On Wed, Jun 4, 2014 at 6:24 PM, Joe McCauley wrote: > I could if I had one :). Doing this also means having to break into the > coax. I probably want to try with a new coax anyhow. I did some tests wit= h > an old antenna last night. In general I noted that the dip in the reflect= ed > power was pretty much where I expected it to be, but there was a change i= n > both dip frequency & amplitude depending on where the coax was routed. > Yes, yes, yes! :) This is the crude reality ! > > I'll also see if I can find a meter. Boats are being launched soon, so I > probably won't get to do this until we have them back on dry land. > > Thanks, > > Joe > > > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of Sean Breheny > Sent: 04 June 2014 15:52 > To: Microcontroller discussion list - Public. > Subject: Re: [OT] Matching an antenna to a VHF TX/RX > > Joe - you could simply put a directional power meter in-line with the > antenna, right at the antenna feedpoint to eliminate the effect of the > coax. The forward power minus the reflected power will be the actual powe= r > delivered to the antenna. Assuming that the antenna is not faulty or > installed near objects which absorb power, this will be close to the actu= al > radiated power. Beyond that, the only remaining variable is antenna patte= rn. > > > On Wed, Jun 4, 2014 at 6:44 AM, Joe McCauley wrote: > > > Does a spectrum analyser with tracking generator & directional coupler > > not do the same thing? (Measuring reflected energy from the antenna.) > > I have the TG output connected to the through port of the coupler & > > the antenna connected on the other side. The coupled port of the > > coupler is connected to the RF input of the analyser. > > > > Thanks, > > > > joe > > > > -----Original Message----- > > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On > > Behalf Of Vasile Surducan > > Sent: 04 June 2014 09:17 > > To: Microcontroller discussion list - Public. > > Subject: Re: [OT] Matching an antenna to a VHF TX/RX > > > > If you have a network analyzer will be much easier. Just connect the > > antenna on one port (with the whole cable you are using between the > > antenna and the input port) and see the S11. Then tune the antenna > > lenght (or adjust the trimmer capacitor if has one) until the max > > absorption appears to be on your required frequency. > > > > I think between 153 and 156 MHz you should do nothing unless you have > > small emitting power. > > > > > > On Wed, Jun 4, 2014 at 6:02 AM, Justin Richards > > > > > > wrote: > > > > > On 4 June 2014 03:38, Joe McCauley wrote: > > > > > > > That is the next step I think, how far apart do you put the > > > > antennas? I'm guessing they can't be too far apart. > > > > > > > > They are close, approx 20 m. If you had a portable B that you > > > > could > > > position the same distance from each and save trace to disk so you > > > can move analyser to the other boat. > > > > > > I recall that the farming community I once belonged to were adamant > > > that a two way radio (UHF) would fail to work if the antenna was > > > mounted on the roof of a vehicle and the two way radio was mounted > > > directly under the antenna inside the cab. > > > > > > justin > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .