[ARC5] ARC-5 Output Spur Tests- Some Figures.

[David Stinson]

Well, I'm no EE and am not qualified to talk about
conjugates; I thought that was what prisoner's got
when their wives came to visit.
I made an effort to find those
figures from the work I did in 1996.  I managed to find
one page, covering tests with a T-22 at 7 MC and a T-19
at 3.5 MC.

I don't remember the name of the test equipment,
but I set the fundamental as a zero-reference and read
harmonics in dbm relative to the fundamental.
IIRC, anything -80 dbm or more below the fundamental
was in the noise floor of the test set.
It may have been better, but I haven't found the page
that had the set-up data; -80 dbm is my best recollection.

Load was 50-ohms resistive.
The ARC-5 was set up 100% "as designed," with
modulator/dynamotor/racks/antenna relay etc.
I used the 50-pFd series vacuum cap
provided with the antenna relay.

All tests were made with the transmitter in "VOICE" mode
to lower the power levels- Remember, these were plate modulated
AN/ARC-5, so you can tune up in VOICE, unlike the 274Ns
which must be tuned in "CW" mode.

I made tests with combinations of the series cap,
an UNUN 1:4 auto transformer and with no external
antenna tuning elements ("50's ham" tuning).
I made no attempt to use a variable cap, which
would have provided a better match and allowed
more power out.  I was interested in harmonic suppression,
not power.  I never got back to the tests to
find the "correct" matching cap for 7 and 3.5 MC.
I'm sure getting the cap closer to "correct value" would
have made the harmonic rejection even better, but
these figures were good enough for a first illustration,
which was all I was trying to do.

I don't attempt to explain the numbers-
I just report them.  I'll leave explaining to
the multitudes of people brighter than me on this subject.

T-19 Trans., 3500 KC. No Cap, No Xfmr.
Ep 550 V / Ip 75 ma / Iant unreadable
Loading coil 0% / Ant. Coupling 100%  / Pout 18W
2nd Harm -30 dbm  /  3rd Harm -41 dbm

T-19 Trans., 3500 KC, With 1:4 Xfrm and Series Cap 50 pFd
Ep 540 V / Ip 90 ma / Iant 1.5 A
Loading Coil 70 % /  Ant. Coupling 65 % / Pout 17W
2nd Harm -46 dbm / 3rd Harm -58 dbm
(obviously need a bigger value cap here).

T-19 Trans., 3500 KC, With Series Cap 50 pFd (No xfmr)
Ep 545 / Ip 85 ma / Iant .2 A
Loading Coil 70% / Ant. Coupling 55% / Pout 22W
2nd Harm -50 dbm / 3rd Harm -50 dbm

The sheet is torn, so I'm missing the tune-up
date for "Transformer, but no Cap,"
but the important figures are still here:
2nd Harm. -30 dbm / 3rd Harm. -44 dbm

On to 40 meters...

T-22 Trans., No Xfmr and No Series Cap.
Ep 550 V / Ip 55 ma / Iant unreadable
Loading Coil 0% / Ant. Coupling 100% / Pout 6W
2nd Harm. -40 dbm / 3rd Harm. -60 dbm

T-22 Trans., With Xfmr, No Series Cap
Ep 545 V / Ip 90 ma / Iant 1.25A
Loading Coil 45% / Ant. Coupling 70% / Pout 16W
2nd Harm. -56 dbm / 3rd Harm. -64 dbm

T-22 Trans., With Series Cap, No Xfmr
Ep 575 V / Ip 80 ma /  Iant 0.2A / Pout 20W
Loading Coil 45% / Ant. Coupling 90%
2nd Harm. -55 dbm / 3rd Harm. -62 dbm

(Data with both missing)

Please note that, with every transmitter tested,
beyond the 3rd harmonics,
I found no, nada, none, zip-any
spurs or harmonics strong enough to peek up out
of the -80 noise floor all the way up to 1 gHz.

73 DE Dave Stinson AB5S
arc5 at ix.netcom.com