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G8MNY > TECH 18.10.24 08:34l 141 Lines 6199 Bytes #999 (0) @ WW
BID : 18056_GB7CIP
Read: GUEST
Subj: Testing Auto ATUs
Path: IZ3LSV<I0OJJ<LU4ECL<K1AJD<VE3CGR<KA1VSC<GB7CIP
Sent: 241018/0730Z @:GB7CIP.#32.GBR.EURO #:18056 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Oct 22)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
If an auto ATU (matcher) misbehaves, here is my way to test it.
KIT NEEDED direct
Dummy Aerial _ _ _ _
ÚÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿ /ÚÄÄÄÄÄÄ¿\ ÚÄÄÄÄÄ¿
³HF ÃÄÄ´1st SWRÃÄÄÄ´AUTOÃÄÄÄo/ÄÄÄÄ´2nd SWRÃÄÄ´MANUALÃÄÄ´DUMMY³
³RIG³ ³ BRIDGE³ ³ATU ³ o ³ BRIDGE³ ³ ATU ³ ³LOAD ³
³50%³ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÙ ³ ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÙ ÀÄÄÄÄÄÙ
ÀÄÄÄÙ ÚÄÄÄÄÄ¿ ÚÄÄÁÄÄÄ¿ \_______________________/
³SCOPE³ ³MFJ259³ VECTRONICS ATU VC300LP
ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÄÙ
Set up needed to acurately test the performance & enables calibration to be
done to the auto ATU.
1/ With Manual ATU in through mode, measure the settled Rig seen 1st SWR bridge
Is it the same or better than 2nd SWR bridge. What is the power loss?
Repeat for all bands.
2/ Now do 1/ with manual ATU adjusted to give an SWR of 1.5:1 on 2nd SWR bridge
Does the Auto ATU settle & does the 1st SWR bridge always give a lower SWR?
3/ The actual Z of the presented load can be measured on an MFJ259 analyser & a
2D map drawn of the aerial Z the tuner can match for each band.
4/ Now do 1/ with manual ATU adjusted to give an SWR of 3:1 on 2nd SWR bridge.
Does the Auto ATU settle & does the 1st SWR bridge always give a lower SWR?
5/ Now do 1/ with manual ATU adjusted to give an SWR of 6:1 on 2nd SWR bridge.
Does the Auto ATU settle & does the 1st SWR bridge always give lower SWR?
N.B. Many Auto ATUs can't do this!
TYPICAL SWR CIRCUIT
--------- HEAD UNIT -------
Tx o)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄ(o LOAD
ÃÄÄÄÄ======= C1³/\ ³
³ T1 ()))))) === ³
³ ³ ³ ³ /'³ ³
³ ³ ÀÄÄ)ÄÄÂÄÁÄ´ÃÄ´C2
³ ÃÄ68RÄ´ ³ n3 ³
³ _³_ _³_ ÀÄ2K2ÄÄ´
³ D1\_/ \_/D2 ³ R AUTO TUNE
³ ³ ÃÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄ> DECISION
³ ÃÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄ> CIRCUIT
³ 1n=== ===1n ³ F
ÀÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄ
HOW BRIDGE WORKS
A short length of thick wire goes through the screened ferrite transformer T1
making a 1 turn primary, & the lead joins the XTMR & LOAD sockets together. A
pick off voltage attenuator is formed with trimmer C1 & C2 cap. This RF voltage
is fed to T1 secondary centre tap. Load current is transformed by T1 into a
voltage across the 5W non-inductive 68R.
When the load is exactly 50R the diode D2 sees no RF as the voltage sample &
the current sample are in opposition & cancel dependent on the calibration of
the trimmer C1.
The 2K2 is needed to complete the DC meter circuit & will affect the lowest
frequency calibration, as will the inductance value of T1.
BRIDGE CALIBRATION
As there are no meters, C1 is calibrated to give zero Reflected volts on a
scope connected to D2, once an 1st SWR bridge sees a 1:1. Fine Tweeking of
Manual ATU will achieve this as long as the Auto ATU does not go hunting again.
Doing this adjustment means the Auto ATU will now aim for a "1:1 as seen by the
Rig" so giving a better matching result. (if it was out of adjustment.)
On one Auto ATU I tested, it always gave a poor SWR, there was not enough C1
range on the trimmer, so I added a small Tx grade C across it. QED.
CONTINIOUS HUNTING
This can be a result of load out of the 3:1 range limit of most Auto ATU, or a
faulty Binary step value in the L or C values. (poor relay contact?). Or too
"fine a target" control loop gain (less than 1 step change).
INSIDE ATU Inductace ratio not turns!
64 32 16 8 4 2 1
Rig__SWR______()))))))_())))))_()))))_())))_()))_())_()_____Aerial
BRIDGE ³ ³ ³ ³ ³ ³ ³ ³
³³ ³___\____³___\___³___\__³__\__³__\_³_\_³_\³
ÚÄÄÄÁÁÄÄ¿ ³__________________ _____________________³
³ CPU ³ Rig\ Ant
³CONTROL³ ___________________³______________________
ÀÄÄÄÄÄÄÄÙ \ \ \ \ \ \ \ \
³128 ³64 ³32 ³16 ³8 ³4 ³2 ³1
=== === === === === === === ===
ÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄ
Here the 16 relays under CPU control, gives 65536 matching options, by
selecting 1 of 128 binary step values of L, & 1 of 256 binary step values of C,
& whether the C is needed on Rig side for Low Z aerials <50R, or Ant side for
High Z aerials >50R.
_ _
/| /|
Rig _________())))________ Ant Rig ________())))____________ Ant
³_ / / ³_
³/| ³/|
50R === <50R 50R === >50R
/³ /³
ÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄ
High Z Low Z Low Z High Z
Rig sees a Ant sees Rig sees Ant sees a
Parallel LC Series LC Series LC Parallel LC
MANUAL ATU COMPARISON
Most have 3 variables in T configuration, 2 caps & switched or roller coaster L
With time & care these can always give very fine adjustment down to 1:1, & with
aerial loads worse than 10:1. Assuming 0.5deg shaft control, that can look more
like 360x 360x 360 (46 million tuning options).
Manual T ATUs also gives much better out of band filtering, with the Hi Q
resonant circuit. And do an excellent job of protecting the Rx from DC static,
& strong signals on lower bands, that some poorly filtered SRD Rx can suffer
from! (e.g. removing MW Broadcast signals as it is >-18dB for each frequency
halving.)
See also my Tech buls on "A Homebrew HF SWR Bridge", "PEP Meter modification",
"QRP SWR Bridge", "Meter Damping & Speed Up" & "Palstar AT1500CV ATU", "HF ATU
& SWR Bridge VC300LP/QT-1"
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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