Cobra 18 WX ST II (don’t laugh)

[Shadetree Mechanic]

@Handy Andy
I will take all that advice! At this point I will run it when I need the extra push. I have a longer 4ft antenna that I will try and see what those numbers are. I also looking into better coax. I will start with the jumpers. This is a brand I am looking at:
View attachment 34885

From what I read this brand is good. If not please say so.

thanks!!!

Jefa has good quality, that's where I get all my coax from. The 240 flex is excellent for mobile applications. I plan on redoing my Sirio 5000 mag mount with it. Their made to order cables have a good warranty too.

 

[Slowmover]

I spend a bunch (relative), but don’t worry about it as I’ve spent FAR MORE and gotten less in other pursuits. I’ve been better this time (this pursuit) in buying quality tools and supplies; getting a shop built BEFORE buying the jalopy to restore is how I look at it.

So I don’t sweat buying. Some things I would again, some I wouldn’t. I haven’t had 20-years to amass a cabinetful. Now, when I’m home, I have my choice of projects. Which is what I really wanted.

Some projects are just R&R (water heater). It works or it doesn’t. Not much mystery (or challenge). Radio is beyond me, so I plod along. THAT I’m fairly good at. “Damn, you got a long row to hoe, dontcha, boy” (my Dad; reflecting on my life; yup), but long past dark after the others have cleaned up and gone to play or chase girls, I finish up AND usually know more than when I started.

It’s not the purchase price (for me), it’s my laying my hands on the right next thing without looking.

.

 

[ForestRunner98]

I have been taking notes on everybody’s suggestions. I am going to try to replace the cheap jumpers I have first. One jumper are two 3ft w/ a barrel connector. So I ordered a 6ft Jefa 240 coax and see how the system reacts. The jumpers are not quality. They came with my SWR meter so....ya. I also ordered a filter from RM as @Shadetree Mechanic suggested. I assume the filter goes just before the antenna. I will try that too!!

Trying to hunt down these gremlins is a challenge!! I don’t want to give up on a hobby that I started enjoying.

 

[ForestRunner98]

Okie dokie...some updates!

I received that JEFA coax and it’s real nice but it wasn’t that flexible. It’s the 240. No biggie. I removed the 2, 3’ jumpers and SWR went down by .5 to 2.5 It had jumped with the current set up to 3!! Ok we’re getting there! I installed this guy:



The RM filter. I didn’t have any barrel connectors so used my 3’ jumper. Well.......amp “on” the SWR at ch 40 and ch1 went down to 1.9 and 1.7 at ch19!! That filter cut all those “harmonics” that were above 30 MHz I assume. This with a 3’ firestik. I haven’t tried the 4’ yet. I bet with the longer antenna and bonding of the doors, hood and gate should make it even better!!

I have some barrel connectors coming tomorrow so if it’s not raining I will give them a whirl. When the weather gets better I might replace the 18’ cheapie coax with the JEFA brand. It wasn’t much more expensive than the 6’....almost $30 for 6’ but it helped!!

So...I will keep updating as it goes. You guys helped a lot and I thank you!!!

 

[ForestRunner98]

I installed the barrel connector to the filter for a direct connection to a amp to see if the SWR level goes down further. Well...that didn’t work. Level actually went up a few ticks. So I tried using a barrel to connect 2 3ft sections of coax. Radio didn’t like that either. So...I went back to the 3ft jumper but I coiled it a few times and that made the SWR at Ch 19 go to 1.6! I will take it...for now!! Now to bond the doors and see how that goes. Still trying!!!

 

[Handy Andy]

Hmmm...

Ok, keep us posted on your progress...

I see you tried the SWR approach so - "OK we now know" let's get back to the fun at hand and make this work...



Barrel connectors can get finicky - they tend to loosen due to their structure. They are stiff, hard-shaft and unable to bend or absorb much vibration without some type of help.

Mounting the two devices in the same plane, and sharing the same bracket are pretty much the best option when it comes to "bolting" and barrel-ing the system together. It's a lot like hardline - low-loss and can withstand a lot - but requires a lot of effort in alignments and construction to make the line work and stay put for any type of service life.

Coax does better in mobile setups. If for any reason - the amount of vibration it has to withstand.

Because of it's flexibility and ability to withstand flexing bending and their stress', it can stay in position without any sort of help once they're tightened. You can add a sealant but that is your choice - if you're if a job positions' like a slip seater or only wanted it for seasonal uses, then something quick, flexible and easy to adjust and or remove - like this approach is the best. Sealant can only work if you want a more permanent or weatherproof bond. Unless you have any sort of outdoor exposed connections that require sealing (like a bumper or lip-mount or "twin-Trucker" dual co-phasing or other types of exterior harness applications) it may be more of a hassle than it's worth to use. Easy assemble and disassemble takes precedence - you never know what you may encounter while driving or having to maintain your vehicle.

Simple setups work far better and are easier to maintain than a sealed up and unable to be removed setup that got whacked and is now cracked and leaking and SWR is beginning to climb...

Barrels, well, no - they are more tubular solid shaft, like hardline. So any torque placed on either side can cause the connection to break loose and you get a loose connector problem. So - we did do it if - Only for checking SWR issues and no because you'd need more of a bolted down - spaced right and properly seated permanent mount solutions do they work

So Barrel connectors - if they can be avoided for those short plug in runs - are out for long term solutions.

