Does SWR Matter on my Receive-Only Antenna? (
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- Опубліковано 15 кві 2021
- Frank Wilson, KJ7LAN, asks if SWR matters for his receive-only antenna. We explore this a bit, looking at different options.
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Dave, I think you may have missed the boat on this question. A mismatched antenna is unlikely to damage a receiver. BUT, a resonate and impedance matched antenna is going to perform better. That said, how much better is dependent on a slew of variables. In general, a larger and higher antenna is likely to yield better results, especially at HF/SW frequencies.
As a teenager in the early 1970s, I used a few feet wire between the curtain rod in my bedroom and my 5-tube Heathkit SW receiver. I listened to stations from all over the world including the VOA from Rome, Italy. I also ran a wire into and across the attic and saw little difference.
yeah exactly NOT FOR TRANSMITTING JUST RECEIVING.. any antenna will not damage a radio just receiving, BUT a properly tuned antenna will work best FOR RECEPTION! and to properly tune an antenna you use an swr meter! Heck I use my matcher and wait for a signal and once a signal comes i can tune it to make the signal go higher to get into the ballpark (dont need a transmitter)
I can absolutely see a huge difference on my waterfall with tuned versus untuned when listening. I recently got an external tuner, and when I first hooked it up I thought something was wrong because I was seeing almost nothing on the waterfall (before ever pushing the tune button for the first time). Once I tuned I could then see a huge difference in audio (and hear of course). This was with a Flex 6400-M and a Palstar HF-Auto.
Dave, you are off on this one. Maximum signal transfer occurs when the impedance looking down the line is a conjugate complex impedance to the impedance looking towards the antenna. If the antenna (load) is purely resistive, this just means that the two resistive components are equal. If there is a reactive component (say capacitive), then an inductance will cancel it (hence the complex conjugate of the impedance as the imaginary signs of capacitive and inductive loads are opposite signs). Also, an antenna matching network (tuner is a misnomer) does not "fix" the problem by reflecting the power back towards the antenna. It simply provides the aforementioned conjugate match so 100% of the power goes forward. The proof is that you will hear louder signals in RX, and the remote station will hear your station louder proportionally to the quality of the match.
The catch is that the receiver is a high impedance input. It cares about voltage, not power. In that sense SWR matters in VHF and above, but the receiver SWR is meant to be high. Below VHF the receiver gain should compensate for funky receive antennas. If you can hear noise with the volume turned up all is well.
Maybe it has changed (I doubt it) but when I was in avionics in the '70s the industry standard for measuring receiver sensitivity was the "hard microvolt." The theory was that the high rx impedance caused a near doubling of received signal level so the sensitivity had to be measured with a 6 dB pad at the receiver input. That made zero sense to me but it was the standard. I haven't seen it anywhere else and it seems nobody outside avionics has heard of it. Huh.
@@flagmichael it should be into 50 ohms, because of the impedance of the coax, maximum energy will be transferred if they match.
@@kq6up There is no coax - it's random wire. Therefore only resonant on the actual received frequency (which is never).
@@rickvia8435 the random wire needs a transmission line to the transceiver, and in most cases today will be coax.
@@nojiratzlaff4388 Did you make it to Cheyenne this year? Anyway, a random wire terminated directly on the receiver will work best if it is 1/2 wavelength and the receiver has a high impedance input. However, my ICOM 7300 has a series of bandpass filters on receive (and transmit) and if the impedance is not 50 ohms the bandpass filters will likely react to the reactive components of a non-resonant, non-50 ohm antenna. Not a big deal for receiving but could end up very sensitive to noise instead of signal.
I just built a vertical 102" dipole waiting on my swr meter to come in running a cobra 19 ultra as a base station, thank you for your videos very helpful I'm picking up fellas 35 linear miles away
Great explanation and example to a excellent question... thank you !
Good explanation of the differences between tubes, transistors, and FETs and their requirements in receiver front-ends.
One interesting point -- a lot of RX SDRs are built on quadrature sampling detectors (aka Tayloe detectors), where the preamp stage after the sampling caps is configured for feedback. The gain of this preamp stage will be seriously affected by the characteristic impedance of the antenna. E.g., say your antenna impedance is 4x the expected 50R. The feedback ratio will change, reducing the gain by 4x. That's a 13dB drop in system gain, and two S-points in sensitivity loss.
Using an antenna tuner with a receiver has the big advantage of rejecting out-of-band noise and large signals that may cause cross modulation in the receiver's mixer. The disadvantage is that it will also have in-band loss that will attenuate the wanted signals. The real question is: will the net effect of using the tuner be better or worse than direct connection to the antenna?
