[SECC] Testing The Internal Tuner in your Radio

[Jim Worthington]

The results of your tests are normal for an internal tuner. I would try a 50 ohm dummy load to see if you can reproduce the problem your buyer had. The tuner should be able to match 50 ohms on all bands in addition to the 3:1 loads  that Jerry suggested.

The range of internal tuners varies considerably by manufacturer, so the buyer may have had unrealistic expectations based on his experience with another rig. My TS-870S would match a wider range than my FT-1000MP Mark V. The Elecraft K2 and K3 tuners have a much wider range (10:1 SWR or more).

Jim AD4J


On Jan 25, 2011, at 11:44 PM, Jerry Flanders wrote:

> He might have expected it to load his bedsprings on 160 M like some 
> of he better external tuners can do.
> 
> ICOM specs the tuner to only handle 17 - 150 Ohm loads (3:1 SWR). One 
> way to verify ATU operation is to use three 50 ohm dummy loads, first 
> connected in series, then in parallel. Just check it on all bands to 
> see if it can cope.
> 
> Jerry W4UK
> 
> At 10:46 PM 1/25/2011, Jeffrey Clarke wrote:
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>> 
>> Hi All,
>> 
>> I sold a radio to this guy (my IC756PRO) and the day it's delivered 
>> to him he calls and tells me the internal antenna tuner in the radio 
>> is not working right. He was unwilling to have someone look at it at 
>> his own cost (he wanted me to pay for that) so I told him to send 
>> the radio back to me and I refunded his money.
>> 
>> I got the radio back tonight an hooked it up.  I have 160 , 40 and 
>> 20 meter antennas that are cut for the CW bands. The SWR is higher 
>> in the phone parts of the band.  The internal tuner worked just fine 
>> when I turned it on the tune out the slight mismatches in the higher 
>> parts of those bands.  I also hooked up my 135 foot zepp with 450 
>> ohm feeder line to a DX Engineering 4:1 balun and went directly to 
>> the radio on the 50 ohm side of the balun. I was able to get the 
>> antenna to tune across the whole 80 meter band.  I wasn't able to 
>> get it to tune with that setup on 20 meters. I would imagine the 
>> impedance is more complex using that antenna on 20 meters and up.
>> 
>> I'm trying to determine if I really have a problem with the internal 
>> tuner.  This guy supposedly hooked the radio directly to a dummy 
>> load to test the internal tuner. Is this really a good test ?
>> 
>> 
>> Thanks, Jeff  KU8E
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