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Making Contacts / On the Air - Have a question about getting on the air or how to make a contact? Just want to brag about your latest DX contact or contest score? This is the forum for you.

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  #21 (permalink)  
Old 10-22-2016, 2:49 PM
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Re: 6 meters
There is a reason forestry service/forestry products users are Iicensed on low band. I have several tall structures around my property that are covered with thousands of 1/4 uhf wave spikes called loblolly pines. They do an outstanding job of sucking signals from the aether causing them to be greatly attenuated.

Don't want the nosey Nates/meddling Matts to follow you all over 2/.7 meters butting in or harassing, go to one of the 6 meter repeaters or a simplex. Most of them don't have 6 so they can't continue to bother you. If they can and do there is always 33 and 23 cm. Very few amateurs bother with them.

6 shows some of both the best and worst traits of the ha and vhf bands. It is what you make of it. AND yes you can make long distance contacts hand held to hand held when the band is open.
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Old 10-27-2016, 3:06 PM
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At one time, everyone was on the low band.
The reason why they were on the low band is due to the fact that the technology of the day
( Superheterodyne ) did not work well on what they then called UHF - Anything above 300 MHz.
The first commercial two way radios were of a very simple design.
The one limit was the amount of power available in a mobile to run them.
Especially with a 6 volt DC charging system.
Think Tubes and a vibrator power supply to run the radio, along with a larger generator and extra batteries in the trunk, along with the radio.
DIRECTORY OF MOTOROLA POLICE RADIO EQUIPMENT 1942-

As you will read, after 1947, all new FCC applications for police radio licenses, required the applicant to use the high band, which freed up the low band for commercial use. Ironically, Fire, Game Commission, Forest Fire, and Lumbering remained until the 1990's.

Last edited by jbantennaman; 10-27-2016 at 3:33 PM..
  #23 (permalink)  
Old 10-27-2016, 3:21 PM
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Quote:
Originally Posted by jbantennaman View Post
The reason why they were on the low band is due to the fact that the technology of the day
( Superheterodyne ) did not work well on what they then called UHF - Anything above 300 MHz.
I don't know where you learned that but it's wrong. Most modern receivers are superheterodynes. That has nothing to do with the receiver's frequency range.
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Old 10-27-2016, 4:04 PM
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https://en.wikipedia.org/wiki/UHF_te...n_broadcasting

Another effect due to the shorter wavelength is that UHF signals can pass through smaller openings than VHF. These openings are created by any metal in the area, including lines of nails or screws in the roof and walls, electrical wiring, and the frames of doors and windows. A metal-framed window will present almost no barrier to a UHF signal, while a VHF signal may be attenuated or strongly diffracted. For strong signals, UHF antennas mounted beside the television are relatively useful, and medium-distance signals, 25–50 kilometres (16–31 mi), can often be picked up by attic mounted antennas.
On the downside, higher frequencies are less susceptible to diffraction. This means that the signals will not bend around obstructions as readily as a VHF signal. This is a particular problem for receivers located in depressions and valleys. Normally the upper edge of the landform acts as a knife-edge and causes the signal to diffract downwards. VHF signals will be seen by antennas in the valley, whereas UHF bends about  1⁄10 as much, and far less signal will be received. The same effect also makes UHF signals more difficult to receive around obstructions. VHF will quickly diffract around trees and poles and the received energy immediately downstream will be about 40% of the original signal. In comparison, UHF blockage by the same obstruction will result on the order of 10% being received.[2]
Another difference is the nature of the electrical and radio noise encountered on the two frequency bands. UHF bands are subject to constant levels of low-level noise that appear as "snow" on an analog screen. VHF more commonly sees impulse noise that produces a sharp "blip" of noise, but leaves the signal clear at other times. This normally comes from local electrical sources, and can be mitigated by turning them off.[4] This means that at a given received power, a UHF analog signal will appear worse than VHF, often significantly.

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Old 10-27-2016, 4:18 PM
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https://en.wikipedia.org/wiki/Superheterodyne_receiver
One major disadvantage to the superheterodyne receiver is the problem of image frequency. In heterodyne receivers, an image frequency is an undesired input frequency equal to the station frequency plus twice the intermediate frequency. The image frequency results in two stations being received at the same time, thus producing interference. Image frequencies can be eliminated by sufficient attenuation on the incoming signal by the RF amplifier filter of the superheterodyne receiver.

Early Autodyne receivers typically used IFs of only 150 kHz or so, as it was difficult to maintain reliable oscillation if higher frequencies were used. As a consequence, most Autodyne receivers needed quite elaborate antenna tuning networks, often involving double-tuned coils, to avoid image interference. Later superhets used tubes especially designed for oscillator/mixer use, which were able to work reliably with much higher IFs, reducing the problem of image interference and so allowing simpler and cheaper aerial tuning circuitry.

