I had a 989C and it worked great until I tried to load an 80 meter G5RV on
160 to work VP6DX. I made the contact but the roller inductor warped due to
the loss in the tuner in the form of heat. Just a word of caution. In fact
the ARRL Antenna book talks about "T" type Tuners used at low frequencies.
Apparently they can lose up to 25% energy in heat. That is 250 watts out of
1 KW. The cabinet did feel a bit warm to the touch. A lesson well learned
since I had to buy a new roller inductor. The warping caused the roller to
lose connection now and then depending on where it was down the length of
the coil.
Should have loaded the G5RV as a capacity hat vertical by connecting the
bottom of the feedline together against a ground system.
Best Regards
Dan Schaaf
=================================
K3ZXL www.k3zxl.com
=================================
-----Original Message-----
From: Roger (K8RI) on TT
Sent: Monday, February 03, 2014 1:39 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] MFJ-989C
On 2/3/2014 1:19 PM, Tom Osborne wrote:
HI All
I purchased a MFJ-898C roller inductor tuner that I got for a really good
price. It had a problem that it took a while to figure out.
This was discussed on the Amps reflector in just the past couple of weeks.
One thing brought up was the need for preventive maintenance (cleaning
the coil and contacts as they can and often do get dirty. If used with
low impedance loads they are derated (all tuners are derated for low
impedance loads AFAIK) the wire in the 989 series is pretty small for
the legal limit into low impedance loads. I used a pair of them for
some years and with cleaning the rotary coil periodically they worked
fine. I've forgotten what they were derated to on 160 with a 35 ohm
load, but think it was 500 or 800 watts.
On 160 I had to raise the resonant frequency of the antenna to near the
top end of the band or they'd arc. No damage, just a hiss like cat,
snake, or a leaky tire. That did cause some concern about the current
at the low end of the band, so I now have an AT5K and an AT5K HP
Your point about cleaning the coil and contact is a good one and should
apply to most tuners with rotary inductors.
73
Roger (K8RI)
It would tune an antenna at low power fine, but at high power, the SWR
would slowly creep up and not stay tuned right. I tried all sorts of
things to fix it like spraying the contacts with cleaner, etc.
Yesterday I happened to notice the roller inside the coil that contacts
the coil wire looked black and dirty. I sprayed it with contact cleaner
and took a real small screwdriver and cleaned the slot in the roller where
it contacts to the coil.
After cleaning it, it now works like it should and the SWR stays put, even
at high power with no arcing, etc.
Posted this because maybe someone else is having the same problem
No comments about MFJ stuff needed - I've heard 'em all :-) 73
Tom W7WHY
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