Thank you! Better answer than having the math explained.
With l match won't be any loses. T tuner can bring them, if tuned in a wrong way. Also with l match if tuned, it's tuned.
Dave, I think you may have interpreted the question to be one of equipment safety, and it may have been. However, I think that Frank's question is more than likely related to signal readability.
Since HF is usually limited by band noise, especially on the lower bands, additional SWR loss in the transmission line can often be disregarded, in a receive only system, since it attenuates both the signal and the band noise equally, leaving the signal to noise ratio about the same at the radio.
Noise generated in a modern radio is usually insignificant compared to the signal degradation from band noise. It's just a matter of turning up the volume and knowing that the S-meter isn't doing the signal justice.
For SWL I've used an MFJ tuner connected to a random wire antenna to "preselect" signals on the receiver. It will raise the signal in a way that otherwise wouldn't be.
Thank you for the hint!
Thank you Dave....I learn more and more every day!
I’ve had this exact same question on my mind for a long time thanks Dave
Hi Dave,
I wonder what your thoughts are regarding an antenna that is tightly resonant to a particular receive frequency and its effect, if any, on helping reduce common mode noise. I am sure that most people have experienced noise, especially in the lower parts of the HF band. I feel that many wire antennas, such as the DX Commander, are poorly coupled to the receiver, which allows noise to mix with the receive signals through the antenna path, including the coax to some extent.
I am thinking of experimenting with building a tightly tuned, high-impedance receive antenna that can be made tunable. I would be interested in your thoughts.
Regards,
John M0XFX
I always pre-tune my antenna for a peak receive before I transmitted to tune, this always got it close to the final setting. This tells me that tuning for receive does help. Doesn't a noise bridge kind of work to show this?
In this last times I have the crush for 6mt and up bands of VHF. Till now I used a piece of wire and I listen few signals in my near place and few radio bridge. The problem is that radio receive much ghost signals from the FM Broadcast and other qrm that with a dedicated and resonant antenne will not receive. I bought a discone antenna and even installed low it goes quite well
Hi Dave ... i belive what you conclude is no need for tuning RX only antennas ? If i look at gain and noise circles from an LNA (technology independend) i think you will agree tuning is important, like if the source loading impedance for your LNA is picked to be in a spot where gain is low and noise is high ,,, then your LNA performance will be reduced ... right ? Thanks Niels OZ1CGQ
An Antenna Tuner is a matching device. As such it will provide a 50 Ohm load or match to the Transceiver. On the other side of the transmatch where the antenna coax connects, the tuner will give a conjugate match. In other words, the impedance looking from the antenna is going to be a match for the coax impedance +/- whatever inductive or capacitive reactance to counter the effect of the combination of the the antenna [mismatch] and the length of coax. Does the Antenna Tuner absorb some power that is reflected back from the antenna? I think not.
Good explanation.
But - different issue - wouldn't the voltage out of an antenna depend, in part, on how suitable the antenna is to the wavelength of the signal of interest? If I use a 6" vertical antenna (as might come with a cheap SDR dongle) would its output will be close to nill at, say, 160M? Or, so long as the antenna is aligned with the signal's electric vector, will I still get a usable output?
In VHF and above, yes. We want the best coupling of signal to our receiver. In HF and below atmospheric noise is the limitation on reception so the signal level is not that much of a concern. As long as you hear noise between signals (at HF) you have all the antenna you need. One detail we don't hear much about any more: at HF and below it is desirable not to get the antenna too high in order to keep the S/N up. Or so "they" say... I never played with it.
@@flagmichael More height is almost always better BUT introduces lobes as you change height above ground (and the composition of the ground). The coax leading from the antenna is also part of the antenna unless you choke it off and without the choke, the coax can pick up nearby electrical interference.
I am n0spw
I have noticed using my ft991a as a shortwave listener radio on HF because I'm only a tech no code I cannot transmit on let's say 160 but thank you built in antenna tuner I can tune the antenna and have better ears versus not worrying about tuning the antenna at least that's what I've figured out and thank you for your little video I enjoy them
Great video. could a high SWR like 3 to 1 damage, the front end of a short, wave receiver, or SDR receiver?
No. SWR only matters on transmit. An atu will match the aerial to the receiver and get the most signal from the aerial.
G4GHB
so its basically i dont have to worry what swr the antenna on my pl 880 shortwave radio nor buy a wire antenna with a balun attached?
