 TX relay ..................................................................................24
7.23 No operation on WARC bands...................................................................................24
7.24 Receiver signal attenuation when keying the microphone or rocking the bandswitch
....................................................................................................................................25
7.25 VOX trip problem.......................................................................................................25
8 Maintenance Procedures..........................................................................................25
8.1 VFO Lubrication ........................................................................................................ 25
8.2 Fan Lubrication .......................................................................................................... 26
8.3 VBT [Variable {selectivity} Bandwidth Tuning] Oscillator Alignment [approx.
8375 KHz]
..................................................................................................................26
8.4 USB/LSB Carrier Oscillator Alignment..................................................................... 27
9 Modifications.............................................................................................................27
9.1 AMTOR modification ................................................................................................27
9.2 WARC modification...................................................................................................28
9.3 RIT / XIT modifications.............................................................................................28
9.4 VFO-230 fine tune mod..............................................................................................28
9.5 TS-830S Low Voltage Supply Optional Improvements ............................................28
9.6 Kenwood TS-830 filter modification .........................................................................29
9.7 TS-830S Operation on 240 V AC ..............................................................................30
9.8 TS-830S Noise Blanker Optional Improvements.......................................................30
10 Product Reviews .......................................................................................................31
5
10.1 Opinions and Ratings of TS-830 owners....................................................................31
10.1.1 Great Radio, Rating: 5 of 5.........................................................................................31
10.1.2 I miss mine, Rating: 5 of 5..........................................................................................32
10.1.3 Good but aging, Rating: 5 of 5 ...................................................................................32
10.1.4 TS-830 The Best of the Best, Rating: 5 of 5...............................................................32
10.1.5 Brilliant audio from 830, Rating: 5 of 5 .....................................................................32
10.1.6 Excellent Radio on the used Market, Rating: 5 of 5...................................................32
10.1.7 Excellent Radio, Rating: 5 of 5...................................................................................32
10.1.8 A quality classic, Rating: 5 of 5..................................................................................33
10.1.9 Still Impressive after all these years, Rating: 5 of 5 ...................................................33
10.1.10 One of the very best, Rating: 5 of 5............................................................................33
10.1.11 Will never say 'goodbye', Rating: 5 of 5.....................................................................33
10.1.12 Nice, Rating: 4 of 5.....................................................................................................33
10.1.13 Nice transceiver, Rating: 5 of 5 ..................................................................................34
10.1.14 Great Rig. Rating: 5 of 5.............................................................................................34
10.1.15 Like putting down a friend; rating. 5 of 5...................................................................34
10.1.16 Going strong after 18 years, Rating: 5 of 5 ................................................................34
10.1.17 TS-830S Finals last forever, Rating: 5 of 5 ................................................................34
10.1.18 Good radio...with a question to other TS-830S owners, Rating: 4 of 5......................35
11 Connectors and Plugs ...............................................................................................36
12 Index...........................................................................................................................37
6
1 Preface
I purchased a Kenwood TS-830S on the used market after passing the ham exam in 2001.
Months before I was searching the internet extensively to get an idea of how an newcomers
shortwave transceiver must look like, especially what features it must have and which of them
are not essentially. The costs did play an important role: my personal limit was 500$ for the
transceiver (a few weeks later the MFJ-949 manual antenna tuner took me again 200$… and an
MC-50 mike from Kenwood again 70$). Regardless of the many (mostly technical) comments
about this decision, which are to be found on the net, my personal opinion is that a transceiver
must look like a transceiver – that means, there must be a minimum amount of metallic shining
knobs and switches and in generally a solid design.
First time using it I didn't really know what I was doing, but the TS-830 knew…and did what it
was expected to do… It didn't take a long time until I encountered the first problems: there was
no output in SSB-mode and I realized the low power output on the upper bands. And here the
story begins. I searched for technical descriptions and procedures to do these repairs and found
them wide dispersed on the Web. And so I started collecting them, in the beginning for personal
use only.
