Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: High swr with Mirage B-310-G  (Read 2338 times)
KG4UPE
Member

Posts: 4




Ignore
« on: November 25, 2003, 10:14:11 AM »

I am having a problem with high swr when using a new Mirage B-310-G amplifier and hope someone can help. Here is some info on the setup, listed in order of how it is connected:

1.) Icom 706 (origional version)

2.) B-310-G

3.) MFJ 2 meter tuner

4.) MFJ 1702C two position switch

5.) Ringo 2 meter vertical

6.) 4 element beam (Horizontal Polarization)

I have disconnected both antennas at the switch and checked the swr using the MFJ 259, the swr is 1.1:1 to 1.2:1 for the section of the band that I am using, but when I connect the antennas back up and power up the amplifer the swr jumps to 1.7:1 or higher (I am checking the swr at the radio at this point). This high swr causes the amplifier protection circuit to trip. At this point I can work with the tuner to bring the swr down so that the amplifier will work but then as soon as I switch on the pre-amp the swr goes up again. I should also note that I can only run my power level at 3 or below on the radio or I cannot get the swr to come down at all.

Without the amplifier everything works fine.

Before the flaming starts, let me apologize for all of the MFJ equipment that I am using, but at the present time it is all that I can afford.

Thanks

KG4UPE

Mike

 
Logged
WB2WIK
Member

Posts: 20636




Ignore
« Reply #1 on: November 25, 2003, 12:14:44 PM »

What if you measure SWR at the coax jumper end that plugs into the B-310-G, so you're looking through that jumper cable, the coax switch and everything else?  

Frankly, 1.7:1 SWR isn't bad and I'm surprised the reflected power circuit in the amp trips at all.  I've had lots of Mirage amps over the years and normally this doesn't happen until the SWR is much worse than that -- it trips for an open or short circuit, or a severe mismatch, but not at 1.7:1 or 2:1.

The preamp in or out of line shouldn't affect this.

Could be a defect in the B-310-G.  You could disconnect the sense line from the internal bridge circuit in the amplifier to prevent it from tripping, that's pretty easy and I've done this many times on many amps...however then you really can lose the small amount of protection it provides, in the event you transmit into no load or a shorted cable.

Of course, you have to be really careful with the B-310-G not to severely overdrive it.  Even 10W drive power to the B-310-G can damage the amp, it's only rated for 3W nominal and about 6W maximum input.

WB2WIK/6
Logged
K7KBN
Member

Posts: 2825




Ignore
« Reply #2 on: November 25, 2003, 04:07:06 PM »

Nothing at all wrong with MFJ equipment.  I have quite a bit of it myself and haven't had any casualties that I haven't had with other stuff.

I'd check the output impedance of the amplifier to see if it really is very close to 50 ohms.  If your VSWR is significantly lower without the amp being in the circuit and turned on, but rises when the amp is on, that's about all it can be outside of coax breakdown.
Logged

73
Pat K7KBN
CWO4 USNR Ret.
WB2WIK
Member

Posts: 20636




Ignore
« Reply #3 on: November 25, 2003, 05:55:05 PM »

With conventional instrumentation (SWR bridge) you can't measure the "output impedance" of an amplifier.  Output impedance must be measured with the amplifier transmitting at full power, by looking back into the output port.

You can check the *input* impedance, however (also while it's transmitting).

Still, this sounds like a bit of a misapplication of equipment and possibly a defect in the trigger point of the SWR "shutdown" circuit in the amplifier.  No reason it should shut itself off with an SWR of 1.7.

WB2WIK/6
Logged
KG4UPE
Member

Posts: 4




Ignore
« Reply #4 on: November 25, 2003, 06:46:48 PM »

Let me start by saying thanks for the replys. I do need to correct the information from my origional post. The swr is actually 2.7:1 and higher when the amplifier is powered on. I was in a hurry this morning when I posted and did not proof my post. I plan on getting into the shack when I get home from work this evening and trying some of your suggestions.

Thanks again!!

73

KG4UPE

Mike
Logged
KG4UPE
Member

Posts: 4




Ignore
« Reply #5 on: December 01, 2003, 03:11:17 PM »

Success!!!

I tracked the problem down to a short in the jumper between the tuner and the switch.

Thanks again for the suggestions.

73

KG4UPE
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!