[TenTec] Orion 1 SWR Indication When Driving an Amplifier

[Lin Davis]

Hi Bob,

I noticed that sometimes I would see something other than 1.0:1 even after 
adjusting my external antenna tuner for a perfect match (according to the tuner 
built-in SWR meter) I just ignored it, but I think this must be the same thing 
you are seeing. I suppose one possible source could be that there is are 
reflections occurring on the internal cable and/or PCB trace because the 
connectors used introduce slight mismatches. I had the cover off my O2 once, but 
I don't remember what kind of cable or connectors were used internally.

73,
Lin
WB1AIW

ROBERT CARROLL wrote:

> 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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