| |
G8MNY > TECH 15.08.16 17:05l 210 Lines 10349 Bytes #999 (0) @ WW
BID : 14688_GB7CIP
Read: GUEST
Subj: T500M 12V 500W HF Linear 2/2
Path: IW8PGT<IZ3LSV<IV3SCP<SR1BSZ<GB7CIP
Sent: 160815/0952Z @:GB7CIP.#32.GBR.EURO #:14688 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jul 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
5/ BIAS
R4 turns on Q2, when Q2 emmiter > 0.6V, Q1 turns on reducing Q2 base drive.
Value of R3 is used to see the exact bias voltage, R4 & supply voltage also
affect the bias to slightly. R5 limits the max current, D2 is a safety
feature. Q1 & D2 are thermally connected to the PA on the same heatsink.
PTT Switched
+12V ÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ R5I This circuit was slightly
R4 Added 5R unstable when scoping
270 47n 10W Scope for R5 (5R) so I added a small
³ Ú´Ã---³ <--1MHz oscillation! capacitor base to collector
³ | ³/c on the large MPN to stop it.
ÃÄÄÄÄÄÂÄÄÄÄÄ´ TIP33A
³ C6 === Q2 ³\e NPN +690mV @ 2.2A
³ 2u2_³_ ÃÄÄÄÄÂÄÄÄÂÄ> via RFC to
³ /// ³ ³ ³ Amp input
NPN c\³ ³ ³ ³ transformers
TIP29 ÃÄÄÄÄÄÄÄÄÄÄÄ´ ³ ³
e/³ Q1 _³_ +³ 2R2
PA BIAS ³ \_/ === ³ Components were not the
QuescentÀ>5R D2 ³ C7³ ³ same as original diagram!
Set 1-2A R3 ³ 2u2³ ³
ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄ
6/ ALC
There is no ALC system on this AMP, & I am used to old Valve amp with a power
ALC control. With PA ALC, the driver power is automatically set to the wanted
level, & with the PA turned off your back to full bare foot power. So I
designed this ALC circuit for this PA...
+12V Tx>ÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
R4 5R ³
270 PA 10W ³
ÀÄ>Bias<ÄÁÄÄ270ÄÄ¿ 15K
Circuit ³ 2n2 ³
ÃÄĴÿ ³ Front panel
PNP e\³ ³ 10K 50W-600W
2N3703 ÃÄÄÁÄ>POWER ALC Control
on POT /³ POT
ÚÄÄÄÄÄ´ _³_
4K7 |³| ///
³ ³Fbead Mounted on 12 way JONES plug
Input -ve³ ³ Fbeed
RF on >Ä1kÄÄ´<ÃÄ´<ÃÄ´ ÀÄÄÄÄÄÄÄÄÄÄÄÄððij<ÃÄÂÄÄÄÄÂÄÄÄ>ALC to rig
Drive 1N4148 ³ long wire 1N4148³ 100 0V to -10V
Atten === ³ ³ -
2n2³ 4K7 === 4u7
_³_ _³_ _³_+20V
/// /// ///
The -ve supply for the ALC is derived from the RF on the attenuator after the
DRIVE relay. The -ve after the 4K7 it is normally clamped to +ve by the PNP.
But when the PA bias current (limited to 2.2A by 10W 5R) reaching the 8 PA
bases, gives a voltage lower than that set on POWER POT & the clamping stops,
letting the -ve through. The series diode & 4K7 load mounted on the rear Jones
socket ensures only -ve voltages are given to the exciter to reduce power
drive. The 4u7 & 100R give a sensiable ALC time constant action.
MY CLEVER ALC DESIGN!
My ALC works very well compaired with manually keeping the drive power always
low enough at all times so the PA never clips. By using bias current demand,
it is quite effective at keeping the PA operating in it's linear region by
reducing the driver power. This is because the large amount of NFB used around
in this commecial PA, that increases the PA's drive power as the amp gain
falls off at full power. The sudden increase in bias current occures before
the PA actually clips. So a usefull & accurate maximum drive threshold point
that caters for any SWR, supply voltage, or Rig power setting etc!
7/ INPUT SWR
The input frequency compensating attenuator circuit was not as the diagram &
the SWR was not all that good, dispite all components testing out OK.
SWR Original Input Match SWR Improved Input Match @ 50W
1.7´ .ú'ú. 1.7´
1.5´''''''''''' 'ú.. 1.5´
1.3´ ''''úúúúú 1.3´ ..ú''ú. ..ú'
1.1´ 1.1´'''''''''' ''''''''
ÀÂÄÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ ÀÂÄÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ
1.8 3.5 5 7 10 14 18 21 24 28MHz 1.8 3.5 5 7 10 14 18 21 24 28MHz
L1 39p 25W L1 39p 25W
>ÄÄ())ÄÄÄÂÄÄÄÂÄÄÄÄÂÄ´ÃÄÄÂÄ>Drive >Ä())ÄÂÄÄÄÄÄÄÂÄÄÂÄÄÄÄÂÄ´ÃÄÄÂÄ>Drive
40W L2( === ÃÄ220Ä´ Splitter 40W ³ L2( === ÃÄ200Ä´ Splitter
( ³56p ÃÄ220Ä´ === ( ³56p ÃÄ200Ä´
ÚÄÄÄÂÁÄÄÂÁÄÄ¿ ÀÄ220Ä´ 100p³ ÚÄÄÁÂÄÁÄ¿ ÃÄ200Ä´
200 200 200 200 220 ³ 220 220 220 ÀÄ200ÄÙ
_³_ _³_ _³_ _³_ _³_ _³_ _³_ _³_ _³_
Actual Circuit New Circuit
There was a bump @ 10MHz & that is from the drive splitter load. L2 & 56pF
disconnects the added load, as the 39pF bypasses the series attenuator Rs on
the higher frequencies, to flatten the amp gain. The original diagram did not
have 220R to ground, but had 20pF to ground @ the L1/2 junction. I found
making this a 100pF (Tx grade) was better on 10m band & changing the load Rs
around gave a better lower band input match.
