sy-27-4 sirio beam antenna

[Robb]

The 12 inch jumper I use does show 62pf of capacitance; but it also shows a .52mh inductance. Less than .07db of loss too. While not ideal, it is still very close. Not all antennas allow for direct coupling to the analyzer due to mechanical restrictions; otherwise I would prefer to do it that way. Not all 1/2 wave jumpers are 1/2 wave at different freq - obviously.

So - while not ideal - a very short jumper provides an acceptable margin of error. The shorter; the better.

 

[The DB]

Wrong. Short jumper can act as capacitor. 180 degrees cable is proper way to measure.

The 12 inch jumper I use does show 62pf of capacitance; but it also shows a .52mh inductance. Less than .07db of loss too. While not ideal, it is still very close.

Both of these methods can be used, and both have their flaws. Neither will recreate completely accurate results, although both of them can get you close.

If tuning for only one frequency the 180 degree cable will get you more accurate results when it comes to X (resonance) for said frequency. However, in the real world, getting a 180 degree cable tuned perfectly for the frequency in question isn't really that easy, it will pretty much always be off to some extent. Due to losses in the coax, this method will also throw off the R reading as well. If you are one of those that thinks resonance is always the best to tune for this method is for you. This method is less accurate the further away from the feed line's tuned frequency, and those inaccuracies add up faster than you might think (at an exponential rate).

On the other hand, if you are tuning for a range of frequencies, the very short jumper method is more accurate. While not providing as accurate results as a well trimmed 180 degree cable for measuring resonance on a single frequency, it's accuracy is much more consistent over a wide range of frequencies. Further, you can control how far off your readings are, at least to some extent, with the length of said coax.

If you are a "perfect SWR match" tuner (that is readings of X=0 and R=50 on the analyzer), then in both cases the closer you get the antenna tuned to that point you are looking for the more accurate both of these methods are going to be, so either can be used equally well by you.


The DB

 

[roger460xvr]

Both of these methods can be used, and both have their flaws. Neither will recreate completely accurate results, although both of them can get you close.

If tuning for only one frequency the 180 degree cable will get you more accurate results when it comes to X (resonance) for said frequency. However, in the real world, getting a 180 degree cable tuned perfectly for the frequency in question isn't really that easy, it will pretty much always be off to some extent. Due to losses in the coax, this method will also throw off the R reading as well. If you are one of those that thinks resonance is always the best to tune for this method is for you. This method is less accurate the further away from the feed line's tuned frequency, and those inaccuracies add up faster than you might think (at an exponential rate).

On the other hand, if you are tuning for a range of frequencies, the very short jumper method is more accurate. While not providing as accurate results as a well trimmed 180 degree cable for measuring resonance on a single frequency, it's accuracy is much more consistent over a wide range of frequencies. Further, you can control how far off your readings are, at least to some extent, with the length of said coax.

If you are a "perfect SWR match" tuner (that is readings of X=0 and R=50 on the analyzer), then in both cases the closer you get the antenna tuned to that point you are looking for the more accurate both of these methods are going to be, so either can be used equally well by you.


The DB

love my siro sy-27-4 now.... been talking a lot of skip on it ...flat side is the way to go when it running here in florida...wish they made a 6-element beam..