high swr with homebuilt amp

[bettyeboop]

Thanks again for your help.............I am so close to having this figured out........
What are some common reasons for high swr when amp is in the loop..I have high swr even if the amp is off. I even took all the wires of the relay except the in and out wires and still high swr. I have tried coax, twisted pair, reg 16-18 gauge. I am out of the silcone wire like you wind the transformers with. my connectors are not grounded out, my patch cords are good, my meter does the same as the swr function in my pres lincoln. way too high...up all the way at 6 or so.
The amp is putting out watts but high swr...................I put the case on no good......It is crazy......or i am crazy......lol. This is lots of fun but after a while it gets old....my wires are six inches long because the way the case is with the power supply inside.
This may be the whole banana.....dunno.

I am calling out to bob 85 , am or any one that will take time to help me.......I will try what ever you suggest.

many thanks for your help.....

galyn davis
ps.

I should get the cleanrf system to go with my scope today or tomorrow. It will be very valueable in tuning radios and amps. one box goes between the radio and amp and is x on the scope...the other box goes between the amp and ant, and is y on the scope......and many other features....i am excited about it and will let you guys know how it works out.

 

[bob85]

if you can post a pic or email me a pic maybe i or somebody else can see what your problem is, i dont know what you mean by connectors not grounded, they have to be grounded to the board ground even if the ground path is through the heatsink and case,

good look

 

[Beetle]

Where, precisely, are you measuring the SWR (output of radio/input of amplifier? output of amplifier/antenna)?

and... What are you using to measure SWR?

Take an analyzer, such as the MFJ-259B, with a six-inch jumper (or shorter) and measure the SWR at the antenna itself.

 

[Crusher]

The SO-239's that are bolted to case ( I hope) need to be grounded to board. EVEN solder wic braid will work for this. As stated earlier, until we know were SWR is high at, it is hard to guess?

 

[bettyeboop]

wanted to check back in.

!. My home built power supply is putting out 12=22 volts dc.
2. I have fried four pills....
3. the pri. stage is not needed for two pill 2879.....especially for new builders
( a straight 2,4, 6 pill can take up to twenty volts) you will burn if it has a pri stage(1x2,1x4, etc)
4. swr corrected itself with a pill replacement on one amp and i suspect that is all that is wrong with all three.
5. I am having trouble finding the best way to bring power supply down to a reasonable voltage. It is non regulated ( trans, rectifier, cap) copied dave made type.
I am running my amps off of a gell batt and a 25amp power supply.....for now intill I fix the problem. My goal is 16 volts dropping to 13 or 14. I have been playing with five watt resistors.....ac side, dc side, pri , sec. whew... I need help with this.

thanks again for your help


davis

 

[bushwacker]

If you have a high swr with the amp on or off, I would speculate that the problem is between the amp input and the relay... or somewhere around that relay.
Its strange your getting high reflect even with the amp off and relay disingaged....
With the amp off, the signal should travel from the input so239, to the relay, then out to the output so239. There should'nt be anything there to really cause alot of loss.
To track down this problem better.... what I would do is remove the relay from this situation and check the reflect...... get a piece of coax and use it as a jumper... solder it in between the input so239 and output so239.... basically making a quick jumper right through the amp...... then check your match.... if the match drops to a reasonable amount then you know the problem is in the area of the relay. If there is a rx preamp relay in the amp I would remove it from the circuit and check it out after your sure the line from input, to keying relay, to output is good.
All this should be pretty fast to do and check.

It might sound like a stupidly simple thing to do... but its a place to start. When the coax jumper is in place, and the match goes down... you will be sure that the feedline going in and out of the amp is good..... you will also know that there isn't a problem with the so239's and grounding of them.
From there you can check for loss from the input to the relay.... from the relay to output....then from input to output through the relay. If you have an rx preamp relay... remove it from the circuit and do all the above checks. Once your sure there is no loss through the keying relay circuit, then add in the rx preamp circuit and check it out.

You just want to be 100% sure that one circuit (area)is working before checking the next.

As far as the power supply problem.... sounds like your doing the right thing with the resistor and increasing the load. And thats the main thing with unregulated power supplies... if you want to lower the voltage you have to increase the load. Just like "walwarts" and power adpaters used in other electronics.... the voltage is set by the current consumed. Thats why your voltage is dropping from 22 volts to 16 volts... the current draw of the rf amp is making the voltage drop.
I'm not familiar with these power supplies specifically... but I would assume that if they are like alot of other unregulated power supplies, if you were to increase the load ( current draw) the voltage would drop more. The dropping resistor is most likly doing just that.
Increase the load on the power supply and see if the voltage drops more.... hook up anything you can that will run off of 13 volts and draw more current( 12 volt auto test lights etc etc) with the amp hooked up. You just want to increase the current draw to check if it will drop the voltage more.
Its just an idea... you most likly have tried or know all this already.
Take care