The problem of no SSB TX operation was quite easy to fix: a broken copper ground connection
on the back of the IF board caused the mike amplifier to fail. Soldering a simple insulated wire
to another ground point on this board and I was in business on SSB. Changing the tubes and
re-neutralizing in generally is a simple procedure, but if one had never done this before, even
simple things can be difficult or at least take a long time. This may be a waste of time – on the
other hand its is only the intensive dealing with a problem that makes us learn and achieve
experience and skill.
Many hams do know how to handle and repair older equipment, but a growing number doesn't
anymore since they grew up with solid state technology only or are not interested in the older
rigs. Many newbees are taught to avoid boatanchors, they hear that dipping the plate and
peaking the load of a tube final is much too tricky and time wasting (takes 5 seconds or less…)
to make dealing with these rigs worthwhile.
If You are the proud owner of one of these 20-year old TS-830's made by Trio-Kenwood You
are probably interested in old equipment – if not for liking so for necessity. This collection of
articles and information about the TS-830 should serve as a reference for those who need it. If
You find this file useful, You are invited to propagate it over the net. If You add Your
experience or improve it's content, please email a copy to me. Feel free to remove my name
from the cover page if You want – I'm not the author but only the collector of this stuff. Please
excuse my poor English…
Halle, Germany, June 25
th
2002
VY 73's
Olaf Rettkowski DL9AI
Email: dl9ai@darc.de
2 Read first !
All information provided here is not verified. Use the modifications and procedures at Your own
risk. Please keep in mind, that malfunction or damage of Your equipment may occur, even if
You follow the instructions of these document carefully.
7
Please make sure You have the latest version of this document. Check
http://www.geocities.com/om6523.
3 History of this document
• First version (1.0) 25
th
June 2002 by Olaf Rettkowski DL9AI
• Latest revised version: (1.1) 13
th
Nov 2002
4 To-Do list
• For part II "Manuals": Rescanning of the layout and the board schemes to make them
READABLE; the additional red lines indicating power supply lines are to be regarded.
• Adding of general information how to repair a rig: measurement equipment, procedure;
where to start for locating errors – the information provided with the service manual
seems to be not sufficient, especially for those of us not so familiar with sophisticated
electronic repairs.
• Adding of personal experience in using a TS-830: maybe someone has developed new
procedures or can give hints helpful in operation.
• Adding of detailed descriptions of the function of certain parts – which resistor or
transistor has what function. This will help not only in fixing problems of this rig but
provide some kind of teaching material to learn electronics…
• Adding of test reports of older ham radio magazines, (if allowed to publish…)
5 General Description
(Author: Richard L. Measures, AG6K)
The ancient TS830S is a still a remarkable radio.
Processing:
The processor is clean and effective. When an 830 processor is turned on, the S-
meter at the receiving end noticeably increases and the perceived volume increases - yet the
audio is clean and understandable. I have never observed a modern transistor-output radio that
could perform this feat. There are several factors at work here. First-off, RF, instead of AF,
clipping was used to maximize the effectiveness of the processor. Naturally, RF clipping
generates IMD products. Trio-Kenwood engineers minimized this problem by utilizing a postRF clipping 455 kHz IF ceramic filter to clean up the IMD products. After the processed
transmit IF signal is filtered and converted to the operating frequency, it is amplified by an
extremely low-distortion tube-type RF amplifier that utilizes [Collins Radio, Co.] RF-negativefeedback. The net result is a clean, effective RF processor that is not objectionable to listen to provided the indicated processing level is kept under roughly 8db.
Strong signal overload:
The 830 has extremely low VFO phase noise. When listening to a weak
signal that is 5 kHz away from a strong local signal, the 830 outperforms many modern radios.
However, at signal spacings of 50–100 kHz, modern radios are better at tolerating strong local
signals. On transmit, the 830 generates a remarkably clean transmit signal with a minimum of
adjacent-frequency phase noise.
S-meter accuracy:
The 830's S-meter is fairly accurate. Above approximately S-5, one S-unit
equals pretty close to the required 6 db. Above S-9, the db scale is reasonably accurate.
Naturally, calibrating the S-meter helps. Some modern radios indicate 3 db per S-unit--a 50 %
error, and 20 microvolts = S-9. Whatever happened to the Collins standard of 100 microvolts =
8
S9?
Drawbacks:
Slight frequency drift during warmup. This problem can be ameliorated by one of the fixes
described below.
