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Author Topic: Perplexed With SWR Reporting Issue and IC-7000  (Read 4889 times)
W8NYY
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« on: April 23, 2011, 04:29:12 PM »

First, let me state that I have ruled out the antenna, a Tarheel 100 A/HP since this issue also happens with feeding the SG-500 directly to a dummy load. 
I use an IC-7000 and have a Palstar mobile meter installed with the remote fed from the SG-500 out.  I don't have the issue on 20 meters.  The issue is the Palstar, recently calibrated to a dummy load, will report from the SG-500 a 1.1 to 1 SWR on 40 meters while the IC-7000 reports on average 1.7 to 1.  To top it off, testing on USB 40 meters into the dummy load the the SWR as reported n the IC-7000 will jump on voice peaks like the meter was set to power.
To further test the issue, I placed the Palstar after the IC-7000 output prior to the Amp to see what it was seeing in terms of SWR when the amp was on fed into the dummy load.  It confirmed that while barefoot the SWR was 1.1 to 1 into the dummy load but when the Amp was put on the SWR raised to 1.7 to 1.
Since this is all happening into a dummy load, the antenna tuning and coax from the amp to the antenna was ruled out.  I replaced it anyway with god quality RG8x in preparation for receipt of the Scorpion SA-680 I ordered last night.  I also replaced the feedline from the radio to the amp for good measure and added a better ground on the remote connector box for the Palstar remote mobile meter.  I also added Mix 31 terroids on the remote head line and at the antenna end of the control line (had one already but replace it and wrapped it better.
What's interesting, is if I overlook the Palstar reading and when the antenna is in line, if I adjust the height of the antenna to lower the SWR reading on the IC-7000 the SWR shows and increase on the Palstar and ultimately, I get a power fold back due to the higher SWR as reported by the Palstar despite the Icom-7000 reporting a less than 1.2-1 SWR.  I haven't tested this on 75 meters yet but what I do know is this happens on 40 meters on a dummy load and not on 20 meters.
I'm tired from working on this most of the day.  I've run out of ideas.
Thanks.
Bob, W8NYY
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K0BG
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« Reply #1 on: April 23, 2011, 04:56:43 PM »

You should have asked me about this.

The CPU inside the 7000 has several 8 bit sections. One of those sections supports the SWR, temperature, fan, ALC, bias, the Tuner port, and provides feed back to the AGC during transmit. When the 7000 gets warm, the indicated SWR increases. If you happen to be watching the SWR readout, when the fan goes on high speed, you'll see the SWR jump up rather explicitly. It is just the nature of the beast. While the Palstar might be ±10% full scale (or whatever it is), I can guarantee the IC-7000's readout (forward, reverse, SWR, and ALC indication), has a much worse accuracy.

All you need to do, is adjust the Palstar so the readout on the radio is at its lowest, even if that appears to be too high. You should see what it reads out when the ambient gets above 100° down here in the Alien Nation!
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W8NYY
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« Reply #2 on: April 23, 2011, 05:13:40 PM »

The Palstar, in my opinion, make the best peak reading mobile meter in the industry.  At lease at a somewhat reasonable cost.  Bottom line, is make sure my Palstar is calibrated well to a dummy load or a Bird meter if available, and ignore the SWR readout on the IC-7000.  Makes sense.  I know when the antenna was adjusted using the Palstar, I was getting full output and great reports.  20 over 9 to EA this afternoon while testing.
BTW, I put a Cap Hat about 60" above the coil (using a 3/8" aluminum Arrow Antenna element on a heavy duty spring).  Was able to reduce the overall height by about a foot.  Seems to have improved the overall performance quite a bit.
Thanks for the reply Alan.  I don't mnd posting here versus sending you a private email.  Others can learn from your responses as well.  I did not know of the 7000 issue you mentioned.  Can't imagine with your heat what kind of issues this causes.  It was finally warmer today, but certainly not hot.
Thanks again.  Placed an order with Ron last night for the SA-680 Black Widow.  Should go well with my black RL.
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W3AHL
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« Reply #3 on: April 24, 2011, 01:22:27 PM »

I wasn't able to recreate the problem where the SWR changes when the 7K's cooling fan kicks into high gear on my radio.  Also, I don't see the SWR display following voice peaks, like W8NYY reported.   Testing was done with my mobile 7K parked in the sun all day, with an interior temperature of 112F.  I transmitted into a dummy load at full power for 10 minutes with SSB full modulation.  The SWR never moved from 1, either due to heating or voice peaks.

I haven't seen the problem during long cross country trips using an antenna either.

