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Messages - RobRich

Pages: [1] 2 3 4 5 6 7 8 9 ... 140
1
Equipment / Re: Modulation Help (AM)
« on: March 22, 2025, 1505 UTC »
Unless experimenting with new features, the process should be mostly straightforward as the base HL platform is relatively mature at this point. There are various guides, FAQs, and communities to help. As S_L noted, the software can be little involved to setup, but that can be true of many SDR products.

Fellow Linux user and occasional software tinkerer here, too. :)

2
0304z - ~6950.10KHz carrier. SIO 332. ~S4 via my Web-888 SDR and 148' LoG. Rough copy at the moment but nonetheless there.

Thanks for the broadcast! :)

3
Equipment / Re: Modulation Help (AM)
« on: March 21, 2025, 0250 UTC »
IIRC there is "unlocked" software for the old Flex 1000, but it does not surprise me about Flex regarding newer models. Took a quick skim. Apparently Flex went to “TURF” files for setting various frequency ranges. Hmm.

There are various SDR-based QRP rigs on the market, but yeah, the Hermes Lite 2 is definitely a popular enthusiast-class network radio. Main PCB, filter board, I/O board, and enclosure for ~$400.

To get above QRP with an affordable off-the-shelf amp, there is the small PA-50+ on AliExpress and similar. Curious if the newer "plus" version resolves the ~1.5:1 SWR limit on the older model, as AFAIK the older model usually required a resistor mod to tweak the reading for wider acceptable range. Anyway I suppose the bigger issue would be SSB versus AM, as I suspect AM without serious clipping and other distortion artifacts would be to be more like 5-10w carrier.



BTW, there is still the $220 50w (PEP!) AM HF transmitter on Etsy. That said I have no real idea on max audio width, low pass RF filtering etc. I would not really surprise me if we have logged a few such transmitters here at HFU over the years.

4
Equipment / Re: Modulation Help (AM)
« on: March 20, 2025, 1613 UTC »
Bandwidth aside, some Icoms can benefit from the "external ALC" mod to better tweak the carrier and modulated power output for AM transmitting. It is basically just a pot and battery connected to an accessory port.

For standalone rigs from the "big three" brands with possible wider audio bandwidths, take a dive into the ESSB communities and forums for ideas. Otherwise some of the newer SDR transceivers like from Anan and Flex can go to 20KHz at least on SSB. See here:

https://www.nu9n.com/essb_ready_rigs.html

5
An inverted-L can be "broadband" in the sense a moderate-sized version can cover much of the HF spectrum. It is likely to also suffice at low frequencies since atmospheric noise swaps even relatively small antennas down there.

I would have to perhaps research it further, but IIRC, even an inverted-L at like 22' vertical by 22' horizontal or so actually shows decent lobes across a considerable swath of HF spectrum. Efficiency drops considerably at lower frequencies, but most receivers have plenty enough gain to offset the differences.

The 9:1 unun should suffice. Oftentimes it is often more about improving common-mode isolation than improved impedance matching for HF receiving antennas; withing reason of course. Considering it is an unun, you might want to experiment with an 1:1 galvanic isolation choke behind it if not already present. Also if just using a ground rod or similar, opting for a few on-ground radials might further improve efficiency.

VLF noise is a common issue even with a clean power supply and good galvanic isolation of the antenna. Unless you are perhaps in the middle of nowhere on a large rural plot, expect plenty of low-frequency noise these days.

That said I am in a neighborhood and often note plenty of NDBs plus even an occasional longwave broadcast, but reception of those tends to fair *much* better with my Airspy HF+D and 31' vertical. The HF+D has rather impressive dynamic range, selectivity, image rejection, etc. for a sub-$200 receiver.



Pending controversy over US government shortwave broadcasts aside, on a technical note, I can probably up amplification on my 148' LoG if Radio Marti discontinues on 6030. Right now it is my worst offender for overload here even with my 148' LoG well into negative gain numbers. o.0

My online SDRs are slightly down on the SNR charts for now. Awhile back I replaced my cheap preamp with the following:

https://www.sv1afn.com/en/product-category-5/high-linearity-pre-amp-(lna)-for-hf-receivers-30-khz-30-mhz.html

It is much cleaner overall, especially from an electrical noise standpoint, but it can sometimes overload a little when Radio Marti 6030 is on the air, even with currently (IIRC) 10dB attention on the input side. That attenuation tends to drop my SNR measurements by a few dB. Anyway.

Next I need to toss the current inexpensive active RF splitter for hopefully a little further signal cleanup. It appears somewhat electrically noisy at lower-HF and below. A passive splitter on a mix 73 binoc core for feeding my online SDRs should likely suffice for my purposes.



Speaking of preamps, I have a couple of inexpensive W7IUV-style preamps from AliExpress needing further evaluation. Not exactly a high-end preamp design compared to more modern designs, but the rather simple circuit is still quite popular. Naturally they have the usual cheap counterfeit 2N5109 transistors considering the low price point, but I have a few vintage (IIRC) RCA 2N5109 transistors available for swapping.

