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G8MNY > TECH 25.05.07 10:02l 90 Lines 4124 Bytes #999 (0) @ WW
BID : 15856_GB7CIP
Read: GUEST OE7FMI
Subj: PEP Meter modification UPDATE
Path: DB0FHN<DB0NOE<DB0GAP<DB0FSG<DB0MRW<OK0PKL<OK0PPL<DB0RES<IK2XDE<ON4HU<
F4BWT<I0TVL<LA1SFS<GB7CIP
Sent: 070524/2337Z @:GB7CIP.#32.GBR.EU #:15856 [Caterham] $:15856_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Update Nov 06)
I was discussing a PEP Power meter project & remembered an old Radcom article
that described the principle of a conversion without much modification & best
of all maintaining calibration. I have now found the article Jan 1989 page 46
& show both my guess at the circuit before I found the article, & my sketch of
the original.
MY GUESS
o Normal
+9V>ÄÄÄÄÄÄ>oÄÄÄÄÄ´>ÃÄÄÄÂÄÄÄ¿+
PEP LED ³ ===10u
³ _³_ C2
Normal ³ Normal
oÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo
>ÄÄÄÄ>o¿PEP ³\³ PEPÚo<ÄÄÄ> +VE
ORIGINAL ÃÄÄÄÄðÄÄÄ´+ \ D1 ³\ ³ ORIGINAL
RF SWR RV1 f.b. ³ A >ÄÂÄ´>ÃÄÂÄÄÄÂÄÄÄÄÄ´+ \ D2 ³ SWR METER
DETECTORS preset ÚÄÄ´- / R2 ³ 1M ³ B >ÄÂÄ´>ÃÄ´
SWITCHING ³ ³ ³/³ 10K ³ ³ ÚÄÄ´- / R3 ³
& CAL POTS ³ ÀÄÄÄÄ)ÄÄÄÄ)ÄÄÄÄÄ´ ³ ³ ³/ 10K ³
³ ³ ³ u1 === ³ ÀÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÙ
³ ³ ³ C1 ³ ³ ³
>ÄÄÄÄÄÄÁÄÂÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄ> -VE
_³_
HOW IT WORKS
A 3 pole change over switch, powers up the modification & also switches in the
circuit between the RF detectors & the meter.
Multiturn Preset RV1 has to be set to exactly the same resistance as the meter
is, in practice this can be finely tweeked later on calibration tests.
Opamps A & B must be the FET type that can function correctly with their input
@ 0V (-ve rail). The Ferrite Bead needs to be as close to the opamp input as
possible & in practice may have many turns to eliminate all RF.
R2 puts a slight load on the opamp allowing any slight O/P current to leak
away & not charge up C1. Silicon signal diode D1 allows the opamp only to
charge up C1 (@ 5mA max peak current, hence C1 is a small value to charge
nearly instantly) to the peak +ve voltage the original meter would see from the
detector etc. N.B. This is a very small voltage! But the beauty of opamps is
that they can accurately compare this with the peak input voltage & stop
charging as the precise level.
To discharge the small C1 over a long time relative to audio peaks, 1M is used.
Opamp B then accurately follows the C1 voltage & applies it to the meter.
Again R3 puts a slight load on the B opamp allowing any slight O/P current to
leak away not through the meter. Another silicon signal diode D2 is used to
drop any minimum opamp O/P DC level so that the meter should be able to read
zero OK.
Calibration of RV1 is just to switch between normal & PEP on a steady hum less
carrier & adjust for the identical power reading. Check this at different
power levels & bands.
THE ORIGINAL
D1 ÚÄ100kÄÂÄÄÄÂÄÄÄÄÄÄÄ´<ÃÄÄ<+4V to 24V
ÚÄ´<ÃÄÄ´ ³ +³ 47u D4
_³_ \³/ ³ === C4
ÚRV3¿ ³ _³_
³50k³ ³
>ÄÄÄÄÄ¿ 1M 1M 3³\³8 IC LM358
ORIGINAL ÃÄ100kÄÁÂÄÄ)ÄÄ´+ \ 1 D2 5³\
RF SWR RV1 ³ ³ ³ A >Ä´>ÃÄ100kÄÂÄÄÄÄ´+ \ 7 D3
DETECTORS 200 C1³ ÃÄÄ´- / ³ ³ B >´>ÃÂÄÄÂÄÄÂÄ> +VE
SWITCHING ³ === ³ 2³/³4 C2 ³ ÚÄ´- / ³ ³ ³ ³ SWR
RV2 u1³ ÃÄÄÄÄ)ÄÄÄ´ÃÄÄÄÂÄÄÄÄ´+ ³6³/ ³ ³D5³ === METER
20K ³ ³ ³ u1 10M === ÀÄÄÄÄÄÄÄÙ ³ _³_ ³u1
³ ³ 100k ³ ³ C3³1u ³ \_/ ³C5
>ÄÄÄÄÄÁÄÂÄÄÄÄÄÁÄÄ)ÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÁÄÄÁÄ> -VE
_³_ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
What amassed me was my memory of the principles were so exact since 1989!
The man differences are..
1/ The offset pot system RV3.
2/ The heavy RF filtering 100k & C1 (may it affect the AF peaks??)
3/ 1 overall split NFB loop DC 100K & AC though C2, rather than my 2 NFB loops.
4/ Meter overdrive protection diode D5.
5/ I included in out switching & PEP LED.
6/ D5 is an idot diode.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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