[TenTec] Orion II AT tuner question

Sat Apr 1 11:32:58 EST 2006

I believe it does, I rely on that behavior when when using an antenna
that is resonant on 80 m but sometimes pressed into service on 160.
When operating on Top Band I use the internal tuner, but if I decide
to go to 80 all I need to do is make the band change - the tuner is
bypassed automatically at that point and xmtr is looking into the now
resonant ant system directly.

Bob NW8L

On 4/1/06, Carl Moreschi <n4py at arrl.net> wrote:
> My guess on the tuner is that it goes into bypass mode when you do a band
> change.  I'm going to ask TT.
>
>
> Carl Moreschi N4PY
> 121 Little Bell Drive
> Bell Mountain
> Hays, NC 28635
> ----- Original Message -----
> From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
> To: <tentec at contesting.com>
> Sent: Saturday, April 01, 2006 9:51 AM
> Subject: Re: [TenTec] Orion II AT tuner question
>
>
> > On Fri, 2006-03-31 at 22:56 -0600, Duane A Calvin wrote:
> > > Gerald - isn't that the purpose of attenuators?  I'm not sure what
> > > benefit is to be gained by mismatching RX antenna impedance, although I
> > > agree it's not highly critical they be exactly matched.
> >
> > Some receivers have no attenuator. Those that do have only one. Under
> > some condition that can be too much attenuation and under other
> > conditions not enough. And sometimes the attenuation is more than
> > attenuation. Like in the Corsair II where the attenuator switch actually
> > removes the low noise RF stage hooking the double balanced mixer
> > directly to the antenna (through bandpass filters) so the receiver gain
> > goes down and the NF rises. In some situations, that double whammy isn't
> > workable. In receivers like the S-line detuning the RF and mixers
> > sometimes was most effective, though tossing the ringing mechanical
> > filters was more effective for standing up to spherics.
> >
> > >
> > > I was thinking Merle might have a point - I'm trying to set up the
> > > conditions where I saw the attenuation on a different band when
> > > accidentally working cross-band, but I'm not able to replicate that
> > > result at the moment.  However, on 30m, where my G5RV Jr is definitely
> > > non-resonant, 4.5 - 5:1 SWR, as a result of using the tuner, band noise
> > > goes from S 3.5 to S5 (relative S-meter reading.)  If the tuner is not
> in
> > > the RX antenna path, how would this be explained (single VFO, simplex
> > > operation)?  Selecting a different band on the TX VFO causes the tuner
> to
> > > turn off, but the S-meter still reads S 3.5. I'm on an original Orion
> > > with 2.56 level firmware in case anyone else is also trying this.  If I
> > > had an RF signal generator, I could do better measurements, but I'll
> have
> > > to live with noise level at the moment.
> >
> > Surely the receivers use the transmitter low pass filters as a minimum
> > of RF selectivity. How fast can the filter selection relays change, fast
> > enough for cross band listening between transmissions. A memory tuner
> > might switch as fast, though when trying to receive on two bands at the
> > same time the single tuner might flip its wig or just switch out of the
> > circuit. It is conceivable that each receiver front end could have its
> > own bandpass filters. That could help my FT-857D which hears 5 MHz BC
> > stations around 10.1 MHz when the 5 MHz paths are strong and 10 MHz is
> > about closed. Switching in attenuation (internal or external) or IPO
> > cleans it up at the cost of the really weak signals left on 10 MHz of
> > evenings lately. I find harmonics and beats between stations. And
> > judging by reports, I'm not the only one hearing them.
> > >
> > > 73,  Duane
> > >
> > >
> > > On Fri, 31 Mar 2006 21:55:10 -0600 "Dr. Gerald N. Johnson"
> > > <geraldj at storm.weather.net> writes:
> > > > On Fri, 2006-03-31 at 22:35 -0500, Carl Moreschi wrote:
> > > > > Of course what you said is true, but it is still better to have a
> > > > matched
> > > > > antenna on receive.   There is always the possibility of very low
> > > > atmospheric
> > > > > noise on a given night and the extra signal just might make the
> > > > difference,
> > > > > especially on 10 meters.  Why do people insist on using a 9 to 1
> > > > balun on
> > > > > receive only beverage antennas?
> >
> > I heard an engineer from Collins talking at a CSVHF Conference saying
> > going better than 2 dB NF at 2m was a waste. He was more concerned with
> > signals that were reliable 99.9% and so would never try a path with the
> > chances for random quiet and signal heard only 2% of the time. I wanted
> > to stand up and point out that we hams weren't concerned about the 99.9%
> > reliability paths, those we considered local QRM, while we waited and
> > searched for the 2% reliability paths and didn't want receiver noise to
> > prevent their use so we strove for fractional dB NF at 2m and higher.
> >
> > The signal from a beverage is really small, its an inefficient antenna
> > and the NF of receivers has generally been neglected on beverage bands
> > because its well known that atmospherics are far stronger than the
> > simple receiver NF when the antenna is a resonant dipole. Sometimes to
> > hear on the beverage requires a low noise preamp and good matching.
> >
> > Fact is, "one size fits all" doesn't make the receiver that works best at
> > 10m and at 160 when the extremes of antennas are used, and when the
> receiver
> > is used on 40 meters in Europe with the local in band BC stations.
> >
> >
> > > > >
> > > > > Carl Moreschi N4PY
> > > > > 121 Little Bell Drive
> > > > > Bell Mountain
> > > > > Hays, NC 28635
> > > >
> > > >
> > --
> > 73, Jerry, K0CQ,
> > All content copyright Dr. Gerald N. Johnson, electrical engineer
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec at contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
>
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>