2970N2-High SWR

[LDG]

I recently purchased a new RCI-2970N2 and I cannot get the SWR down, 3.5:1, to an acceptable level. The radio was bought from Bells CB Radio. The technician at Bells has recommended a Low Pass Filter. My set-up is as follows: a new A-99 antenna 8' above my house, 27' of Belden RG8X cable, a new RCI-2970N2, 30 amp power supply. When a Galaxy 979 is connected the SWR is fine,1.3:1. Is a Low Pass Filter going to help? I have used two external meters and I get the same results. Again, the Galaxy works fine with the set-up. Help would be appreciated.
Thank You.
LDG

 

[davegrantsr]

The radio was bought from Bells CB Radio. The technician at Bells has recommended a Low Pass Filter.

wow. that statement is the same thing as saying 'NEVER EVER BUY ANYTHING FROM US AT BELLS!!! 'CAUSE WE DON'T KNOW WHAT THE HELL WE'RE TALKING ABOUT'.
unless of course he gave you sound radio theory explaining his statement.

now to be helpful....while there could be something wrong with the radio, are you sure the external meters you tried are good? did you readjust the calibration after going 5 watts dead key up to 60? how about the jumpers?

 

[jon666]

wow

the low pass filter has nothing to do with your swr problem
all it does it stop the radio from bleeding over on neighbors.
i would say its the radio if your galaxy works fine. swr will change a little bit because the rci put out much more power. but not that much.

 

[IMD262]

I recently purchased a new RCI-2970N2 and I cannot get the SWR down, 3.5:1, to an acceptable level. The radio was bought from Bells CB Radio. The technician at Bells has recommended a Low Pass Filter. My set-up is as follows: a new A-99 antenna 8' above my house, 27' of Belden RG8X cable, a new RCI-2970N2, 30 amp power supply. When a Galaxy 979 is connected the SWR is fine,1.3:1. Is a Low Pass Filter going to help? I have used two external meters and I get the same results. Again, the Galaxy works fine with the set-up. Help would be appreciated.
Thank You.
LDG

That belongs in this thread:

http://www.worldwidedx.com/general-cb-services-discussion/139096-stupid-things-seen-heard-cb-shop.html

 

[123kid]

my radio

my radio is a bells radio and its been acting funky.
2950dx-3 issue with meter 2950dx - YouTube

 

[Beetle]

The fact that you tried a different radio with good results seems to absolve the antenna and feedline of any defect. With that said, the radio doesn't have anything to do with the SWR, IF its output is clean and on ONE frequency. SWR is directly related to the impedance match between the feedline and the antenna, at ONE frequency.

An LP filter might improve things; the point is, if that "RCI" is a decent radio, it shouldn't need it.

 

[DXman]

Well let see if I understand this right.

A LP is designed to help remove harmonics right?

Is it not right that harmonics can trick a meter in thinking that it may have a high SWR or putting out more power than it actually is?

I have two radio's here right now (both same power output of 125 watts), that when not using the LP my SWR is high and of course the reflect is too, but, by putting the LP on the radio the SWR is down to 1:1 and of course almost zero reflect.

None of the other 3 radio's show this problem and they are all the same model - 2970dx

Also - 259b shows the feedline to be just fine.

Probably need to send the radio to DTB Radio, here on the forum and let him do his tune on it.

 

[Beetle]

Well let see if I understand this right.

A LP is designed to help remove harmonics right?

Yes, BUT the radio should have a low-pass filtering circuit built in. Maybe it does (or did) until some chucklehead produced his Golden Screwdriver to make the radio "talk" "better" (read: to see the meters go higher).

Is it not right that harmonics can trick a meter in thinking that it may have a high SWR or putting out more power than it actually is?

Not quite right. If the radio is spewing "harmonics", IMD and other garbage, the meter can and will show it. It's not being "fooled" at all.

I have two radio's here right now (both same power output of 125 watts), that when not using the LP my SWR is high and of course the reflect is too, but, by putting the LP on the radio the SWR is down to 1:1 and of course almost zero reflect.

Then I would offer that those two radios have serious internal problems which you could see with a spectrum analyzer. You probably could detect the off-frequency junk with a communications receiver, but the Spec-An would allow you to quantify it.

Just as a note, you don't need to specify that your "reflect" is high. An upscale SWR reading for a typical SWR meter is a result of reflected power at the feedline/antenna connection. If you have a higher-than-normal SWR, that implies you also have higher-than-normal reflected power.

None of the other 3 radio's show this problem and they are all the same model - 2970dx

Also - 259b shows the feedline to be just fine.

Probably need to send the radio to DTB Radio, here on the forum and let him do his tune on it.

Maybe you could ask him to provide you with before and after pictures of the signal with his spectrum analyzer.

 

[hookedon6]

... the radio doesn't have anything to do with the SWR,....

actually,.... a poor solder connection at the output connector can do this

 

[DXman]

Is it not right that harmonics can trick a meter in thinking that it may have a high SWR or putting out more power than it actually is?

"Not quite right. If the radio is spewing "harmonics", IMD and other garbage, the meter can and will show it. It's not being "fooled" at all". Ok - I guess "trick" was wrong word.

"Then I would offer that those two radios have serious internal problems which you could see with a spectrum analyzer. You probably could detect the off-frequency junk with a communications receiver, but the Spec-An would allow you to quantify it".
Exactly.

 

[Robb]

For this radio to have a bad SWR, it would have to have more off-frequency harmonics during TX present that it does on that user freq as specified.

IOW, he has the AM modulation limiter clipped out and the 54mhz trap removed as well. Radio MUST sound like crap this way; no doubt about it. Or it has another problem that will need a real tech to repair and set the radio straight once again.

 

[Beetle]

actually,.... a poor solder connection at the output connector can do this

Sure it can, but that has nothing to do with the SWR which, by definition, is determined AT the antenna feedpoint, not at the radio.

 

[LDG]

Update-2970N2

Thank you for the replies. The low pass filter did lower the SWR sharply, but not enough. The radio is in the mail to Ranger for an evaluation.
LDG

 

[The Mad Scientist]

i can see that no one has mentioned this, so perhaps this may help you.

i have been seeing more and more of these rci radio's with these type of swr issues. and 95% of the time the TX chain is not aligned propperly. i have found that this swr issue is being generated by the filter network prior to the first mixer being out of alignment, which would be L34, and L35 in these radios. this
filter network being out of alignment will cause a harmonic issue, that the built in amplifier will make worse.

even after the complete TX chain alignment you may have to go back and readjust L34,L35 for the best swr readings at the center of the band that you plan on using. it would be my advice to either do, or have a complete alignment done on a newly aquired rci radio to help ward off these problems.

hope this helps.

 

[9C1Driver]

i can see that no one has mentioned this, so perhaps this may help you.

i have been seeing more and more of these rci radio's with these type of swr issues. and 95% of the time the TX chain is not aligned propperly. i have found that this swr issue is being generated by the filter network prior to the first mixer being out of alignment, which would be L34, and L35 in these radios. this
filter network being out of alignment will cause a harmonic issue, that the built in amplifier will make worse.

even after the complete TX chain alignment you may have to go back and readjust L34,L35 for the best swr readings at the center of the band that you plan on using. it would be my advice to either do, or have a complete alignment done on a newly aquired rci radio to help ward off these problems.

hope this helps.

Another example of why I have always said a new Export radio needs a proper tune and alignment by a tech that knows what the heck he is doing.