[TenTec] Orion II AT tuner question

[Carl Moreschi]

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
>
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