Devoted entirely to Amateur radio

QTH-locator DS80b, WW/Loc: JO38


d2. General CW/SSB technik for 2m


d6. 6m techniques
d7. 70cm techniques
d21 Converting Magnetic VHF combiner amplifier TU813 (2m) and TU8062 (70cm transmitter)
d24 Converting NEC pager PB-3102A (Norwegian text)
d25 Converting Magnetic pagers PBS817 (and info for Compact9000) (Norwegian text)
d27 Evaluating NMT450 equipment for amateur radio purposes
d28 NOKIA NMT450 base station equipment
d31 Constructing VHF/UHF/SHF beacons
d32 VHF/UHF power modules for signal generators
m11. Griddipmeters
m12. VSWR- and wattmeters

...


VHF/UHF Power amplifiers for the technically skilled radio amateurs

1) NEC 144MHz 150W PEP PA available as surplus about a year ago in Norway, click on the pictures for further details
2) 2x NOKIA 432MHz 200W PEP power amplifier available as surplus in Norway.




1) Panels for selection of RX-antenna/transverters, transceiver keying/PTT, together with 136kHz
and 2m transverter


2) Simplified view of shack wiring for VHF/UHF/SHF operation using transverters and remote operated equipment.
Started off using 23/70cm transverters mounted above the roof, but it later turned out to be complicated since I needed to combine more equipment,
so around 1983 another arrangement was made. This has been optimized many times. The most important seems to have been to use positive short-circuit-proof
voltage on transmit cable to control the swithing, with indication if the remote equipment is not ready for operation.


3) General principles of operation with remote VHF/UHF-transverter, power amplifier and pre-amplifier



Principles for operation with transverter. Basic diagram for remote controlled units
for 2m/70cm/23cm rigs.
The following circuit diagrams are based on this system,
but it is possible have some remote indication of failures or manual blocking.
Remote PA may have a fault, or only cable for RX is connected. Some decide to
use only single coax cable, but I wish to have the possibility to listen on one band
when transmitting on another and have no problems finding sufficient amount of
secondhand cables from work.
The use of +12v (shortcircuit proof) solves the problem with PTT that a shortcircuit
to ground would otherwise cause the amplifier to switch on, while in this case it
indicates a state of failure, which is indicated on an LED in the shack.


4)


Pre-amplifier and RX/TX-control-box for 2m and 70cm. Meters are cheap and directional couplers even cheaper - to make.
So I've included a meter for each pre-amplifier (with remote C/O-relays) and RF power output reading for each
band. Only small meters are needed for antenna-relay and pre-amp current. The RF-indications may have delay or
direct reading, it is just a half LM358 to convert to peak reading on whatever testpoint.



The RX/TX control-box seen from rear


5)


Simple PIN diode switch for 2m linear power amplifier
Coax cable lengths: 'A' = 'C' =
l/4 = 34cm (not very critical not much power passes here, RG58 is good, but I would prefer PTFE type which is easy to solder), 'A' is only used as a simplified RF-choke and any impedance cable will do here.
Coax cable 'B' - any length will do, but here passes the power
Capacitors: Use 2 in parallel, 470pF or 1nF for low impedance
D1 Unitrode UM9401 or similar, D2-D3 not critical RF switching type, D2 may be a smaller PIN-switch type, use 2x 2 smaller diodes to limit the dc in each diode.
Resistor value depends on diode types and TX power.
see diode data at
http://www.datasheetarchive.com/3359.html


6)



Pre-amplifier control-box. It is important that it is shortcircuit proof. If any faults occurs such that the voltage does
not reach the remote pre-amplifier the relay switch to pass the transmit signal to the antenna, and the pre-amplifier is
protected. The meter is not shown, but is connected over the 4.7W resistor.
Note that the TX-line is DC-shorted when the switch is in OFF position. The transceiver or transverter senses this and
cannot operate, I use this function when PA is not switched on, but only want to listen on the band. Since the equipment
is not in my shack, it is also meant as a signal that PA could have a faulty condition and the transmitter should not be
able to send. Since it is only 1mW from FT-902 or FT-7 into the transverter it is no problem and need not feed the signal
into the HF transceiver, but LED's on the transverter indicates that the control box is disabled.


7)

a) My old pre-amp control board. Used then Kenwood TR-7010 with single coax cable for receive and transmit
and control signal did not follow the RF, but used separate PTT-line (which is a bad practice because short circuit
will operate the power amplifier). If you use single cable I suggest you add the modification shown in the first place
to have the DC-switch signals via the coax cable

b) A suggested circuit diagram using relays instead of switching diodes, but I measured the diode switching
at Scandinavian VHF meeting, or to say in other words, nobody could measure any loss at all, so it was approved
by SM6CKU and the rest who didn't like diode switching


8.

