[TenTec] Orion 1 SWR Indication When Driving an Amplifier

[Duane A Calvin]

Driving my Alpha 99, I see 1.0:1 SWR on all bands and with both 1.x and
2.x firmware, so far.  FWIW.

        73,  Duane


On Sun, 5 Mar 2006 22:59:48 -0500 "ROBERT CARROLL" <w2wg at comcast.net>
writes:
> There have been a number of discussions about the accuracy of the 
> Orion 1
> SWR meter.  My feeling has been that it is not a precision 
> instrument, but
> recently I have been puzzled about a situation in which I am seeing
> something other beyond  an approximate but fairly close reading.  I 
> use an
> Alpha 86 and an Alpha 89 amp at various times.  I do not usually 
> look at the
> Orion SWR meter to see how the Alpha looks to it, but on occasion I 
> have
> done so and concluded the readings were between 1:1 and 2:1.  
> However I have
> noticed a few times when the indicated SWR when driving the Alpha 
> was 2.2:1,
> 2.4:1 or as high as 3:1.  The 86 was in the hospital recently for a 
> blower
> change and I mentioned that the input SWR seemed a little higher 
> than I
> expected.  The report back was that the SWR was usually very close 
> to 1:1
> and never above 1.5:1. When I had seen the higher readings there was 
> no sign
> of the Orion having a problem driving either amp, folding back the 
> power,
> etc, which I felt was odd.  I don't like to see a transceiver 
> stressed with
> SWR more than about 2:1 as my feeling is that is asking for trouble. 
>  A
> number of times when I had seen a high indicated SWR I had switched 
> in the
> internal tuner and found it quickly tuned-not the case when faced 
> with a
> really strange load.  Again I felt this was a little odd.
> 
>  
> 
> Knowing that the SWR seen by the exciter can be affected to a 
> certain extent
> by how the amp is tuned and loaded, and that sometimes there could 
> be an
> issue with the length of the cable between the rig and amp (several 
> folks
> have told me that ETO used to suggest a magic length somewhere 
> around 5
> feet), I began to play around a little when the amp came back.  I 
> had about
> a two foot cable between the amp and the rig, and I decided for the 
> heck of
> it to connect the drive cable to a Coaxial Dynamics power meter with 
> a 100W
> 30MHz slug in it and to use a 3' cable on the other side to connect 
> to the
> amp.  I found that though the forward power indicated by the meter 
> is what I
> would expect for the amp power out, there is hardly a discernable  
> wiggle of
> the needle when measuring reverse power.  When the Orion tells me it 
> sees
> 1.0:1 there is no deflection, and when it tells me it sees 2.4: 1 
> there is
> still no sign of reflected power.  If I keep the amp in the standby 
> position
> so that I am looking at good but not perfect antennas I do see the 
> expected
> reflected power on the Coaxial Dynamics.  With the amp in standby 
> mode, I
> also see an approximately correct SWR on the limited accuracy Orion 
> meter
> when looking at the imperfect antenna. 
> 
>  
> 
> I have seen a number of posts regarding the Orion seeing higher 
> than
> expected SWR when driving an amp and questions about use of the 
> internal
> tuner in such cases.  But I am wondering now if these cases might be 
> like
> mine, with the meter apparently more insane than usual when the 
> Orion is
> driving an amp.  I can't come up with a good explanation of why the 
> Orion
> meter would show much worse accuracy when driving an amp.  I have 
> wondered
> if somehow RF could be getting into the Orion and affecting the 
> reading, but
> I really haven't come up with a decent explanation.  By the way, my 
> antennas
> are distant and I use common mode chokes on all of them; I also have 
> ferrite
> on the rig to amp drive cable, given the Orion's tendency to do 
> strange
> things when exposed to noise, RF, etc-at least with earlier firmware 
> (I have
> stayed with 1.372).  Does anyone on the reflector have insight into 
> what
> could be causing this?
> 
>  
> 
> Bob W2WG
> 
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> 


--------------------------------------
Duane Calvin, AC5AA
Austin, Texas

http://home.austin.rr.com/ac5aa