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Author Topic: How to tune a particular frequency with homebrew, non-calibrated tuners?  (Read 2560 times)
KX4QP
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Posts: 289




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« Reply #30 on: February 03, 2019, 03:49:44 PM »

Apparently (based on the reviews here on eHam) there's considerable difference of opinion on how good or bad the S-120 is -- I suspect that has a lot to do with condition.  I've had mine for a few hours now; verified with my multimeter that there is no connection from either cord conductor to the chassis (at least when powered down -- hard to test with power on), and based on condition took a chance and powered it up.

I haven't opened the case yet, but I'm going to bet someone has replaced the critical capacitors already; I've got a pretty dirty 60 Hz hum across the AMBC band but a strong station will cover it (it's completely inaudible when I tune WKTE 1090, which has its tower a few miles away on a mountain top); I suspect it's from aquarium pumps, wavemakers, and fluorescent lights in the next room from my designated shack.  With the internal loopstick I was able to pick up three local stations, even inside the Faraday cage I call home, and attaching the telescoping whip antenna (about 1 m long) found me pulling in a few stations in every SW band -- one that I believe was from Spain, CHU frequency/time broadcast from Ottawa, a number of other Spanish-language stations, and what I believe were pirate stations broadcasting music in (or just outside) the 15 m amateur band.

I was disappointed to be unable to hear WWV again before it goes off the air, but I'm fairly sure that's because it's in Colorado, more than twice as far as with a range of mountain between compared to Ottawa.  If I can get an outdoor antenna up, I'm confident I'll be able to hear it; CHU was clear enough to copy the time announcements easily with the limited antenna I have.

A short break after that first tune-through, and I went back and was able to tune a pair of overlapping or very closely spaced CW stations (both within the narrowest band I could tune) in the 40 m CW sub-band, an SSB conversation in 40 m, and another SSB ragchew in 80 m -- all with a 1 m vertical inside a metal-clad house.  All of this was before dark with everyone getting ready for the Big Game (can't call it by its name, lest the trademark owners appear with thunderbolts and lawyers).  SSB is hard to tune well enough to make sense of the words.  CW will likely be better after dark, and with more antenna.
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G3RZP
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« Reply #31 on: February 03, 2019, 04:07:50 PM »

Sounds like you are getting ready to appreciate(?) the pleasures of the poor performance of receivers of yester year. Yet back in 1948, there was a guy in the UK - a coal miner by trade - who built himself a three valve TRF receiver and had over 50 countries confirmed as an SWL on 160m in 1948.....He could make that TRF sit up and beg! His name was Bob Iball and he passed away many years ago now. I suspect that there are now very few of us left who remember him and his skills as an SWL...
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N3DT
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« Reply #32 on: February 04, 2019, 04:00:46 PM »

My first RX was an S38E in the 50's. Now that thing was a bear to tune, but with the novice crystals I had and listening to the band I could figure out where I was. Seems to me the bandspread worked backwards so I figured how to dial in the main dial so I could tune up from 0 on the bandspread and the novice band maybe covered 1-10 out of 100. Anyhow I got it to work somehow and the DX40 I had with crystals was fixed. I used that for years without problems. Mostly 40M because I had a 40M dipole outside my dad's house. But it wasn't ideal. First good RX was a HQ145 and that worked great. Real calibrated bandspread. What a difference. It wasn't until the mid 70's I got my first SS transceiver, FT757GX. I'd been off the air for many years and then I got my Extra. That was a treat. Somehow I didn't forget the code.

If you can hear CHU at 7350 or whatever it is that's a good start to figure where 40M is.
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KX4QP
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« Reply #33 on: February 06, 2019, 04:12:08 PM »

I'm not sure what I've been hearing would qualify as "poor performance".  Much/most of the 60 Hz hum I had vanished when I unplugged the 8 ohm headphones I was using to try to keep a high whistle (beyond my hearing range, which quits between 10,00 and 12,000 Hz) from driving my partner nuts two rooms away.  On speaker, the hum is barely noticeable.  Further, with just the whip antenna, I was picking up some stations I'm certain were at least a thousand miles away.  Overall, I don't think this S-120 is performing badly.  Get a good antenna up, and I might decide I don't need anything better before I have a transmitter or transceiver.  Listening is handicapped by living inside a metal box, and more so by being down in a valley.

