| |
OE5OHO > YAESU 17.10.04 14:05l 68 Lines 2741 Bytes #999 (0) @ WW
BID : HAEOE5XBR00I
Read: DK8NZ OE5AKM DK7JAN OE3KLU GUEST DK7JY DG8YHH DC9BM VE7HFY
Subj: FT-857 bad audio at high SWR
Path: DB0FHN<DB0RGB<DB0AAB<DB0PV<OE6XHG<DB0WGS<OE2XUM<OE5XBR
Sent: 041017/1247z @:OE5XBR.#OE5.AUT.EU [BayCom-Mailbox] openbcm1.03
From: OE5OHO @ OE5XBR.#OE5.AUT.EU (Oliver)
To: YAESU @ WW
X-Info: No login password
Perhaps you have heard of the "bad audio related to SWR" problem with some
units (newer units should have it fixed hopefully) of the great FT-857.
After some guys from OE9 mentioned that problem to me, I made some simple
measurements on my unit (serialnumber starting with 3F0, the letter gives
you a hint on the production month, the first number on the production year).
Setup: TX= FT-857 -> SWR-cross needle meter -> tuner -> dummy load 50ohm
RX= another yaesu TRX to check for bad audio signal
Mode= USB/LSB, CW, FM
Power= max output abt 100W.
Proc level= 75, SSB mic gain= 50
Mic used= MH-31 original dynamic mic (not! MH-59A8J, note below!)
Method: adjust tuner so FT-857 has a perfect 1:1 match, then de-tune the
tuner until SWR reaches a level where the FT-857 just starts to transmit
bad audio.
Result on the tested unit:
At the following SWR levels the tested FT-857 starts to produce bad audio,
sounding like "stuttering audio", as if the TRX decreases power to zero,
then checks if SWR got better (full output again) and as it didn`t change,
again decreases power to zero! The higher the SWR gets the more stuttering
and nearly zero output.
Band SWR (A SWR equal or above the indicated level will make the TXed sigs
distorted/stuttering)
80m 1:2
40m 1:1,7
20m 1:2,2
15m 1:2,2
17m 1:1,8
12m 1:1,7
10m 1:2,4
It didn`t matter if USB, LSB, or CW was used - at the indicated SWR levels
I heard first stuttering audio in the control RX (2nd trx!). Just using
slightly higher SWR made the transmission a mess - you no longer could
understand the transmission (SSB and CW)!! In FM the signal got distorted
as well.
Solution: Sent to YAESU (Netherlands) under guarantee claims and returned
modified. After this the excessive distorted modulation is gone and one can
operate without the fear of not getting heard at higher SWR levels. The
problem is not gone 100% (YAESU admits it cannot be removed completely!)
but distortion is hardly recognized at 1:3 on all bands after the mod by
YAESU Europe.
So in case you notice bad audioreports at higher SWR levels (above 1:1,5)
do the above test and send your TRX back to YAESU. If you always can assure
a SWR of lower than 1:1,5 then I wouldn`t care about the problem.
One more hint: never ever use the MH-59A8J for serious shortwave operation!
The shielding of this mic is very very bad and leads to RF-pickup, which too
(!) leads to distorted audio. (Be sure you don`t have RF-pickup, do not mix
it up with the problem mentioned in this article!!).
The MH-59A8J is the DTMF mic for the FT-857.
Vy 73 de Oliver OE5OHO
Read previous mail | Read next mail
| |
