Antenna for cramped quarters

tweiss3

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Is it just me, or does it look like there was an arc between the winds on the top right, right in front of the capacitor.
 

tweiss3

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Yea, that's why it looked odd to me. Typically that lead is just soldered/grounded back to the coax shield. Below is mine:

PXL_20210129_021704091R.jpg
 

N8MXL

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I've seen it done both ways, so I went back and forth on it. I did it this way so I'd have the option to use a counterpoise. It's possible that solder joint is iffy. A multimeter shows connectivity through the joint, but maybe it's not good enough for real-world use.
 

N8MXL

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I rebuilt the transformer as a last resort. I'm still getting a high SWR into a 2.5k dummy load. I'm at a loss to explain this. The only thing I can think of is that maybe the toroid core was mislabeled by the seller and I don't have type 43. I have a 240-43 from a different source that I intended to use for a choke, but maybe I'll try building a transformer with it to rule out the possibility I have the wrong core.
 

N8MXL

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The other core made no difference, so I don't think I have the wrong type. There has to be some nuance I'm missing. If I connect the same coax into a 50 ohm dummy load the SWR reads as almost perfect, so as far as I know the meter isn't way off.

I just noticed that the SWR with the 2.5k dummy load is fairly good on 80m but still high on other bands. Could that indicate anything about what's wrong?
 

belvdr

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The other core made no difference, so I don't think I have the wrong type. There has to be some nuance I'm missing. If I connect the same coax into a 50 ohm dummy load the SWR reads as almost perfect, so as far as I know the meter isn't way off.

I just noticed that the SWR with the 2.5k dummy load is fairly good on 80m but still high on other bands. Could that indicate anything about what's wrong?
I'm thinking your BNC connector has failed (or is DOA).
 

N8MXL

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I'm thinking your BNC connector has failed (or is DOA).
I had the same thought. I tried three female and two male BNC connectors in all the experimenting I've done today with no change.

Since you bring that up... I'm using solder-type connectors. The coax braid just gets press-fit into the housing. Will that make a good enough connection? I wasn't worried about it initially since the same connectors work fine with the 50 ohm dummy load, but with no other ideas panning out I'm starting to circle back that way. The multimeter shows a good connection end-to-end and no short between the center conductor and braid.
 

belvdr

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I had the same thought. I tried three female and two male BNC connectors in all the experimenting I've done today with no change.

Since you bring that up... I'm using solder-type connectors. The coax braid just gets press-fit into the housing. Will that make a good enough connection? I wasn't worried about it initially since the same connectors work fine with the 50 ohm dummy load, but with no other ideas panning out I'm starting to circle back that way. The multimeter shows a good connection end-to-end and no short between the center conductor and braid.
When I built one of these, I soldered everything. I would not trust press fit connections.
 

MUTNAV

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I had the same thought. I tried three female and two male BNC connectors in all the experimenting I've done today with no change.

Since you bring that up... I'm using solder-type connectors. The coax braid just gets press-fit into the housing. Will that make a good enough connection? I wasn't worried about it initially since the same connectors work fine with the 50 ohm dummy load, but with no other ideas panning out I'm starting to circle back that way. The multimeter shows a good connection end-to-end and no short between the center conductor and braid.
A possibly unrelated thing about soldered coax connectors (and you may know this already, if so, sorry). But when dealing with the braid of a coax connector, its helpful to "comb" it out, so its very neat (a single layer or braid where none of the metal strands overlap and contact the washer) where everything clamps together.

Other than that, it doesn't sound like the connector at this point.
Thanks
Joel
 

prcguy

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Its actually better to leave the braid intact and braided. To prep it you take a sharp pointy object and wiggle a hole through the braid where the center conductor and braid exit the sheath, then you pull the center conductor through that hole in a loop at first until it all comes out the hole. That leaves you with a nice length of woven braid and this is how most commercial terminations are made.

There is a special tool for this which is hard to find but it looks like a syringe with two finger holes and a thumb plunger. It will have a meta tube with an ID that fits over the center conductor insulation and its tip is angled. You slide this thing over the center conductor until the angled end hits the sheath area, wiggle the end until it pokes a hole through the braid then push the plunger and that pushes the center conductor through the braid.

A possibly unrelated thing about soldered coax connectors (and you may know this already, if so, sorry). But when dealing with the braid of a coax connector, its helpful to "comb" it out, so its very neat (a single layer or braid where none of the metal strands overlap and contact the washer) where everything clamps together.