Now, that said, I've never tried to listen with a modern SDR or IC radio.  The last time I had access to a shortwave receiver was around 1973, and that was a near-new (then) transistor set with a similar band setup and no bandspread control -- and it did little if any better on shortwave than this Hallicrafters.
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AC2EU
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« Reply #34 on: February 06, 2019, 06:04:37 PM »

Now, that said, I've never tried to listen with a modern SDR or IC radio.  The last time I had access to a shortwave receiver was around 1973, and that was a near-new (then) transistor set with a similar band setup and no bandspread control -- and it did little if any better on shortwave than this Hallicrafters.

If you are comparing apples to apples, there is no difference.
If you were using a 1932 Atwater Kent , then moved to the S-120, you would be duly impressed by the difference. The same goes if you upgrade to a real communications receiver. Even an ancient R390 ,which is older, would blow your socks off. 

If it's working for you , then that is all that matters at the end of the day. I don't have the "ultimate" radio either, just  a lowly FT450d, but it works for me at the moment...yet it is still way beyond the Halli s-120.
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KX4QP
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Posts: 289




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« Reply #35 on: February 07, 2019, 02:32:21 PM »

Okay, with no basis for comparison, I'll have to take your word for it.  Which brings the question to, how do I identify a "real communications receiver" when I'm shopping on eBay?  No, going to a local swapmeet won't work, there seems to be only one near here per year and it's in the fall.

I've seen listings for Hallicrafters S-119, which seems to have about six or seven additional controls compared to this S-120.  Those come in around $200 -- which is close to the limit of what I can spend right away.  If I need to spend more than that to get "way beyond the Halli s-120", it's even more important that I be able to tell the good from the merely complex before I tickle PayPal and send off a bunch of money.
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W9IQ
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« Reply #36 on: February 07, 2019, 02:45:25 PM »

Hmmm... this somehow sounds familiar...

When looking at legacy receivers, a key differentiator is often general coverage (shortwave) vs amateur radio coverage. Most shortwave receivers lack the band spread, selectivity, filtering and demodulation features needed for practical use as a receiver for a QSO. Receivers targeted primarily at the ham radio community tend to have better overall features for ham use.

The next major differentiator is the superheterodyne architecture that represents the epitome of legacy receiver architectures.

Having selectable filters such as 3000 and 300 hertz can help to cut adjacent QRM.

A notch filter can help to cut an offending signal or noise.

If you have a computer (even a Raspberry Pi 3) and are willing to invest $200, you can get a state of the art software defined receiver. An example of such a receiver is the Airspy HF+. It is an amazing piece of hardware for the price and will give superior performance to many heterodyne receivers. It even allows you to operate it over the Internet.

For slightly more money, you can purchase an SDR transceiver such as the HackRF One. This will eliminate the need for frequency spotting and transmit/receive relays or PIN diode switching that you would need to accommodate with a separate transmitter.

If you are not familiar with SDR receivers, there is a  network of them on the Internet at websdr.org that are free to use.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KX4QP
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Posts: 289




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« Reply #37 on: February 07, 2019, 03:12:36 PM »

Thanks for the paste, Glenn.  Never mind that none of that stuff is visible in an eBay listing

What I already have is a superheterodyne, and people are telling me it isn't suitable as a station receiver.  It sounds like you're suggesting I really need "modern" equipment.  If I could spent $1000 on a whim, and wanted the latest and greatest equipment, the problem would be solved.  But look on eBay, and everything with one or more shortwave bands on the dial is a "communications receiver."  There are probably a hundred models, from the 1940s to 1960s, that will fill my bill, and likely five times as many that won't -- but I don't know how to reliably tell one like Bill Cosby had as a kid ("two hundred and forty seven knobs, of which only two worked: on-off volume, and tuning") from one that will separate two CW operators who are both using the same crystal, but one has a tuning circuit and moved off the crystal fundamental by a few kHz.
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AC2EU
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« Reply #38 on: February 07, 2019, 03:29:18 PM »

Okay, with no basis for comparison, I'll have to take your word for it.  Which brings the question to, how do I identify a "real communications receiver" when I'm shopping on eBay?  No, going to a local swapmeet won't work, there seems to be only one near here per year and it's in the fall.