6
Amateur Radio / Re: PJ2T 14237 USB after 11PM local time
« on: March 18, 2025, 0032 UTC »
Even if upper-HF looks deserted, consider occasionally checking the spectrum right above 11m CB at night. Sometimes it is just Caribbean ops working each other, but many of them are running serious power with directional antennas.

7
2356z - Music. ~6947.1KHz. SIO 433. ~S8 peaks via my Web-888 SDR and 148' LoG. USB sync tuning. UTE on the low side.
2358z - Moved to ~6961.3KHz. SIO 433. AM sync tuning. Some static crashing and band noise but generally copyable.
0007z - Sternradio ID. "Transmitter is smoking..."
0008z - Moved to ~6954.05KHz. AM sync tuning. "Transmitter is smoking..." into music.
0124z - Sign off into repeating tone.
0125z - OTA.

Thanks for the broadcast! :)

8
Equipment / Re: Modulation Help (AM)
« on: March 17, 2025, 2352 UTC »
Are you doing any audio processing? AGC along with multi-band compression, limiting, clipping, etc. can and typically do squish audio dynamics, but those techniques are what most commercial radio stations do for a higher overall average sound level to keep the transmitter closer to peak wattage outage. Just note way too much dynamic compression can lead to excessive clipping, which can seriously degrade sound quality, so it is a balancing act.

StereoTool is popular audio processor for broadcasting. The free options are typically enough for most hobbyists. There are various presets, including for AM radio, as well.

https://www.thimeo.com/stereo-tool/

As for the transmitter in use, the 7300 has a rather narrow audio filter width. Dropping a quick search reports 100-2900KHz. Fine for spoken content but somewhat narrow for musical content. Some hobbyist make ~3K-wide music sound okay for HF listening but plan on processing the audio to get there. Also you can try ramping up the EQ curve above and below those values to help a little, but YMMV, as I suspect the filter skirts are probably rather sharp on the 7300.

9
0241z - Music. Been listening in the background since the start of transmission. SIO 344. S5 via Web-888 SDR and 148' LoG. Decent to good copy.
0246z - WTF Radio World Wide ID.
0304z - OTA.

Thanks for the broadcast! :)

10
Often one get away with no radials on an end-fed halfwave like many of the popular ~18' CB/10m verticals. The RF path for the "other side" of the antenna tends to be common-mode on the coax. Kirchhoff's current law applies even to end-fed antennas. For some deployments it can work fine, while others might incur common-mode noise and/or RF feedback, thus why many recommend short RF ground radials at the feedpoint and/or a common-mode choke like an 1/8 wave down the coax from the antenna feedpoint.

My 18' end-fed vertical is mounted over 8x 9' on-ground radials and uses an 1:1 choke. Not that I have really bothered analyzing it, but I have no discernable (to me) common mode on the feedline back to the transceiver when transmitting.

End loading with capacity hats is used to lower the "resonant" frequency. If you shorten the primary antenna element(s), you would raise the resonant frequency, thus you could use capacity hats or other typical loading techniques to bring the resulting antenna back to the desired resonant frequency. Thing is antenna loading tends to lower antenna efficiency and narrow the available operating bandwidth from resonance.

11
Equipment / Re: EDIT: Inverted L antenna... read on
« on: February 26, 2025, 0206 UTC »
Impedance increases as an antenna becomes a very tiny fraction of a frequency's wavelength.

Depending upon the core material, transformers for HF can act differently at low frequencies, thus the ratios can be a YMMV situation at longwave and similar. I often opt for mix 73 for low frequencies, though it tends to suffice for most basic receiving applications to 30MHz and sometimes higher.

I use a LDG 4:1 unun (mix 43 perhaps?) on my 31' vertical, and it works fine from longwave to upper-HF for receiving. I have tried various homebuilt and commercial transformer over the years on it. It more or less finding a decent compromise if going for a wideband 0-30MHz antenna.



Alternatively you could opt for a preamp at the feedpoint to deal with the impedance mismatches.

12
0025z - Music. SIO 344. S5 via Web-888 SDR and 148' LoG. Decent copy with some band noise and occasional static crashing.
0030z - OM on the mic.
0036z - WDOG ID.

Thanks for the broadcast and shout-out! :)

13
0022z - "Music." SIO 344. S6 via Web888 SDR and 148' LoG.

14
Amateur Radio / Music 3894 LSB 0940 UTC 17 FEB 2025
« on: February 17, 2025, 0945 UTC »
0940z - Country music on 3894lsb. S7 via KiwiSDR 2 and 148' LoG. Might be QRM as there is overlapping QSO activity on 3895lsb.

0948z - 3895 ops talking about the music. Reportedly has occured before.

15
0002z - MRI ID. SIO 233 trending 344. ~S4 via RTL-SDR V4 and 60' LoG. Good modulation and wide audio as usual.

0010z - ID over music. SIO 544. S9 peaks via Web-888 SDR and 148' LoG. Better copy now.
0013z - UTE activity noted.

0052z - Moved to 6917usb awhile ago. Radio 48 via MRI ID.
0231z - Still rocking.
0316z - OTA.

Thanks for the broadcast! :)

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