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Magnum 257 HP - Sideband TX problem.

Discussion in 'CB and Export Equipment and Accessories' started by stall84, Mar 5, 2013.

  1. stall84

    stall84
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    Hey Guys,

    Happy to be a new member to this forum, and have a quick question to throw out there.

    Got a Magnum 257 HP (80W) a few weeks back and have it nicely installed in my Explorer wired directly to the + - of my 12V car batt.

    AM is AMAZING! on this unit, I've been making contacts all up & down the east coast from the CA/NV border here in Lake Tahoe... But both sideband modes have not worked for me at all.

    Here's what happens in either USB or LSB when transmitting: when keying the mike on medium variable power the tx bar meter briefly spikes a few bars & then will drop off to no bars or just 1 (whereas on AM all bars are illuminated and stay so through tx). When I speak into the mic it may bump up to 1 or 2 bars on the TX meter. When I increase the variable power to full or near full I will get 3-4 bars on TX dropping to 0 when not talking. I also basically have to yell into the mic to get the 3-4 bar 'swing' on the TX meter when it's at max variable power.



    As of yet I've made no contact at all on Sideband...

    Anyone ever experienced this problem or have an idea what it may be?

    Thanks, love to hear your opinions!
     

  2. Johnno

    Johnno
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    Hi

    SSB has no carrier, so it is normal for there to be no bars showing when in this mode, you have to talk to produce the signal. It should not even show one bar when you are not talking, unless you have noise in the background, if not then you have another problem, perhaps the radio needs attention.
    I have one of these and it needed some work before the guy sold it to me, maybe you have one from the same batch which were released on to the market, yet were faulty. Do a forum search, I am sure it has been covered here.
     
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  3. stall84

    stall84
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    John thanks for the reply!

    I actually realized that one night about sideband being a suppressed or no carrier mode & thus there would be no "dead key" TX on the meter since no carrier... But it's still really strange how on full power and the mic right up to my mouth with full mic gain I still only get 4 out of 8 bars 'swing' ...

    I sent an email to GI Joe's who did the "tuning" package on it what they thought was the problem.. so hopefully this will get sorted out soon enough

    Thanks again!
     
  4. Robb

    Robb
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    Yep, I agree with Johnno.
    There is NO CARRIER in SSB mode - like there is in AM or FM mode!

    Here's what you may want to do:
    Hook up an external power meter between the radio and antenna, key the mic in either SSB mode, talk into the mic and watch the meter move. If there isn't any movement, make sure you have the Mic Gain knob up about 2/3 to 3/4.

    If no movement; then you might call up Sam Lewis of RF Limited, he will give you a RA#, and send it off to warranty repair. Magnum does take pretty fair care of their customers.
     
  5. stall84

    stall84
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    I actually JUST finally made a very tenuous/sketchy contact with West Virginia on the USB on 27.305MHz & then again on .300 .. But there was so much traffic it was nearly impossible to actually get tuned in and talking.

    The "fix" seems to be literally running the SSB modes with the variable power knob starched hard clockwise to the 5oclock position which is at maximum power... I'm hoping since the carrier is removed that running at that power setting doesn't burn my finals out... By the way it's putting out about 75w Power running through a palomar 250HD ... AM through the amp yields 200+ Watts.. so I'm guessing that this drop to 75W out on SSB is due to the math of subtracting the power the carrier emits.

    Anyone know if this makes sense?
     
  6. Robb

    Robb
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    Ummm . . . Let me get this straight . . . You are running a Magnum 257 HP with a 200 watt linear . . . Am I the only one that can see a problem here?
     
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  7. RADIOOMAN

    RADIOOMAN
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    What problem?!........lol
    If that is truly the case then I will be surprised if something ain't already toasted.
     
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  8. stall84

    stall84
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    well I've tested the variable power to get a 10w dead key & right at 50W swing which is the rated inputs for the High Drive 250fet amp.. seems to be holding up fine through two week at least ... get quite a few crystal clear "sittin right next to me" sound/signal reports from the people I've hit DX so far (20+)
     
  9. Robb

    Robb
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    Pop the cover on the amp. If it has two SD1446 transistors ('pills') in it; then it is a low drive amp. That means a TOTAL of 10 watts/PEP. If it has two ERF-7530 transistors in it; then it doesn't need more than 40 watts PEP.

