VHF/ UHF SWR measurement

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Walter Hess:
I have a cheap swr meter suitable for HF frequencies, but I understand that one must use a meter specific for VHF/ UHF to measure swr on those frequencies. Can someone explain why this is? I know that there is a rather expensive do-all meter the ML 269 which I cant afford at this time. Can someone recommend a good alternative? At this point I'm just looking to measure my current antenna performance, but want to eventually build my own antenna. Thanks

Mark Brueggemann:
The issue is due to the wavelength and frequencies involved, which require greater physical accuracy of construction as well as "better" components.

This might be of some help.  Here's an old timer's trick.  If all you want to to is check SWR on your 2M antenna, you don't necessarily have to buy a dedicated VHF/UHF SWR meter.  What I keep in my toolbag for that is a cheapie $5 hamfest special CB SWR meter.  They really don't work well on 2M but there's a trick you can do that will net a reasonably accurate SWR reading on 2M with one of these meters.  What you do is connect up the meter as usual, key the rig with the switch in the forward power position, and set the adjustment for full scale.  Now, without touching the controls, swap the coax connections so that the rig is connected to the "ANT" side of the meter, and the antenna is connected to the "XCVR" side.  The reading you see on the meter will be very close to your real SWR.  The closer to 1:1  your SWR is, the more accurate it will be.  

Mark K5LXP
Albuquerque, NM

Steve Katz:
"At this point I'm just looking to measure my current antenna performance, but want to eventually build my own antenna."

::Measuring SWR doesn't tell you anything about your antenna "performance."  It only gives you a snapshot of data regarding the impedance match of your antenna, and if you have much of a transmission line (e.g., coax), it doesn't even tell you that much unless you disconnect the cable and make the measurement right at the antenna feedpoint -- something that most don't bother to do.

Although your HF SWR bridge may not read accurately at VHF, it will give you a relative reading to allow your adjustment of the antenna matching network or antenna length to trim for "lowest possible" SWR.  That's all you really need to know.

Antenna "performance" is much more based on the antenna design, installaton and elevation than it is on SWR.  Of all the things that are important about VHF antenna installations, SWR is pretty far down on the list.

WB2WIK/6

Kenneth Meyer:
I agree with both LXP and WIK.    Always remember that a dummy load that has a very low VSWR will not work very well as an antenna! So low VSWR is only one thing to watch for.
And as VSWR measurements are only relative anyhow, Do the procedure outlined by LXP, And then have a local ham who owns a good high quality meter like a Bird 43 stop over someday just to check to see how close your measurements are. Once you know how your meter compares to a really good one, You should be all set.

A great homebrew VHF/UHF directional antenna is the proven "Quagi"
http://commfaculty.fullerton.edu/woverbeck/quagi.htm

Allison:
>>Here's an old timer's trick. If all you want to to is check SWR on your 2M antenna, you don't necessarily have to buy a dedicated VHF/UHF SWR meter. What I keep in my toolbag for that is a cheapie $5 hamfest special CB SWR meter. They really don't work well on 2M but there's a trick you can do that will net a reasonably accurate SWR reading on 2M with one of these meters. What you do is connect up the meter as usual, key the rig with the switch in the forward power position, and set the adjustment for full scale. Now, without touching the controls, swap the coax connections so that the rig is connected to the "ANT" side of the meter, and the antenna is connected to the "XCVR" side. The reading you see on the meter will be very close to your real SWR. The closer to 1:1 your SWR is, the more accurate it will be.<<


I have a Bird and a VHF swr meter but I've used the CB meter trick.  Mine is really old but works well.

The trick above can be modified if you have some patience.  Do what he wrote then try the meter as is
without physically reversing it.  Seems 1 out of three are fine at 6M and acceptable at 2M and mine is passable at 432!.  If the forward/reflect switch
do not agree with physical reversal then it's time to go inside and bend the sampling lines until it does.
Those meters are a simple trough with the center conductor and two sample lines along side often they
need a bit of bending to be accurate at low to mid
VHF.  With care you can get it accurate for relative SWR measurement and thats good enough.

The only thing to watch is they are more sensitive
with increasing frequency. Keep the power low.


Allison

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