Flat gain is less important than driver rig linearity, due to poor load. The
input SWR will change with drive level (higher Z at more power), as the RF NFB
level reduces, correcting each amplifier gain, as each amplifier works harder.
T E S T I N G
At a club meeting, 2 of these amplifiers (modified & unmodified) were tested
with 2 tone linearity test & with a spectrum analyser for harmonics. Both amps
performed well to the sudden (like AF Amps) 600W clipping level. This due to
the effective NFB keeping good lineararity until it fails. But even brief full
carrier testing on lower bands did provide smoke from the underrated input
attenuator!
The 2 tone test showed very good linearity to 400W PEP, so I think the quoted
IMD looks right.
The harmonics tests on a spectrum analyser showed the need to have the "right"
low pass filter selected, as these un-tuned broadband amps are quite harmonic
rich otherwise!
dB Topbands with dB Topband with
0_³ f1 15-30MHz Filter 0_³ f1 2-3MHz Filter
-10_³ ³ -10_³ ³
-20_³ ³ f3 -20_³ ³
-30_³ ³ f2 ³ -30_³ ³
-40_³ ³ ³ ³ f4 f5 -40_³ ³ f2
-50_³ ³ ³ ³ ³ ³ f6 -50_³ ³ ³
-60_³ ³ ³ ³ ³ ³ ³ f7 -60_³ ³ ³ f3
ÀÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄÄÁÄ ÀÄÄÁÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄ
On Topband the 2-3MHz LPF is not really that good for the 2nd harmonic! Higher
bands fared better with filter performance. Of course no problem at all after a
good ATU.
On actual testing into aerial via a high Q QRO ATU, I found it was possable to
get slight PA parasitic oscillation (of the RF envelope) at very high power. It
never did this into my dummy load or an actual aerial on Spectrum Analyser! But
with the final tweak to the input attenuator, it tested OK across all bands,
with ATU tuning over a range of SWRs. So sudden high SWR in a tuner may
indicate a Tx "parasitic" as well as aerial "arcing" failure!
H A Z A R D S
Current Loops:
Although 12V is fairly safe (compared to 230V or 3kV), with high currents
anything metal is a hazard! This includes the PL259 plug & mains earth wiring!
I put heat shrink sleeving on 259 plug rig lead near the +12V terminal. Care
must be taken to ensure the "75A" does not flow around unsuitable leads in
parallel e.g. Mains PSU earths!
Battery leads:
With single battery, use short "starter gauge" cables, with soldered on copper
tabs/lugs, made from thin Copper sheet 0.5mm, wound on a 8mm drill 1.5 turns.
Then flattern one end, solder to cable (on cooker).
__________ heat shrink
Drilled ___ _____________
Hole ____/ ³~STARTER CABLE
~~~~ÄÄÄÄÙ~ÄÄÄÄÄÄÄÄÄÄÄÄÄ
~~~~~~~~~~~~
Clean up & apply heat shrink sleeve or tape. Drill hole for PA & battery
connections. Mark up + & - with coloured tape. Apply water repellent grease to
tabs, bolt tread, washers etc.
Lead Acid Batteries:
Other than high current & fire hazard of melted leads, batteries have Sulphuric
Acid that always seems to get out & damage cloths etc, you can replace clothes,
but eyes are something else! Take care!
H2 Anti Explosion Tip:
Always "blow" at the battery, before making/unmaking connections, this simple
action reduces the chance of hydrogen being around for sparks to ignite!
High Power RF:
At these powers RF leakage from loose PL259, high Filter & Aerial voltages are
dangerous! Double checking connectors & everything is SAFE before keying up, &
testing is essential. Otherwise you will soon learn about deep RF burns & gain
"Respect for the RF" the hard way!
RF Chokes:
Wind coax or balanced aerial leads to make "RF chokes" near shack end, this
helps keep shack RF fields & RF lead currents down!
I N U S E
Running it /P for 8 days at a summer camp on HF with autocaller & pleanty of
pile ups, I did find a fan system was useful, to cool the front part of the PA
(used a small Germanium transistor to sence temp & a high gain Tip Silicon to
operate fans in series.)
A 25A linear PSU floating batteries worked well. The rig was floated on another
battery & PSU. This did allow a much smaller petrol generator (650W 2 stoke)
to be used rather than a 2.3kW 4 stroke & QRO Valve Amp. (That was used for
cold night to keep the operating tent warm!)
Reports were all pritty fantastic, good clear comms quality AF from the old
IC735 with its hard AF clipper mic processor, & a strong signal. A local looked
at the remote Hack Green SDR website radio, only to comment "my /P station much
was stronger than his & narrower!"
See my Tech buls on "AF 2 Tone Test Osc Design", "Transistor PA Biasing", "Lead
Acid Batteries", "Variable Speed Thermal Fan", "12V 75A Del SMPSU Mods", "2nd
Car Battery for /M & /P", "Rig DC Power & RF Hazards", "Using 2 HF PAs" &
"NORTHERN 650W 2 Stroke Genny".
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