The bouncing SWR during modulation seems like a grounding/RFI issue, perhaps.

Steve, W3AHL
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W8NYY
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« Reply #4 on: April 24, 2011, 02:40:47 PM »

Thanks Steve.  I'd suspect using the dummy load with the antenna and antenna control line disconnected pretty much rules out a ground plain issue.  The body of the 7000 is installed under the passenger seat of the Ridgeline and is grounded via the grounding screw and copper braid to the seat bolt.
It's really strange that the Palstar meter is reporting a 1 to 1 on the dummy load on all bands.  The jumping SWR on the 7000 meter is only happening on 40 meters and when the SG-500 is on.  I'm keying the SG-500 via the 13 pin din cable with the amp relay cable that I got on eBay which claims to have the following:
Icom Amplifier relay cable that works with the IC-7000, 706 (all versions), 703, 718 and 78. The entire circuit is housed inside the 13 pin DIN plug and provides TOTAL isolation between your radio and amplifier high voltage keying circuit. There is an actual miniature relay inside that will switch up to 200V @ 1.5A. The cable is 6' long, has 100% shielding and terminates into a standard male RCA plug.
I'm wondering if I switch to an Ameritron Amp relay if it may make a difference.
In my testing, I repositioned the Palstar meter to see what SWR the 7000 was actually seeing when the Amp was keyed so the Palstar was placed after the radio and before the SG-500 and it confirmed it was seeing about 1.7 to 1 when I was transmitting with the amp on into a dummy load.  1.7 isn't bad but it should be no more than 1.1 when your on a dummy load.  Very weird.
I tend to agree that it may be RF or a ground but have tried about everything other than how I am keying the SG-500.
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KE3WD
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« Reply #5 on: April 24, 2011, 02:59:20 PM »

...In my testing, I repositioned the Palstar meter to see what SWR the 7000 was actually seeing when the Amp was keyed so the Palstar was placed after the radio and before the SG-500 and it confirmed it was seeing about 1.7 to 1 when I was transmitting with the amp on into a dummy load.  1.7 isn't bad but it should be no more than 1.1 when your on a dummy load.  Very weird.
...

Hold on there.  

The Icom is NOT "on the dummy load" in this scenario.  

Only the output of the Amp is looking into the 50 ohm dummy load.  

The output of the Icom is reporting the Input impedance of the power amp.  

1:1.7 isn't all that bad anyway.  Don't know the amp in question but it might have adjustments on the input internally that could bring that figure down although most solid state amps likely do not.  And again, it is under 2, so you should still be driving the heck out of the amp.  

What matters is the SWR between last PA and Antenna system, and that will not be reflected back thru the amp to the ecxiter when the amp is in the circuit.  


73
« Last Edit: April 24, 2011, 03:02:20 PM by KE3WD » Logged
W8NYY
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« Reply #6 on: April 24, 2011, 03:16:05 PM »

Thanks for the reply.  Also for the clarification as to why I was seeing 1.7:1 versus 1.1 to 1.  The SGC SG-500 doesn't require a lot to drive it to full power.  In fact, I am only driving it with about 45 watts.  If you drive it much more than that the SGC kicks in an attenuator to cut back the power.  It does have a lot of safety features to prevent ending up with a heavy doorstop. I'm using the RF keying option which some do not like as there is about a 500ms delay but I haven't noticed that to be an issue.  I'm also using RF frequency detect so don't have to worry about changing bands on the amp.  It's done automatically.  Not totally bullet proof but pretty close.  Set it and forget it.
Thanks again for the additional schooling on SWR and circuits.  I am always learning something.
73,
Bob, W8NYY
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W3AHL
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« Reply #7 on: April 25, 2011, 06:14:27 AM »

Bob,

There is no need for ANY relay interface between the 7K and SG-500.  I couldn't find the switching current spec's for the PTT/Relay circuit in SGC's documentation, but according to K0BG'S web site it is well within the 7K's specs (only 4.3 VDC at a few ma.).  I would eliminate the ebay cable, connect ACC HSEND directly to the SG-500 PTT input and change from RF keying to PTT keying. 

I wouldn't be concerned about the 1.7:1 SWR between the 7K and amp, but the bouncing SWR display on voice peaks indicates a problem somewhere that definitely needs to be solved.