About 8 years ago upon physical experiment of my own, I would say "Yes." If nothing else, get an antenna analyzer and "tune" it to the frequency/band that you want to listen to.
A good explanation. Thanks.
I think question was about SWR checked by antenna analyzer and tried woth SDR. In this case we simulate transmitter's work, in fact, rf power goes in opposite direction, from antenna to receiver.
This question appears, because sometimes, antenna tuner can tune SWR to minimum level(for transmitter), but for receiving it will be not optimal. This especially visible on cheap Chinese hand tuners: where they can tune to 1.01 SWR, but hits SWR is only for tuner, to antenna it will not transfer full power...
Another well produced & informative presentation.
An atu helps a lot in matching the aerial to the receiver, I found that out in my early short wave listening days.
For receive it's cheap to make, a coil with tapped turns and two transistor receiver type variable capacitors in a Pi configuration works well.
G4GHB
Ive seen only plastic boxes used for 9 to 1 Un un.....why can't I use a metal bell box if I insulate the end fed wire connection???? I would also insulate the wound ferrite core from touching too...would this cause other problems,,or would it actually help with the external RF affecting the input of the radio?????thank you K3RJW...,73
The 9:1 secondary winding is quite high impedance (~450 ohm). Unless the windings are kept far from the grounded metal covers, the extra capacitance added to the transformer windings will make the un-un's performance unpredictable.
Regardless of what sort of device is in the front-end of the receiver, if the input to that device has been designed to match 50 Ohms, then the antenna will perform best when the antenna impedance as seen at the receiver's input is at 50 Ohms on the received frequency. Unless you have an antenna that is 50 Ohms at all frequencies, then a tuner will help.
A lot of the time the impedances may be close enough for there to be no noticeable difference with a tuner peaked up or without one, and receivers have a huge dynamic range of usable input signals, so if you have a -50 dBm signal coming in, and you lose 3 dB to a mismatch the AGC takes care of that and you won't notice the loss. But, especially when working weak signals, or when listening on a band the antenna is not designed to receive on, so the SWR is very high, an antenna tuner will make a noticeable improvement in S-meter readings and readability. Because of the many strong signals on the radio bands and the dynamic of signals that a typical receiver can satisfactorily receive, most hams won't be affected by a mismatch problem until they are trying to copy a very weak signal. But those are usually the most interesting stations, and a good, low loss, properly tuned antenna tuner will indeed help pull them in.
Although the input impedance of a transistor based amplifier is much greater than that of an antenna, as is correctly said, the input is normally terminated to 50 Ohms with a resistor to ground (or virtual ground) close to the socket. For example on the RSP1A that you mention, the SMA input is 50Ohm terminated and the HiZ input on other RSP models is 1k terminated. The explanation that I have always reasoned for why the RX does not need to be SWR matched is solely because there are not large amounts of RFpower being reflected back into the circuitry to cause damage on a receiver (as is mentioned in the video), and normally the loss of a few dBs due to mismatch can be compensated for with a bit more RX RF gain - assuming that RX is not on the limit of acceptable SNR, in which case the loss in RF signal is problematic and SWR tuning is beneficial.
I look at it this way: if the present SWR causes energy being reflected back to the radio in TX, it will also reflect energy (EM waves picked up by the antenna) going the wrong way ('away' from the radio) in RX. It makes sense since a bad SWR is caused by an impedance mismatch between the antenna system (antenna + feed line) and the radio. This mismatch will occur in both TX and RX because all impedances remain the same. The only difference is the radio cannot be damaged in RX mode. There is a simple experiment you can do if you have a manual tuner: put your radio into RX without any squelch and start dialing the knobs on the tuner. You will hear volume going up and down significantly (highest volume would be best SWR usually). Or if you have an SDR with a scope you will be able to see it as well.
I'm not sure that's entirely correct as I get better reception if I manually tune my SDR Transceiver (remote tuner at feed point). Now I'm using a non resonate vertical about 23 ft high(flagpole). This is true with HF radios as old as my old Icom 735 and up to my Flex 6400. I know this is an age old controversy that's been around for a long time but it's always worked for me. Thanks, M Evans K7URA
Is using 1/2 inch or 3/4 inch Hard Line Coax better on HF bands? as I know its great on VHF & UHF bands.
Save your money and use LMR 240 or 400 for HF...
Yea, respectfully... I'd have to say this one video is a bit off. Still love and appreciate your content Dave.
Thanks Dave, as a radio listener only that’s very helpful.
I just need to find out the input stage for my radio now.
