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Author Topic: CG-3000 autotuner luses match - RF feedback?  (Read 7755 times)
GOUDURIX
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Posts: 206




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« on: December 15, 2013, 10:11:37 AM »

I use a home-built multiband vertical: 9,2m wire along 10m long glassfibre pole - CG3000 atu at the base - 4 "combined" elevated radials (4 stranded wire per radials cut for 40m-20m-17m-15m bands).
Base of the vertical (where the atu is located) is 6 meters high , 3 meters above the metal roof of a carport.

I have installed chokes:
- on the coax just below the atu: 4 x FT240-31 stacked ferrites with 11 turns of coax
- on the feedline of the CG3000 atu: 12 turns on twin FT240-61 ferrites

Transceiver is an ole' Kenwood TS-850.

On 12m and 10 metres, the ATU initially tunes to good SWR (1,2:1) on 10 metros and acceptable (1,7:1) on 12 metres, using 10 watts CW carrier.

When transmitting SSB  voice on full power, I see the ALC shooting up quite quickly, with the ATU losing its tune (I have the tune controller that goes with the CG3000) and off course SWR shooting up highly.

It is worse (happens more rapidly) on 12 metres.

I do not have that problem on any lower frequency.


Could it be RF feedback into the ATU?
Should I maybe apply less turns (e.g. 8 turns) in the quadruple ferrite-stack choke?

Any clues?

Jan
ON3ZTT
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LA9XNA
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Posts: 109




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« Reply #1 on: December 15, 2013, 10:02:23 PM »

Check the manual about accepted antenna length..
For similar tuners like the Icom AH-3/AH-4 there are restrictions about multiple of the transmitting frequency.
Check also the connections for antenna and radials.
It might be an idea to solder the radials inside an lug before connecting it to the tuner.
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GOUDURIX
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Posts: 206




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« Reply #2 on: December 16, 2013, 12:45:17 AM »

Hi,

the CG3000 does tune (at 10 watts) , in the case of 10 metres to 1.2:1, but loses its tune once real power is applied.

The 9.2m antenna wire is most critical on 20m and 17m since the closest to 1/2 wave on those frequencies, but it does tune there and no issues like losing its tune.

The 4 radial sets are bolted to a stainless steel base plate but I have heavy tinne stranded wire straps going from those bolts to the ground lug on the tuner.

I would be surprised to have a counterpoise issue but one never knows....I did not cut radilas for 12m or 10 meter since normally this 9.2m vertical should become a cloud burner above 15m (where its length is > then 0.625 wavelength).

I was thinking it was an RF feedback issue since the tuned CG3000 subsequently loses its tune or is reset when applying power > 50 watts. Or some issue with resonance frequency in the choke at these higher frequencies?

I use a similar wire antenna on my sailing boat: 9.2 m sloping wire, 2 four-stranded radials cut for different bands, and some more metal hardware included in the RF ground system. But the tuner there is the SGC-230, no issues at all for tuning.

I might swap the CG3000 at home QTH and try what happens with the SGC230 but that is a lot of work.

Jan
ON3ZTT


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W5WSS
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Posts: 1744




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« Reply #3 on: December 16, 2013, 03:38:53 AM »

Hello, I am not familiar with the CG3000. I am familiar with the system and have used similar techniques.
Your sloper vertical on the boat sounds very similar to a system I built for a summer cottage excursion.
I used an switched L auto tuner at the feed point with elevated, sloped sets of two per band roughly 1/4 wave length IE 20m radials were 16.4ft each. etc per set that were sloping downward and traveling in opposite direction relative to the central feed point position to insulated ground anchors effectively dc isolating the radials.One possible issue is radials sets destructive mutual coupling but one must methodically perform a controlled step by step process of elimination which sounds more difficult than it actually is!
As you are aware and have indicated of course, the half wavelength can be very hard on a tuner and perhaps with the CG3000 this is causing too much heat for the toroidal material regardless of what the manufacturer rates his tuner the half wave will test any tuner.
Two approaches. 1) Adjust the length of the vertical and try the auto tune or the radial sets evenly either way.
2) If there is any coaxial cable between the tuner serving as an antenna feed line to the antenna then one must consider an impedance transformation potential since such an antenna line could be problematic is such cases as multi band service.
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W5WSS
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« Reply #4 on: December 16, 2013, 03:42:05 AM »

Yes and furthermore try the SGC tuner incidentally the switched L I used was an LDG 200 Pro
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W5WSS
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« Reply #5 on: December 16, 2013, 03:57:55 AM »

My radials were 1/4 wave elevated sloping and dc isolated from ground and were installed over under or  fanned longest above and shortest below attached to dedicated DC insulated anchors driven into earth.