Steve, W3AHL
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W8NYY
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« Reply #8 on: April 25, 2011, 08:35:09 AM »

Thanks Steve,
I got a reply offline from another ham who is having the exact same issue wth the 7000 and the SG-500 and says he's been working on trying to find a resolution with a rep from SGC.  Apparently, I'm not the only one with the issue.
As for the keying, I may have miss spoke.  I have to check, but I know the keying is taking HSEND to ground off of the 13 pin din.  I have both cables.  The one with the relay and the one without.  I used the relay because of a post K0BG has on his site and knowing he uses an SG-500 and the IC-7000:
Tech Talk: I'm a firm believer in keeping things as simple as possible. After all, every piece of gear is just one more thing that can fail when you need it the most. This said, I believe a keying interface is a very good idea on any transceiver, if for no other reason than circuit isolation. This minimizes the chances of a ground loop between the amplifier, and the transceiver in use. It also protects the transceiver from inadvertent shorts.
Alan did confirm he does use a circuit in the HSEND line.  I figured it was a safe way to go.  If it's contributing to my issue then out it comes and the original 13 pin din connection goes back in place.  That's an easy switch.  I'm almost certain though that I have PTT keying turned on and not RF sense.  I'll have to check the jumper settings later to be sure.
Thanks.
Bob, W8NYY
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K0BG
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« Reply #9 on: April 25, 2011, 09:12:45 AM »

Just for clarification....

The keying voltage on the SG500 is plus 5 volts. The keying current is less than 2 mils. The keying capability of the 7000 is 200 mils, and it rests at 8 vdc. If you key the radio via the HSEND line (pin 3 of the 13 pin socket), the keying current is less than 20 mils. You really don't need a switching buffer, however, my comments about it remain.

One really big problem with the 7000, is its SWR reading accuracy across its bandwidth. In a few words, it stinks! The CI-V readout of the SWR is even worse, if that's possible. I have owned three 7000s (I have two at the moment), and none of them agree even when into a known-good dummy load. If that wasn't enough, one would assume that on any given resistive load, that doubling the power out would also double the reflected power which could be seen on the readout. Au contraire! Every band is different. It is just the price you pay for miniaturization.

One more item. There is one thing you do not want to do with a 7000, that you can get by with on a 706, and that's pulling the TKEY line high to supply (≈13.8 vdc). A lot of aftermarket tuners, and interfaces do this. If you do it on a 7000, the fan doesn't run when it should, with predictable results.
« Last Edit: April 25, 2011, 09:15:32 AM by K0BG » Logged

K8KAS
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« Reply #10 on: April 28, 2011, 10:25:14 AM »

If the SWR is 2:1 or better you will not really see an improvement in far field signal strength, what is the big deal about a 1:7 to 1
SWR, it's nothing.
I use the Palstar bridge mobile and always tune to it, never the built in meter on the radio. The SWR bridge is between the Amp and Tarheel 200, the radio can Easily handle the low SWR between the radio and amp, I don't need full power to drive the ALS 500 to full output. Relax and enjoy... Denny K8KAS
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K0BG
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« Reply #11 on: April 28, 2011, 01:56:13 PM »

I kind of touched on this above. If one takes the time to plot the SWR readout from the CI-V, and compare that with the calculated phase angle of an off-resonant antenna, you get a feel for what Icom is doing. It appears the readout is tied to the phase angle, and not the SWR per se. Unfortunately, the CI-V readout doesn't perfectly coincide, but I believe it is close enough to assume that it is. However, to average Joe Ham, I suspect it doesn't mean squat, but there you have it.
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KE3WD
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« Reply #12 on: April 28, 2011, 02:57:03 PM »

If the SWR is 2:1 or better you will not really see an improvement in far field signal strength, what is the big deal about a 1:7 to 1
SWR, it's nothing. ...

Reread the posts. 

Ain't no farfield involved here. 

His 1.7 reading involves the meer on the rig and is reporting the input to the power amp...


73
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W5DXP
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« Reply #13 on: April 28, 2011, 04:01:04 PM »

I replaced it anyway with god quality RG8x in preparation for receipt of the Scorpion SA-680 I ordered last night.

Sounds like you've got your problem solved and I have just one question. How much do you have to pay for "god quality RG8x"? Sorry, the devil made me do it.Smiley
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K8KAS
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« Reply #14 on: May 07, 2011, 07:07:01 AM »

3WD, you miss the whole point of my comment, and far field is whats its all about/the signal old timer, and the 1.7 SWR between the rig and input to the amp means very little in terms of powering down the IC7000's output. With a 1.7 SWR the 7000 may limit its output a very small amount BUT its still more than enough to drive the amplifier. That's my point, none of this worry means beans in the final result the transmitted signal from the station... period. as long as the amplifier sees a good match between the antenna
and it's output stage...my dog's tail wags when I transmit in the car but it doesn't mean beans. 73 Denny K8KAS
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