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Author Topic: AL-80A problem interfacing to Icom 718  (Read 3886 times)
KE7RTV
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Posts: 35




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« on: February 16, 2013, 04:54:24 PM »

Hi,

I'm new to amplifiers. I just bought an Al-80A. My radio is an Icom 718. The problem is that when
I transmit using the Al-80A, my transmission works but every incoming signal after it
is distorted to the point that I'm unable to understand what's being said. If I turn the radio off and
back on, the distortion goes away.
Sometimes, I've had to turn the radio off and on several times before the distortion clears up.

Any help would be greatly appreciated.

Thanks,  Steve KE7RTV

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KM3F
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Posts: 519




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« Reply #1 on: February 16, 2013, 05:30:55 PM »

Does it do it without using the amplifier or only when you use the amplifier?
Only way for distortion to occur is the receiver it'self if you need to turn it off/on several times to stop it.
The amplifer is out of the picture at that point.
What is the SWR when using the amplifier?
It's possible RF feedback is overloading the radio until you stop it by turning it off then on again.
Good luck.
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KE7RTV
Member

Posts: 35




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« Reply #2 on: February 16, 2013, 09:59:58 PM »

Hi,

Thanks for the reply. In answer to your quesion; the distortion only happens when the
amp is being used.  SWR  was between 1.5 and 2. 

73 and thanks again,

Steve
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KE3WD
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Posts: 5689




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« Reply #3 on: February 17, 2013, 05:14:03 PM »

Maybe too much RF in the shack and getting into the radio. 
\
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K0CWO
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Posts: 419




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« Reply #4 on: February 17, 2013, 08:43:25 PM »

Can the distortion you are talking about be described as an intermittent receive situation?  If so, it could be a sticky transmit/receive relay.  If your reception is fine without the amplifier in line, that would be a thing I'd look at. 
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N4CR
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Posts: 1694




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« Reply #5 on: February 17, 2013, 09:21:15 PM »

Maybe too much RF in the shack and getting into the radio.

Yes, this seems very likely. Describe your antenna configuration.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
NO2A
Member

Posts: 822




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« Reply #6 on: February 17, 2013, 10:07:53 PM »

Can the distortion you are talking about be described as an intermittent receive situation?  If so, it could be a sticky transmit/receive relay.  If your reception is fine without the amplifier in line, that would be a thing I'd look at. 
I think it`s the radio relay sticking. I have the same problem sometimes when using my FT-857D with my AL-80A. When this happens I put the amp in standby and tap the cw key,then the `857 goes back to receive with normal sensitivity. It`s the radio relay,not the amp relay. I think that`s what`s happening in his situation. The relay gets hungup somehow.
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N4CR
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Posts: 1694




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« Reply #7 on: February 17, 2013, 10:37:19 PM »

Next time it garbles, turn off the amp, disconnect the antenna on the amp and connect it directly to your rig. If the problem doesn't change, it's not a problem in the amp.

I suspect your rig is being subjected to strong RF and is getting confused.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
KE7RTV
Member

Posts: 35




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« Reply #8 on: February 20, 2013, 06:12:06 AM »

Thanks to everyone for your suggestions.

My antenna is a inverted V dipole. It's about 25 feet above the ground. Fed with RG8x coax.
At the time, I wasn't using a choke balun which, to my understanding, isn't necessary when
in the inverted vee config. I've been testing the amp on the 40 meter band.

The distortion only occurs when I'm using the Al-80A. I've discussed this problem with Ameritron
and they agree that the intermittent distortion is somewhere in the transceiver.

I have ordered new RG8X coax because I was using the very cheap stuff from Ebay. I'm waiting
for this to arrive before I attempt another test. I'll also make a choke balun.

Thanks again to everyone for your help and as soon as possible I'll try your suggestions and report
back with the results. ..................    Steve KE7RTV



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N4CR
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Posts: 1694




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« Reply #9 on: February 20, 2013, 08:37:10 AM »

Thanks to everyone for your suggestions.

My antenna is a inverted V dipole. It's about 25 feet above the ground. Fed with RG8x coax. At the time, I wasn't using a choke balun which, to my understanding, isn't necessary when in the inverted vee config. I've been testing the amp on the 40 meter band.

The type or diameter or quality of coax very seldom has anything to do with RF in the shack. Common mode current is caused by antenna imbalance. One side of your antenna leads to one half of your dipole and the shield leads to the other half of your antenna and the outside of the shield. That's the imbalance.

A balun is primarily used to prevent common mode currents, which manifest as RF in the shack. An inverted V is in no way immune to having common mode currents. If you choke off the path to the outside of your coax shield with a balun, you force the current on your antenna to be more balanced. This reduces RF in the shack.

