Antenna Tuning

[Solfan]

I just have a quick question about antenna tuning. To cut a browning br450ngp antenna, do you measure from the bottom of the metal connectar on the phasing coil or from the black plastic section of the coil? Sorry if I'm in the wrong group.

 

[arg0s]

Take a look at the attached file.

 

[merlin]

Generally, it is the rod length that goes into the fitting at the top of the coil.
Not the chart posted and the difference with or without the spring.

 

[Solfan]

Generally, it is the rod length that goes into the fitting at the top of the coil.
Not the chart posted and the difference with or without the spring.

The chart posted is the same chart that came with the antenna. When I measured from the bottom of the metal fitting on the center coil and cut for 467mhz I got a 1.48, interesting thing is that at 462mhz I got 1.00. So I thought maybe I was supposed to measure from the bottom of the black plastic part of the coil rather than the bottom of the metal fitting.

 

[Ubbe]

The chart says it's a 14mm difference between 465MHz and 470MHz, the same 5MHz difference as between 462MHz and 467MHz.
Do you see a 14mm difference in length depending of where you measure from?

/Ubbe

 

[Solfan]

I dont know what the origional length was. I have 2nd br450 coming, when it gets here I will check the measurements.

 

[Solfan]

What do you think the length should be for tuning to 467.700mhz?

 

[arg0s]

So I thought maybe I was supposed to measure from the bottom of the black plastic part of the coil rather than the bottom of the metal fitting

I agree, there is logic in your consideration. The chart is not 100% clear in this regard. Assume it's meant to measure from the bottom of the metal fitting. In this case you still have the chance to cut more if the antenna is too long.

What I ask myself is why you have to adjust only the bottom but not the upper half of the antenna? This looks to be a a collinear antenna with two stacked 5/8 lambda whips with a phasing coil inbetween.

 

[Solfan]

I agree, there is logic in your consideration. The chart is not 100% clear in this regard. Assume it's meant to measure from the bottom of the metal fitting. In this case you still have the chance to cut more if the antenna is too long.

What I ask myself is why you have to adjust only the bottom but not the upper half of the antenna? This looks to be a a collinear antenna with two stacked 5/8 lambda whips with a phasing coil inbetween.

That's exactly what I was thinking. It is a 5/8 over 5/8 CL. And you would think that it would need both ends cut, but everything I have seen says only cut the bottom. A small diagram on the cutting sheet would have helped. Can't find browning website to try and call them about it. Only one that comes up is nolonger working.

 

[Ubbe]

When the other BR450 arrives, measure the top part from the top of the coil to the top of the whip. Then measure from the bottom of the coil to the top of the loading bottom coil. The 5/8 lengths should probably be the same for the uncut frequency and when cutting you should be able to use the percent value by which you raise the frequency to also shorten both 5/8 elements by the same amount of percent. If one only cuts the bottom element it has to be cut more to compensate for the non tuned top part and the chart are probably showing that.

/Ubbe

 

[Solfan]

The chart says it's a 14mm difference between 465MHz and 470MHz, the same 5MHz difference as between 462MHz and 467MHz.
Do you see a 14mm difference in length depending of where you measure from?

/Ubbe

So if i cut at 260mm should bring it to 467mhz?

 

[Ubbe]

The chart goes from 450 to 470Mhz and that are a 4,4% change in frequency. The cut length for the lower antenna part goes from 305mm to 265mm and that are a 15% change. They compensate for not cutting the upper part of the antenna. Instead cut both bottom and upper part 4,4% shorter if you want to use it at 470MHz.

You can always test antenna lengths by clipping a crocodile clip on top of it to lengthen it a bit and see if SWR goes up or down. If SWR goes down it is already too short and can't be cut any shorter.

/Ubbe

 

[Solfan]

Does Browning or Tram-Browning still exist? I can't find any contact info and the web site domain is nolonger used.

 

[AK9R]

Tram-Browning exist only as marketing names that have been sold to manufacturers of inexpensive, Asian radio products.