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Messages - OgreVorbis

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31
FM Free Radio / Re: Antenna Height vs Gain
« on: July 20, 2018, 1908 UTC »
Can you guys give me your general thoughts on this?  I know there is no right answer.

I've finally built a circular polarized antenna to try to get a more consistent signal no matter what type of receiver.  My original idea was to build a second CP antenna and feed it in phase a wavelength below the first.  Now I'm having second thoughts on the two-bay idea.

I'm in a rural area and my existing ground plane antenna is nearly 100 feet above the terrain.  It doesn't quite clear the treeline, but it's as high as I'm likely to get without a real tower, which isn't going to happen.  It's a good transmitter site, but despite some pretty cavalier power levels, I just can't get the signal to my house.  I think I'm terrain-limited rather than power limited.

Here's my thought.  I'm not really comfortable using high power long-term.  It seems like asking for trouble.  I'd like to get the most out of a lower output power, but if adding another CP antenna will just lower the center of radiation by one half wavelength, would you expect to get any additional range out of the higher gain?

All things considered, I can just run more power to a single antenna at the same height.

I have some decent experience with this although I've never tried a CP antenna. I've tried ground plane antennas, dipoles, and the "dominator" antenna (which is a 5/8 wave with interesting matching). Anyway, in a hilly location, I've actually found the ground plane type antennas work better at a lower height than anything with higher gain. The lack of gain almost compensates for low height (I'm considering 100ft - low). It shoots the signal up more. Yes, some of it will be lost in space, but on the low end of the FM band, there's some bending that can occur and the GP will cause the signal to go over hills a bit better.

With the amount of power you're using, you should be getting farther than that. My guess is the transmitter site is just in a bad location. Something I've thought about doing, was putting a solar powered TX on a hill nearby with a directional wifi dish for streaming audio and controlling the transmitter. You could get away with only 15W on a hill and go much farther than 150W on the ground. Height is pretty much everything, not power. I did a test with a 30W transmitter on a mountain that I lugged up with a car battery (wasn't easy). The signal went about 30 miles.

Another thing to consider if you just want to make it from the site into town is a yagi.

One more thing - Don't use stereo. Give mono a try. When you're really close to the TX, it won't sound as good, but I came to find that with my setup, using mono made the signal much clearer longer distances away. And at those distances, nobody is going to be hearing the advantage of stereo because receivers default to mono with low signal level anyway.

Are you getting multipath distortion? When you drive listening to the signal, does it pop in and out. Sounds  pretty clear, but with bursts of static. If yes, use mono or SSB stereo mode instead of normal stereo.

32
Equipment / Re: Starting a pirate radio in Spain
« on: July 20, 2018, 0257 UTC »
I just discovered two things about that transmitter today.

You will need a -10db attenuator on the input to the amp because it drives it to almost full power even when you adjust the power pot. You won't be able to modulate it without (only CW).
You should put a simple RC audio filter on the input because it might create spurs from random high frequencies.

33
Equipment / Re: Starting a pirate radio in Spain
« on: July 19, 2018, 1023 UTC »

Dear OgreVorbis,
Thanks for answering all of my questions and helping me shape much better this project. I've definitely learned a lot. I'll report back when I have everything up and running!

Thank you very much and 73!
Best regards,
Diego

You're welcome. And if you didn't see it, the REL Map button in VOACAP seems to be the most straightforward. The rest of it is a little confusing.

34
Equipment / Re: Starting a pirate radio in Spain
« on: July 18, 2018, 0057 UTC »
Dear OgreVorbis,
Thank you very much once again for your very informative message.
I will take a look at those amps you linked. Sorry if I'm asking too many questions, but would you recommend I acquire or try to assemble an audio compressor? Would a software one work?

Thanks and best regards,
Diego

Not a problem. Stereo tool is a good one. It has compression and limiting and it also has an adjustable low pass filter for the audio, which should be set around 3-7 khz. The lower you set it, the signal will go a little farther, but the audio quality is obviously less.

I use a DSP board from China that has a ADAU1701. I've also used stereo tool in the past, but I've had audio buffering problems with it. It seems like it works fine as long as you don't use a virtual audio cable to route the audio within the computer. You should use a physical audio cable. The problem with this is that the computer can no longer be a sound source because its output is the stereo tool only. So if you have another sound source (or another sound card) and a mixer, etc. Then you just put that into the line-in of the comp and the output to the TX.

35
Equipment / Re: Starting a pirate radio in Spain
« on: July 17, 2018, 0334 UTC »
Dear OgreVorbis,
Thank you once again for such an informative reply. I'm learning a lot from posts like this.

I think I will go with SW for now, as the antenna will be easier to set up, more discreet. Regarding the transmitter you linked on your previous post, what would be the maximum power recommended with an HF linear amp? Would something like this https://m.ebay.com/itm/2MHZ-30MHZ-50W-HF-linear-amplifier-RF-power-AMP-13-56MHZ-shortwave-transmit/272762087295?epid=19005363907&hash=item3f81e3277f%3Ag%3A%7EuUAAOSwlRpZaKRO&_nkw=hf+linear+amp+am&_sacat=163853&_from=R40&rt=nc&_trksid=m4084.l1313 work? If not, what amps do you recommend and how many watts? Would I need anything else, like filters? If so, would they be easy to build or obtain?

