SMA Adaptors – Signal Loss or Not


Does adding an SMA adaptor 45o 90o or flexi effect the received or transmitted signal.  Whilst the amount of loss in adaptors is perceived by some to be minimal and nothing to concern, others will avoid them to maintain that perfect signal.


The test

Here I test some adaptors on a simple set up of a 25mW vtx ( FT951 it was outputting a max 14.12dbm, power 27,62mW), a DB attenuator and an ImmersionRC power meter, the idea of the test is to make a reference measurement with the db attenuator, then connect each of the adaptors with a simple deduction of the reading from the reference it should give us an indication of the loss.


Reference Reading no adaptor: 14.12dbm




45 degree adaptor: 13.97dbm   Insertion loss of 0.15db

90 degree adaptor: 13.84 dbm Insertion loss of 0.28db

5cm flex extension: 10.61 dbm Insertion loss of 3.51db

Rigid Extension: 13.71 dbm Insertion loss of 0.41db


From the results here we can see that the loss in the adaptors is 0.15 to 0.28db where as the loss in the rigid extension is marginally more at 0.41db but the flex extension is much more at 3.51db. (This does seem really high, I tested 10 and they all gave similar results so either a bad batch or a really bad extension best not to use the flex extensions)

Note Added 12-Dec-2016:   The flex extension is so bad due to the fact it is RG316 cable which is good to approx. 3Ghz, anything above that frequency and it is extremely lossy.

On the face of it this does not look like a lot of loss in the adaptors or rigid extension however it is subjective to which antenna we are using the adaptor on.

For example you have a CP (clover / skew / spironet) style antenna with a typical 1 db gain then the loss as a percentage of the antenna gain can be as much as 28% for an adaptor and 41% for an extension.


If you have a directional antenna (patch / helical) with a gain of say 10db then the loss as a percentage is 2.8% for the adaptor and 4.1% for the extension.



From this the advice is pretty clear adaptors / extensions are going to be fine on higher gain antennas where the loss is minimal like directional patches or helicals, however avoid using adaptors / extensions on CP Skew, Clover Spironet low gain antennas as the loss is quite substantial and will reduce the signal level. If you do use an adaptor on a CP antenna then it is not the end of the world but with out one you might be able to see a bit more of the world 🙂



*Please note all measurements and discussions here is from my own findings either by testing or research and whilst I am not the expert in the room I hope this is helpful…