We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: A little detail about RelayStation  (Read 1520 times)

Offline TheRelayStation

  • Sr. Member
  • ****
  • Posts: 445
  • 5150 Khz AM 60W Hack RF
    • View Profile
    • Live Streaming
    • Email
A little detail about RelayStation
« on: January 25, 2017, 1808 UTC »
not that anyone would particularly care and might not understand the technical aspects of this, but i thought id share some specifics about my HF station in case there are inquiring curious minds.
the transmitter is a Yaesu FT-757GXII, chosen for its simplicity to modify.
it is completely modified by me for full audio spectrum on AM only, from DC to at least 20Khz (70% power drop at 20Khz sine 0dB).
i also modified the unit for better carrier and peak envelope power output, 50 watts and 200 watts PEP respectively, power output is adjustable.
the cooling circuit of this unit has also been modified and improved for full duty operation using a linear 20 amp power supply (which is also cooled) operating at 15VDC.
the RF output travels through LMR400 at 100 feet to a 3 wire matched dipole for 5.150Mhz (modified bushcomm brand).
the height of the dipole antenna to the ground radials is specifically set to provide 60% angle of RF radiation for NVIS and 40% at a near horizon angle.
the audio processing is performed by "stereotool" (excellent software audio processor) on an Asus windows 10 netbook using a virtual sound card for the input and the headphone jack output matched at 75 ohm line level using shielded 75 ohm cable connected to the transmitter, the audio bandwidth is currently set at 5Hz to 5Khz as most self contained radio receivers besides SDR's have filters set at 5-6 Khz.
the netbook is remotely controlled using "Team Viewer" which can be used on any device including smart phones.
the transmitter also has thermal, VSWR, current and voltage shutdown protection that i added.
the frequency 5.150Mhz was chosen after extensive research prior to using it to be certain of its assigned status in the USA.
i cant think of anything else but if anyone has questions, ill be happy to answer them :)
5150 Khz AM 60W Hack RF
shortwavepirate@aol.com
https://vaughn.live/cabletv

Offline JCMaxwell

  • Hero Member
  • *****
  • Posts: 767
  • Central NC, USA
    • View Profile
Re: A little detail about RelayStation
« Reply #1 on: January 25, 2017, 1846 UTC »
Thank you for the info!

I listen to you often. Thank you for broadcasting. 
IC-R9000L, FDM-S2, Belka DX, HF+ Discovery, RSPdx, IC-R30, BC125AT, PL-880 <- W6LVP Loop

eQSLs appreciated - johnnyclerkmaxwell@gmail.com

Offline TheRelayStation

  • Sr. Member
  • ****
  • Posts: 445
  • 5150 Khz AM 60W Hack RF
    • View Profile
    • Live Streaming
    • Email
Re: A little detail about RelayStation
« Reply #2 on: January 25, 2017, 1907 UTC »
Thank you for the info!

I listen to you often. Thank you for broadcasting. 
you're welcome.
my broadcasting is really done during the daytime work week, just sharing the media content i play over the HF airwaves.
what would be great, is if someone else could provide media entertainment over the HF airwaves for me to listen to when i am not broadcasting during the daytime work week.
for those who are waiting for a QSL card, i have not forgotten about you, i will eventually get to completing them, i have all of your information saved, the reports are sincerely appreciated.
i just have a rather busy life outside of work, it leaves me no time to enjoy my hobby.
5150 Khz AM 60W Hack RF
shortwavepirate@aol.com
https://vaughn.live/cabletv

Offline Josh

  • DXing Phenomena
  • *******
  • Posts: 4212
    • View Profile
Re: A little detail about RelayStation
« Reply #3 on: January 25, 2017, 1910 UTC »
The 747 and 757s are underrated rigs. I never used mine outside the HAM bands however.
We do not encourage any radio operations contrary to regulations.

Offline TheRelayStation

  • Sr. Member
  • ****
  • Posts: 445
  • 5150 Khz AM 60W Hack RF
    • View Profile
    • Live Streaming
    • Email
Re: A little detail about RelayStation
« Reply #4 on: January 25, 2017, 1930 UTC »
The 747 and 757s are underrated rigs. I never used mine outside the HAM bands however.
agreed.
i have had this particular rig for several years, i know the technical aspects of it very well inside and out.
it is an extremely clean transmitting radio, the LPF circuit in this radio rivals that of the newer computerized models out today, the second harmonic barely exists.
i have nothing negative to say about the transmitting aspects of this radio, it is exceptionally easy to make modifications to tailor and suit specific needs.
it is a rare model to find in decent working condition though it is very easy to repair, most parts are available but some parts must be taken off a "spare" model of the same (i have a non-working parts spare).
the low level modulation circuit of this radio is just basically DSB with "carrier unbalanced", any over modulation simply becomes a mix of AM and DSB of which SAM on a receiver can correct, you cant "splatter" with this unit no matter how much over modulation you introduce, it simply becomes distorted.
the benefit to the design and modification of the low level modulation circuit of this radio, is the significant increase in PEP power.
a second advantage to low level modulation is the ability to operate at milliwatts of power with no change in modulation.

5150 Khz AM 60W Hack RF
shortwavepirate@aol.com
https://vaughn.live/cabletv

Offline redhat

  • DX Legend
  • ******
  • Posts: 1532
  • USA
  • Music is my drug.
    • View Profile
    • Email
Re: A little detail about RelayStation
« Reply #5 on: January 25, 2017, 1953 UTC »
"a second advantage to low level modulation is the ability to operate at milliwatts of power with no change in modulation."

Commercial transmitters do this with high level PWM modulation by summing the program audio with a DC bias, representing carrier level, then feeding this signal through a VCA thus changing the level of carrier and modulation together so the ratio is maintained over the entire power control range.  The control voltage to the VCA is relative to the desired power level, usually controlled by a micro controller.  The downstream PWM comparator converts this signal and a precision triangle wave to a string of pulses used to feed the modulation switch.

For simplicity and frequency agility, low level modulation is definitely the way to go.  If you have a limited power budget, such as when working with battery power, every watt counts :)

Thank You for the virtual tour of your station.  It sounds like a lot of thought and research went into it.

+-RH
« Last Edit: January 25, 2017, 1956 UTC by redhat »
Somewhere under the stars...
Airspy HF+, MLA-30/Mini-whip/Chi-Town Loop
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

 

HFUnderground Mug
HFUnderground Mug
by MitchellTimeDesigns