Thank you for the VOACAP website, as it seems to be a very useful resource.

And again, thanks for the detailed posts.

Best regards,
Diego

That Chinese one needs about 1-5W input I think, so it won't work.

Here are some options that all support around 1mW input:
https://www.ebay.com/itm/10W-HF-PA-10-watts-13-5v-HF-amplifier-for-HAM-radio-CW-SSB-FM-digital/332237134236?hash=item4d5ae0599c:g:LcEAAOSwux5YNJ3f
https://www.ebay.com/itm/20W-HF-PA-20-watts-24v-HF-amplifier-for-HAM-radio-CW-SSB-FM-digital/332643829840
https://www.ebay.com/itm/50-Watt-SSB-linear-Power-Amplifier-for-transceiver-intercom-Radio-HF-FM-CW/252126056815
https://www.ebay.com/itm/100W-HF-PA-RD100HHF1-13-5v-HF-amplifier-HAM-radio-CW-SSB-FM-DIGI-1-55-MHz/332672297281?hash=item4d74d06941:g:OTsAAOSwScJbEolE

Filter:
https://www.ebay.com/itm/LPF-300W-1-8-54MHz-low-pass-filter-1-pc-for-1-band/151916768969
(You specify what band you want, so assuming you want to test 69xx khz, say the 40m band filter.)

The third one I listed there is the cheapest, but it Chinese, so it may not do what you want. It says 1-5mW input, so it might produce less power than they claim with only 1mW. The other three are more expensive, but they should work as advertised.

I don't know how much you know about this, but you should be aware that when modulating AM, you set the power to 1/4 of what the amplifier can produce and then the audio will peak it to full power. Most of these have a PTT (push to talk), so you have to remember to short it to make the TX work all the time.

36
Equipment / Re: Starting a pirate radio in Spain
« on: July 16, 2018, 0016 UTC »

Dear OgreVorbis,
Thank you very much for your detailed reply, I really appreciate it.

Regarding FM, I've pretty much discarded that option as all of the FM frequencies in my city are taken and authorities are really strict on that.

On the other hand, AM is pretty empty yet available everywhere (cars, most radios...). I live in an apartment block, so the only place I would be able to set up a MW antenna would be on the rooftop, so no buring ground sticks (those metal things, sorry for the lack of vocabulary) and space could be a little bit of a problem. How big are we talking about? Would a 1/4 dipole in an inverted vee work?

I've considered shortwave and I've talked with Stretchyman about it. I don't really have the budget to spend on a powerful transmitter, so I'd be TXing low power with one of his transmitters (I'm still learning about building one and I wouldn't want to mess it up, so building one myself is not an option, currently), meaning that I maybe wouldn't be able to reach very far, yet also wouldn't make it locally due to the skip.
What do you recommend? I'm still doubting about which route to take.

Again, thank you so much for your help.
Best regards,
Diego

In terms of antennas:
For SW, an inverted V is probably my favorite because it doesn't take up too much space and only requires one support. The skywave propagation with them is also pretty good.

For MW:
I've tried a full half wave inverted V - this was huge and the local coverage was poor, but I was able to tune into myself from an SDR about 500 miles away. (This was with 300W on 1710). The local coverage was only 2 miles interestingly.
Isotron - the worst
Long wire - second worst
1/4 wave ground plane - the best (this was temporary because I had to use a balloon to raise the wire)

If you want local, you'll need a vertical antenna. I don't know how high your block is, but maybe hanging an antenna from the roof instead of trying to fit it on top would be better. The ideal situation would be if you were on the middle floor of a tall building because then you could put the center of the dipole out the window and have one leg run up to the roof and let the other hang to the ground.

EDIT: If you decide to go with MW, you're likely going to need an antenna tuner. Unless your antenna is in the middle of a field, the surrounding objects will make it not resonate at the proper frequency. There is a formula to calculate the length, but you'll find that on MW the calculation ends up being so much different than the actual length the antenna needs to be. With shortwave, as long as you have an SWR analyzer, you won't need a tuner because generally, you can just cut the ends of the V until you get it perfect.

I also really recommend that transmitter I linked to in my other post. It will work on both MW and SW, so you won't need to buy another transmitter if you change your mind. You'll need an amplifier for it though because it only makes 1mW.

You should also check out VOACAP btw. You put in your location and a few other parameters and it will give you a theoretical coverage map. You can select the frequency and do it again to see the difference in propagation.

37
Software / Re: Pitch shift idea
« on: July 15, 2018, 0147 UTC »
a better idea is to have a TX that has full audio range and use a professional sound processor to control, filter and tailor the audio to your specific desires.
obviously, loss of the audio amplitude level is greater at higher audio frequencies which is why (modified) pre-emphasis is used as an industry standard for AM broadcasting.
this is why many SWBC stations generally have their audio frequency set at 5Khz (10Khz total occupied bandwidth), audio density is greater with less bandwidth being used.

