2.5ghz reciever, adding ext antenna, N-connector loss?

[gwargantua]

I have an old 2.5ghz wavecom-type reciever I'm modifiying to accept an external antenna instead of using the stock patch antenna. The reciever module connects to the patch antenna with about 5" of very thin coax (about 1.5mm). My initial thought was to use a readily available panel mount N-connector with solder tab and solder it in. But I'm concerned this will cause a big impedence bump and excessive signal loss where the coax attaches and is unshielded. Ideally I'd want a panel mount or bulkhead N-connector that accepts the small diameter cable and has a nice solder in pin/shield arrangement. I've looked for specialty connectors, but none are available for such a small diameter coax. Some made for semi-rigid cable are close, but won't work since they rely on the center conductor to hold the pin in place after the connector is assembled.

Solutions? Or is a plain panel mount-N ok to use in this application? All suggestions welcome and thanks for reading.

 

[fsmyth]

You can get a cone-shaped shield for the N panel
connector that the outer conductor is soldered to.
It takes some finesse with RG/316 and similar small
cables, especially if double-shielded, but works
well. If done properly, the insertion loss will
be no more than any other connector (usually about
0.2 dB) and reflections will be 20 dB or so down.

But - Pasternak lists a bulkhead connector for 213
and 405 that should be usable directly.
<als>

 

[Comcokid]

There are some small diameter coax that are used by Hirose with their U.FL series of connectors/cables, Amphenol AMC series and a small Macom series (that dissappeared when Macom was bought by Tyco). These are around 1.5 mm in diameter.

The most common small diameter coax to N bulkhead connector will be for semirigid coax. With careful soldering of the shield to avoid melting your coax dielectric these can be used. Such kinds are Pasternack PE4655 (0.85" dia) and PE4946 (.047" dia).

Otherwise, you might find a SMA connector that fits better on your coax than a N-size. Then you can use a SMA-to-N bulkhead adapter. Pasternack makes such a bulkhead adapter as a PE9104 and PE9252.

Your use of metric to describe the coax leads me to believe you are in Europe. If so, you may want to find the Huber+Suhner equivalents to these.

 

[zeitghost]

I would suggest SMB or SMC connectors with an adaptor.

The right angle plugs are easier to do in my experience.

rgds
Zeit.

 

[fsmyth]

Yeah, but...
coax-->SMA-->adaptor-->N-female-->N-male-->coax-->N-->N-->ant
= 0.1 + 0.2 + 0.35 + 0.28 + 0.22 + 1?? +0.45
= 1.5 dB just in connectors. Assuming quality connectors.
<als>

 

[zeitghost]

Use a bulkhead smc then.

 

[gwargantua]

Thanks very much for your replies. To address your suggestions:

I've already obtained one of the bulkhead connectors for semi-rigid coax (Amphenol 82-6096-RFX). However, in the connector I obtained, the center pin doesn't lock into the dielectric and apparently relies on the center conductor to hold it in place. The thin (stranded) center conductor of the existing cable would not support the pin and would surely break. Does anyone know for sure if other manufacturers connectors are basically the same, or if they have a center pin that is held rigid by the connector itself?

The coax has no markings, I had to estimate it's diameter, about three .5mm pencil leads, sorry it's all I had on hand.

I've seen some people use a 1/2" copper pipe cap available from any hardware store. They simply drill a hole in the top and solder in on the back of a panel mount N. Seems like it would work well enough as a shield, though probably a challange to solder everything up with out messing up the coax. There would probably still be an impedence change, though I'm not sure how large. Seems like a cone shaped backshell would work better and allow the smallest exposed area at the connection, though it would still be difficult to solder up properly. I also don't have a TDR on hand to check the connection with.

I thought to use SMA, but the antenna and cables I'd like to interface with are all type N and, as was mentioned, adaptors are going to add more attenuation which I'd like to avoid. Still, if it's the best electrical solution of all mentioned I'd go with it.

Thanks again for all your suggestions and please feel free to add any further comments or ideas you may have.