[TenTec] 229B tuner: Slight upward creep of SWR

[Bob McGraw K4TAX]

Your description is typical of some component or components heating and 
changing value.  This is not uncommon with this tuner,  but usually with 
higher power.   Three areas of concern are; (a)  the 4 parallel pairs of 
220pf capacitors which are switched by the HI LO Z switch.  (b) the 
internal balun, and (c) the series combination of C7 & C8.

My solution to all of this is replace the capacitors and balun.

(a)  use 470pf  doorknob capacitors, 4 of them, to replace the 4 pairs 
of 220pf disk ceramic capacitors.   Tight fit but can be put in on the 
base plate at the rear and keep the leads short. Requires drilling 4 
holes in the bottom plate to mount the capacitors direct to the bottom 
plate.

(b)  replace the series pair C7 & C8 with a 25pf doorknob capacitor 
mounted on the rear panel.  Requires drilling 1 hole. And a short jumper 
to the HI LO Z switch.

(c)  forget about using the internal balun.  I use a Balun Designs 1:1 
balun model 1171T.    An 18" coax jumper connects the balun to one of 
the SO-239 outputs.  Balun sits on top of the tuner.  The balanced 
feedline runs from the feed point of the antenna all the way to the  
balun.  No long coax jumper is used.

Further your description of the extra required capacitors and heating 
are clear indication you are using the wrong balun.  A 4:1 balun will 
transform the antenna impedance to a Z value divided by 4.   Thus the 
tuner has to match a low impedance which is the values where loss is 
greatest.   Thus if your antenna feed Z is 35 ohms, the 4:1 balun will 
transform that Z to 8.75 ohms, which is what the tuner must match.   Hi 
Z load impedance has less loss internally.     Many hams believe, 
incorrectly so, that a 4:1 balun should be used with a balanced 
feedline, i.e. 450 ohms. This is absolutely incorrect.   You are not 
matching the feedline but the antenna Z.

Problem solved, all bands, and up to legal limit high duty cycle power.

73

Bob, K4TAX


On 7/21/2018 2:26 AM, Peter Klein wrote:
> I've just noticed something interesting about my Ten Tec 229B tuner. 
> It happens on 80m-30m, where the center switch is in positions Lo2 - 
> Lo5 and various fixed capacitors are switched into the circuit.
>
> I use non-resonant antennas fed with ladder line.  I normally tune the 
> tuner with a noise bridge or at 10 watts.  Then, when I operate at 100 
> watts, I notice a slight upward creep of SWR over a few seconds after 
> key-down.  Then the SWR backs down a little and remains stable while 
> I'm transmitting. The creep is very slight, from 1:1 up to maybe 1.2 
> or 1.3:1 on my IC-7300's SWR meter.  My guess is that this is the same 
> issue some people report with the Ten Tec tuners on 160m.  On low 
> impedance loads that require the extra fixed capacitors to switch in, 
> those capacitors warm up slightly and change value as we transmit.
>
> I never noticed this before.  But I just picked up a used Daiwa 
> CN-101L cross-needle SWR meter, because the tuner's switched meter and 
> the IC-7300's multiple displays make monitoring SWR inconvenient.  The 
> Daiwa's "reflected" readings are a bit overly sensitive. On that 
> meter, I could clearly see the creep happening. Sure enough, when I 
> looked on my IC-7300's SWR meter, it was happening there, too. The Ten 
> Tec tuner's meter barely shows it, if at all.
>
> My guess is that everything is fine.  The SWR creep is too small to 
> endanger my finals, and I can always touch up the tuning.  I just want 
> to be sure that the SWR creep doesn't indicate that the fixed 
> capacitors in the tuner are failing. Can someone give me a reality check?
>
> Thanks and 73,
> --Peter, KD7MW
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