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Questions about issue with new install.

R

rickou812

New Member
Apr 9, 2014
17
0
1
N. Florida
The install details:
Cobra 29 classic with RFX-75 professionally installed, set to DK 15w and pep 80w. The radio is running the upgraded power chord straight to battery with an additional ground wire from mount to metal dash frame. Mic is a 636l.
Texas Star DX500v with upgraded power cables, (4gauge) straight to battery. Negative 4 gauge to battery and seat mount bolt.
Wilson 1000 magnetic mount, top of roof, centered.
Radio shack swr/power meter.
Good quality 6 foot coax used for jumpers.
All mounted in F250. Have ran bonding straps from cab to frame. (I have more strap ordered to bond the bed..etc..)

My SWR is at <1.5 channel 1 - 40 with linear off.
SWR goes to 3.2 or so with linear on.

The issue:
The radio without linear on sounds great and gets out good. Per radio shack meter, dead keys 20w with engine running, Volts=14. PEP 90-100
If I turn the linear full on, (NO variable), I get a high pitched wine, and talk back sounds diminished, also confirmed with a another driver, that my sound deteriorates with linear on.
If I switch on variable and turn knob just off full, the degradation goes away and the great sound returns, per RS meter- DK100-120 with PEP 450'ish

If the engine is off, I can go all the way with variable pot without degradation, but if engine is running, I have to back it back a bit.

Thoughts?
Rick
 
Last edited:

I am not the most experienced person here but sounds to me like with the variable all the way up you are over driving the amp. An Rfx 75 with a 15w dk seems like way to much drive. Unless you want to smoke it.

Hopefully someone with more experience will chime in.

Sent from my SCH-I545 using Tapatalk
 
The 500v is a 4 pill all 2879? If so your over driving it.

Sent from my SCH-I545 using Tapatalk
 
No need to sell. it's not long for this world.Sounds like it's over driven with the engine running. turn the cobra down and run the amp without the variable .Got to do something about that swr increase. how is the swr with the amp running at a lower level.?
 
rickou812 said:
The install details:
Cobra 29 classic with RFX-75 professionally installed, set to DK 15w and pep 80w. The radio is running the upgraded power chord straight to battery with an additional ground wire from mount to metal dash frame. Mic is a 636l.
Texas Star DX500v with upgraded power cables, (4gauge) straight to battery. Negative 4 gauge to battery and seat mount bolt.
Wilson 1000 magnetic mount, top of roof, centered.
Radio shack swr/power meter.
Good quality 6 foot coax used for jumpers.
All mounted in F250. Have ran bonding straps from cab to frame. (I have more strap ordered to bond the bed..etc..)

My SWR is at <1.5 channel 1 - 40 with linear off.
SWR goes to 3.2 or so with linear on.

The issue:
The radio without linear on sounds great and gets out good. Per radio shack meter, dead keys 20w with engine running, Volts=14. PEP 90-100
If I turn the linear full on, (NO variable), I get a high pitched wine, and talk back sounds diminished, also confirmed with a another driver, that my sound deteriorates with linear on.
If I switch on variable and turn knob just off full, the degradation goes away and the great sound returns, per RS meter- DK100-120 with PEP 450'ish

If the engine is off, I can go all the way with variable pot without degradation, but if engine is running, I have to back it back a bit.

Thoughts?
Rick
Click to expand...
the amp is being wasy overdriven .radio should be down to around 2 watts.
the swr thing is more complicated to desribe . but you must re-calibrate when you
turn amp on or off. and even then you might still see a change. but power doesnt
change your swr BUT it does foool a meter into thinking that. your install is very good NOTHING wrong with that
 
I have gotten all sorts of conflicting information about appropriate drive levels for the DX500v. But most have said the RFX-75 is perfect with 15w DK.
I was told since it is a straight 4 pill, it does require a drive, a stock 4w radio would barely get 100-150w pep out of it, which sort of defeats the purpose...

BUT I have to agree, that something is a miss. Just not sure where to start trouble shooting, but all arrows put at the amp.

I will check my SWR at different amp levels and get back with the results.
However, I was already advised that the SWR will be affected by the variable and that was actually one of the downfalls of the TS variable style amps.
 
Right on the Texas star Web site the spec sheet calls for 20 watts of drive. Your over driving the amp and saturating the pills probably throwing everything off. The next thing you will get is 10 ohm smoke.

Sent from my SCH-I545 using Tapatalk
 
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Just to be clear, I am not arguing with any of you about over driving. I am just trying to learn.
What does not make sense to me is why would using the variable function change anything. I am still putting the same wattage into the amp?
Unless using the variable actually changes the amount of drive the amp see's. If that is the case, then I should be able to safely use it that way...But I am not sure this is how it actually works.
 
Thats right the variable changes the input into the amp.Rather than wasting amps and heating up a resister network run the amp wide open and turn down the drive on the cobra.
 
Well I will report back that I received a lot of misinformation about what a TS DX500v takes to drive.

after reading what everyone here was saying. I went out and put a brand new out of the box cobra 29 classic in, and it will DK just over a 100 and pep at about 470 - 480.
However the SWR still goes up to about 3.2 or so with the amp on.
SWR is <1.5 with amp off.
SWR is being measured between the amp and antenna.

The swr on the radio is <1.5 with amp off and goes to about 1.8 with amp on.
 
Higher swr with the amp on is a common thing. The output tuning might be off or something.

Sent from my SCH-I545 using Tapatalk
 

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