[R-390] AN/URM-25s

Thu Mar 1 19:59:15 EST 2012

I worked on the Nike myself as a sys engineer for an European defense contractor. Our systems were Block 3 with solid state receivers, digital angle encoders ( replaced the potentiometers for az-el) and a norden pdp-11 dig ballistic computer (replaced the 2 cabinets of the analog mech computer).  The reliability of the block 3 system was very good.... No need to balance those vacuum tube op-amps!

It was fun...  

Sent from my iPhone

On Mar 2, 2012, at 8:43, rbethman <rbethman at comcast.net> wrote:

> I've worked with the guys performing repairs on radar sets and the like, 
> all the the same time the massive search radar was just above us in 
> Western PA.  It saw out into the Atlantic.
> 
> We certainly didn't have all this isolation that has been described.  
> Yet - we were able to get the MTRs, (Missile Tracking Radars), repaired 
> and tested.  Sorry, but these were antiques in the early '70s.  Some of 
> the circuit boards had discrete components such as 2N110s on one of the 
> little boards.
> 
> One of the MTRs requirements was to lock on the top 12 inches of the 
> Nike Hercules, AND stay locked for the entire launch until intercept.
> 
> So such extreme measures really aren't all that necessary to perform a 
> high degree of adjustment and tweaking of equipment.  That is a simple 
> reality that some folks do not grasp despite their intellectual acumen.
> 
> BTW - We were required to take an entire Missile battery to Ft. Sill, OK 
> annually, and perform actual firings against drone aircraft such as T-33 
> and/or F-89s.  So I know from experience the ability to achieve this level.
> 
> Bob - N0DGN
> 
> On 3/1/2012 6:25 PM, 2002tii wrote:
>> It can be done, but it is a challenge.  I generally find that most
>> hams' measurements of sensitivity at HF are optimistic by 10 dB or
>> more due to signal leakage.  For all of their good qualities, R390As
>> are particularly egregious offenders -- they leak RF like a sieve, so
>> ANY leakage from your sig gen will make them appear to have very high
>> sensitivity.
>> 
>> Note that there are two issues -- signal from the generator leaking
>> out of the cabinet and into the DUT, and external QRM and QRN leaking
>> into the DUT (possibly including RF that leaks into the sig gen and
>> then appears at its output jack, or is induced into the cable
>> connecting the sig gen to the DUT).
>> 
>> It helps greatly to use a well-shielded external coaxial attenuator
>> (e.g., HP355A + 355B, or JFW adjustable attenuators, or Mini-Circuits
>> in-line attenuators), placed right at the input of the DUT, rather
>> than using the internal attenuator in the sig gen.  (By "right at," I
>> mean connected using just a coax adapter, no cable at all -- prop the
>> attenuator up on a stack of books or something so it isn't just
>> hanging there.)  That way, the level in the connecting cable is much
>> higher and any QRM/QRN introduced before the input jack of the DUT is
>> attenuated by many dB.  Ideally, you would move all of the
>> attenuation to the DUT end of the cable and run the sig gen at 0 dBm
>> or more.  If nothing else, get three or four Mini-Circuits HAT-30
>> fixed attenuators (http://www.mini-circuits.com/pdfs/HAT-30+.pdf)
>> ($10 each) and put them right at the input of the DUT to do 30, 60,
>> 90, or 120 dB of your attenuation there, and do the rest (always less
>> than 30 dB) at the sig gen.
>> 
>> Preventing leakage into the DUT other than through the antenna jack
>> can be harder (and, of course, to the extent that you reduce it, your
>> results will not represent how an off-the-shelf unit works).  A GOOD
>> power line filter is mandatory, on both the DUT and the sig gen.  Use
>> copper mesh gaskets at all cabinet joints (or these days, conductive
>> polymer shield gaskets).  One of the greatest sources of this ingress
>> (or egress, in the case of signal generators) is the chassis openings
>> for controls.  One thing that helps is to put mesh grounding collars
>> on the shafts of rotary switches, capacitors, and potentiometers to
>> ground the shafts to the cabinet (look inside the front panel of an
>> HP8640B for an example).  These days, you will probably have to make
>> your own -- coarse stainless-steel wool works OK (do NOT use regular
>> steel wool).
>> 
>> If the input jack of the DUT is floating (not galvanically connected
>> to the chassis right there at the jack), make sure the body of the
>> connector is RF-grounded using a 0.01-0.1 uF capacitor (best practice
>> is to use the cap in parallel with a 10-100 ohm resistor).  This
>> applies to any other floating connectors, as well, not just the input
>> jack.  You also may want to wind 10 turns or so of the cable
>> connecting the sig gen to the DUT around a ferrite toroid core (Type
>> 43, say 2.4" OD) to keep any QRM/QRN riding on the shield from
>> getting to the DUT input.  Put this choke immediately before the
>> external attenuator (or the DUT input, if you are not using an
>> external attenuator -- but understand that if you are putting -130
>> dBm and lower signal levels into the sig gen end of the cable, you
>> are unlikely to get good results no matter what else you do).
>> 
>> If you have a chance, taks a Harris 590 apart and observe what they
>> did -- the 590 is the best-RF-sealed receiver I have seen
>> (interestingly, the 590As I have seen are not as good by 15-20 dB at
>> some frequencies).
>> 
>> Best regards,
>> 
>> Don
>> 
>> 
>> Copyright (c) 2012.  Not for redistribution
>> 
>> 
>> 
>> 
>> 
>> 
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> 
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> | Bob Bethman                \\\|///     " The absence of a danger |
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