Just tune the antenna to resonance (cut to proper length) and use a low loss coax matching your receiver. That's all there is to it, no need for fancy equipment to measure SWR of some sort. SWR only matters on transmit where reflected power will fry some RF semiconductors. But for receivers, there's no reflected power to fry component. The only thing that will damage a receiver is the static build-up in the antenna if it reaches the FET preamplifier stage of the receiver, but can be remedied with a protective back-to-back diode known as "diode clipper distortion" which also protects the front end from signal overload. By way of note, even your body can act as an antenna when you hold the antenna terminal of the receiver without causing any damage.
Dave I've spent 30 minutes here trying to leave you a message. If I quit talking the phone quits writing and so I'll try to get to the point here and keep it going. I would ask you to please include more VHF and UHF information on their antennas and scenarios. Because there's just about no one that does videos on UHF and VHF antenna work, and you were able to include a little more information for some of us that are watching the video hoping to glean information on our topic being it won't come up on a search regardless of keywords how about the hams wouldn't mind the extra information especially considering their in VHF and 4hf to aren't they. Dave my scenario today is a repeater 2 1/2 mi out of town 100 ft higher elevation but just inches off the side of a airport airplane hangar roof. I'm trying to put something up that doesn't command attention and complaints. I am going with the Larson base station antenna for transmit at 467.625 I want to play the receiver antenna about 25 ft away either in the middle of the hangar roof or off the end of the building like the transmit, but I don't want this one to be noticed much. I've looked at the scenario you mentioned about going 3/4 wavelengths longer and using that for receive but what do you think's best for me considering I could stick a whip up in the air as much as 64 inches without a coil on it and I can paint it sky colored somewhat I'm pretty sure a quarter wave sitting on a 12-inch plate would be good but do you think that would receive a 1 watt HT inside of a home not particularly held vertically or by a window?
The airport is 100 FT elevation higher than the town but the antenna cannot be much more than a foot higher than the roof and there are other structures in between though just one large building that's taller. Thank you Dave great to talk to you finally.
Maximum energy is always transfered from source to load when the two are matched, regardless if the receiver's input impedance is high or low. This principal applies to every thing in nature.
lololol
Yet the rule for receivers is high input impedance to increase the voltage at the receiver. Beyond that the theory makes my eyes glaze over but I'm assured that is how it works.
My favourite part is at 2:39 lol!!!
1$ tablet and stylus combo :D when low tech is all you need... genius!
Quick answer then, No. The receive system G/T (Figure of Merit) is a function of antenna gain, feeder loss, receiver gain and Noise Figure (lowest is likely NOT 50 Ohms, looking in). NB: At the desired Freq.
At the receiver end, it is not the power but the S/N which is important. If you have a lot of local QRM, then having a matched antenna will give better S/N, but if the antenna is also picking up that QRM, then you are out of luck. In very "quite" place a 10 db loss at the antenna input will be noticible on the S meter but there will hardly be any difference in S/N at speaker.... VU2INL
if you look at schematic of elecraft K144XV front end ATF34143 FET, tuned tank circuit at gate of the FET, which connect to antenna with 5.6pF in series. that's it. such high impedance input, impedance of antenna does not effect that much.
So maybe an actual demonstration with the reference Icom 7300 should be in order. I've seen at least two other ham radio YT channels demonstrate getting good signals across an entire specific band with the 7300 and then they change to a different band and get ZERO signals until they press the Tune button on the 7300. After pressing the Tune button the waterfall display on the new band lights up like a Christmas tree. I've also seen other channels that seem to match your comments. How do you rationalize and explain those real world examples?
It depends on the frequency band. Below VHF (roughly) atmospheric noise is the limiting factor for receivers. Tuning the antenna brings up signal and noise but does not improve SNR. Starting around 20 meters receiver sensitivity (and antenna output) become more important, so that at upper VHF it is crucial.
Before I retired from a large electric utility I was the Power Line Carrier guru (my HF ham days helped a bunch with that!) LF signals using FSK - usually on the low side of 100 KHz - were exchanged with the next 500KV substation 200 miles away. Received signal was an indication of system health but was also critical to proper levels in the logic input. The noise issue was nil in good conditions, but rain (or worse yet, snow) falling on the lines produced wideband "tribo" noise that often put the receiver into alarm. RF makes its own rules.
In the end, it is always a question of SNR in any receiver. Gain is cheap, quiet is not.