    But let's go back to the radio. You have a power meter, because you said you are seeing 200 watts. Test the radio as I described a few posts back with that meter. What kind of meter is it BTW? That is pretty important too. Kinda curious now . . .
     
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  10. stall84

    stall84
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    it's a crappy RadioShack power/SWR $70 model meter. Everything's running through rg8x coax, antenna is 4' Wilson Silverload vertical well grounded by mount and ground strap tap-drilled into the steel frame of the explorer. I've got both the amp ('palomar 250fet High Drive) (its still listed at Palomar FET 250 HD Export Ham Radio Mosfet Linear Amplifier )

    Anyway both amp and radio are connected by 10ga wire to the battery terminals in the truck, it's a 2 month new battery..

    I dunno I think I beginners lucked out... except for the sideband probl which probably could be due to the amp... might have to bypass the amp on SSB even though its supposed to be 'ssb-switching'
     
  11. stall84

    stall84
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    the QSL 2 days ago with Indiana from my perch on the passes of the Sierra Nevada (which likely has a lot to do with it, although local stations report great audio as well) said that I was metering 9 "pounds" which I assumed meant dB's mid day on the D band 26.805 I think. And the RadioShack meter is showing 150-200W when my trucks ignition is on and the battery is producing 14V .. about 100-150 with truck ignition off.
     
  12. RADIOOMAN

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    Are you saying that you have a PEP meter or are you saying that you are seeing 50 W swing with a average responding meter.
    If you do it properly you can make an average responding meter read very close to what a PEP meter will read when on SSB. (this will not work for AM)
    ROBB advised you to check the power output of the radio with the wattmeter between the radio and the antenna.
    And I agree with ROBB that this will be most useful information to try and determine what the nature of the problem is with SSB.
    If you do this test then do it at a frequency where the SWR is the lowest on the antenna.
    Your wattmeter will be more accurate when the standing wave is the lowest.
    If you whistle a good low tone whistle into the microphone and don't over drive the audio your SSB will generate a carrier with no apparent modulation. (as viewed on the oscilloscope)
    This will allow the average responding wattmeter to indicate very closely to what a PEP meter will indicate.
    A PEP wattmeter will read slightly higher due to the effect of unburdoning the power supply and its voltage will be higher momentarily which will produce slightly more output power.
    While whistle turn the mic gain up till the wattmeter starts to drop, it will be at this point (just before the meter drops) that will be real close to what a PEP wattmeter will indicate.
    And is completely valid information for the purpose of trying to determine about what the PEP output of the radio is when on SSB.
     
    #12 RADIOOMAN, Mar 6, 2013
    Last edited: Mar 6, 2013
  13. stall84

    stall84
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    lol I thought that as soon as I reread my post. Sorry

    All on AM.
    150-200W AM
    At least 20 dx 'qsl's' West Virgina mostly, Indiana, Ohio, Georgia, Florida, SC & NC. All from ridge above Lake Tahoe CA/NV

    Had one WV dx I got to move over to USB today after hailing & connecting with him on AM .. that's where I got the 'sketchy' USB operation with my variable power maxed into the amp. I could hear him responding to my statements like "wow we're even getting flooded out on USB" and he responded by me saying "roger PM84 were trying to tune you in here a little better" which I'm guessing meant clarifying.
    On SSB my meter shows around 50 -80W swing even through the amp. However the calibration won't work on the meter I've got in SSB .. when I deadkey to calibrate the meter it won't move the needle (prbly cuz no carrier).. But if
    I calibrate it for AM, then switch to SSB with meter still in PWR setting it shows 50-80W swing when talking.
     
  14. Robb

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    If that 257 is OK and you have it on SSB into that amp, it will put ~70 watts into it.
    I see that as a problem . . .
     
  15. stall84

    stall84
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    good call. I think I'll run the amp only in AM mode & turn the sucker off in SSB to preserve its life. It does do a great job on AM though.

    Thanks for the feedback
     

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