I've seen listings for Hallicrafters S-119, which seems to have about six or seven additional controls compared to this S-120.  Those come in around $200 -- which is close to the limit of what I can spend right away.  If I need to spend more than that to get "way beyond the Halli s-120", it's even more important that I be able to tell the good from the merely complex before I tickle PayPal and send off a bunch of money.

The blurbs on Ebay won't help to separate the good bad and ugly because there isn't enough detail.
If you see something interesting, do more research on it . Find the spec sheet and read reviews, etc.
A good one would have sensitivity around 0.25 microvolts or less the s-120 is probably 1 microvolt or more.
If you want something old, look at the collins 75A-4 , it even has a product detector! - but it will need more maintenance than the newer stuff.
A newer one might be something like Icom IC-R75. (DDS with no "bands")
As I mentioned before, the important difference in a communications receiver is bandspread. for instance , the entire dial start to end is only
550KHZ , just enough to cover the entire 80 meter band, instead of being a 1 inch section of a 12 inch slide rule dial.
the old ones would have more "bands" to cover HF because the bandwidth is greater.
On the newer ones it's in terms of 'resolution"; 10Hz is typical.  You want as much resolution as your wallet can afford.
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W9IQ
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« Reply #39 on: February 07, 2019, 03:50:42 PM »

Thanks for the paste, Glenn.  Never mind that none of that stuff is visible in an eBay listing

What I already have is a superheterodyne, and people are telling me it isn't suitable as a station receiver.  It sounds like you're suggesting I really need "modern" equipment.  If I could spent $1000 on a whim, and wanted the latest and greatest equipment, the problem would be solved.  But look on eBay, and everything with one or more shortwave bands on the dial is a "communications receiver."  There are probably a hundred models, from the 1940s to 1960s, that will fill my bill, and likely five times as many that won't -- but I don't know how to reliably tell one like Bill Cosby had as a kid ("two hundred and forty seven knobs, of which only two worked: on-off volume, and tuning") from one that will separate two CW operators who are both using the same crystal, but one has a tuning circuit and moved off the crystal fundamental by a few kHz.

My modern recommendation was $200 - I don't know where your $1,000 comment comes from. The $200 version will beat out any legacy receiver for comparable dollars. Don't bother with eBay to buy the new technology - get brand new with a warranty from a reputable dealer for only $200.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
VK6HP
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« Reply #40 on: February 07, 2019, 08:33:55 PM »

I'm pleased that you took up my suggestion and got a receiver and, performance shortcomings not withstanding, you'll undoubtedly get a lot of fun out of it for not a big investment.  As the previous two posters have suggested, you can usefully spend a bit more time researching your next receiver.  With due respect, everyone starts from a "don't know what I don't know" situation and we all progress from there (well, most do).  One very valuable thing you could do is to link up with a local radio club, or some individual hams.  That way, you'd form some idea for yourself about the spectrum of performance of various radios, all of which may be labelled "communication receivers". Believe me, that label is downright imaginative in some cases!

To give you an example of the wide performance range you may encounter in tube receivers, I'm staring up at my restored Heathkit HR-10B, which I built as a teenager.  By most measures, it's a poor receiver.  But with ham band only coverage and OK sensitivity, I worked quite a bit of CW DX with it, using my one tube crystal controlled transmitter built from scrounged TV parts. The unstabilized B+ made me adept at copying code with all sidetone frequencies, especially as we lived at the end of a long SWER mains line in the bush. However, the HR-10B now gets many friendly glances from shack visitors, most of whom have no idea of how terrible it is.  (With the addition of some zener stabilization it's actually not quite as bad as it once was).

Looking a bit to the side, I see a Collins 75S-3 and 51S-1, both working as well as the day they left the factory (maybe better, in the case of the 51S-1).  These are serious receivers that lose little to modern HF radios, except for the lack of DSP noise reduction.  That may or may not be a factor, depending on your location.

I could go on, but in between the extremes, you could expect to pick up nice Drake R3 or similar for not a lot of money (almost certainly less than the Collins radios mentioned by me, and others).