In terms of sound processing, I'm currently using an ADAU1701 DSP from analog devices. It works really well and I'd highly recommend. The DSP eval board is $200, but you can find Chinese clones of the board for cheaper on aliexpress.

It is controlled by a flow-chart type of software called SigmaStudio. It can be modified in real time to hear the changes to the audio. Cheaper and better than a pro-processor imo.
i use "stereotool", $35 USD it cost.
dont let the name fool you, this software is used on many commercial broadcasting radio stations.

I've also used that and I like it, but it lags for me sometimes with the virtual cable. I just like the solidness of a DSP - knowing it's not going to lag or fail randomly.

38
Equipment / Re: Starting a pirate radio in Spain
« on: July 15, 2018, 0127 UTC »
Another thing to keep in mind about the effectiveness of AM: You should look up what the ground conductivity is in your area. I am in the US and it is 0.5 - 1 here (i forgot what units it's in). It seems to be on average 10. If it's low, AM won't work well in your area because it travels by groundwave. This might be a good way to decide if you want to do it. The difference is huge. Where I live now, a 1kw AM station only goes 6-8 miles!!! I used to live in another part of the US and stations with 1kw can go up to 100 miles.

39
Equipment / Re: Starting a pirate radio in Spain
« on: July 15, 2018, 0122 UTC »
I would say go with shortwave or FM, but not AM (MW). Getting an effective antenna set up for AM is hard. You need a lot of space. There any many designs for shortened AM antennas, but none of them work well. You'll go farther with the same power on FM. If you do have the space for a massive antenna, then go with AM. You'll find the range to be really good if you use the right antenna. I know this from experience.

To decide between FM and shortwave, you have to think about your target audience. Is it a bunch of radio geeks from around the world, or is it the average local person?

If you want a good FM transmitter: pcs-electronics or "The Radiomaster"
If you're looking for a SW: Stretchyman or https://www.ebay.com/itm/DDS-AM-LW-MW-SW-TRANSMITTER-MODULATOR-100KHz-30MHz-AUTO-LPF-BPF/323346484122
... then you can just get an HF linear amp and you'll cover MW and shortwave with the same transmitter.

The PWMs are better, so if you looking for higher power and more efficiency, then take a look at stretchyman instead. But for low power a linear amp should be fine (and more broadband).

40
Software / Re: Pitch shift idea
« on: July 07, 2018, 0038 UTC »
a better idea is to have a TX that has full audio range and use a professional sound processor to control, filter and tailor the audio to your specific desires.
obviously, loss of the audio amplitude level is greater at higher audio frequencies which is why (modified) pre-emphasis is used as an industry standard for AM broadcasting.
this is why many SWBC stations generally have their audio frequency set at 5Khz (10Khz total occupied bandwidth), audio density is greater with less bandwidth being used.

In terms of sound processing, I'm currently using an ADAU1701 DSP from analog devices. It works really well and I'd highly recommend. The DSP eval board is $200, but you can find Chinese clones of the board for cheaper on aliexpress.

It is controlled by a flow-chart type of software called SigmaStudio. It can be modified in real time to hear the changes to the audio. Cheaper and better than a pro-processor imo.

41
Software / Re: Pitch shift idea
« on: July 07, 2018, 0033 UTC »
Just TX a wider B/W, I usually cutoff over 7KHz.

The pitch shifting kinda sounds like a very wierd idea bud!!???

Str.

Is the range compromised by that? It would be ideal, but does it have a significant impact on range or is it small enough that it doesn't really matter?

42
Software / Re: Pitch shift idea
« on: July 06, 2018, 0205 UTC »
So, I just tested it in audacity. Audacity doesn't have the feature to pitch shift only a specific range, so:
I added the track twice.
Put a high pass filter on the first one.
Pitch shifted the first one.
Then put a 2.5Khz low pass on both tracks.
Played them together.

It sounds about the same as it would if you just used an EQ to the higher frequencies. Maybe it could be done better though. This was just me messing around. You could probably optimize the pitch shift to make it better. You might get distortion if the pitch shift isn't right.

43
Software / Pitch shift idea
« on: July 06, 2018, 0020 UTC »
So I was thinking about the limitations of audio bandwidth for broadcasting. I was wondering what it would sound like if instead of filtering at something like 2-5khz (which is around the standard), you instead pitch shift down everything above that. I don't mean pitch shift everything, just what is above where the filter cuts off. What would this sound like? Clearly it would sound lower, but would it improve the quality of the music without using more bandwidth?

Also is this possible in any software (like audacity maybe)?

44
Shortwave Pirate / Re: unidentified 6810 AM 0102 UTC 5 July 2018
« on: July 05, 2018, 0313 UTC »
How was the modulation?  ;)

This is my first transmission and I don't have a PEP meter, so I just kind of winged it.

UNID 6810 AM S5 in NY

0103: Paul Basic "Cloak & Dagger" (that was a great movie back in the day)
0111: Keeno "Piano Only"
0117: Keeno "Eos"
0121: Helios "Every Passing Hour"
0126: Galimatias "Noelle's Eloquence"
0132: Tom Middleton "Serendipity"
0136: Off the air

Impressive ID. You must have used Shazam?

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