SWR Spike on 6m


Adrian McGonigle
 

I saw a few posts about this and just wondering if anyone got to the bottom of it, been using my IC-7000s on HF and 2 without problem for a long time, decided to have a play on 6m and both of them show the initial swr spike on 6m, to antennas with excellent matching and also going through a high power ferrite core choke/balun, the spike is not evident into a dummy load. 

Adrian G0KOM


Adrian McGonigle
 

Just further. to this, tested two other 6m radios not IC-7000s and neither exhibit the issue so its definatley 100% IC-7000 related.

Adrian G0KOM


 

Do you have an SWR meter external to the IC-7000? What does it say? The SWR bridge is the same for HF including 6 meters. They measure imbalance pretty accurately on my IC-7000s. I have seen external tuners and SWR meters disturb the SWR on the radio due to their internal wiring. 
I have a MFJ998 that my IC-2KL does not like due to this problem, too much unmatched wiring in the box. The ALC and SWR is very touchy on my IC-2KL. 
The IC-AT500 lines up perfectly, but then this is not 6 meters.
6 Meters at a higher frequency might be touchier, perhaps.


Adrian McGonigle
 

There is nothing external to the radios, direct coax to the antenna, the one thing I havent had a look at is to put a meter in line just to see if it agrees with what the 7000 meter is doing when it spikes, the radios works perfectly in HF and 2m and also perfectly on 6m apart from the SWR Spike at the beginning of every TX period. 

Adrian G0KOM


Adrian McGonigle
 

Just tested with an external meter, no spike on the external meter which I thought anyway which shows antenna is fine, still spikes on the radio SWR. meter which is obvious at first TX as the power folds back momentarily as well as the meter spiking up to unity for a split second, definatley an issue with the 7000

Adrian G0KOM


Adrian McGonigle
 

The strangest thing is that the spike does not occur on SSB, only on FM and CW, albeit that maybe simply as they are full duty cycle modes.

Adrian G0KOM


Howard Jones
 

Try sampling the output on a storage cro and see if it shows an rf spike. 


On Thu., 14 May 2020, 02:56 Adrian McGonigle, <adrian@...> wrote:
Just tested with an external meter, no spike on the external meter which I thought anyway which shows antenna is fine, still spikes on the radio SWR. meter which is obvious at first TX as the power folds back momentarily as well as the meter spiking up to unity for a split second, definatley an issue with the 7000

Adrian G0KOM


Adrian McGonigle
 

Unfortunatley I dont have access to any test equipment, but I suspect there is an RF spike or some sort of overshoot as I tested the radio again tonight just for peace of mind and there is also a spike in RF power momentarily, the Power meter when the PTT is pressed in SSB goes full scale for a split second before settling down to nothing before any audio, this does not occur in any of my other Icom equipment. I seem to have found a lot of posts in various places about an RF spike or ALC overshoot etc etc but not once have I actually seen anyone who has solved the issue

Adrian G0KOM


Adrian McGonigle
 

The RF Spike is evident on an external PEP meter as well, really surprised there hasnt been some sort of a fix documented for this, the radios work perfectly in every other way.

Adrian G0KOM


 

In the IC-7000 power is regulated by the input to the circuit that looks at the desired power level, SWR, external ALC, if SSB mode has been selected, etc.
The output from this circuit goes to the CPU that controls the power level as a feedback. 
I think that you could check values around this comparator and see if you can see a problem, but many have noticed that there is a spike when the power is reduced to drive a linear amp. 
I had to work in this circuit when I had a problem in the SSB detect part that meant that I could not control the power at all.
I don't think that the spike is a problem if not driving a solid state amplifier.
That comparator gets inputs from fwd power, SWR, ALC and is damped when SSB is selected if I remember correctly.
If you want to pursue the problem this would be the circuit to examine first, but be warned the parts are very very small.


Steve W3AHL
 

Icom hasn't acknowledged or fixed any problems since after the first year of the 7K's release in 2006.  They released a couple of changes, but as far as I'm concerned they didn't fix anything.

There are several problems in the ALC circuit that cause power spikes, typically noticed on CW with short rise times at faster keying rates.  I posted some data on that in the Files area of the group years ago.  I am not aware of SWR being affected by that though, but maybe your references to SWR were really meant to be just power spikes on the "SWR" meter??

There are also power spikes on SSB when compression is turned on.  It is caused by the PTT switch click in the HM-151 mic getting amplified greatly via the mic audio circuit. It varies by compression level setting and by how hard and fast you press the PTT switch.  Using a foot switch will cause the problem to disappear.   I also documented that in the files area.  But it wouldn't affect AM/FM, nor SWR.  

I'll take a look at my 7K's this week and see if they exhibit the problem you see, but don't expect any fix for it.....  If it was just a power spike on AM & FM (but no SWR  problem) I would look at the Transmitter Adjustments in the Service Manual, specifically TX Total Gain (50 MHz) and TX Output Power (50MHz).  If those are set wrong, the ALC spike can be more of a problem.  But I doubt it would affect SWR.  There are adjustments for the ALC circuit, but not specifically for 50 MHz band only.  

Steve, W3AHL


david vanhorn
 

How clean is the output of the radio on 6M?  It may be out of band energy being reflected by the antenna. The SWR meter doesn't know frequencies.


On Sun, May 24, 2020 at 12:34 PM Paul <pg321@...> wrote:
10 cents worth

Maybe it might be close or similar on those selected icom's that are later model radio's , there was a few about and still is i seem to recall with spikes .

Maybe i also might have to look into it as i'm planning 6m mobile as well as the current 80 then 40/20m mobile . 73



--
K1FZY (WA4TPW) SK  9/29/37-4/13/15


 

I think the spike is an artifact of the circuit used to control the power output. The drive to the final is controlled by the circuit and has inputs from the CPU that sets the output (from low to high from the memory setting), the SWR, the forward power output, and SSB mode. The time constants that are in the circuit means that the drive is high and then cut back as the control takes effect. This is why I think that perhaps some of the circuit values might make some difference.
I have attached a PDF of the pertinent schematic page for reference.

On Sun, May 24, 2020 at 1:34 PM Paul <pg321@...> wrote:
10 cents worth

Maybe it might be close or similar on those selected icom's that are later model radio's , there was a few about and still is i seem to recall with spikes .

Maybe i also might have to look into it as i'm planning 6m mobile as well as the current 80 then 40/20m mobile . 73



--
J.D. Barron


Adrian McGonigle
 

Been testing this at work over the weekend, the RF spikes are not just confined to 6m they are on HF as well, although the SWR spike is 6m only (will test again though but pretty sure it was only on 6m)  it momentarily throttles back the output power as it should, literally for a split second then every thing is good, if I dont drop out of TX in CW it stays fine but the moment theres a slight break in TX times the first key up shows the same SWR Spike momentarily. 

Adrian  G0KOM


Philippe PARIS
 

Hi Adrian,

I don't test if there are RF spikes on 50 MHz, anyway, i can show you there are huge ones on UHF...

CLICK THERE

Then an IC-7000 in front of an UHF PA could cause some problems.

For information, no spikes on UHF on an FTM-400...

CLICK THERE

If i have some time one day, i will check the IC-7000 on HF, 50 and 144 MHz, just to know how it is ?

73 to all.

Philippe