VLP SWR Meter

[IdunBenhad]

Hi:
As postulated in "SWR Meters & Antennas", I have been working on a SWR Meter to be used with low power FM transmitters.

Even though the paper is dated April, this is not an April Fools joke. It is a viable and working SWR meter.

There are several attachments in PDF format and the PC board layouts are entered under Library/Copper/VLP SWR Meter.

Good luck and I hope you find this instrument useful. It is the result of many hours of construction and experimentation.

Addition: 4-10-2012--Changed PCB file under "Library/Copper/VLP SWR Meter. Cosmetic changes only. The original is OK to use.

Addendum: 4-27-2012--Added "VLP SWR Meter Addendum" to attached files.

[Mactayl]

Very good Idun,, looks like I will have to have you make me a home etch board for me..how much will it cost...

[ukewarrior]

Wow.
This is just fantastic.
I can't wait to build this and test it.
Most Excellent. Thanks.

[dirknerkle]

What a tremendous addition to the DIYC arsenal of valuable pieces of gear! Just an AWESOME tool that can take all the ambiguity out of tuning an antenna to a radio!

Well done, Idun!

[imbluenote]

Very cool! Good job on putting it together. I keep ,wanting to take my dipole in to work to sweep it on one of the Anrisu site masters that we have at work but never thought about power being to high for it. I think, I'll take this on as a project. If any one winds up making the boards, I'd take one, other wise I'll have to try it on Perfbaord.

[IdunBenhad]

Hi:
imbluenote: I don't know how your antenna is constructed, but the power of the instrument you refer to should make no difference. The antenna should be capable of handling hundreds of watts if it is constructed of RG58/RG59 or similar coax.

The power referred to in the VLP SWR Meter is the power required to run the meter itself, not to the power handling of the antenna.

[T.D.Sutton]

Hi Idun,

Nice bit of development work, I would expect that the "VLP SWR" meter would have some insertion loss due to the 52 Ohm resistor being permanently in series between the Transmitter and the Antenna, or am I being pedantic, or showing my age :-)

I am running an aluminium block 50 Ohm matched stripline reflectometer on my 500mw Tx into a 50 Ohm matched antenna. My test gear tells me the antenna has around 25 Db return loss over the band of interest. Needless to say the reflected power is minimal - thankfully, but would sure show up if the antenna was damaged in any way as the metering is very much more sensitive in the reflected direction :-)

To reduce the coverage area I run a 3.5 Db pad in series with the transmitter before the strip line, the transmitter hasn't got a "power control" on it, as these are "Illegal" in this part of the world.

Cheers,

Terry

[IdunBenhad]

Hi:
Terry: You are right, there is insertion loss. The VLP is not intended to stay in-line, as pointed out in the writeup.

Because this is a very simple instrument, it will not measure return loss. It is meant to help get the antenna in tune at the operators chosen frequency.

In your case, you could leave the VLP in line and reduce your transmitter power to 1/4 of the 500 Mw. or 125 Mw. This would eliminate your 3.5 db pad, which is reducing your power to about 275 Mw. I would suspect that your range is way more than adequate with that much power.

I haven't run a test yet, but I am curious to see what the range is with the FM02 reduced to 7.5 Mw.

Thanks for your input.

[IdunBenhad]

Hi:

Return loss is a measure of how well the load and antenna are matched. The higher the return loss, the lower the SWR and the better the match.

The VLP Meter does not directly measure return loss in db, it is only a relative indicator of the SWR and impedance matching.

For a much better explanation of Return Loss, see this entry:

http://www.k5rmg.org/tech/rtn-loss.html

http://en.wikipedia.org/wiki/Return_loss

Do a Google search for "Return Loss" for much more information.

[Jrd]

Wow, looks great Idun! Thanks for your hard work!