2. Inability to work split frequency at typical frequency differentials.
3. As with any ancient machine, maintenance requires an extra effort. However, newer radios
appear to be far from trouble free. I have spoken with owners who had to return their highlycomplex new radios to factory service five times during the first year.
6 Problems and known Fixes
6.1 Excessive delay in relay control signal to external amplifier--which
causes hot switching in the amplifier's RF relays
Cause: The RF relay in the TS-830S also switches the external amplifier relay control line.
Thus, the amplifier relays can not begin to close until the RF-relay in the TS-830S has closed.
Fix:
Install a NPN >200V switch transistor [MPS-A42 or=] in the TS-830S to take over the job
of relay control line switching. The input [base] of the switch transistor is driven by the +12V on
transmit signal ["RL"] that drives the coil of the TS-830S' RF-relay, RL1. The base-current is
limited to approx. 11 mA with a 1 KOhm series resistor. Connect another 1 KOhm resistor
between the emitter and the base to drain off the stored charge in the base. The emitter connects
to chassis-ground. The collector connects to the wire from pin 4 on the Remote socket. Pin 2 of
the remote socket should be connected to chassis-ground or to the emitter of the transistor. The
NPN transistor can only switch a positive relay-control line voltage, so this circuit will not work
on negative relay-control voltage amplifiers like the SB-200 and the 30L-1. The fix is to convert
these amplifiers to [standard] positive V relay control line polarity. A solid-state electronic
cathode bias switch [ECBS] is useful in this application. Such a circuit is shown in QST
magazine, January 1994, "The Nearly Perfect Amplifier."
6.2 Frequency drift
(Author: Tommy Hayes)
Before making any internal modifications for the frequency drift please try this:
Take both the top and bottom covers of the rig off the transceiver. Find each and every philips
screw that you can get to with a philips screw driver and loosen it about 1/4 of the way. After
doing that, retighten the screws.
9
This includes but is not limited to each and every PC board that you can get to. Done this with
my 830 that had severe drifting problems and so far (4 months) have not had a problem with the
drift yet on any band.
6.3 Frequency drift during warm-up
Cause: Change in humidity and temperature inside the VFO Unit.
Semi-Fix:
The amount of frequency-drift during warm-up can be reduced if the radio is
equipped with a "damp-chaser" resistor that will keep the VFO slightly warm when the radio is
switched off. This is accomplished by placing a 7.5 KOhm nominal, 2 W metal-oxide-film
[MOF] resistor in parallel with the contacts of the power-switch, S9. When the radio is off,
roughly 115 VAC appears across the switch contacts, which causes the resistor to dissipate heat
underneath the VFO. The full lead-length resistor is mounted on two, standoff insulators which
are fastened to the shield partition that is between the VFO and the PLL Unit. The resistor is
positioned under the VFO shield-can. A strip of insulating tape is placed on the bottom of the
VFO shield-can and on the inside of the bottom of the 830 cabinet to provide extra electrical
insulation in the event that the insulating coating on the MOF resistor fails. Each resistor lead
should be placed inside approx. 28 mm of heat-resistant insulating-tubing, such as Teflon, so
that the wires can not touch chassis ground.
6.4 TS-830S Frequency Drift - "FIX" switch
(Author: Alan N5LF)
If your TS-830S drifts or jumps frequency up & down 100 to 200 Hz, the problem may be a
dirty FIX switch. The FIX switch disables the VFO and is used for crystal control. The switch
conducts voltage in both the on (crystal) and off (VFO) positions. Dirt, corrosion, or wear makes
the switch provide uneven voltage to the VFO and therefore causes the drift/jumping.
To test for this problem, wiggle the FIX switch or press it in & out a few times and see if the
drift/jumping stops for a few minutes.
Temporary cure:
Spray the switch with contact cleaner. This works for me for 1 to 3 months,
then it starts acting up again.
Permanent cure:
Use a jumper to bypass the switch, so it is permanently in VFO position.
If someone knows a solution that doesn't disable the FIX switch's function, please let us all
know.
