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kom
09-10-2015, 05:05 PM
I have a radio with a built-in SWR meter and SWR Graph; behind the IC-706MKIIG is a Heathkit SB-200. Connected to the output side of the amplifier is a Yaesu YC-60 wattmeter; connected to the antenna terminal of the meter is a Dentron Super Tuner Plus which feeds my OCF dipole antenna.

Radio ---> Amplifier (in standby) ---> Wattmeter ---> Antenna Tuner ---> Antenna.

On 160 and 80 meters, the SWR readings on the external wattmeter and the meter in the radio are the same with maximum forward power and zero reflected power. On 40 meters, the meters do not correspond, if I tune to satisfy the meter in the radio, the meter "in front" of the antenna tuner is not happy and, shows high SWR and reflected watts. If I tune to make the external meter happy, I receive a high SWR indication from the radio and, it starts to fall back in the power. On the 30 and 20 meter bands, the indications are close and the reflected power is less than 5%.

I cannot tune the 15 or 12 meter band period; 27, 28 and 29 MHz all tune fine with the radio meter and the external meter indicating nearly the same readings.

40 meters was my favorite band to work until the speed bump appeared (after a storm brought down one end). Any and all suggestions on finding and fixing the speed bump would be appreciated.


.

kb2vxa
09-11-2015, 10:22 AM
For technical reasons beyond the scope of this discussion, placement of an SWR meter in the transmission line makes all the difference in the world. (That's not the case with a true VSWR bridge like the classic Bird 43.) The simple answer is, with the amp off go by the meter in the Icom, the remote meter is giving you a false reading. With the amp on, the remote meter gives a true reading, but since the overall length of the transmission line is shorter, touch up the tuner to bring the SWR down. The meter in the Icom now reads the SWR looking into the amp, if it's more than 2:1 and drive power folds back the input tuning in the amp needs attention. Ah, for the love of boat anchor days, tube finals with pi network output tuning were happy with 3:1 and could easily match 20-600 ohm loads with a smile.

BTW I have a 706Mk2G, I guess you're aware of the SWR meter doesn't work on 2M or 70cM so I used a Comet CM-420. (;->)

kom
09-11-2015, 05:24 PM
For technical reasons beyond the scope of this discussion, placement of an SWR meter in the transmission line makes all the difference in the world. (That's not the case with a true VSWR bridge like the classic Bird 43.) The simple answer is, with the amp off go by the meter in the Icom, the remote meter is giving you a false reading. With the amp on, the remote meter gives a true reading, but since the overall length of the transmission line is shorter, touch up the tuner to bring the SWR down. The meter in the Icom now reads the SWR looking into the amp, if it's more than 2:1 and drive power folds back the input tuning in the amp needs attention. Ah, for the love of boat anchor days, tube finals with pi network oh piece of utput tuning were happy with 3:1 and could easily match 20-600 ohm loads with a smile.

BTW I have a 706Mk2G, I guess you're aware of the SWR meter doesn't work on 2M or 70cM so I used a Comet CM-420. (;->)

The amp is in the bypass mode at all times during there readings.
I only have one measuring element for my Bird 43 and that's a 10Kw slug.

I use my MFJ 259 analyzer to check everything above 60 MHz, that's as far as the YC-60 will go. It says that my 2 meter antenna is in the ballpark.

Speaking of the MFJ-259, I guess I could sweep each piece of coax and see what happens at 7 MHz, maybe something will jump out at me.

ETA: on 40 meter band with amp ON the SWR reading is 1.2:1 on the 706 but still high on the external meter. On other bands, input SWR is acceptable and antenna matching is O.K. Only 40 meter (and its third harmonic, 21 MHz) is problematic. I gave up on 15 meters long ago.

K0RGR
09-15-2015, 11:38 AM
What does high SWR mean? How big a difference is there between the two? With the amp on, what you're seeing at the radio is the SWR of the input circuit to the amp. If you tune the tuner for a good SWR with the amp on and it goes haywire when you turn the amp off, that
is something else. If you're going to use the amp, ignore the meter on the radio unless it's very high. As I recall, the input SWR on some bands on my SB200 was less than desirable.

kom
09-15-2015, 12:38 PM
What does high SWR mean? How big a difference is there between the two? With the amp on, what you're seeing at the radio is the SWR of the input circuit to the amp. If you tune the tuner for a good SWR with the amp on and it goes haywire when you turn the amp off, that
is something else. If you're going to use the amp, ignore the meter on the radio unless it's very high. As I recall, the input SWR on some bands on my SB200 was less than desirable.

"High SWR" is above 2:1 on the radio indicator, which is the point where the radio (looking through the standby amp ) starts to want to go into "protect mode" by decreasing the power output.

I have a 50 ohm non-radiating "Cantenna" that tell me that all the bands on the radio are O.K.

On all the other bands that I use the tuner on, the SWR meter in the radio will correspond to the SWR on the external meter. "Something" that "I" am not seeing causes my radio NOT to want to tune on the 40 meter band.

I need some new "Coax and Antenna" grease, the 40 meter portion of mine has worn off, you know what i mean? :-?

kb2vxa
09-16-2015, 09:16 AM
What you're not seeing is the difference in transmission line length between amp on and off. With it off tune for lowest reflected power on the Icom, with it on tune for lowest on the external meter. If you can't bring it down that way you're doing something wrong with the tuner. As you can see it's a common parallel L series C T section matching network, always use the L tap that gives a reflected power dip with both variable caps. That is to say they must tune within their ranges and not at either end which would put proper tuning out of range. Look inside to see if the knob calibrations conform with minimum and maximum capacitance. If not set them for full mesh, loosen the set screws, set the knobs for zero and tighten the screws. You never know what the blind retarded monkeys did at the factory so it's best to check it out.

One last thing, that circuit leaves a bad taste in my mouth and once a burning sensation on my finger. My MFJ being the same I had to be careful to hold the knobs so my fingers didn't contact the set screws. Doing so adds body capacitance that upsets tuning and being they're hot with RF and could easily be a voltage point an RF burn can result.

kom
09-17-2015, 04:31 PM
For technical reasons beyond the scope of this discussion, placement of an SWR meter in the transmission line makes all the difference in the world. (That's not the case with a true VSWR bridge like the classic Bird 43.)



I took the Yaesu YC-60 wattmeter out of line and replaced it with the Bird 43P; I only have one accurate Bird element and that one is a 10K slug. Now, I do have a "Indicator" element marked 100KW that has been opened up, shortened and "recalibrated" to about 500 watts.

With the Bird meter inline, I tuned the antenna for 40 meters with lowest SWR indication on '706MKIIG and then, flipped the element around in the Bird meter and the reflected wattage was 2 watts while the forward was 40 watts out.

You're probably saying to yourself, "Why did you use the Bird meter in the first place?" Because the YC-60 has remote mounting capability with the sensing unit and coax connections out of sight.

Something in the Yaesu meter gets weird around 7.0 MHz but seems to be okay across the rest of it's measuring range; go figure?

.

WTKX
09-17-2015, 05:26 PM
I've used two tuners often; from the exciter to the amp (typically auto tuner), and one from the amp to the antenna. This lets the new rig be happy going into the older amp when needed. Never worried about it otherwise. :dunno: