Valve Radio Vs Solid State Radio

"roughplanet"
** Must be low orbit, ham radio satellites - the usual commercial ones are all geo-stationery.
I guess you would get about +/- 50 ppm frequency shift or about +/- 7 kHz in 144 MHz, worst case.
BTW
Those two "radios" are Icom wide range jobs.
........... Phil
Reply to
Phil Allison
Loading thread data ...
filter"
latest
station's
hangs on
kludge,
design a
the
& I
Why is there Doppler shift with FM satellite reception? Are you talking about satellites that move?
Reply to
Ayn Marx
Yes.
ruff
Reply to
roughplanet
Hello Patrick,
Not really. I have a 6kHz filter in mine. Then you can tune it "to the side" and get excellent sound. Of course, you'll have to have a good speaker or even an amp connected.
Also, you can design your own filter. Most of them feature four or more selectable filter sockets so there is usually a free one to have at it.
But the best is SSB reception of AM stations with a 6kHz filter. That runs circles around any regular radio.
Don't know but I bet it can't suppress and replace the carrier in bad fading situation, like my comm receiver can.
Regards, Joerg
formatting link
Reply to
Joerg
Hello Phil,
Yes, I see what you mean. But you would notice that because there would be a "hysteresis" in frequency, you'd have to get closer to the station frequency for it it pop in versus where you lost it.
I never use AFC. In radios where it can't be disabled I usually go in there and do a little surgery.
Not if you want to listen to a weak station next to a strong one. A high IP front end and a good crystal filter is the ticket here. My old Kenwood did great but anything after that was, well, close to junk in performance.
No, I don't use AFC.
Little cost but often at the expense of not being able to listen to a weak station on the next frequency.
This is one of those. But the lack of a reasonable IF filter does it in.
Regards, Joerg
formatting link
Reply to
Joerg
Hello Ruff,
Agree. But that is an application where you don't compensate for sloppy engineering but for something that is happening because of the laws of physics, where there is nothing other than an AFC that would fix it.
Regards, Joerg
formatting link
Reply to
Joerg
"Joerg" Phil Allison
** That is correct. One receiver I saw ( Goodmans 110 from the late 1970s ) allowed you to move the dial pointer half way along the band before the AFC finally let go and the frequency snapped back to match to pointer !!!!!
** A very rare thing for anyone living in a major Australian city.
I understand Yanks are far more keen on that hobby activity.
** Errr, IP = "intercept point" ??
Short for: "third order, intercept point" ??
Jargon I can handle, but abbreviated acronyms for jargon is bit much.
** Shame how that contradicts your comment above.
** I see you like to ignore facts and post red-herrings.
( Nearly all radios have AFC disable switches )
** I just checked my hi-fi FM tuner ( digital tuning) and found that with a strong signal I can offset the frequency by +/- 200 kHz before the signal deteriorates to a garbled noise.
This suggests that the IF filter is 400 kHz wide at the -60 dB points.
The IF filter for a hi-fi tuner is likely to be about 200 kHz wide at he -3dB points.
I reckon that is OK performance.
.............. Phil
Reply to
Phil Allison
Most comm radios I have repaired have lousy AM, but quite reasonable FM.
I am not a radio expert.
Most folks wouldn't know about this, and not want to get a comm radio for the lounge.
6 kHz isn't a great deal of bw.
Of course not.
The original poster wanted good local reception i thought, and for that an AM radio doesn't have to have the complexity of a comm set, especially if tubes are to be used. There is the synchrodyne type of circuit, which can be done with a chip, but I have not seen an easy to make tomorrow kit.
Patrick Turner.
Reply to
Patrick Turner
AFC isn't normally needed in a well built tube AM tuner, especially if they have a temp compensated C in the oscillator circuit.
In FM sets with all tube tuners and ratio detectors, AFC is easy with the detector DC applied to a 1/2 twin triode at the input to make a reactance tube, thus a small DC offset change prevents the oscillator from drifting much, because little C change is needed to tune a large F change at 100MHz.
Most old AM/FM receivers did not have and did not need crystal filters for local stations.
Tube sets drift a bit without AFC.
Patrick Turner.
Reply to
Patrick Turner
Hello Patrick,
The ones I dealt with never had FM. The pro-receivers are usually 10kHz to 30MHz. I did see some that went all the way to a GHz but I wasn't too impressed.
It's usually their wives who'd object to that ;-)
For one sideband it's plenty. In the US stations must not emit anything past their slot which is 9kHz wide. In other countries it is 10kHz but that also won't allow more than 5kHz audio BW. Else the radio authorities would come out and shut the place down.
Kits aren't around much anymore these days, at least not in the US. For good local AM I'd still vote for the tube set. Plus, a glass of Merlot just looks nicer in front of that versus some plastic transistor thingie.
Regards, Joerg
formatting link
Reply to
Joerg
Hello Phil,
Oh man, I haven't seen AFC this bad.
They are actually not too far away but we have some interesting stations that are low power (the ones that play the real blue grass country stuff...). So their signal might be 60dB or more below the mainstream stations. Unless you live right in the city, which we don't.
Sorry. Yes, I meant 3rd oder IP.
Huh? I hope I didn't leave the impression that I advocate AFC. To me it is and always was a kludge. The guys that designed the tube sets somehow were able to come up with a stable oscillator, despite the intense temp changes in these sets. But that doesn't surprise me. Once when I mentioned the tempco of a cap in a meeting all the young engineers looked at me with wrinkled foreheads.
I have seen (and repaired) a lot that didn't. The one I had went under the knife and after that it no longer featured an AFC.
Heck, I even repaired a TV set once that had an "automatic station finder" that used the AFC principle. No disable switch. It was terrible. You watch a nice old movie, an airplane flies through the path and the set whooshes to some moronic show on the next channel.
200kHz at 3dB is a bit wide but ok. 400kHz at 60dB would be quite stunning. They must have had good engineers (or a decent enough cost-of-goods budget). Are you sure it's 60dB down there? That would be highly unusual for an FM tuner unless it is in the >$1000 class.
Most of them I measured wouldn't reach -60dB anywhere.
Regards, Joerg
formatting link
Reply to
Joerg
Hello Patrick,
Not much though if their designers were clever and had enough budget. They used variable caps with dissimilar metals in them that compensated for temperatur expansion. These old engineers also knew how to gauge the drift of an inductor and compensate for that with capacitor tempco.
Seriously, I have met young engineers who didn't even know that capacitors had a temperature coefficient.
The best radio I ever saw was an old (tubed) Drake short wave receiver whose oscillator barely drifted 100Hz. It doesn't have to be this good but there should be no problem keeping an FM tuner to within a few kHz without an AFC.
Regards, Joerg
formatting link
Reply to
Joerg
Here the appear to allow 9 kHz of AF bw. Oz is a big place, and its easier to spread out all the stations.
I couldn't find an AM radio quite good enough for me so I made my own. I first tried a synchrodyne using tubes, but I couldn't get the diode ring demodulator tranny to work, and then when i tried a self oscillationg 6BE6 mixer tube for the AF I still got poor selectivity and other problems. Afaiac, superhets are king.
Patrick Turner.
Reply to
Patrick Turner
AM sets below 1,600 kHz don't drift much with a tempco cap in series with the oscilator tuning gang section.
But the FM sets drift a bit, but the AFC using detector DC applied to a triode to vary C on the oscillator LC tank works very well and once tuned a set won't drift. Set up right, it can run without a disable switch as it is in my set, and once one of two tuning meters indicates strongest limiting and the other
indicates 0VDC as a centre reading for the ratio detector, the set would stay tuned for years if left on.
The point of using FM is that tuning does not have to be spot on, and few kHz off the station F doesn't matter.
Patrick Turner.
Reply to
Patrick Turner
As I said before, check out the Tivoli Audio range of am/fm radios
Steve
Reply to
Steve Batt
The manuals on line for the Tivoli Audio AM/FM radios don't include the AF response data.
So I will assume the products are junk.
Ain't it grand the way idiots advertise their products, but they don't tell you what you could expect.
Patrick Turner.
Reply to
Patrick Turner
Remember Patrick that assume made an ass out of u and me.
I have one of these table radios and they certainly do not sound 'junk', have a listen before you pass comment.
Steve
Reply to
Steve Batt
To escape from what I am left to assume, what is the measured AF bw for the AM radio?
Patrick Turner.
Reply to
Patrick Turner
You know, I cannot answer that question I am at least going on what my ears tell me not what is not told to me by the manufacturers. As I said above 'have a listen'
Reply to
Steve Batt
One day I might.
Too busy right now to farnarkle around with AM radios.
Patrick Turner.
Reply to
Patrick Turner

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.