Co-Phase/dual antenna tuning.

[E412B]

Decided to install dual antennas.
What is the best/easiest way to tune. Read several different methods.

Method 1
Set SWR using 50ohm coax from radio all the way to 1 antenna. Tune to SWR of 1:1. Then adjust 2nd antenna the same way. Then install the Co-phase 75ohm coax to antennas.

Method 2
From radio to antennas with co-phase coax. Then adjust both antennas at the same time.

Method 3
From radio to antennas with co-phase coax. Disconnect 1 antenna and connect a dummy load to that side. Then adjust the antenna on the other side of the coax. Then remove dummy load, connect that antenna, then adjust that antenna.

Have 2 SWR meters. One is an Astatic PDC2, the other is a Workman HP202S dual needles. The Workman paperwork says it doesn't handle 75ohm coax very well. So will have to see how that goes.
Another weird question could I hook it this way. Radio, 3' 50ohm coax, PDC2, 3' 50ohm coax, HP202S, coax to antennas/tunning method?

Using Uniden 510XL to set SWR, then installing a Connex. Will I have to reset SWR after radio swap?

 

[midnight special]

all 3 methods i have seen work,,,,, as for putting the 2 swr meters in line at same time no it would just make ya think something is wrong even if they said same reading,,,2 jumpers and 2 meters could show a false reading,,,,,and after you set the swr there should be no change in putting the connex in,,,,if there is it would be because the connex is causeing a false reading,, happens alot ..nothing to worry about,,,that is why i use a mfj 259 antenna anylizer,,,,,

 

[The DB]

The twin 75 ohm coax is part of the matching system for running two near 50 ohm antennas in parallel, they essentially convert the two antennas parallel impedances together to be near the 50 ohms radios expect to see. It isn't a perfect solution, at best it is functional. The best way is to have two new antennas, and tune them together. The other ways will work, but not quite as well, only use them if you are starting with two antennas that are not pre-tuned identically. Honestly, of the other two methods, the one utilizing a dummy load is the better solution.

If SWR is not the same on all parts of the coax, then you have a problem that needs to be dealt with. Another way of saying that is if you get a so called "false reading" then you have a problem that needs to be dealt with. Many people treat said issue like it is normal and supposed to happen, and even try tuning antennas with it. It is not supposed to happen, and if you see it happening you should ask about it and get it fixed properly.


The DB

 

[E412B]

Cool. Thanks for the replys.

I understand that tuning both NEW IDENTICAL antennas at the same time is the best option.
I understand there should only be one meter in use.
If I sub 1 meter for the other it should have close to the same swr reading (accounting for the accuracy of meter(s))
I understand that once best swr is there it shouldn't change just because a radio does.
I understand it could be a PITA to tune.

A few more questions or statements.

The co-phase coax is 18 ft (each leg). The way it's ran, to keep from being pinched, is not long enough to reach the radio. What I have NOW is radio, 9ft 50ohm coax, meter, 75ohm coax the antennas.

What I want to do is radio, 3ft 50ohm jumper(already have it), meter, 9ft 50ohm coax (cause I already have it), female couplin, 75ohm coax, then antennas.

I know there will be line loss because of the extra 9ft and the couplin'. The only other option is to either re-route the 18ft co-phase coax or make a longer one and route the same way.

The reason I was thinking the HP202S didn't/doesn't handle 75ohm well is because of the paperwork that came with the meter. see below

 

[midnight special]

i think the 75 ohm deal is using the meter with dipoles which are 75 ohm instead of 50 ohm,,,,that is why dipoles are best used with 75 ohm coax,,,,,

 

[E412B]

OK cool.
Made a dipole sunday for spark-o-matic base station. just a rush job. was 4' foot off ground, horizontal, and inbetween 2 mountians, ends east and west. north only about 30 ft to mt and south was 80 ft. was still able to get about a mile out. didn't think that was too bad. rush job and 4ft off ground. cheap cheap cheap on sell .15/foot rg59u and 14 gauge strand wire. center feed but only had about 2' drop until coax started to follow ground side of coax.

 

[E412B]

line of sight west was less that 1/4 mile. elev bout 740 at dipoloe 1250' or so to top of hills around me.

 

[rabbiporkchop]

I would hook up the analyzer to the phasing harness and see what the resonant point is.
If it's resonant at too low a frequency that means they are too long and they need to be trimmed. I would trim both whips simultaneously . If it's resonant at too high a frequency then you cut too much off.

 

[sp5it]

Method 1 is proper way to tune.
I would check phasing lines if they are cut to proper length, but for that you need VNA or other antenna analyser.
Mike

 

[Needle Bender]

I set up a dual Wilson Trucker 5000 last month.

I set both antennas whips all the way in, then tested them to see if they were identical.

Had to cut 3/16" from one to get them to tune identically on one mount.

Set both for 27.185 on one mount.

Assembled system.

Had 1.7:1 on ch.40, 1.2:1 on ch.1

Shortened both equal amounts (about 1"+/-) until flat on ch.19.

I believe they will interact to some degree so tuning each should include the other in it's near-field.

(Velocity factor of 75Ω x 1/4 wavelength for a 1/4 wave matching transformer.)

 

[Wes Tanner]

Trying to find a schematic, or just a pic of the workman HP202S. Had to take apart to snap meter back in after being dropped...broke red wire to one of the meters, didn't take a pic fo reference...help please.

 

[9C1Driver]

You might try starting a new thread rather then highjacking an old thread like this. That way more people will see your post by looking at the title.