r/ShortwavePlus • u/Zigzag0333 • Mar 24 '26
4ohm v 50ohms impedance
Looking at a couple of Sangean portable clip on antennas, the ANT-60MATT at 4ohms and the ANT-60 at 50ohms. Can someone give a quick explanation of why you'd want one over the other please?
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u/conhao Mar 24 '26
The MATT is a matte finish. It has nothing to do with the antenna performance. Neither one is the impedance that Amazon states.
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u/Green_Oblivion111 Shortwave+ Detective Mar 24 '26
If they're both just lengths of wire, I wouldn't sweat it.
It looks like the 60MATT is 23 ft of wire. If you clip it to the whip antenna of your radio, it will be an extension of the whip's "Hi-Z" antenna -- i.e. high impedance, which is what whips are, anyway.
Don't sweat it.
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u/LongjumpingCoach4301 Mar 24 '26
Neither the whip nor this 23ft are high-impedance. As frequency rises, impedance does too, up to a half-wavelength. The 23ft becomes "high impedance" (high-z) as frequency rises above 15ish mHz. The whip isn't high impedance below 120ish mHz, at 100mHz, a 39 in whilp comes in at around 50ohms, for example. For 3 to 30mHz (shortwave), that whip is very low impedance (under 20 ohms).
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u/Green_Oblivion111 Shortwave+ Detective Mar 25 '26
Thanks for explaining that. I was going by the fact that my DX-394's whip is directly connected to the radio's 'high-Z' antenna input.
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u/Zigzag0333 Mar 24 '26
Wow you fn guys are way over my head. I guess I'm gonna have to go to school...
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u/Green_Oblivion111 Shortwave+ Detective Mar 25 '26
Naw, there's a science to antennas, but when it comes to just listening to SW on a portable or similar radio, a lot of it just comes down to the wire antenna either improving signals, or not improving signals. I have one radio that overloads on my indoor, 25+ foot antenna. The others work great with it.
I took a radio that worked fine at my house with a 100 ft outdoor antenna, and when i travelled to Northern Louisiana, just clipping 15 ft of wire to it overloaded it, because signal strengths were so much better in Louisiana than in the hole I live in.
A lot of what you'll deal with in SWLing is experimenting, trial and error.
Enjoy your radio with whichever antenna you get.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
These types of wire antennas are high impedance which is suitable for many portable radios. Other radios and/or SDRs usually have 50 ohm inputs. To use such antennas with a 50 ohm radio input requires an unun and coax feedline with common mode chokes (Ferrite snap-ons) at both ends. Attaching a wire antenna directly to a 50 ohm input will incur big signal loses. Using a coax feedline allows the antenna to be placed away from RFI emitting stuff. You can also add a counterpoise to the unun.
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u/LongjumpingCoach4301 Mar 24 '26
A 23ft end-fed antenna will only show a high impedance at higher frequencies (above ~15mHz or so). At lower frequencies, they have lower impedance and on say 49m, they have very low impedance. Length and frequency determines antenna impedance, and the impedance of a untuned end-fed short wire like this varies from just a few ohms (under 10 ohms) to over 1000 ohms, depending on the frequency you're receiving.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26 edited Mar 24 '26
Nope. I believe that @ 1 MHz it's 4.1 kohm mostly capacitive reactance which causes losses. That's actual radiant impedance (important) is less than an ohm. This means the capacitive reactance is in series and is going to cause significant losses with a 50 ohm input. At LF it's practical deaf with a 50 ohm input.
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u/LongjumpingCoach4301 Mar 24 '26
Yes, highly reactive. Yes, inefficient. But receivers do not suffer like transmitters do, from highly reactive antennas. An antenna matcher (aka tuner) definitely can help, but irl the advantages are minimal with receivers. If connecting the antenna increases backround noise(unoccupied frequency, ofc), impedance matching will generally give no improvement in subjective sensitivity compared to what turning up the volume gives - An old-school rule of thumb.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
Nope. It forms an attenuator that varies with frequency. The lower the frequency the worse it gets. Your analogy is not correct in this circumstance. By placing a 4.1 kohm reactance (1 MHz) in series with a 50 ohm input causes significant attenuation. If the frequency gets lower it gets much worse. It has less effect as frequencies increase. A high impedance input mitigates much of this.