Glenn and James have made some good comments, and you might get a bit more information from looking at our (and others') qrz.com pages.  But try and get yourself a bit of radio club activity and see what's out there in terms of equipment (homebrew and other) and performance.  Many hams are all too happy to help a newcomer and like nothing better than trying out various radios. 

73, Peter.

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KX4QP
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Posts: 289




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« Reply #41 on: February 08, 2019, 04:41:57 PM »

Peter, I'm already having a lot of fun with the S-120 -- easily worth the $50 I've got into it.  "Bad" receiver or no, I put a better antenna on (the FM antenna that came with the Realistic stereo I bought in 1983, hung over an old dry aquarium on a shelf above my radio table), and about tripled the number of stations i could hear.  Last night, I was hearing overlapping CW stations, what sounded like FSK data, as well as AM and SSB.  I'm getting the hang of tuning the combination of main tuner and bandspread (which lowers the main tuning a bit as you reduce it, requiring two hands) and using the "BFO" (regen) to augment AM signals and make CW audible and SSB more or less intelligible.

The receiver came before the local club because the most local club meets on a weeknight, too late for me to attend and still drive an hour each way to work the next day.  The slightly less local club I chose instead (roughly an hour drive, instead of 30 minutes) meets the first Saturday of every month for breakfast (that's tomorrow), and I plan to be there, my S-120 in tow so I can both show what I have to work with so far, and learn more about how to get the most out of it (assuming there are still some Elmers there who remember vacuum tubes as something other than a cleaning accessory).

Glenn, you're missing the point I thought I'd made both here and on the Stack Exchange: if I can do the job with tubes, I'd prefer that over transistors, never mind surface mount ICs and SDR.  I don't need or want a waterfall display -- I'm not working sonar in a submarine.  My hearing isn't what it once was, but it's still good enough to pick a weak signal out of noise (and that's a learned skill, meaning I'll improve with time and practice).  The physics of propagation hasn't changed since the 1930s (though the current super-quiet sun doesn't help).  The superiority of Morse for getting a signal through with minimum radiated power hasn't changed (hence why I'm learning code, too).  And honestly, a part of the thrill for me is being able to build my own equipment, just as, for photography, half the fun is the smell of the chemicals and watching a print come up in the developer.

Once I have my license, I'm sure I'll build a small transceiver kit (the under $50 QRP type) to get on the air, but longer term, I want to work the world with a homebrew vacuum tube station, and I won't learn any more about that with a "magic" receiver or transceiver that has more computing power than a Space Shuttle.  This isn't a technology hobby for me -- I got tired of technology for its own sake when computers had megabytes, not gigabytes.  To me, this is a "building stuff and using it" hobby, similar to stick-and-tissue free flight model airplanes, rather than "install the radio and engine, then go fly" radio control.
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WB6BYU
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« Reply #42 on: February 08, 2019, 06:47:11 PM »

Many of us have managed contacts with relatively "primitive" general coverage receivers.
They may not be ideal for that purpose, but can still be a lot of fun.

Some of the characteristics of a "good" receiver:

Sensitivity:  the ability to hear weak signals.  This typically is set by the noise figure of the
RF amplifier stage, or, in receivers lacking that, by the mixer stage.  A pentagrid mixer tends
to be noiser, for example, than a triode amplifier.  On HF, where received noise is often more
of a limiting factor than internal noise, this may not be as much of an issue.  A quick check is
to tune between stations and disconnect the antenna:  if the received noise level goes down,
then you are limited by received noise, and improving the receiver won't make much difference.
If the first stage is a pentagrid mixer, then it may help to add a low-noise RF preamp, but use
only as much gain as is needed:  too much makes the receiver more prone to overload.

Selectivity:  the ability to separate adjacent signals.  The regenerative IF stage will improve
selectivity with careful adjustment, and this may help with broadcast stations, but my
experience was that it didn't provide as much selectivity when it was oscillating to provide
a BFO for CW or SSB reception.  Typical bandwidth for SSB is 2 to 2.5 kHz, while for CW
a couple hundred Hz bandwidth will help pick individual signals out of what otherwise may
seem like a jumbled mess.  But to use such a sharp filter, the receiver frequency must be
stable.

