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Was having a weird problem on 2 meter where the SWR reported by my analog SWR meter was around 1.1, but my transceiver was reporting 2.5-3! I tried replacing the cable with two new ones I crimped, of more or less the same length (around 2 feet), but the problem remained. :(

When I put in a pre-made 3 foot cable in, the problem went away! :/

The weirdest thing is that I crimped all of the cabling between the SWR meter and antenna, so is the length of the transceiver–SWR meter leg the issue? :(

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in reply to Neil E. Hodges

W6KME
W6KME
• •

1/2 Connectors and feed line do need to NOT be resonant partials of the frequency in use. The feed line to the antenna also should really be at least a 1/4 wavelength (pretty easy to do with 2m).

1/4 wavelength at 2m is about 19", but everything in the vicinity, connected or not, has SOME influence on resonance.

Does this mean your cables were to blame? It's possible.

in reply to W6KME

Neil E. Hodges
Neil E. Hodges
•
Even though the cables I crimped are 26" and 28" in length, I still feel like the length might be the issue here. None of the other cables I made had such a negative impact, but they were further from my transceiver on the feed line.
in reply to Neil E. Hodges

W6KME
W6KME
• •
My first exposure to the idea was from another ham who WAS an electrical engineer, mentioning that in his gigahertz world, even PC board trace lengths were critical.
This entry was edited (7 months ago)
in reply to Neil E. Hodges

W6KME
W6KME
• •

2/2 The other possibility is a poor connection in one of the crimps or soldered tips. I've found (my unscientific experience) that behavior that changes with power level is sometimes a connection issue.

This video, which becomes a favorite of all hams who see it, will help show why coax length matters. EVERY connector is an impedence change, which causes reflected energy.

https://www.youtube.com/watch?v=DovunOxlY1k&list=PLsn1h8dbrxYOmJEBVwgzurfD1VBA4RMF2&index=36&t=1s

This entry was edited (7 months ago)
in reply to W6KME

Neil E. Hodges
Neil E. Hodges
•

I did run into the power issue with another cable I made for HF a couple days back that was caused by there not being enough solder in a coax pin, but that taught me to be more careful at that part.

I don't think the SWR changed with power in this VHF case, so I feel like that might not be it here.

in reply to Neil E. Hodges

W6KME
W6KME
• •
Sorry, I should have been clearer...your SWR meter works by sending an RF signal, very low power. Then the radio transmits at a much higher level, which is what can lead to a different result. As long as you're checking the solder quality of the centers in your connectors, you're doing the right thing. I've overlooked that more than once.
in reply to W6KME

Neil E. Hodges
Neil E. Hodges
•
Thanks. I think we might be talking about two different things here. The SWR meter I'm talking about is one of these. It displays what's happening on the line rather than generating its own signal.
in reply to W6KME

Giovanni - ZL2GX
Giovanni - ZL2GX
• •

@W6KME "EVERY connector is an impedence change" -- I was under the impression that both BNC and N connectors preserve the 50 ohms characteristic impedance, unlike UHF/SO239 which don't. Thoughts ...?

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in reply to Giovanni - ZL2GX

W6KME
W6KME
• •
@gmoretti I overstated the case, based on the connectors used overwhelmingly in ham radio. Guilty.
@Giovanni - ZL2GX
Unknown parent

KF7CCC Andrew
KF7CCC Andrew
• •
@tswartz07 @gmoretti A couple of other possibilities: if the cables are *too* short, you might be below the minimum bend radius and shorting the center conductor (or almost shorting). And it's also worth checking the cable and connectors to verify no 75 ohm stuff has snuck in.
@Tom Swartz @Giovanni - ZL2GX
in reply to KF7CCC Andrew

Neil E. Hodges
Neil E. Hodges
•

In my case, the cables weren't bent because I'm using 90° connectors at each device along the line. :3 Oh, I also always check to make sure there's no continuity between the center conductor and shield right after soldering. 👍

I pretty much only have 50 ohm stuff. :P

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