Api Rp 90-2 Pdf

[Darth Gupta]

Agreethat Antenna looks like the 63 antenna or the early Navy contract PRC-90s. The regular 90 had its own style anternna with a fat base too and then 90-2 had another improved antenna as well plus a small hook at the base of the radio to hold the antenna in a stowed pos. vs needing a rubber band like the 90 needed. That is certainly the latest contract 90-2 I have ever seen and its a USAF contract.

This is my PRC-90-2 radio. Can see the antenna base on the 90-2 has a blue colored packing/washer and how it clips to the lower side with a hook to stow it. Not sure if what yours has is a earlier antenna someone just threw on or if its the correct antenna just broken and missing the pull out portion with the ball. I have a box of some late made batteries for these that Ive used to test if these radios power up. The later batteries were a grey color body vs the older OD green ones. Also have some Navy contract CR-123 battery adapters for these, only problem with those is it requires you to remove the battery cap at the bottom from that strap and then screw it on the long adapter that threads in.

There are also test sets for the PRC-90s called a PRM-32 that comes with cables and antenna adapters to connect 2 radios to the test set to test the Transmit and Receive functions. That set come with a small spanner wrench to help remove the antenna with that packing/washer.

The darker ones are usually repaints from what Ive seen some various overhauls. Some Army ones were fully overhauled at Depots and the tags were replaced showing that, they are usually marked Tobyhanna Army Depot in PA.

Ive never really dug deep into them but Ive heard they were designed for Govt Agencies down in Central and South America, stuff like CIA and Dept of State Air Wing etc but again not sure on those details. Maybe Bob can chime in on them. I thought this 1 was cool because it actually had a matching antenna marked PRC-106 which I never saw on others, and the serial number is 0001.

The -106 transmits on both civilian and military distress frequencies of 121.5 and 243. 282.8 is not used on this radio like the -90. The wide frequency spread is the reason for the specific antenna for the radio. A -90 antenna would not work well on 121.5.

We can probably trace it to the BC-611 Handie-Talkie but it was a bit too bulky for personal use among other deficiencies for ASR work. The first two-way transmitter was that of the AN/CRC-7, designed as an emergency transmitter radio and homing beacon. Exempted from this would be the SCR-578 (Gibson Girl), AN/CPT-2 (Walter) and AN/CPN-16 which were transmitter and radar beacons only. All were of WWII origins and immediate post war implementation. The CRC-7 was not fielded until 1946. The next in this evolution would be that of the AN/PRC-17, similar principles as the CRC-7 for two-way communication and as a homing VHF frequency.

In 1946 we see a step towards the radios we seen posted here designated as the AN/CRN-16. However, it did not have the valuable feature for two-way comms and was strictly used for homing. Its advantages were its small size and weight, carried as personal equipment.

Correct me if I am wrong, but what we are going to see next was a consolidation of the CRC-7, PRC-17 and compact CRN-16 in the form of the URC-4 with two-way comms and homing, compact and light weight.

I haven't done too much digging into the earlier stuff pre Vietnam, but I do believe that the URC-4 was slightly before the PRC-17. The earlier URC-4 were yellow, and I have seen OD green ones as well. I have seen some units with 121.5 VHF and 243.0 UHF. They had separate batteries and a battery cable to connect to the radio, with the USAF has radio carrying vests for these in the 50s. Them the URC-11 came around which seems like a more compact version of the 4 followed by the URC-10 which later developed into the ACR RT-10 which no longer had a separate battery with a cable. USAF then had their URC-64 compact radio, the Navy had the PRC-63 and then the PRC-90 came around in the late 60s. During that late 60s time frame the Army also introduced the URC-68. There was some other misc radios I'm sure the Navy had in those earlier years but once the PRC-90 came out that was around for a while in a few variations til the PRC-112 came around. Again even in later times there was a handful of other radios out there in smaller use that I havent listed. Its funny looking at it overtime, we'll say since Vietnam era aircrew survival radios have changed technology wise tremendously, but the size and weight of them really hasn't changed. The PRC-112 series and the current PRQ-7 CSEL are pretty large.

Yes, the URC-4 was the 1st of its line. It was also a dual band radio transmitting on both 121.5 and 243. It came out in the late 1940's to early 1950's. The original radios and batteries were yellow. There were two different lengths of cables that connected the radio and battery depending on the use. When not in a radio carrier vest, there was a slot and tab on the radio and battery so they could be put together.

Don't forget the PRC-49. A contemporary of the URC-4. The US Navy fielded an A,B,C and D variant, and was replaced by the PRC-63 circa 1966 or so. The small, cylindrical pocket on the SV-2 vest was for the battery.

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I had the 100mm 2.8 APO on the Leica R for years and it was my favorite lens. It is exceptionally good. It will be better in the closer ranges, for the obvious reason that it is a macro lens. I have the 90mm APO Summicron in M mount and it performs extremely well on the SL2, though it does not hold up quite as well close up and wider open as compared to dedicated macro lenses. It is noticeably better than the 90-280mm, which is probably one of the best telephoto zooms of all time, so I would think the R version (same formula) will still be fantastic. Optically, I think both the 90mm and 100mm are extremely close and extremely good. Both will do brilliantly on the SL2, let alone the SL. The newer 90mm APO SL is even more exceptional (as is the 75mm). To give you an idea, already at f2 it is about 85% contrast at 40lpmm, while the older lenses are around 60%. The new lens is so sharp even at close distance that it is almost certainly sharper than even the 100mm APO at the close range. The biggest difference will likely be additional microcontrast...a bit more snap and a total absence of longitudinal chromatic aberration. The older APO lenses are APO at the point of focus, while the new ones are APO in the out of focus areas as well, which is experienced as showing no shift towards green or magenta in the bokeh. I have found that the 50mm APO Summicron SL is as sharp as my S 120mm APO Macro in close range, so I have taken to using it for artwork reproduction if it is easier to have a 50mm than a 120mm. The new lenses are that good...still, the differences between the 90 and 100mm R lenses will not be that huge on 24mp, which is a testament to how good those designs were themselves.

In terms of focusing, the 100mm has a notably damped focus...pretty tight and a good amount of travel. It has been awhile, so I cannot recall how much to get to 3m, but probably at least a half turn of the ring. It is multiple turns to rack it all the way out to 1:2. The 90mm APO will be a lot less travel from infinity to close focus and should also be easier to turn, as it was designed for further distances, not precise focusing in the macro range.

If it were me I would go with the SL lenses, as they are spectacular, particularly for landscape use. I don't think I have ever heard of anyone saying a single negative thing about the 75mm...that said, if you are truly wedded to MF, the R lens will have a nicer feel. But having auto aperture and autofocus can be great, and using the spot AF point and back button focus is not really much different in terms of precision.

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