Almost as described, not bad!
Diode switch for 2m to split signal for transmitter and receiver used for Trio TR-7010 transceiver (out of use), measured very well.
It was made in 1982, wouldn't use RG-174 today, but thin PTFE-cables since they are far easier to solder without any risks of damage.


9.



A low-noise pre-amplifier (BFT66) for 144MHz. Developped by DJ7VY, submitted by DC7CW
DUBUS VHF-UHF Technik 1 pp.153.

This extremely sensitive amplifier is very easy to build, using a microwave transistor BFT66 (Siemens)
in 50 ohm input impedance configuration. It exhibits an interception point of -3.5dBm, which is only 8.5dB
lower than that of the VHF receiver with outstanding performance (using a 3N200 mosfet with NF=3dB)
as it is described in DUBUS 2/75.
With respect to the high power gain (24dB) of the BFT66 an oscillation-free operation and proper input
impedance is to achieve by excellent grounding of the emitter. The length of emitter lead shall not exceed
1mm! The other parts of the circuit are not critical. The bias voltage of the base is temperature stabilized
by three diodes 1N914 connected in series. The collector current is 12mA at the supply voltage of +6V.
A shield between input and output circuits is recommended. The coils L1 and L2 are made of 5 turns 6.5mm
dia., length of coil 8.5mm, 1mm dia wire. L2 is tapped at 1.5t and at 1t from cold end.

A later article in UKW-Berichte by DJ7VY describes some recommended input filters, and I've also mounted
a quarterwave notch filter for 168MHz, and still the NF was measured to 1.1dB. The pre-amplifier was mounted
using pcb laminate, with the transistor mounted in a hole at lower side of the screenwall between input and
output section.



10. Complete 2m pre-amplifier with BFT66. Note the input protection diodes (BA182 or BA282)
NOTE *) Jumper is only used for voltage supply from the RX-coax cable. FB= Ferrite bead.
L1 = 3T 14mm dia, 8mm long with 2mm silvered Cu wire (airwound)
L2, L3 = 5T 6.5mm dia, 8.5mm long, 1mm cu wire (18SWG), tapped at 1 and 1.5turns from cold end
In later version I used a BC557 instead of the zener diode to stabilize the operational point (see note at right side).
R1= 4k7-10k, R2 470-680W, R3 = 910-1000ohm, C1= 15pf, C2 = 15pF, C3 27pf, C4 = 12pf trimmercap, C5=22pF,
C6 = C7=C8 = 470...2200pF feedthrough capacitor, C9 = 12p trimmer, C10 = 27pF, C11 = 470pF, C12 = 01,
C13 = 450-1000pF chip, C14 = 1nf disc ceramic, D1=D2=D3 = BA282, D4=1N4002, D5 = 5.1 or 5.6V zener diode.
nominal collector voltage is +6V.




11. Mechanical construction of the preamplifier. Measures: 80x100 mm.
L1 forms a combined notch and highpassfilter, to attenuate band I and II signals.
See: 1) article by DJ7VY in UKW Berichte nr 4/77 or VHF Communication 1/78 for new type of preamplifier
2) AR nr 3/82 and 1/83.



12



Pre-amplifier wiring. The dc wire marked +RX goes to the RELAY. It is drawings from VHF communications article I
once wrote...


13.



For the mastmounted pre-amplifier I used the MD951 relay with max 200W. You'll find the data for MD951 type
coax-relays in SSB Electronics catalogue 1984. I bought such relays
at a rally in UK, and have used one for my remote 2m BFT66 pre-amp since 1980. According to Ian, G3SEK
the power limit (not switching power) is 450W on 2m, so it is really a useful piece to remove before you discard
the rest! Careful to take care of the old mounting hardware as it is difficult to connect the coax cables without.


14)



Here is my old rig selector and transverter selector unit
tried to have the receivers through the unit, but crosstalk between the different RX sides of transverters was a bad
problem, used small screened relays, but result was bad and I had to revert to the BNC patch panel for receivers/-
antenna/transverters.
I use 14MHz IF for 6m, and 28MHz for 2m, 70cm, 23cm (and 144MHz for 2320, 5760, 10368 and 24192MHz).
HF drive is from FT-7 or FT-902, and VHF drive is from IC202E., separate receivers: Drake 2-B and R-4C, with
FT-7 as spare transceiver.
The drive level from FT-7 and FT-902 are equal, as is the drive from the 2m transverter and IC-202E, so it is not
much problem if one rig should fail, but I've really never had such problem for over 30 years. Only had some xtal
oscillator problems with FT-250 (Yaesu), and no problem with any other equipment for over 40 years.


