[AMRadio] dds information


James M. Walker chejmw at acsu.buffalo.edu
Sat Jul 17 22:48:58 EDT 2004


Hello Jim and group,
Ah, I hope your VFO458 is in the case from Central Electronics. Both of
mine are in cases, when I received them I checked them out per the VFO
portion of the manual, I have to mention that I used the TEK 2712 
spectrum analyzer to set them up with frequency wise. Also there is a 
technique to getting the multiplication right. Mine operate 160 - 10 and
are right on with no drift. The resistor is mounted on the rear and is
outside of the cabinet that CE uses to hold it after modification. If
you have an older VFO458 that didn't get put together correctly it will
have drift and also heating problems. Also the 4 K resistor was changed
from 5 watts to ten watts, and the cables for interconnect, have a
length
requirement, can't extend them or shorten them without problems.

As for the PTS you listed in the message, the guy is on drugs or
something
and I did NOT have a typo I paid 50.00 from Government liquidations
auction
and all I have to do to the unit was clean about 5 years of dust off the
outside top of the unit. Mine is a rack mount version, there is a
picture
of it on my web site. It cost me 25.00 to have it shipped to me from the
Depot at Mechanicsburg, PA. On E-bay I have seen them go for as much as 
75.00 but NOT more than that, and as I stated PTS still sells them at
the high prices if you link to the price list, it will gag you to see
what they sell for. I have three and two were given to me because they
were
no longer needed and the guys didn't want to throw them in the trash.
All of the three have GPIB the 250 MHZ model had no switches on the
front
and I use it as my "Lab" frequency source, stable is the word. They also
make a desktop version comes in a snazzy "Bud" cabinet and all.

We use them at the university to calibrate the MRI equipment for
research.

I use my 10B on SSB and the guys I talk to are amazed when I tell them
what I am using. I drive a single 813 in AB1 with the 10B and VFO doing
the mode/frequency control. They say I am pulling their leg. The carrier
is reduced by at least 65 DB as per the TEK 2712 and then I pop the
drive
into the 813 set it for the proper operation and power output and I am
told it sounds like maybe a TS820 or better.

As for E-bay, I just checked the completed items list, might want to
give
a look, anyone trying to get high dollars ends up keeping the unit. They
are
good equipment, and stable with facilities for external reference input,
but I see them in places other than E-bay and they are usually quite low
in price, and reasonable shipping costs, I think 25.00 is reasonable!
Heck I watched four TEK2712s go on Gov Liq for 200.00 for the lot. FWIW
Jim
WB2FCN
http://eshop1.chem.buffalo.edu Netscape 7.0+ or Exploder 5.0+




Jim candela wrote:
> 
> Jim,
> 
>         You got me excited and then I realized that the $50 price you mentioned may
> have been a typo. If not where are these to be had for 50 bucks? There is a
> PTS 040 on Ebay now "buy it now" for nearly 4 grand.... These would fit
> nicely next to a boat anchor..
> 
>         I have two BC458's modified as per CE bulletins. It is true that I never
> went through the long procedure to align them, and to temperature compensate
> them. They have one major drawback, and that is the series dropping resistor
> in the back heats things up pretty well, and the dang thing drifts as a
> consequence in two stages. The parts near the 1626 heat up first, and later
> the parts within the oscillator shielded enclosure start heating up.
> 
>         I once got on 7215 where there were some that would say they were running
> hi-fi SSB (is that an oxy-moron?). Initially they were impressed with my
> phasing QRO'd 20A setup. I was between the two stage drift, and remember on
> 40m, the BC-458 output is tripled. Then I drifted up 200 hz during an old
> buzzard 60 second transmission as phase two of the drift started. I switched
> to receive, and there were 20 people screaming at me for "drifting out of
> the band"!
> 
>         I hope to have better luck with the DDS.... See link below for a PTS 040
> for sale:
> 
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4683&item=2585135703&
> rd=1&ssPageName=WD1V
> 
> Regards,
> Jim
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net]On Behalf Of James M. Walker
> Sent: Friday, July 16, 2004 10:52 PM
> To: Discussion of AM Radio
> Subject: Re: [AMRadio] dds information
> 
> Well Gang,
> I have several PTS signal sources here, and they provide coverage over a
> wide range of frequencies at adjustable output levels. I use one as  a
> signal source for my RCA BTA-1M, that would be the PTS 040 model. As a
> shop signal source I use the PTS 250 with the GPIB interface for
> computer
> control. They are stable and highly accurate over their frequency
> ranges,
> and no drifting. I know you will say, what a lab instrument, is going to
> be expensive, but none of mine cost more than 50.00, they are still easy
> to purchase from the Mfr, at their full price, but more and more they
> are
> showing up at bargain prices. Well worth the effort to look around for
> them.
> 
> On the case for the BC-458 VFO used with the Central Electronics 10A-10B
> and 20A series, I have two of the modified vfos per the CE manual, they
> both work great and do not drift in NORMAL operation. The CE manual
> gives
> good directions for using them, and applied per the manual they BC-458
> as
> a "mixing" signal source is extremely stable signal source.
> 
> FWIW
> 
> Info on PTS can be found here http://www.programmedtest.com/
> including spec and ratings and current pricing info.
> Jim
> WB2FCN
> http://eshop1.chem.buffalo.edu
> 
> "KC8OPP Roger S." wrote:
> >
> > Neal,
> >
> > I use a Raytheon RA-250 on 160 and for the VFO I
> > bought a master oscillator for an ARC-38 from the Fair
> > Radio Store.  I think that it was around $35.  Inside
> > this beast is a Collins PTO that tunes 1.75-3Mhz, I
> > may be off a bit on the freq range.
> >
> > I built a regulated power supply and added a cathode
> > follower circuit for the PTO and use it to feed the
> > grid of the oscillator in the RA-250.  Works great,
> > very stable and easy to use.
> >
> > Looked at your web site and saw the RCA, looks great.
> > I am in the process of re-working a RCA BTA-1R for
> > multi band operation.  You can have a look at it here,
> >
> > http://photos.yahoo.com/kc8opp
> >
> > I will be using a Kenwood 520 for an exciter for the
> > RCA.  I have been using this same radio with a HB rig
> > for the last year and seems to work good.
> >
> > Good luck with your projects.
> >
> > 73's
> > Roger
> > KC8OPP
> >
> > --- Neal Newman <groucho at skyweb.net> wrote:
> > >  Jim Do you have a website up?
> > > I run a few broadcast transmitters on 160 Meters
> > > AM.... looking for a
> > > crystal replacement to change Frequencys On 160
> > > meters..  any plans on a
> > > VFO for these type Rigs?
> > > Neal Newman-KA2CAF
> > > Big Iron  collector
> > > http://www.angelfire.com/nj4/wttm/rca.html
> >
> >
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