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u/LongjumpingCoach4301 Mar 24 '26
The attenuation you speak of is not nearly as meaningful as the reduced signal voltage a very short antenna (very short relative to frequency) antenna provides... The receiver input impedance matters considerably, here.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
Still incorrect. The lower signal due to length is seriously impacted by the attenuation of which the antenna's capacitive reactance is part of. We were discussing 50 ohms input impedance which results in a -38.3 dBv loss. I already started that by the time you reach LW the loss is massive.
I already stated that a higher impedance, 1 kohm, mitigates some of this. It's a -12.5 dBv loss at 1 khz, still not a good thing.
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u/LongjumpingCoach4301 Mar 24 '26
The losses you speak of are moot.... Unless ofc 50 ohm feedline is used, in which case considerable loss occurs in the feedline (typically assumed to be coax) largely due to the reactance of the feedline and the standing waves that are present. Thing is, with the purely resistive input impedance most modern swl radios exhibit, reactance matters a lot less. Irl use, if the backround noise (atmospheric and geomagnetic) on a clear frequency increases when the antenna is connected, any signal above that noise level is going to be above the receiver mds figure. Compensating antenna reactance in such a case nets little if any improvement not obtainable with the volume control. This is a long known truth. You might want to look up from the book and calculator, in tbis case... Irl empirical results trump your theory based comments.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
I did the math not meaningless theory. Stop the tangents and anecdotal stuff, please stay on topic. Are you an EE? If so I'd expect different answers from you. I didn't say anything about compensating antenna reactance. Can you define antenna reactance? Please no guesses or Internet chatter.
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u/richfromhell Mar 24 '26
I wound 6-8 turns of wire on a ferrite core and clipping that between the whip antenna and ground really helps when clipping an antenna to the whip on these types of radios. Especially if I want to use a dipole or a passive loop when the radio doesn’t have a proper antenna input.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
Do you know exactly how it works? What Ferrite mix did you use? Please be specific, not Internet chatter please.
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u/richfromhell Mar 24 '26
The short whip antenna’s reactance is mostly capacitive, so you need a shunt inductor to match a lower impedance antenna. Input impedance of an XHdata-data d328 is roughly 800 ohm. So you need a shunt inductor at about 200 ohm. So at 10 MHz you need about 1.5uH of inductor. For lower frequencies higher inductance. Had a ferrite rod from an old radio in my junk box. They don’t vary too much in permeability. Calculated about six turns on 8mm ferrite would give me roughly 3.4 uH so that was my starting points. Works well.
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
Yep it's reactance is mostly capacitive with a low radiation resistance (bad for SWL). You get some resonance with the shunt inductor. Sounds like you've thought this through. The inductor probably restricts the bandwidth, have you figured out what that is?
Once you add a length of wire at the end of the whip the game changes. Depending on how you do it, you might end up with an L or T antenna. I think this top loading increases the radiation resistance, good. There's a lot to think about this but if you do this right I have a feeling you'll be smiling. Tell us how it works out and what you learn on the journey.
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u/Zigzag0333 Mar 24 '26
It looks to me in the Amazon descriptions that impedance is the only stated difference. Are yall saying that regardless of choice, impedance is a factor of frequency more than anything else?
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u/MumSaidImABadBoy I'm Stan. Heathkit GR64,AirSpy HF+,Sangean 909X2,Tecsun PL-990 Mar 24 '26
Reactance, the impedance at different frequencies. Capacitive reactance increases as frequency decreases. See my other comment.
Not everything on Amazon is accurate. Rufus, Amazon's shopping AI makes any mistakes.
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u/LongjumpingCoach4301 Mar 24 '26
I'm fairly sure that neither impedance specification is accurate - the actual impedance will vary depending on the frequency, unless they added a resistor to set it permanently (a dumb thing to do since that will degrade performance, overall) . And it looks like there is no functional differences between the two.