15)



28MHz transverter remote control boxes used for 6m, 70cm, 23cm operation. Indication for level, PTT-state and inhibit


16)



Simplified version transverter 28MHz remote control box. TX1 and TX2 when transverters operates as normally,
while TX2 will not light when the remote part is inhibited (manually or because of a remote fault).


17)


Another version of transverter switching using
2N7006 fets which are readily available here in large
amount. An LED indicates that the transmitter is
blocked.


VHF SSB/CW transverter with pre-amp and power amplifier. My equipment is spread into two different rooms and
some provisions are made such I cannot transmit when the antenna is not connected or the amplifier is not switched
on. The circuit diagram shows some signalling used for 6m, 2m, 70cm, 23cm band transverters to avoid damaging
the power devices when not all equipment are available


18)



FT-221 modifications. The components marked with red rings have been changed. The problem with chirp is
the usual problem when you don't understand capacitive pulling from a keyed stage. And when the buffer is
pulled makes it not better. The key-up attenuation is poor and has several reasons. Primarily the first stage
has too drive high level, it is then a problem for the next stage, too, but further improvement can be achieved
by using RF transistors in the IF amplifier stages. BF199=BF224 are readily available in Europe at low price,
so it is really no problem to sacrifice a few (the same problem in FT-101B). It is also a problem that key-up
voltages for the two stages are not equal, some voltage dividers must be changed. Then I also replaced the
switching diode on the output with another BA182 which has better attenuation.
The mod is easy and done in few minutes when you know what to do.


19)



Some commonly found coax connectors.
Conhex type connector is usually found on radiolink equipment and used for BB and up to 70MHz IF.
Have seen diode mixer for 10Gc/s using conhex type, so I suppose it has been a 50 ohm version.
I use phono connectors for control lines; keying, PTT etc, but not for RF. For short interconnections I prefer
conhex or BNC (incl. 136kHz) indoor applications Generally speaking, I use the connectors fitted on the
cables because often they are mounted proffesionally, and save a lot of trouble if kept as they are.
Use SO239/PL259 up to 432MHz if they are already used on surplus equipment. Remember; even BNC
connectors are not good for UHF.


20)



Heliax LDF5-50 7/8" coaxkabel


2nd harmonic filter for 2m transmitter, it is very sharp, and notchdepth is at least 40dB. It is somewhat tricky to install the trimming capacitor, but it seems to work. The line is cut somewhat too short for quarterwave resonnance on 288MHz and the length is increased by the capacitor to notch on the desired frequency.


22)



Type No. PYE AT.29908/AB Freq. range 132-174MHz Antenna filter
A good 2m bandpassfilter found in PYE equipment. Believe I found them in some PYE R17FM receivers for 160MHz. Have used the filter on the output of my 2m transverter running 2W RF for some years without any problems, and the filter seems to be stable. Have not done any measurements on it.


23)



BSP MD510 2m CW/FM 0.8W exciter. Built 3 in 1978 with my own components, but too bad oscillator noise, modified two for LA3VHF and LA3UHF, and later discarded all, used modified SRA C400 for 70cm (LA3UHF, LA3UHG, LA4UHF, LA6UHF, LA9UHF), and PYE Westminster exciter for LA3VHF and LA6VHF (PYE T30FM) with DJ2LR 12MHz low-noise xtal oscillators for all 2m and 70cm beacons.



DJ2LR very low noise xtal osc modification shown for 4MHz xtal, for 12MHz the capacitor C4 should be reduced to 1000pF (film or NP0)


24)

25-30W QRP PA for mobile operation with IC202, a kit made in Switzerland.




It is still possible to have more cables here.




Seen from above:
2m power monitor and circulator.
2m/70cm control panel
second 2m power amplifier (25W)
70m 50W power amplifier


27)


Improved cathode bias regulator.
Q1, Q2 BC237B (2N3904), Q3 BD140 or other suitable PNP power (MJE2955), Q4 2N7006 or any other,
R5, R6 chosen for suitable values dependent on meter current range.





Still a useful book for finding VHF/UHF circuit diagrams and components (SSB Electronics 1984, Componenten & Systeme)


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2005.04.07