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
> > > >
> > > >
> > > >_________________________________________________________
> > > >DO YOU YAHOO!?
> > > >Get your free @yahoo.com address at http://mail.yahoo.com
> > > >
> > > >
> > > >--
> > > >FAQ on WWW: http://www.contesting.com/ampfaq.html
> > > >Submissions: amps@contesting.com
> > > >Administrative requests: amps-REQUEST@contesting.com
> > > >Problems: owner-amps@contesting.com
> > > >Search:
http://www.contesting.com/km9p/search.htm
> > > >
> > > >
> > >
> > >
___________________________________________________________________
> > > You don't need to buy Internet access to use free Internet e-mail.
> > > Get completely free e-mail from Juno at
> > http://www.juno.com/getjuno.html
> > > or call Juno at (800) 654-JUNO [654-5866]
> > >
> > > --
> > > FAQ on WWW: http://www.contesting.com/ampfaq.html
> > > Submissions: amps@contesting.com
> > > Administrative requests: amps-REQUEST@contesting.com
> > > Problems: owner-amps@contesting.com
> > > Search:
http://www.contesting.com/km9p/search.htm
> > >
> > >
> >
> > _________________________________________________________
> > DO YOU YAHOO!?
> > Get your free @yahoo.com address at http://mail.yahoo.com
> >
> > --
> > FAQ on WWW: http://www.contesting.com/ampfaq.html
> > Submissions: amps@contesting.com
> > Administrative requests: amps-REQUEST@contesting.com
> > Problems: owner-amps@contesting.com
> > Search: http://www.contesting.com/km9p/search.htm
>
>
>
>
_________________________________________________________
DO YOU YAHOO!?
Get your free @yahoo.com address at http://mail.yahoo.com
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|