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IC-706MkIIG front end protection


#1

I have been using the Icom 706 MkIIG mainly on 2m ssb and have found it a fairly good piece of kit for working weak signal stations on summits, but I am finding a lot of weak stations are escaping due to the receiver backing off when strong local stations call. If Mike GW0DSP who is only 1/2 a mile away calls before I get the weak station the RX backs off and I can not here any weak stations for about 10 minutes. There are other local stations who do the same but they are not regular chasers so are not usually a problem, however one other station that effects the 706 in this way is about five miles away.

Does anyone know of a way to improve the handling of these strong signals or do I need to replace the rig with something better?

Note this doesn’t happen on FM and it was not a problem on my old Kenwood TR9130.

73 Steve GW7AAV


#2

In reply to GW7AAV:

Set the AGC to fast for SSB. :wink:

AGC setting is independant for each mode on the 706 IIRC.

Andy
MM0FMF


#3

In reply to GW7AAV:

I think you bought your 706 2nd hand Steve and was just curious if any other 706 owners suffer the same plight, or is it a fault with your radio?

73 Mike

PS: I’ll knock my power down to 3.75 Kilowatts and beam 2 degrees off your heading and see if that helps:-)


#4

In reply to GW7AAV:

Steve,

The AGC should recover within seconds. If it doesn’t then you may have a component fault. Play about with a combination of AGC speeds and modes and you should be able to work out where the fault lies.

Actually someone had to nobble the Connahs Quay mafia… 100 plus SOTA chaser points in a day. It’s just obscene! :wink:

73, Gerald


#5

In reply to MM0FMF:

Cheers for that Andy - Duh! I never thought of the AGC control, but I never had one on a 2 metre rig before. Hopefully that will make a difference, it appears to be much better during tests with the 817 2 feet away. You just may have just ruined my excuse for a new rig - Tee Hee

In reply to GW0DSP:

Not your problem Mike I will just come you to your house when there is a rare one on. You can grill me some bacon on the linear ;o)

In reply to G4OGI:

This weekend looks like a 100 chaser point weekend with all the alerts. I was going to activate one myself but maybe I will stay home and chase instead.

Steve


#6

In reply to GW7AAV:

Welcome anytime Steve but no bacon sorry a certain Clitheroe person wiped out my supplies.

73 Mike


#7

In reply to GW7AAV:
Hi Steve

I have the 706 II G and I have to say that the AGC recovers way quicker than that even when set on “slow”.

No problems digging weak ones out… might be worth having it checked.

Any mods. done to it? 5MHz etc?

73 Marc G0AZS


#8

In reply to G0AZS:

Well it looks like it is an AGC issue as setting it to fast seems to reduce the problem. However, 10 mins recovery seems a little excessive! Mike might be close and running 100W or so but it’s not like he’s got a Tempo in the shack! So it should come back in some seconds. Perhaps the effect is exacerbated by the desire to work the summit and DX-time-dilation is occuring (*). Before I moved to GM, there were 3 of us QRV on 2m SSB within 1/2 mile radius. My old Icom IC290 would take upto 30 secs to fully recover if one of my locals let rip with 100W down a yagi in my direction. You might find that simply switching between slow and fast and back is enough to give the AGC a chance to recover. It did the trick on the Icom.

You could try listening to a beacon and getting Mike to transmit as you try different settings. But it’s hard to measure these things with off-air signals as if you used a beacon such as Wrotham, the normal fading makes it difficult to be sure the AGC has recovered and it’s not QSB.

Andy
MM0FMF

(*) DX-time-dilation is the effect that makes a normal DX/contest style exchange that takes 10 seconds or so (roger roger you are 59 in IO85FU, 73 and good dx) appear to take about 5 mins. Normally observed when you can hear EA9 stations on 2m SpE and everyone in Western Europe is working the DX and you’re not! The more people who work the DX excluding you makes each exchange seem to go slower and slower. The time dilation ends when you finally work the EA9 and are feeling smug only to find someone up the road worked 2xEA8, a CT3 and D44 and that was barefoot as they forgot to switch the PA on! :slight_smile:


#9

In reply to G0AZS:

Yes it has had the 5mHz mod.

In reply to MM0FMF:

What has been happening was typified today. I had been listening to a weak EI station on 144.28ish while I was waiting for John GW4BVE on 3.666. The reason I was hearing the EI was because I had set the beam up on the bearing of NW-037 (roughly East). While I waited my turn on 80m to work John I retuned on 144.310 where I expected Frank G(W)3RMD to appear. I spoke to John and then turned my attention to Frank. I was receiving Frank at 5/1 and had called him four or five times but each time was beaten much stronger stations (I heard the reports) Mike then called in and Frank peaked his beam on Mike but I heard nothing of Franks transmissions. The bar graph took about 30 seconds to drop after each of Mike’s overs. After that I heard other stations go back to Frank but no sign of Frank. I retuned to the frequency where the EI had been and could hear the station he had been talking to but not him. I turned the rig off for a while and turned it back on and I could hear the EI again as I had before. I checked on 144.310 and Frank was still there I called a couple of times and then he turned his beam to work someone and I never heard him again.
The same thing happened on Frank’s second summit and just as I thought I was going to get him Mike came back on to pass a message that Peter GW3TJE was on a summit and by the time the rig recovered Frank had either gone or turned the beam. I listened for a further 20 minutes but heard nothing of Frank.

There is a lot of activity tomorrow so (if I don’t go activating myself) we will see if changing the AGC has made any difference. If it has not then it maybe worth doing a complete factory reset of the rig as long as that doesn’t effect the wide-banding for 5mHz.

Thanks to all

Steve GW7AAV