HF Assistance

[Aaron Wasson]

Anyone up for a quick test?


Sent from my iPhone using Tapatalk

 

[Aaron Wasson]

Ive done a little bit of work to the grounding of the bed rack, but the system still doesnt seem to be working the way you would expect.



I dont know why the image is sidways, but you can thank the forum for that one. This is the AH4 auto tuner that is controlled by the 706mkiig in the truck. Power and control cables run through a small hole under the tuner back into the cab. At the bottom of the tuner there is a ground (which I just changed while typing this) that in the picture used ground strap to the bed bolt. Ive changed that to go back to the DC ground for the radio. So both the radio and the tuner are on the same DC ground bus.

The strap coming down from the side is ground strap to add the bedrack to the ground plane of the truck. There is no paint between the rack and the strap. Then the strap is attached to the bolt and runs to the frame.

On the inside of the truck (not shown) the radio power/dc ground come from a distribution system that pulls power directly from the battery and grounds at the same chassis ground as the battery system. The ground wasnt like that at first. It was originally at the seat mounting bracket (and it may go back there) and it worked fine. I moved it forward after getting info from k0bg.com.


This is how the antenna is mounted to the truck. Its up high enough to not be blocked by any of the sheet metal, and I would "assume" that since the roof of the truck is below it, that it might help. Not sure though. The coax under the antenna uses the center element and runs down to the tuner. Ground on the coax isnt used, the antenna is the ground side.

If anyone has an idea on what to check/try, let me know.

 

[DaveInDenver]

Can you hear the tuner rattling through solutions when you try and tune? Does it settle quickly or randomly run a tune cycle?

My guess is your radiating element isn't coupling properly with the ground/return. I wouldn't worry about making sure the DC path is the same for the radio and focus on getting the tuner /well/ grounded to the truck and all the sheet metal in the cab and bed bonded together.

I might also connect the feed line (the part between the whip and tuner) shield to ground at one end. Floating it becomes part of the antenna and might be shorting or presenting some sort of weird impedance. I personally also run a choke at the point where the feeding coax from the radio enters the tuner as well as good EMI suppression on the control lines at both ends.

Contrary to popular myth these types of tuners (I have an AH-4 and Alinco EDX-2 currently) don't remove the need to build a proper antenna, so all the best practices still apply. They just allow you to use otherwise marginal antennas over broader ranges. Point being you need to see antennas as antennas still, transmission lines as transmission lines and be particularly wary of sneak paths.

My AH-4 is currently installed in the attic of our house feeding a doublet and the whole system from the back of the radio to the ends of the dipole are floating above ground with the tuner itself being balanced feeding window line from the antenna & ground lugs, so they don't need to be tied to the same ground as the radio to work fine. When you do that you do absolutely need to be aware of what potential things are sitting and when is and isn't a path back to ground, but it does work.

 

[Aaron Wasson]

I'll give that a shot. Also, when I altered the dc ground on the tuner, power output maxed out. So that helped a lot.
Before when I would transmit and watch the output meter, it was low. Now it's maxing out like I would expect.


Sent from my iPhone using Tapatalk

 

[DaveInDenver]

The 706 has high SWR fold back, so that probably means the tuner tried to tune. But don't assume that means it actually found a meaningful match. If you hook a tuner up to a terrible load it will maybe find a combination of L and C that makes appear like 50 ohms, but all the power will dissipate inside it if the load is way, way off. The AH-4 can tune from I think about 5 ohms to 2,000, so the match can be way out but anything more than maybe 20 to 200 at the antenna lug means the tuner is just warming up the inside.

 

[Aaron Wasson]

Can you hear the tuner rattling through solutions when you try and tune? Does it settle quickly or randomly run a tune cycle?

Its typically quick to tune to the frequency.

My guess is your radiating element isn't coupling properly with the ground/return. I wouldn't worry about making sure the DC path is the same for the radio and focus on getting the tuner /well/ grounded to the truck and all the sheet metal in the cab and bed bonded together.

I might also connect the feed line (the part between the whip and tuner) shield to ground at one end. Floating it becomes part of the antenna and might be shorting or presenting some sort of weird impedance. I personally also run a choke at the point where the feeding coax from the radio enters the tuner as well as good EMI suppression on the control lines at both ends.

This I should be able to do soon. May need to rebuild the line between the antenna and the tuner, but that wont be a huge issue. Ill cut the coax probably a ft or two long and leave the braid as intact as possible to reach ground, and then fit it all together. It will be a couple days though. Im heading to Missouri over the holiday weekend. Ill have the radio on for testing/playing on the way up there. When I get back, Ill make the new cable.

 

[Aaron Wasson]

I might also connect the feed line (the part between the whip and tuner) shield to ground at one end. Floating it becomes part of the antenna and might be shorting or presenting some sort of weird impedance. I personally also run a choke at the point where the feeding coax from the radio enters the tuner as well as good EMI suppression on the control lines at both ends.

Hopped back on K0BG's site and from what he is saying, using coax between the tuner/coupler and the antenna is a bad idea. Then I found these images:

That is solid wire going from the tuner to the antenna. I would probably need to change the antenna mount that Im using, or find a way to put that solid core into the pl239. Then cover it with silicone tape and run it down to the tuner. I dont want a line running power to hit the outside of the truck.

 

[Aaron Wasson]

Got into touch with K0BG. He has some stuff that he wants me to change and test. Finding something to go between the tuner and the whip will be the biggest part.

 

[DaveInDenver]

That is solid wire going from the tuner to the antenna. I would probably need to change the antenna mount that Im using, or find a way to put that solid core into the pl239. Then cover it with silicone tape and run it down to the tuner. I dont want a line running power to hit the outside of the truck.

I guess this confuses me, why are you messing with trying to put a solid wire into a PL259. The antenna feed should be a lug terminal for a ring. A piece of #12 wire with crimped and soldered ring terminals on each end is all you need. There's no need to run a coax between the tuner and antenna just as long as the antenna mount isolates the radiating element from ground, maybe with nylon or phenolic. It's best to keep that length short and not close to metal (it'll want to couple with ground).

 

[Aaron Wasson]

You're 100% correct. The "ham god" that told me to do all this has proved to have wasted my time. So I'm in the process of replacing the mount and the lead along with a couple other things.

So don't be confused. Because you're right.


Sent from my iPhone using Tapatalk

 

[Aaron Wasson]

I have a heavy duty Breedlove mounts and some other parts on the way.


Sent from my iPhone using Tapatalk

 

[DaveInDenver]

Nice. Breedlove's mounts are serious.

BTW, that Jeep outfit is a super nice way to do it. Really dig the mount of the tuner and whip. Cool.

 

[Aaron Wasson]

This was supposed to be a serious setup. Not a "because I can," like a lot of builds. That's why I'm not happy. I'll have to depend on this radio for remote check ins.

I am worried about the potential proximity of the feed line to the cab. What do you recommend the minimum distance to be?


Sent from my iPhone using Tapatalk

 

[DaveInDenver]

Assuming feedline being the section between the whip and tuner (just want to be clear). As you've figured out it's the part that runs near metal that is the problem and at HF there's really no way to find sufficient distance that it would not couple. Your best bet is to mount the tuner as close and keep it short. There's not much else you can do. Why don't you mount the tuner on the under side of the rack? Looks like you have a RTT so maybe a plate under that.

 

[Aaron Wasson]

That could be an issue

Because It's close!!

I guess I could remount the tuner under the rack. Not really a lot of places.


Sent from my iPhone using Tapatalk