(These and other hints mentioned also in section 6.5, page 6)
6.5 Frequency jumping
Alan Wormser had the problem caused by the FIX switch (see section 6.4, page 9) and also
supplied some other answers to his question:
1. Grounding the AF/AVR board: Connecting a wire from TPG post to ground screw, and
inserting star washers between board and heat sink, in accordance with Kenwood bulletin appeared in QST Hints & Kinks in the mid-1980s. (Ian G3SEK, Art N2AH, Paul K0PW, Frank
Kb0ZFN, and many others)
2. The grounding screws on the PC boards may not make good contact. (Bill W7US)
3. Although I have not seen this problem in a Kenwood, I have seen it in Icom and Yaesu- both
with the same cause- small single turn variable caps. In case of the Yaesu it was a frequency
netting cap on a heterodyne oscillator- drove me nuts. It occurred randomly and never when I
10
had the rig open. A hint from another ham sent me looking in that direction. Replaced 2 or 3 and
that was the end of it. (Dale W4OP)
4. Check the external VFO DIN jack in the rear. Actually you will need to check it from the
inside. If you have one, put the matching DIN plug into the jack and pull it in and out several
times. This is a common problem with the 830. This jack has a contact which is shorted
WITHOUT an external VFO. If the contacts get dirty, it will do exactly as you described. You
might also want to spray a small amount of contact/electronic solvent on the jack and do the
plug in and out. (Brian KJ5AG)
5. I had what sounds like the same problem with a TS-830S. Turned out the FIX switch labeled
was intermittent. It is in the path of the voltage to the VFO and if it has some extra resistance,
the frequency would change. I tried "Deoxit" and that worked for a while but finally I jumpered
around the switch contact since I never used crystals for operating. Try operating the switch
many times and see if goes away for a while. (Dennis NT0V)
6. Maybe one of the xtal trimmer caps is going bad. The center pivot point is getting rusty.
Contact cleaner will fix this for a month or so but you need a new one.
6.6 Intermittent shift in display and operating frequency
(Author: Trio-Kenwood Communication, Inc.: “TS-830 frequency shift”)
Some users may report an intermittent shift in the display and operating frequency. This may
typically be a 1 to 4 KHz random shift. Cause will be a loose grounding screw on the AF/AVR
unit heat sink.
On the AF/AVR unit X49-1140-00, there are three self-tapping screws holding the aluminum
heat sink to the PCB. These also supply the ground connection to that section of the board.
Between the heat sink and PCB foil, add a tooth-lock washer N17-1030-41 at the two selftapping screws on the side of the heatsink that has the two transistors attached. (The remaining
screw already has a lock washer.)
When replacing the board to the chassis, add a solder lug E23-0420-05 to the heat sink
mounting screw as shown, and tighten all screws for this board. Solder an insulated lead
between the TPG (Test Point Ground) wrap post adjacent to C81, and the added solder lug.
Procedure:
1. Remove the top cover (8 screws) and unplug the speaker.
2. Remove the bottom cover (8 screws).
3. Remove 5 screws holding the AF/AVR unit and swing the board over. Leads do not have to
be unplugged.
4. Add two tooth-lock washer as shown.
5. Replace the circuit board and heat sink to the chassis, adding the solder lug as shown.
6. Solder a jumper between the TPG wrap post and the added solder lug.
7. Replace the top and bottom covers.
11
Installation time for this procedure is 1/2 hour or less.
6.7 Intermittent ALC on transmit
6.7.1 Problem 1: Intermittent ALC indication [TX] on only one band
This indicates that the trouble is different than was the case in Problem 2 {which would be the
same on all bands}. The bandswitch is usually the culprit. This occurs most often on the 7 MHz
band-switch position, on the two, rear-most bandswitch sections in the RF Unit.
Cause:
The bandswitch (also) has dissimilar-metal crimp-connections that turn into semiinsulators due to electrolysis. This takes place between the bandswitch's riveted-on,, tin-plated,
stationary contacts and the copper-foil on the printed circuit board [PCB]. Fix:
Apply a small
amount of conductive-paint where the stationary switch contact touches the copper-foil on the
PCB. The conductive-paint will be drawn, by capillary-action, into the problem area where the
two, dissimilar-metals touch each other.