Other than that, it doesn't sound like the connector at this point.
Thanks
Joel
 

N8MXL

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I attached the connectors the easy way: strip the insulation, fold the braid back over the collar, solder the pin to the center conductor, and screw it together. I was a little concerned that the braid wouldn't make good contact, but everything seems to be working in that regard with the 50 ohm load. When I'm more experienced I'll probably try the more advanced method.

At this point I think we've ruled out the connectors, the cores, and the wiring. Here are pictures of the original transformer that started all this. Now that it's out of the box maybe something screwy is visible that wasn't before.
IMG_6334.jpgIMG_6333.jpgIMG_6332.jpgIMG_6331.jpg
 

prcguy

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I've probably made at least 20 of these and don't see anything obviously wrong. You could bunch up all the windings on the primary side, all 7 or so of them much closer with the two primary right against each other then no more than about 1/8" spacing between the rest. The secondary crossover windings should be spaced about like you have. It sounds like something else might be wrong and the closer spacing won't fixt that but if you get it working the closer spacing should improve it slightly.
 

N8MXL

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Well this officially makes no sense. I'm out of ideas. The SWR into the 2.5k load is very low on 80m and fairly low on 20m, almost to the point of being acceptable if it happened with a real antenna. Everywhere else it's moderate to high.
 

belvdr

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Well this officially makes no sense. I'm out of ideas. The SWR into the 2.5k load is very low on 80m and fairly low on 20m, almost to the point of being acceptable if it happened with a real antenna. Everywhere else it's moderate to high.
Bad coax maybe?
 

N8MXL

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Bad coax maybe?
I don't think so. The same coax works fine into a 50 ohm load. It's only when the unun is attached that it acts up.

That said, just to be certain, this is the procedure I used to attached the connectors to the coax: Installing Connectors the Right Way

My connectors are slightly different from the ones they used, but have the same basic components:
IMG_6336.jpg

Is that the best way to go about it for someone who doesn't have the tool mentioned earlier? I'm still unclear how the braid makes good contact to the connector housing.
 
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MUTNAV

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I attached the connectors the easy way: strip the insulation, fold the braid back over the collar, solder the pin to the center conductor, and screw it together. I was a little concerned that the braid wouldn't make good contact, but everything seems to be working in that regard with the 50 ohm load. When I'm more experienced I'll probably try the more advanced method.

At this point I think we've ruled out the connectors, the cores, and the wiring. Here are pictures of the original transformer that started all this. Now that it's out of the box maybe something screwy is visible that wasn't before.
View attachment 131624View attachment 131625View attachment 131626View attachment 131627
are those wires coated with some enamal or something, and nothing is worn off, I don't know if it would effect anything.

Thanks
Joel
 

MUTNAV

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I don't think so. The same coax works fine into a 50 ohm load. It's only when the unun is attached that it acts up.

That said, just to be certain, this is the procedure I used to attached the connectors to the coax: Installing Connectors the Right Way

My connectors are slightly different from the ones they used, but have the same basic components:
View attachment 131653

Is that the best way to go about it for someone who doesn't have the tool mentioned earlier? I'm still unclear how the braid makes good contact to the connector housing.
after combing out the braid, and moving it over the "clamp", it'll make great contact when you screw it down. make sure you slide the approriate items over the cable BEFORE you cut it.

The only other thing I can suggest is that when screwing the whole thing down, just turn the nut part, not the connector part.

They're sometimes (frequently) a little different from each other, the following instructions might help, hopefully the connector came with instructions.
 

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N8MXL

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are those wires coated with some enamal or something, and nothing is worn off, I don't know if it would effect anything.

Thanks
Joel
They are enamel coated. Given how hard it was to strip the ends for soldering I don't think anything wore off where it shouldn't. If part of the coating did wear off the core isn't conductive anyway.
 

N8MXL

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after combing out the braid, and moving it over the "clamp", it'll make great contact when you screw it down. make sure you slide the approriate items over the cable BEFORE you cut it.

The only other thing I can suggest is that when screwing the whole thing down, just turn the nut part, not the connector part.

They're sometimes (frequently) a little different from each other, the following instructions might help, hopefully the connector came with instructions.
They didn't include instructions (bought a bulk pack), but what you sent is what I did. All the connectors feel firmly in place and the multimeter shows good connectivity end-to-end with no shorts. It looks like we can rule out bad cabling, which in a way is disappointing as it means I'm back to having no idea what's messing things up.

Maybe it's time for me to bite the bullet and spend the money for an analyzer so I can see more precisely what's going on. Fifty dollars for a NanoVNA H, or even $80 for an H4, isn't going to bankrupt me.
 
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