2 each 20m,17m,15m,12m and 10m.

one option to consider is attaching a wire trap vertical to a non conductive structure such as you previously described as 10m long. perhaps The Alpha Delta types would solve the vertical lengths to the least problematic 1/4 wave length and much easier on an auto tuner.
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GOUDURIX
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Posts: 206




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« Reply #6 on: December 16, 2013, 05:26:48 AM »

Hi W5WSS,
thanks for your comments & advices.
The CG3000 is a chinese-made clone of SGC-type atu's but it is clearly smaller and more cheaply built than the SGC-230. It is also only about 60% of the price of an SGC230 but users of the CG3000 are quite happy with it.

Before the SGC230 I used the Yaesu FC40 atu on my boat, steered by the Yaesu FT897. The F has a far more limited impedance matching range than the CG3000 and the SCG230. Whatever the sloping wire length, there was always one or more frequencies it wouldn't tune.

Installing the SGC230 was like day & night difference...it tunes every frequency.

Having experienced all the tuning trouble with this FC40, I rather doubt that this CG3000 is having a tuning problem (too high an impedance range to match) since initially it tunes with a 10W carrier.
I expected the CG3000 to have trouble with matching impedances below 50 Ohms but it does easily tune the 80m band with the 9.2metres vertical wire.

As for the elevated radials I only have the possibility to hang 4 in my QTH that is why I chose to make the combined radials. Off course they will couple into each other....they are not even fanned but for different wire lengths tie-wrapped together....

I will see what happens when I change the vertical wire length in small increments....normaly the 9.2m wire should be more of a problem on 17m since it is closest to a 1/2 wave on 18 Mhz.

Jan
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W5WSS
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« Reply #7 on: December 16, 2013, 05:51:37 AM »

OK, The tuner typically "remembers" effectively helping to progressively quicker tuning eventually becoming rather instantly yes?

If so then try choosing a remembered frequency and present a  higher power level perhaps a 50 watt RMS power level auto tune and perhaps the tuner will compensate to the higher power, finding a more suitable combination that will work best when power level is 100watts PEP ssb.
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GOUDURIX
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Posts: 206




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« Reply #8 on: December 16, 2013, 06:19:10 AM »

My "on the job" experience with this CG3000 tuner is that sometimes (changing weather conditions, rain etc) it sometimes offers worse tuning on some frequencies, like 17m. If the I go well under or above the band (off limits...I know I know) then make it tune, then go back to the target frequency, I often get a better tune. Strange. It is certainly not working as good as the SGC230.

Now last night before "retiring" I tried again, tune 10W carrier on 28.500 and 24.960 then to full power vocie and it kept its tune.

So unfortunately it has a not very consistent behaviour....hence more difficult to find the problem and its remedy......

Let's say the CG3000 is female Smiley

Jan
ON3ZTT
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W5WSS
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Posts: 1744




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« Reply #9 on: December 16, 2013, 06:32:15 AM »

The sloping radial technique where they are elevated and approximately tuned must be mirrored and positioned symmetrically for the antenna to behave as one with more manageable feed point Rr attributable to a vertical dipole/doublet, rather than an end fed vertical with problematic very high impedance.

In my opinion a vertical with only one horizontal radial is some form of Dipole variant where one element is horizontal and the intended element is vertical but splitting the power betwixt and between the two elements angles forming a different pattern than perhaps wanted. Since the horizontal radial is radiating attributable to a dipole that element is close to the ground and that coupling could be problematic presenting hard loads for the tuner periodically throughout the HF bands. To avoid this difficulty it is feasible to seriously consider, and it may be easier for you to evaluate when sets of two radials are installed with position equivalency (opposite each other relative to the central feed point position) when doing so the antenna is a Omni directional vertically radiating Ground Plane where the radials are not radiating but are sinking the system to return power to the vertical for total vertical radiation and pattern develops properly in conjunction with easier impedance loads.

A single horizontal radial will radiate unless another radial is opposing or cancelling each other leaving the vertical to do the radiating.

Two opposing 45 degree or thereabouts sloped radials that are DC isolated from ground and attached to a range of quarter wave radiator to 5/8 wave radiator should be a manageable load for the auto tuner.
This technique is a dipole where the radials are contributing to radiation since only horizontal radials totally cancel each other but the advantage with the sloping isolated elevated radials add to the total field strength out in the Fresnel Zone whilst effectively alleviating problematic load for the tuner and retains Omni directional pattern development.

73 See a photo of my mobile here in Eham it uses the antenna I just described.
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VE7RO
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« Reply #10 on: December 16, 2013, 03:42:06 PM »

one thing no one has mentioned is where the power is coming from,  if from the coax then the bypassing may be inadequate for the higher power.
This could also be responsible for the intermittent nature.  If power is from a separate wire it should be run at 90 degrees from radials and be thoroughly  bypassed.

John ve7ro
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GOUDURIX
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Posts: 206




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« Reply #11 on: December 17, 2013, 01:13:30 AM »

Hi W5WSS, it is practically very difficult or rather impossible to have separate radials and perfectly mirrored, I don't have the points to hang them from.
They are now slightly sloping down but it is possible to hang them horizontally.