Barrel connectors are better for only for checking SWR without amp - to attach the Antenna to radio more direct - we will just have to use the Coax jumpers to get your mobile setup working and longer lasting.

 

[ForestRunner98]

I now realize that adding or subtracting hard connectors or coax can play a major role on how it affects a system. I am way more familiar with car audio. RX and TX is a whole different world!!

 

[Handy Andy]

It ok, I see what you're trying to do, and barrel ends, both male and female types, have a lot of drawbacks.

Male types have a "split ring" - Circular spring clip that the outer sleeve, ferrule - work with to stay clamped together - these can work for dry environments but are useless when it comes to keeping out water or the elements and they do not take to torque very well. so vibration will easily loosen them. On top of, connection quality they are pieces of parts like a ferrule (Female) type but have the outer sleeve twist ring or ferrule - held in place by a spring clip, that again, only makes contact in specific areas of the whole body it's clamping. - they are not the best clamping systems used to make repairs, but more like for quick fixes and maybe a means to jumper two devices to make one removable to the other for service.

Female are better but that's again an operators opinion - I got flamed before - but to use them - Use only for short term repair or checks and reinstall what was there at the breakpoint - sooner the better..

Both types can offer headaches of their own - I call them impedance bumps and that is putting it mildly - for you have to, not only - make a secure SHIELDED connection - but RF has to pass thru there without getting impeded in it's travel across the junction.

So to keep it short, AHEMN - just use Barrel as temporary stopgap measures only and route coax accordingly.

But I'm glad you tried this for you just got brownie points for the effort in doing it and posting results that not many people realize in trying this themselves.

 

[ForestRunner98]

I installed my 4’ Firestik w/o the spring and was able to tune it to 1.5 at ch 40 & 1 and 1.3-1.4 at ch 19. Those numbers with amp “on”. Amp off and the numbers are 1.1 - 1.2

I prefer having the 4’ antenna but my work parking structure has a max height of 6’8”. Pretty sure it will hit even w/o the spring installed. I will try the 3’ Firestik sans spring and see how it performs.

 

[ForestRunner98]

So 3’ Firestik w/o spring was a no go. Radio did not like that and SWR went up. So..came to this 4’ no spring and 3’ with spring. TX & RX to Compton Ca. little more than 30 miles. Not bad.

 

[Redbeard U812]

So 3’ Firestik w/o spring was a no go. Radio did not like that and SWR went up. So..came to this 4’ no spring and 3’ with spring. TX & RX to Compton Ca. little more than 30 miles. Not bad.

Step up to a 102" w HD spring. Can always tie it forward with chute cord. Don't forget the tennis ball. LOL .

 

[ForestRunner98]

Step up to a 102" w HD spring. Can always tie it forward with chute cord. Don't forget the tennis ball. LOL .

That would certainly get me out a lot further!!!

Tied forward looking military!! Tennis ball.....well? LOL I used to see that a lot as a kid and wondered why they have a tennis ball.

 

[ForestRunner98]

I was wondering if a MFJ-909 mobile impedance matcher would work in lowering SWR’s even more. Seems like a good idea?

 

[Handy Andy]

Sometimes, it's the simplest approach that works best...

​

Here's why...

You can predict the SWR match, and as far as we know, you are ok using it.

The one thing that a tuner might be to honest about, is what you DID NOT want to do...

Which can be something you couldn't do...

Relocate the Antenna to a position you didn't want it to be...because the antenna isn't in the Best Resonate Spot for this system to work - it's not Ideal.

I've faced this many times.

Not everyone has an Antenna Farm with a HUGE backyard to use - or the best Mobile setups often their antennas are not practical driving in traffic or even parked...

Remember; a Tuner - simply "masks" over the SWR/Matching problems into a workable solution for those that want to use their installation as it currently stands.

There are reasons for that, like neighbors, proximity to other objects - interfering with Near Field of the antenna - unable to place antenna in an IDEAL LOCATION so it has to be installed in an otherwise unlikely position or location in order to even be useable. Not everyone lives with a Radar Dish like this...

​

So to insert another variable into this, might not be the best approach - but I do understand your curiosity over the approach. I cannot guarantee your success in this - you already have pretty GOSH DARN good results already...why change it?

 

[Slowmover]

I was wondering if a MFJ-909 mobile impedance matcher would work in lowering SWR’s even more. Seems like a good idea?

Had my Peterbilt with cab-mounted co-phase antenna pair at a shop that has serviced drivers many years. Owner is a long-time HAM operator.

With an MFJ-259 connected:

40: 1.7

20: 1.8

01: 1.8

My little cheapie SWR meter showed a little higher. The UNIDEN 980 meter showed a little less.

The PRO-COMM Quad Wrap antennas were soon well above 2.0 with little change in stinger height in either direction I had already learned. When I was setting it up a month or so ago I had to get out a tape measure to be exacting. Originally, I wasn’t going to worry over being “ideal” until I’d had a tech with an analyzer check things over.

Turned out it was a VERY narrow range of adjustment.

The nice thing after readings above is that there wasn’t anything for me to do once they gave the above “equal” readings. Under 2.0 is good-to-go.

That problem resolved for now, on to the next item.

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