Thanks David, mostly well understood (by me). Tomorrow (4/17) I take my Tech and General test (at age 78, finally getting a-round-2-it). Quick question, by "tuner" do you mean a variable cap or an LC network of some kind?
Good luck!
Tuners have a means to correct both impedance and resonance issues. Back in my day the usual form was a fixed inductor (with taps for the band selection) and a pair of variable capacitors in a "pi" configuration, so called because the schematic looks vaguely like a "pi" symbol. I don't know anything more recent than 1970 in the ham world!
I use SDR Play (clone) and a random wire antenna (5+5 meters in dipole configuration). I have put a 250p variable capacitor in series with the antenna, and can clearly see a huge blob of noise moving around the spectrum when I turn it around (zoom out to see 10Mhz at once for best demonstration). This also rises SNR for some very weak signals making the difference between them being heard or not. When I attach NanoVNA to the antenna system, the capacitor settings that create those noise blobs match the very low SWR dips (less than 1:1.5 in 5-7 Mhz range).
So while true that the difference between SWR mismatch on transmit (blows up your radio) and on receive (getting a little less signal) is obvious, I wouldn't underestimate its effect while trying to receive weak signals in a high noise environment.
73 de YU4HAK
I did some experiments earlier today. Simple set-up with two receivers, an ancient Codar CR-70A, the other the receive side of my Alinco-70, plus an L-match and about 100 ft of wire at about 20ft, and a good earth. I selected two bands only (7MHz and 14MHz). I left the controls on the receivers alone, except for the main tuning and just tuned the L-match. The most significant difference was in the received noise as I tuned, although I was able to peak signals. I did this out of interest before I spotted your video!
You should have mentioned it to use 75 ohm wire such as RG6 for like listening to police scanners 50 ohm coax is better for transmitting
The variable coil on the bottom of a base loaded vertical (like a wolf river coils antenna) is essentially a "tuner", right? Consider the level of receiver noise/rf which "peaks" when the coil is properly tuned for resonance.
This is also how you tune a magnetic loop antenna to near resonance during receive. You tune for peak receiver noise. It can rise quite noticeably near resonance.
I think resonance is important as we hear the signal lift. But the question was about swr and I am not sure if there is a subtle difference, yes there is no swr on a resonant antenna, but maybe swr is only relevant on Tx because of direction.
Dunno, Dave’s content was over my head in that I could not deduce the answer.
Translation - It don't matter. Hook up the best wire you can - the longer the better - longer brings in more signal.
SWR does not matter for receiving only, but a tuner will peak signals by matching the aerial to the receiver.
G4GHB
Most of the time it is hypothetical, the losses. Every extra connector loses some signal and increases SWR. Every meter of cable has the same effect. Eventually you would be better of without an external antenna and get best results with an tiny telescopic aerial (Receiving) . Spending thousands of dollar to get the SWR right, hmm? If you wanna receive signals from Alaska or ISS, yes maybe that is necessary. Suddenly A.I. shows us the best antenna design and that will shock us.
Thanks so much ! love your videos ,I am not an electronics expert by any means .
Doesn't the reflected power join the forward power in same way as with a tuner in line, obviously if under the fold back limits of radio , just that the radio wouldnt have transferred full power into the mismatch impedance unlike with a tuner in line tuning the system to resonance for maximum power transfer
Yes. The presence of SWR simply multiplies the coax loss across each reflection. If you reduce the loss, such as with a "ladder line", the presence of reflections is relatively inconsequential and will reinforce the signal.
@@thomasmaughan4798 most believe there's only one reflection and don't realise power is conserved unless attenuated bybthe feedline
Their is no swr in receive. A matched antenna compared to a random length antenna is little to no difference as long as the antenna has adequate length to gather signals, enough height to avoid obstructions and interference and good solid connections. For noise abatement a good quality balun and coax are good, as well as a short ground close to the radio.
I found that tuning my antenna while shortwave listening on my IC-7300 can greatly improve the received signal. MFJ sells a device called the MFJ-212 Matchmaker that makes this fairly easy. It can also be used to tune the antenna for transmitting without actually having to activate the IC-7300's transmitter. The device is installed between the radio and an external tuner. It is NOT designed to work with the internal tuner. It injects a pulsing noise into the radio and you then adjust the tuner until the noise is nulled out. I have recorded the tuner settings for each SW broadcast band and can now quickly peak signals when I change bands.
Swr must matter because of the difference I see in the natural noise when the antenna is properly matched. Its HUGE and I can tell the difference even by ear.