Given the fact that each "radial set" has a 40m, 20m, 17m and 15m radial (2 stretches of 2 stranded 0.75mm2 speaker wire) bound together, it is impossible (for me) to model this in EZNEC since the radials are too close together. The only thing I can do is model per frequency with its own set of4 radials hence this will not give the real situation for impedance and radiation pattern.
I had read that for a vertical "groundplane" type of antenna 4 elevated radials can more or less replace a ground mounted vertical with 20-80 ground mounted radials....
The problem is that (if I recall well) if I model this multiband vertical with e.g. only 4 horizontal elevated radials cut for 40m band, the elevation angles will greatly suffer on higher frequencies so missing my goal for this antenna: multiband and low take-off angles for DX.

I might try the following setup:
- 2 "cut" radials in opposite directions, fully symmetrical
- for 4 bands: 40m - 20m - 17m -10m
So I would have 8 radials in a symmetrical star

John VE7RO,
the power wire is seperate on the CG3000 and has a choke just before entering the atu.
Both coax and power line run down vertically for 3 metres from the atu  until the carport roof; from there horizontally over the roof and to the house wall about 6 m in total before entering the house. So yes there is a horizontal stretch or power line (and Coax) about 3m below the radials.
Should I move my chokes or add chokes in another location?
- on the coax just below the atu: 4 x FT240-31 stacked ferrites with 11 turns of coax
- on the feedline of the CG3000 atu: 12 turns on twin FT240-61 ferrites

Remark: In my boat I have 9.2 m sloping wire, a compromise RF-ground system (2 sets of 4 wire combined radials running from aft along the aluminum "toerails" running on boath sides of the deck + also bonded to the S/S lifelines running both sides + 3 metres of copper tape connecte to and underwater bronze stud) which is not a bad setup in a sailing-boat situation....
The atu is SGC230, this one has coax and power line combined in 1 bundle, and I have this choked at the atu 9 turns through 2 stacked FT240-31 toroids.
In this boat situation everything runs close, there is a lot of coupling into the rigging, electrical wiring in the boat, but I do not have any of the problems I encounter with the CG3000 (losing an initial tune when applying more power).

Jan
ON3ZTT

 
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N5GZH
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Posts: 87




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« Reply #12 on: December 17, 2013, 03:06:58 AM »

The question is why the tuner is handling the match at low power but not at higher inputs.  Short of swapping out another tuner of the same type,  this could be hard to diagnose.  Sounds like one of those cases where you could really use some factory support.  Just thinking-- how hard  would it be to open up the tuner to check inside for signs of arcing or moisture intrusion?   You might also gradually up the power on a given band to see exactly where the problem starts, then add chokes to the coax and DC lines to see if this makes is any difference.     

4 "combined" elevated radials (4 stranded wire per radials cut for 40m-20m-17m-15m bands).

Is bundling radials like this for multiple bands accepted practice?  Not sure.   At any rate,  I would try to attack the problem one band at a time.   An antenna analyzer would also be a great help as well.


Good luck.

Jim
N5GZH
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GOUDURIX
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Posts: 206




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« Reply #13 on: December 17, 2013, 03:29:06 AM »

Jim,

yes off course I can open up the atu if I bring down the glassfibre pole on its 3m fiberglass base mast.

I can also try out what happens when I use the SGC-230 that I have installed in the boat.

When you mention an "antenna analyzer" I trust you suggest measuring out per frequency WITHOUT the atu?

Jan
ON3ZTT
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W5WSS
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Posts: 1744




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« Reply #14 on: December 17, 2013, 06:04:02 AM »

Yes agree with your logic Jan.
As Jim N5GZH pointed towards the tuner issue is an area I would look to improve as you have already addressed.

A word about multi band elevated radial systems.

It is as you stated Jan not an easy modeling endeavor and without modeling, can leave questions as to just exactly what is happening to the pattern on any band, As a result due to such valid questions relative to how they behave when slicing the radiation and mutual coupling pattern skewing etc. Tom Rausch W8JI mentioned to me that he was/is investigating these questions looking for a system that is least problematic for the elevated multi band trap vertical system with multi band elevated radials system as we know that IF we can find a system that only uses 2 or 4 radials sets per band would reduce total amount of radials( when elevated) needed. Of course the goal is to compete with the ground mounted optimized systems.
Perhaps 4 trap slope elevated radials? Made strong to serve as guy lines as well.

The system I used where the radials were fanned downwards and dc isolated were simply 1/4 wave and slope angle was dictated by practical angle to reach the ground then the non conductive anchor was driven I mirrored this procedure for all and my system tuned and behaved Omni directional with expected field strengths and was with my very many years of experience very gratifying.

I admittedly avoided the case where I expected problematic load to the tuner, which was located right at the feed point but never a case where moisture was a question and worked a stable tune with the vertical to a single high point and the radials all originating from the shield driven location which was directly underneath the drive point of the vertical antenna base feed point. As a matter of fact the entire elevated radial system was held in strain relief and bundled together at that single point of origin using a water proof very large wire nut after first crimp and soldering them all together.
So the system looked like a peace sign and I worked very good communications.
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