6.7.2 Problem 2: Intermittent ALC on transmit
Cause: As in problem 1, this problem is usually caused by an intermittent crimp-connection on
the pins at the ends of the coax cable that brings the transmitter intermediate-frequency ["TIF"]
signal from the IF Unit to the RF Unit. The ends of the TIF coax cable can be found in the same
connectors that were discussed above, in Problem 1.
The fix
is the same: Make good electrical connections at the crimps on the connectors' pins.
6.8 Lack of crispness in receive audio
Cause: The intermediate-frequency bypass capacitors, C62/C63, at the audio output of the
product-detector, are so large that they noticeably attenuate the treble audio frequencies.
Fix:
Reduce the value of these capacitors and reduce the terminating resistance, R78, across the
output capacitor, C63, to reduce the treble attenuation. R78 is changed from 47 KOhm to
approx. 3.3 KOhm - 4.7 KOhm. C62 and C63 are changed from 0.022 µF to 0.0075 µF -
0.01 µF. {the factory value varies depends on the radio's S/N} These components are on the IF
Unit, about 4cm in front of the left-rear corner. Note: After this change is made, the full range of
audio frequencies will be present in the background/"sky" noise. It is beneficial to compensate
for this by turning down the RF Gain control until the sky noise decreases to a comfortable
level. [This is the main reason to have an RF gain control.]
12
6.9 Lack of crispness in transmit audio
Cause: The RF-bypass capacitor, at the collector of the 1st audio amplifier, is so large that it
bypasses the higher audio frequencies along with the RF. {The amount of treble-rolloff in a
stock radio is about 4.5db at 2800Hz.}
Fix:
On the IF Unit, at Q19, change C106 from .015µF to approx. 0.001µF. Q19 can be found
directly behind the filter space for the larger of the two, optional CW-filters.
6.10 No power output on most bands
Cause: This is usually due to the final unit bandswitch being out-of-sync with the bandswitch
shaft. This problem is caused by a cracked, plastic shaft-coupling between the RF unit and the
final unit. Trio-Kenwood did not use Locktite, or a similar thread-locking compound, so the
setscrews in the coupling had to be over-tightened, by the assembler, to prevent the setscrews
from loosening during operation. The constant stress on the plastic, caused by the combination
of ordinary use and the over-tightened the setscrews, eventually causes the plastic couplings to
crack.
Fix:
Remove the cracked plastic coupling and either epoxy it together, buy a replacement
coupling from Trio-Kenwood, or find a replacement shaft coupling made from metal. Use
Locktite in the setscrew threads during re-assembly so that the set-screws will not need to be
overtightened. Plastic shaft couplings can be cracked by overtightening the setscrews. Allow the
Locktite to set 2 minutes before operating the switch.
6.11 Noisy or intermittent front panel control potentiometers [pots]
Cause: The grease, that is used to lubricate these pots, oxidizes and becomes gummy with age,
causes an intermittent connection between the rotating wiper-arm and the resistance-film in the
pot.
Fix:
Stand the radio up on its back, on the original rear packing cushion. Pull-off the knobs of
the offending pots. Using a syringe and small-gauge needle, inject TCE degreaser down into the
clearance spaces next to the concentric shafts of these pots, rotating the shafts back and forth to
loosen the gummy grease. When the pot is no longer intermittent, inject GC Electronics Co.
"De-Ox-Id" . This material should be thinned with about 50% TCE to help fluid penetrate down
into the pot.
Note:
TCE is carcinogenic and should be used with good ventilation.
6.12 On the AF-AVR Unit, the 4-pole relay contacts which switch the bias
to the finals may fail after extensive use.
This relay is neither cheap nor easy to replace. The failure is caused by th.00000 repeated
shorting to ground of a charged capacitor in the bias circuit by one set of the relay contacts
during T/R transition.
Fix:
On the circuit diagram, find the leftmost set of contacts. The arm [movable contact] of this
set of contacts is grounded.
Fix:
cut the trace from the arm to ground in 2 places about 5mm apart. Remove the foil between
the cuts. Solder a approx.100 Ohm, 0.25 W resistor across the gap. The resistor will limit the
peak discharge current during T/R-R/T switching to a value that will not burn the relay contacts.
Loading...