Quote
The distortion only occurs when I'm using the Al-80A. I've discussed this problem with Ameritron and they agree that the intermittent distortion is somewhere in the transceiver.

Of course they agree. They don't want you to blame their amp. (and it's probably not the amp)

Do the test. Transmit with the amp in line until it garbles. Once it's in that state, leave the radio on and remove the antenna from the amp and connect it directly to your radio. If it's still garbled, the amplifier is vindicated. No phone calls required to understand where the garbling is occurring.

As to WHY the garbling condition is occurring, it's very likely to be from RF in the shack and a quality 1:1 current balun at the antenna feed point might completely eliminate it.

A 1:1 balun need not be expensive. You can build one with a #43 toroid and length of coax or a pair of wires (bifilar).

You can test the 'RF in the shack' hypothesis by running the amplifier into a dummy load. If the problem doesn't occur, you've eliminated everything but the feedline and antenna.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
K4RVN
Member

Posts: 791




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« Reply #10 on: February 20, 2013, 03:00:15 PM »

Hello Steve,
To see if you have stray RF  in the shack overloading your 718 after a transmit with the AL 80A, you should borrow or buy a field strength meter to determine that is the problem, or is not the problem. I have the AL 80A and also a field strength meter. Here is a link to an inexpensive one. http://www.universal-radio.com/catalog/meters/1015.html. Also I use a MFJ 704 interface
althought it was not needed. My little ICom 7200 had such a tiny relay that I wanted to protect it. The interface requires only a minute amount of milliamps to trigger a transistor while the transistor
acts as a relay. I have at times in the past experienced what you described and always found that it was stray RF in the shack getting back into my transceiver. I have a field strength meter that
is mounted on the wall for many years so it alerts me to a coax or antenna problem. A field strength meter is less than 30 bucks. If you can find one at radio shack they used to sell for around 20 bucks. I made mine from the junk box. Good luck and keep us posted.

Frank
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K4RVN
Member

Posts: 791




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« Reply #11 on: February 20, 2013, 05:45:22 PM »

Steve,
I forgot to ask if you had a good ground on the amp and transceiver. It is important to have a good grond and tie the transceiver ground and amp ground to your ground wire at a common point.
You probably have done this but I did not want to assume anything. A good ground rod with short as possible ground wires can eliminate some problems with RF. I don't think any one installation
would solve all installation problems as grounding is often discussed and seldom understood, myself included.

Frank
« Last Edit: February 20, 2013, 05:49:22 PM by K4RVN » Logged
KE7RTV
Member

Posts: 35




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« Reply #12 on: February 22, 2013, 10:28:58 AM »

Thanks once more for all the help and suggestions.

As for my station ground; I have a buss to which the transmitter and amplifier are
connected. The buss is connected by solid copper wire to a rod which is five feet into
the ground. The distance from the buss to the rod is approximately 15 feet. I live in
the desert where the soil is dry and sandy.

I've ordered new RG8X coax for use with the amplifer and as soon as it arrives, I'll try
all the suggestions.

I really appreciate all the help.

Steve KE7RTV

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K4RVN
Member

Posts: 791




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« Reply #13 on: February 22, 2013, 06:24:59 PM »

Steve,
I bought some bargain  RG8X coax with the crimped ends already on from Giga parts at a low price. I connected 100 ft of it in two 50 ft lengths with a barrel connector and ran 800 watts on it with my AL 80 A on 40 meters with a low SWR. Then after a time the  antenna went dead. I checked where it connected to the antenna and it was fried black with all the insulation melted. I learned my lesson and bought high quality RG8X from the wireman at our local hamfest and replaced the cheap stuff. I suspect the pl259 s had  poor connections and caused a lot of current and heat. I use soldered PL259 siver teflon fittings for outside use when possible. That's the fun of learning by doing. I hope your problem will be solved, but I suspect RF floating around now as a guess.

Frank
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KE7RTV
Member

Posts: 35




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« Reply #14 on: March 13, 2013, 08:46:49 PM »

I want to express my thanks to everyone who helped me with this problem.

After trying everything I could think of, including all the suggestions made on this forum,
I placed a relay buffer between the amp and the Icom 718, and that did the trick. The
relay buffer now seems like an obvious solution but the symptoms were weird and even
Ameritron didn't think a buffer would help.

Many thanks to Ron, K4POZ, who made the relay buffer and provided invaluable
support. I'm all the way across the country from Ron but I had the buffer within
48 hours of placing my order. If you need a relay buffer then you can't do better than
Ron.

Thanks again to everyone!!

73,

Steve  KE7RTV
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