Local oscillator radiation

It is difficult to keep stray radiation from the local oscillator below the level that a nearby receiver can detect. The receiver's local oscillator can act like a low-power CW transmitter. Consequently, there can be mutual interference in the operation of two or more superheterodyne receivers in close proximity.

Local oscillator sideband noise

Local oscillators typically generate a single frequency signal that has negligible amplitude modulation but some random phase modulation. Either of these impurities spreads some of the signal's energy into sideband frequencies. That causes a corresponding widening of the receiver's frequency response, which would defeat the aim to make a very narrow bandwidth receiver such as to receive low-rate digital signals. Care needs to be taken to minimize oscillator phase noise, usually by ensuring that the oscillator never enters a non-linear mode.
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Old 10-27-2016, 4:32 PM
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So, if modern receivers are not superhets what are they? Sure they are a few direct conversion types on the market. SDRs are growing in popularity but they are still in the minority. Yes early single conversion superhets had image problems. I'll be willing to bet you cannot name a current production single conversion superhet receiver, DC yes, single conversion superhet no.
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Old 10-27-2016, 5:06 PM
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Most modern VHF and UHF amateur radios use the super-heterodyne design. If you look at the receiver's specs and see an Intermediate Frequency (IF), the receiver is most likely a super-het.

Television receiver technology really has very little to do with the topic at hand. Now that U.S. broadcasters are all using digital modulation and almost all U.S. broadcasters have moved above Channel 7, interference from 6m amateur transmitters is fairly rare.

Discussions of UHF receivers also has very little to do with the topic at hand.
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Old 10-27-2016, 9:54 PM
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Quote:
Originally Posted by jhooten View Post
So, if modern receivers are not superhets what are they? Sure they are a few direct conversion types on the market. SDRs are growing in popularity but they are still in the minority. Yes early single conversion superhets had image problems. I'll be willing to bet you cannot name a current production single conversion superhet receiver, DC yes, single conversion superhet no.
What your problem is - is that you are too young to understand what I am talking about, and you failed to read the links I posted. OK

The frequency allotments for Forrest Fire, Game Commission, Some Ambulance, Fire were distributed after the second World War.

After the Second World War - the only type of radios we had were all TUBE TYPE.

The Scheme might have been the same, but the design was much different then the solid state - PCB stuff we have today. The filtering - and there wasn't a lot of filters to speak of - other then Collins Mechanical Filters, was poor at best.

Collins Rockwell's biggest customer was MA BELL - The Phone Company.
As most telephone companies is phasing out their COPPER lines, going to fiber optic and cellular coverage, the demand for these filters shrank and Collins went out of the filter business a number of years ago.

Unfortunately, our amateur radio exams given today are nothing more then match the questions to the answers, and most licensed hams are nothing more than Appliance Operators.

Do you even understand HOW A RADIO WORKS?

The most basic radio is nothing but a detection circuit. A pair of high impedance head phones, a diode, an antenna, a razor blade and a sewing needle - Fox Hole Radio - is a good example.
A more complex example of a Fox Hole Radio is a Yaesu FRG - commonly referred to as a FROG.

Yaesu FRG-7 Product Reviews

1. The first receiver built by a hobbyist is usually the plain old crystal set. If you are unfamiliar with the design then check out the crystal set page.

2. The T.R.F. (tuned radio frequency) receiver was among the first designs available in the early days when means of amplification by valves became available.

The basic principle was that all r.f. stages simultaneously tuned to the received frequency before detection and subsequent amplification of the audio signal.

The principle disadvantages were (a) all r.f. stages had to track one another and this is quite difficult to achieve technically, also (b) because of design considerations, the received bandwidth increases with frequency. As an example - if the circuit design Q was 55 at 550 Khz the received bandwidth would be 550 / 55 or 10 Khz and that was largely satisfactory. However at the other end of the a.m. band 1650 Khz, the received bandwidth was still 1650 / 55 or 30 Khz. Finally a further disadvantage (c) was the shape factor could only be quite poor. A common error of belief with r.f. filters of this type is that the filter receives one signal and one signal only.

Let's consider this in some detail because it is critical to all receiver designs. When we discuss bandwidth we mostly speak in terms of the -3dB points i.e. where in voltage terms, the signal is reduced to .707 of the original.

If our signal sits in a channel in the a.m. radio band where the spacing is say 10 Khz e.g. 540 Khz, 550 Khz, 560 Khz.... etc and our signal, as transmitted, is plus / minus 4Khz then our 550 Khz channel signal extends from 546 Khz to 554 Khz. These figures are of course for illustrative purposes only. Clearly this signal falls well within the -3dB points of 10 Khz and suffers no attenuation (reduction in value). This is a bit like singling one tree out of among a lot of other trees in a pine tree plantation.