Hi Dave: I did a lot of experimenting with a tuner in line for receive antennas, but the signal was always strongest on the "bypass" setting of the tuner. So there was no point using a tuner. I do however use small gain LNA's on my receive only antennas.
Losses are bidirectional. On stronger signals it won’t make a difference. Weak signals may absolutely be affected. Don’t believe me? Get a manual tuner and start tuning while monitoring the receiver. You can easily hear the difference.
If you're worrying about the SWR of your receiving station, you may as well end it now. There's no way you could discern by ear if the SWR was up a bit, let's say 2:1 or more. The use of a tuner is likely to create a greater loss in signal. People need to stop fussing over the SWR, as most don't even understand what it is, apart from potentially blowing up sensitive transmitting equipment.
That must be a bad tuner then. It should match the aerial to the tuner and signals should increase.
G4GHB
Short answer: Yes.
Seems to me this man’s in general question could have been answered in under 100 words instead of getting a whole semesters worth of radio transmission/antenna theory.
I see Elmer.
4:01 "often there would be a little capacitive tuner to peak the antenna..."
4:15 "this is going to come through some sort of a matching thing to the base..."
From this I'm going to assume receivers circuits already have SOME compensation for antenna mismatch, and for MOST stations that will be "Good enough".
However - when chasing extremely weak stuff, where you need every trick to get away from background noise, external antenna tuners may give you give few extras dB you need.
I actually had this question. lol
As mainly a SWL, I see things a bit differently, It is handy if you can easily by-pass a tuner.
For general scanning through the bands, Looking for general listening, you leave it out of circuit or bypassed, so the tuner does not block signals due to the antenna being out of tune or tuned elsewhere.
And once you find something, or if you are looking for something specific, then you would bring the tuner into circuit to tune it and make it have a much better signal strength.
Leaving the tuner in circuit, and already tuned to some specific frequency just seems to block too much, that could normally be heard if it wasn't there.
It is tedious to tune the radio, and then tune the tuner, as you move though the dial. So, give the tuner a simple by pass switch, to make it easier, if you just listen, and do not transmit.
I like recive antenna. You can use junk wire. It dosen't care. I get out the look up chart an toss her out. A tunner helps. But not needed. When you are in the window. Good show tks de kv4li. 73
So does SWR matter or not for receiving?
yes and no. It can help, but you can likely receive without worrying about it.
Field-effect transistor has much more capacitance between gate and source, so it should be compensated, isn't correct?
It depends on the frequency band. Above about 100 MHz the receiver front end should be designed for the input device (transistor, FET, pentode...) but below that it is left to AGC to handle.
Yes it will "work" with a poor match antenna but much better performance with proper antenna. Back to the rabbit ears with tin foil😊
I think it depends. My radio was hearing everyone fine but SWR went off the scale one day triggering transmit shutdown and high SWR Alarm.
I found out later the set screw had fallen completely out of the whip.
I thought an "antenna tuner" was designed to dissipate reflected RF as heat to protect your transceiver, instead of what it is really supposed to do, which is turn reflected power back into forward power and give the antenna a "second chance" to radiate it. It's the antenna system itself that heats up in the case of a severe mismatch.
Whoa! No wonder you hear quieter background hiss if your antenna is not properly matched to the frequency a receive-only radio is tuned to. The better the match, the louder that hiss for a specific AF gain setting.
73 VE7NDE
Hmm,
BJTs are current driven? Ever heard of the Ebers-Moll model of a BJT? It is driven by the EB VOLTAGE!
Yes, I think thats correct. I think if one models a transistor using an alternative circuit, as it were, it can be demonstrated that when push comes to shove, its actually voltage driven..
@Chris Carini Ooh! ooh! This reminds me: in the 1960s Bendix made a marker beacon receiver (used for identifying locations on approach to runways). The service manual warned techs of a problem with transistors: eventually all the holes would be filled by electrons and the transistor would fail!
Sometimes I think there is more misinformation bout antennas and SWR on the internet than about politics! Thanks for the practical explanation!
👍👏👏
This is everything I hate about HAM's. They can't just answer a question. They have to dive deep into electrical engineering when the answer is a simple yes or no. If you are just scanning and listening on something like SDR or a scanner, the answer is "No". Get a tunable antenna from the start and when you are ready to transmit, get an SWR meter and tune your antenna for best results. Anything else is just radio snob gibberish.
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When I was a wee lad I used a very long wire for SWL. My neighbor who was a Ham laughed. He showed me how to make a little tuning circuit.
AND, what is your point? What happened? Did it help? Did it hurt? Did it make no difference?