Stablity:  the ability for a receiver frequency to remain constant over some period of time.
(There are other forms of stability, such as freedom from oscillations in the stages, but we'll
focus on frequency for this discussion.)  If the frequency shifts 500 Hz when your hand comes
close to the tuning knob, it probably will still work fine for AM signals, because they rely
on the transmitted carrier for demodulation.  But it will be difficult to listen to SSB or CW,
because they will shift to where the signal is unintelligible (for SSB), or even out of the
receiver passband (on CW).  The same is true for frequency drift, though a deft hand on
the tuning knob can sometimes counteract it.  The wider tuning range you are trying to
cover on each band, the smaller the capacitance across the tuned circuit at the high end
of the band, and therefore the more the frequency shift due to changes in capacitance as
devices heat up.

Tuning Rate:  how fast the frequency changes as you tune the tuning knob, often measured
in kHz / revolution.  Again, this isn't too much of a problem receiving AM stations, but for
SSB and CW you want a slow tuning rate, especially with narrow CW filters.  Even with a
large tuning knob, I find it uncomfortable to use a tuning rate of more than around 25 kHz
per revolution (for CW), and half that, or less, is better.


All of these can be improved by various sorts of modifications and/or additions to the radio,
though if the VFO itself isn't stable that may be more of a major upgrade.
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WB6BYU
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« Reply #43 on: February 09, 2019, 09:33:40 AM »

One I forgot to add (and others are welcome to contribute as well):

Product detector:  a circuit designed for demodulation of SSB and CW signals
with minimum distortion.  You can introduce a BFO into just about any IF stage
(or even at the signal frequency) and get a beat note on CW, but a product detector
is a specific circuit designed for that purpose - basically a mixer that takes two IF
signals and produces the audio difference between them.  Many older receivers
didn't provide enough BFO injection to properly demodulates stronger signals.  That
usually meant that reception was best when the audio gain was turned up all the way
and the manual RF gain control was used to adjust the volume. The BFO would also
activate the AGC, so manual RF gain was really the only option.  With a product
detector you typically get more audio output for gage same RF input, and it handles
a wider range of signal strengths with minimal distortion.

If you add a product detector / BFO to your receiver then you can still use the IF
regeneration to control the selectivity when receiving CW, because it doesn't need
to oscillate tobprovide the BFO function.


Generally for Hallicrafters receivers, the S-xxx model numbers are for general coverage
and the SX-xxx models are ham band only.
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KX4QP
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Posts: 289




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« Reply #44 on: February 10, 2019, 02:40:15 PM »

Thanks, BYU -- that was a much more useful explanation than I've had before.

However, someone pointed out something on Stack Exchange on Friday that I'd just realized the same day: I can get a transceiver for about the same money as a ham-oriented receiver, and then I don't have to worry about having a "matching" transmitter, setting up muting when I key down (to protect the receiver), having to manually switch the antenna from receiver to transmitter, etc.  I put in a bid today for a Heathkit HW-101 (80, 40, 20, 15, 10 bands, 100 W, dropping off to around 80 W on 15 and 10, SSB and CW), though I got outbid in minutes (and it didn't include a power supply anyway).  It looks like I can get a vacuum tube transceiver that will cover a range of bands for around $200 shipped, if I'm not in a hurry.  Any of the Heathkit SB-100 or HW-100 derivatives will do the job (100, 101, 102 -- but the 104 was when they transitioned to transistors, so less desirable for me).  Knowing what Drake, Knight, Collins, etc. models were similar would aid in searching eBay for used units.

Of course, those Heathkit transceivers tune only the amateur bands -- 500 KHz up from the bottom frequency.  That means they won't tune any of the frequency standard stations (WWV at 2.5, 10, 20, and 25 MHz, or CHU at 3.33 MHz), because all of those are outside the ham bands. Once I have a proper antenna up, my S-120 should be able to get WWV (as long as it transmits) and I can barely hear CHU in daytime, clearly at night, even with a crappy antenna -- but that's not much good for calibrating the transceiver's built-in frequency standard, especially with CHU not on a harmonic of 1 KHz.  Fortunately, I've got a frequency counter/crystal tester kit on the way, and I should be able to calibrate that against CHU and then use it to check the built-in frequency standard.
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