TX 350HD SWR Input Tuning Issue?

[RCIGuy]

Im have a bit of trouble with what i believe to be the input tune on the amp, heres the issue.
Using the radios internal tuner it is flat 1.0 across 11 meters, same for the antenna,
When using 2 different radios there are no swr issues and the LP meter still shows 1.0-1.1 swr.
Adding the 350HD in line, variable all the way up, radio power turned down to proper input watts
to drive it, swr on the radio shoots up to 1.6 -1.7 swr. I can use the radios tuner to get it down some but
then another problem is i cant use the radio with amp off cuz now its tuned to make up for the amp,
i dont want to run the amp all the time. Am i correct in thinking C8 is failing or it needs to be replaced with a different value mica to straighten this mess out? C8 is currently a 150pF, should i be going down or up in value?
I hope ive givin enough information so the knowable people here can understand what im trying to say
and point me in the right direction.

 

[Shadetree Mechanic]

I put an Arco trimmer on the input of mine a while back.

Texas Star DX 350 HDV Input SWR

Hey Guys, I had this at the end of someone's thread so I thought I would start a new one to make it easier to find. The input on my DX 350 had an SWR of around 5:1. I was able to coil up some coax and help it some. The Dial A Watt was useless because it would peg the SWR meter to the right. The...

www.worldwidedx.com

 

[Elliott Hart]

What is your input tune with the amp inline and the amp in standby mode? Please check your pass-through tune first before you do anything.

 

[Xracerx13]

*** Tune with amp inline and amp OFF only. ***
Most Texas stars have around 1.5 swr when turned on. I wouldn't want to see you blow the transistors in the amp while auto tuning swr with the amp on. So don't do it.

 

[RCIGuy]

What is your input tune with the amp inline and the amp in standby mode? Please check your pass-through tune first before you do anything.

*** Tune with amp inline and amp OFF only. ***
Most Texas stars have around 1.5 swr when turned on. I wouldn't want to see you blow the transistors in the amp while auto tuning swr with the amp on. So don't do it.

Was having no issues running the amp for 2yrs, this problem started this summer and this is the current fix i have for the problem. I have no choice but to tune with amp on. Hope this will answer these questions.

This pic is with amp inline and off, (radio tuned to run with amp on)

This pic is with the amp on

I put an Arco trimmer on the input of mine a while back.

I read your thread about it, great info, that trimmer you use is already at a higher minimum in value than with i have (150pf) unsure if it would be the one to try?

 

[Shadetree Mechanic]

Was having no issues running the amp for 2yrs, this problem started this summer and this is the current fix i have for the problem. I have no choice but to tune with amp on. Hope this will answer these questions.

This pic is with amp inline and off, (radio tuned to run with amp on)

View attachment 66964​

This pic is with the amp on

View attachment 66965​

I read your thread about it, great info, that trimmer you use is already at a higher minimum in value than with i have (150pf) unsure if it would be the one to try?

It's range is 175pf to 680pf, I believe I used it because I already had it. RF parts no longer has it, but I see a generic version on eBay. Six Star has this one that could be put in parallel with the capacitor. But this may not fix your problem because what you have going on is a little different than what I was dealing with.

Pkg 2 Variable Mica Capacitors 464 - 45pf To 280pf - CB Ham Linear Matching QRP | eBay

Value = 45pf to 280pf. Change Out Those Fixed Capacitors & Tune Maximum Power. Use For Making Your Own Matching Network.

www.ebay.com

 

[loosecannon]

what radio are you using?
LC

 

[linearone]

Leave it alone

 

[RCIGuy]

It's range is 175pf to 680pf, I believe I used it because I already had it. RF parts no longer has it, but I see a generic version on eBay. Six Star has this one that could be put in parallel with the capacitor. But this may not fix your problem because what you have going on is a little different than what I was dealing with.

Pkg 2 Variable Mica Capacitors 464 - 45pf To 280pf - CB Ham Linear Matching QRP | eBay

Value = 45pf to 280pf. Change Out Those Fixed Capacitors & Tune Maximum Power. Use For Making Your Own Matching Network.

www.ebay.com

Thanks, maybe ill give it a try.

what radio are you using?
LC

7300

Leave it alone

Thats an option to.

 

[9C1Driver]

Im have a bit of trouble with what i believe to be the input tune on the amp, heres the issue.
Using the radios internal tuner it is flat 1.0 across 11 meters, same for the antenna,
When using 2 different radios there are no swr issues and the LP meter still shows 1.0-1.1 swr.
Adding the 350HD in line, variable all the way up, radio power turned down to proper input watts
to drive it, swr on the radio shoots up to 1.6 -1.7 swr. I can use the radios tuner to get it down some but
then another problem is i cant use the radio with amp off cuz now its tuned to make up for the amp,
i dont want to run the amp all the time. Am i correct in thinking C8 is failing or it needs to be replaced with a different value mica to straighten this mess out? C8 is currently a 150pF, should i be going down or up in value?
I hope ive givin enough information so the knowable people here can understand what im trying to say
and point me in the right direction.

I have several Texas Star 250’s and one of them does the same thing. I can understand wanting to have that adjusted just a bit. Once you finished just remember to watch your pass through watts when you turn the amp off.

 

[RCIGuy]

Well something needs to be adjusted, i put a meter in after the amp and it pegs the swr in am, ssb it also pegs the swr.

 

[loosecannon]

Well something needs to be adjusted, i put a meter in after the amp and it pegs the swr in am, ssb it also pegs the swr.

how did you check the SWR on SSB?
LC

 

[Captain Kilowatt]

how did you check the SWR on SSB?
LC

More appropriately is WHY? AM and SSB are the same frequency so SWR will be the same plus SSB having no carrier requires you to whistle or something into the microphone but that just causes fluctuations in levels and throws things off. I keep seeing people check SWR in all the different modes including SSB and I just want to SCREAM.

 

[RCIGuy]

Im not really "checking" it on ssb, merely an observation that it also pegs the meter, didnt think it would do that.
I am not an expert, all i know is there is reflect back to radio when amp is on either in high/low and swr is pegged in am, this does not seem right to me. Tryed different Lenths of jumpers, different jumpers, different meters with same results, this cant be right? I dont know what to do so im asking for help, maybe im doing this all wrong but i have no way of knowing unless somebody can educate me. About ready to put it all on a shelf and call it a day.....

 

[Xracerx13]

i put a meter in after the amp and it pegs the swr in am

Is that with the amp off? Which it should be off...
Did you disable the tuner in the radio?

Antenna SWR is only calibrated and checked after the amp with the amp off and radio in AM or CW mode with a power level of 4-20w and only with a deadkey, no voice. Once you do that if you introduce more power or talk into the mike the extra power from modulation will make any analog SWR meter swing. Especially with the amp on. Anytime there is a deadkey power increase an analog SWR meter needs to be re-calibrated for the extra power.
The problem with having a radio with a antenna tuner built in is that it is designed to be connected to only an antenna when tuning. As soon as you add an amp inline the radio now tunes for the SWR before the amp which is an incorrect method as it will drastically change the SWR after the amp when it does its tuning.

I have an MFJ 1500w antenna tuner/meter after the amp. I can read the swr at the radio(TS-480HX with no built in tuner), but that is the SWR before the amp or in other words the amp input tune.
Try getting an SWR read after the amp with the tuner in the radio turned off and amp turned off and tell us what you get on both the swr meter on the radio and the swr meter after the amp with a deadkey only.