Igor: Does the AOR 7030 plus spec give a number for MDS? Also, does it give
the signal spacing used for the measurements? Most transceiver manufacturers
use whatever signal spacing gives them a good IP3 number. 50 and 100khz are
not uncommon. ARRL and the ham receiver experimenters I know of usually use
20 khz spacing , a much more severe test. If the AOR 7030 does have a
decent MDS (i.e. -135dbm to -140dbm using CW bandwidth ) and an IP3 of
+30dbm measured using 20khz signal spacing, it is better than I have ever
seen in any amateur transceiver. I have tested a hundred or so of the top
line jobs. My elderly FT1000D has quad fet mixers and I believe that is
state of the art for commercial gear. I am not sure if this discussion is
appropriate for this reflector so better cut it short. 73, Dan, N5AR
igor rosky wrote:
> No not a typical scanner, but the AOR 7030 plus, this receiver has
> created quite a controversy. Its 3rd order intercept point is +30dbm,
> for a $1500 dollar receiver is very good. It certainly blows the pants
> off a Watkins Johnson. Ham radio makers have been very slow to improve
> receiver performance. You can now buy surplus Racal receivers from the
> early eighties with very good intercept points. It is unacceptable to
> pay big bucks for a FT 1000mp or any ham radio and have to turn on the
> attenuator. You should come to Europe dring the CQWW, and watch the
> FT1000 and all ham radios just fall into a heap, i use the AOR its the
> only one that will take the punishment. Most new high perforance
> receivers are now hitting +40dm third order points with front end
> preselectors. The big problems with the Jap designers is they refuse
> to use American high performance RF components. The AOR designer is
> English and knows how to design a good receiver, the japs are just
> good at stuffing 5 lbs of junk into a 1 l lb box.
>
> Anyway all these problems have been well documented in QST/QEX by
> Ulrich Rhode, DJ2LR. We wont go into it here.
>
> > Igor: you say some scanners have +30 dbm IP3. Have you actually
> measured
> > that? If so what was the MDS? You can increase the IP3 of any
> receiver by
> > reducing the RF amp gain or even eliminating it if MDS is not
> important to
> > you. For that matter, you can increase the IP3 of a receiver 20db by
> putting
> > a 20db attenuator ahead of it. Only problem is weak signal
> reception. Dan,
> > N5AR
> >
> > igor rosky wrote:
> >
> > > Yes there appears to be some techniques that develop high thrid
> order
> > > IMD with solid state devices. The modern trend is to use
> "Feedforward
> > > rather than Feedback" Feedback being patented back in the 1930s.
> > >
> > > The patented feed forward method claims that the single advantage of
> > > feedworward over feedback, is that the error(being distortion) is
> > > corrected while it occurs, rather than correcting for an error
> which
> > > has occured and is being transmitted.
> > >
> > > Cited advantages for feedforward methods are broadbandwith with 3rd
> > > order imd figures of -60 being a typical minimum. As Carl has said
> > > beeing mostly being used in the digital cell phone business.
> > >
> > > Anyway we can just dream on about this being available in ham
> > > equipment. It is the same problem with receiver 3rd order intercept
> > > points, we seem to be stuck on 20dbm 3rd order intercept point. Even
> > > the miserable scanner makers in the likes of AOR have receiver
> with a
> > > 3rd order intercept point of +30dbm. At the current rate of receiver
> > > performance increase in ham equipment, most of us will be dead
> before
> > > we see a high performance transceiver with a good receiver and
> > > transmitter. Yes the FT 1000MP is lousy, so is the Kachina, sorry of
> > > the subject.
> > >
> > > Igor
> > >
> > > ---km1h@juno.com wrote:
> > > >
> > > >
> > > >
> > > >
> > > > On Thu, 18 Feb 1999 18:09:05 -0800 (PST) igor rosky
> <irosky@yahoo.com>
> > > > writes:
> > > > >
> > > > >
> > > > >
> > > > >I have would also be interested in this area, my 4cx10000 has
> superb
> > > > >3rd order IMD. The problem is the driver,(all ham radios). My
> idea is
> > > > >to use TS830s with a modified 6146, modified for improved 3rd
> order
> > > > >IMD to drive a 4cx600J(3rd order imd -46 db at 500 watts) then to
> > > > >drive a 4cx10000.
> > > > >
> > > > >My question, has anyone optimized a 6146 for best 3rd order
> IMD, and
> > > > >what is the typical figure. I would use solid state but typical
> > > > >driver
> > > > >transistors have very low 3rd order IMD performance.
> > > >
> > > > There are some interesting developments in SS IMD performance in
> the
> > > > microwave wireless industry.
> > > > Using circuitry to sense the IMD and then phase shifting back to
> the
> > > > input, performance in the area of -50dB is attainable. I do not
> know
> > > the
> > > > details but understand it is somewhat involved.
> > > >
> > > >
> > > > The TS-830 is a nice xcvr Igor, I use a pair of them here on
> VHF/UHF
> > > to
> > > > drive transverters.
> > > > For HF you may want to add a low series R regulator to the screens
> > > of the
> > > > 6146's and the 12BY7A driver. It appears that you will have more
> than
> > > > enough drive for the 4CX600J so consider reducing the Ep and Es
> on the
> > > > 12BY7A primarily for longevity.
> > > > With some fine tuning of the various voltages and currents you can
> > > expect
> > > > around
> > > > -40dB or better IMD under voice condx. The negative feedback
> used is
> > > > based upon the Collins design.
> > > >
> > > >
> > > > 73 Carl KM1H
> > > >
> > > >
> > > >
> > > > >
> > > > >On another note i cannot measure the improved 3rd imd of the
> > > > >4cx10000J, its just as good as the plain 4cx10000. I use a
> HP141t, i
> > > > >might be doing something wrong in the measurment prcocess. I have
> > > > >played with numerous settings of plate/screen and grid volts, but
> > > > >cant
> > > > >seem to get the improvement. The 4cx600J however is superb with
> > > > >bypassed cathode resistor.
> > > > >
> > > > >Igor
> > > > >RW3
> > > > >
> > > > >
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