Sorry if this is going to be long but you MUST understand these basic principles.

In an idealised receiver we would want our signal to have a shape factor of 1:1, i.e. at the adjacent channel spacings we would want an attenuation of say -30 dB where the signal is reduced to .0316 or 3.16% of the original. Consider a long rectangle placed vertically much like a page printed out on your printer. The r.f. filter of 10 Khz occupies the page width at the top of the page and the bottom of the page where the signal is only 3.16% of the original it is still the width of the page.

In the real world this never happens. A shape factor of 2:1 would be good for an L.C. filter. This means if the bottom of your page was 20 Khz wide then the middle half of the top of the page would be 10 Khz wide and this would be considered good!.

Back to T.R.F. Receivers - their shape factors were nothing like this. Instead of being shaped like a page they tended to look more like a flat sand hill. The reason for this is it is exceedingly difficult or near impossible to build LC Filters with impressive channel spacing and shape factors at frequencies as high as the broadcast band. And this was in the days when the short wave bands (much higher in frequencies) were almost unheard of. Certain embellishments such as the regenerative detector were developed but they were mostly unsatisfactory.

In the 1930's Major Armstrong developed the superhetrodyne principle.

3. A superhetrodyne receiver works on the principle the receiver has a local oscillator called a variable frequency oscillator or V.F.O.

This is a bit like having a little transmitter located within the receiver. Now if we still have our T.R.F. stages but then mix the received signal with our v.f.o. we get two other signals. (V.F.O. + R.F) and (V.F.O. - R.F).

In a traditional a.m. radio where the received signal is in the range 540 Khz to 1650 Khz the v.f.o. signal is always a constant 455 Khz higher or 995 Khz to 2105 Khz.

Several advantages arise from this and we will use our earlier example of the signal of 540 Khz:

(a) The input signal stages tune to 540 Khz. The adjacent channels do not matter so much now because the only signal to discriminate against is called the i.f. image. At 540 Khz the v.f.o. is at 995 Khz giving the constant difference of 455 Khz which is called the I.F. frequency. However a received frequency of v.f.o. + i.f. will also result in an i.f. frequency, i.e. 995 Khz + 455 Khz or 1450 Khz, which is called the i.f. image.

Put another way, if a signal exists at 1450 Khz and mixed with the vfo of 995 Khz we still get an i.f. of 1450 - 995 = 455 Khz. Double signal reception. Any reasonable tuned circuit designed for 540 Khz should be able to reject signals at 1450 Khz. And that is now the sole purpose of the r.f. input stage.

(b) At all times we will finish up with an i.f. signal of 455 Khz. It is relatively easy to design stages to give constant amplification, reasonable bandwidth and reasonable shape factor at this one constant frequency. Radio design became somewhat simplified but of course not without its associated problems.
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Old 10-27-2016, 10:06 PM
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The reason why we have 2 way mobile amateur radio transceivers today is due in fact to the Two Way Commercial Radio business and the nature of radio.

The first radios worked because their signals were very wide and loud.
Since there was not a lot of activity on the band, they got away with it for a while.
When the radio traffic became congested, the FCC stepped in and told them that they had to narrow band their commercial transceivers, this freed up more bandwidth.
The older commercial radios became obsolete - because it would cost more to retrofit them then what they were worth. After World WAR II - Television Channel 1 was taken away from the broadcasters and given to Commercial Radio. This moved up TV to a Frequency above 56 MHz, which made room for experimentation by AMATEURS - Amateur radio.

The amateurs scarfed up these cast off obsolete radios and retuned them for use on the newly formed 6 meter amateur radio band.

There is an excellent write up of this on one of the Cleveland Ohio amateur radio club websites.

Each time PLMRS - Private Land Mobile Radio Service - ran out of frequency's, they narrow banded their radios, until we got to the point where we are at today, where if they take any more bandwidth away from them it will be AM again!

Superheterodyne receivers of the day, trying to operate them on UHF frequencies - didn't mix.
Just like trying to use an antenna amplifier to amplify a digital TV signal, when you amplify noise, all you get is a louder noise. The phase noise inside of the receiver was so loud, it blocked most of the signal, and unless you could see the other person, they were terrible for any amount of range.

This is why UHF TV broadcasters were given permission to use 4 times as much power to operate UHF then VHF. And the reason why VHF signals travels further than UHF - for the same amount of effort ( Power). Power is mostly irrelevant. The only people that worries about power is CB'rs, because it is easier to deceive unacknowledged people then someone that is educated!
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Old 10-27-2016, 10:09 PM
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History - The Lake Erie Amateur Radio Association - WB8CQR WR8ABC
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Old 10-28-2016, 5:39 AM
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And none of this has anything to do with the OP's question.

We're done here.
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