Astrobeam

[Marconi]

I did tune the antenna without the amp it was just when I hooked it back up when I noticed the problem.

Thanks for the heads up guess I will get it looked at, I will see how Bretts 500 turns out.

2020, I think your amp setup worked OK previously, right?

If so, then try a couple of different short jumper lengths (3'-7') at the radio/meter end of your setup. See if the match looks to change noticeably, good or bad. This may give you a clue if your amp is bad or you just have a terrible match at the radio end of your feed line that is due to feed line transformation.

If you were lucky, it might even settle the amp down a bit, but that is not a fix. It would tell you if the antenna match was heavy with reactance even though it was showing 1.3 SWR and looking good to go.

When the antenna match is bad enough to cause issues regardless of what the SWR reading is, then changing the feed line length short amounts can cause the issues and changes you may be experiencing.

 

[RT2020]

Yes it was working fine before, but Marconi I just seem to have dumb luck like this on everything I do. For instance I put new heads on my work car and then my temperature gauge started fluctuating, turns out my thermostat took a dump right after I changed the heads. Thats just my luck!

I will try your idea, I also have another 667V I was gonna throw inline and see if it does the same thing.

 

[Marconi]

Yes it was working fine before, but Marconi I just seem to have dumb luck like this on everything I do. For instance I put new heads on my work car and then my temperature gauge started fluctuating, turns out my thermostat took a dump right after I changed the heads. Thats just my luck!

I will try your idea, I also have another 667V I was gonna throw inline and see if it does the same thing.

Well 2020, I wouldn't look at the thermostat deal as a negative, IMO it is a good lesson to always change a thermostat when you're in there. Change the seal too and maybe the hoses.

I've suggested this short jumper diagnostic idea many times before, and from what I've heard back...it has never worked according to the operators that said they tried it. So I'm not holding my breath.

It is just a non-fix idea that may help tell if there is a feed line problem due to a bad mismatch and feed line transformation as a result. I also describe it as guys sorta' chasing their tail trying to fix the problem.

Since your setup is not working so good at the moment, for this idea to be of help...you will have to see an improvement. If that don't happen then the idea didn't help, but you haven't lost much in the trying either.

 

[RT2020]

Just hooked up my other 667 and it works as it is supposed to on my Sigma IV.

Guess I will get the amp repaired and stick the beam in the air.

 

[Marconi]

Hey 2020, while your at it I'd check your water too. Keep us posted.

 

[RT2020]

You lost me. What water?

 

[RT2020]

Oh and I climbed the tower, its a little too windy for me right now to mess with the beam.

 

[Marconi]

You be careful.

 

[2RT307]

You lost me. What water?

Coolant, I suspect. With the work vehicle.

Glad at least one of yours is working good, Greg. This weirdo SWR thing has been bugging me for quite some time now, but I have yet to get them repaired. I'm hoping that Shockwave's theory is correct. Have discussed this with Mad Scientist, and he is looking at doing his that way. Once I see it works, both of mine will get repaired the correct way.

73,
RT307

ps what happened to your Skipper?

 

[Shockwave]

Unless something unusual is going with the amp being tested, this removal of RF from the bias line will stabilize these amps. It's been known for some time that replacing the bias circuit cures most of these problems and I think Mad Scientist has already confirmed this. The question is why? Poor regulation of the bias alone should not cause an amp to oscillate. However, if you let output RF get into the bias voltage and pass this onto the base of the output transistors, you just made an oscillator.

There is no better way to insure a large amount of RF will enter the bias circuit than to combine the DC bias and 500 watts of RF on the same relay contact. This is absolutely absurd! Using small chokes and bypassing caps to isolate DC from RF is something commonly done with mast mounted pre-amps so the coax can power the pre-amp. It works well when dealing with milliwatts of RF. Thinking these same parts can decouple half a kilowatt from the sensitive DC bias was about as bright as a two watt bulb.

 

[RT2020]

Coolant, I suspect. With the work vehicle.



ps what happened to your Skipper?

Oh yeah the work car...duh! yeah its good just using as a reference to the way things go for me.

As far as the Skipper I got tired of messin with the sweep tubes and traded for the second 667. I wanted a 500 but that is what he had and I went for it.

 

[2RT307]

Oh yeah the work car...duh! yeah its good just using as a reference to the way things go for me.

As far as the Skipper I got tired of messin with the sweep tubes and traded for the second 667. I wanted a 500 but that is what he had and I went for it.

Cool on the amp trade. I know what you mean about bad luck. Reminds me of Hee Haw... "if it weren't for bad luck, I'd have no luck at all".

So your SWR's are ok with the second amp on the GP, so theoretically they should be good with the beam. Just curious, how is the bandwidth with the Astrobeam?

73,
Brett