HAM and RA

[Nathaniel Butts]

Howdy all,

In the midst of the craziness, I've been working on my technician license to open up opportunities (like funding educational opportunities, networking, etc) and also would like to send/receive in my area.  Hope to take the test soon.

I know many here are already licensed.  My question is what special considerations does one need to take when doing both RA and HAM to avoid unnecessary RFI or other conflicts?  Any best practices I should incorporate in my setup(s)?

Thanks,

Nathan Butts

Wannabe Astronomy

Bowling Green, KY

[James Abshier]

Hi Nathan,

For me it has been either/or. I can either run  the radio telescope or use my transmitter but not both at the same time. The radio telescope gets jammed when the transmitter is on, and when the radio telescope recording computer is running, it interferes with my HF receiver by producing excess background noise. Although I have had my license since 1954, I have not been very active on the air over the years. But I do occasionally get on 40 meters CW just to maintain code skills.

Jim Abshier W8QOP

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[Lester Veenstra]

Jim: Does the system crash when you transmit, if you put a termination on the LNA input, with everything else active as normal?

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

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[James Abshier]

Lester: I haven't tried that. The radio telescope doesn't actually quit working. It just gets overloaded.

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[Captain Anne Flint]

Hi Nathan, 

Do you mean the FCC licenses, or something else? 

Wende 

[StricklySpeaking]

For Wende, Yes he is talking about the FCC Amatuer Radio License.

Nathan, If you operate a transmitter for ham radio and you apply a filter that stops any RF energy above som frequency, let say 30 MHz and on the Astronomy side you apply a filter that limits the input RF to a narrow band lets say 1400 to 1440 then you may have some possibility. Since  technician license transmit priviliges limit you to operating at 50 MHz  or above  with some operation at around 28 MHz you are moving closer to the 1420 MHz input of RA.

The idea is the multiples of the frequency you transmit on should not fall in the 1420 +- receiving space or you can have issues.

If you can reduce the multiples (Harmonis) and reduce the bandwidth of the RA receiver you may make it work for you.

When you move to a high class license you can operate on lower HF frequencies and have a better chance of doing both.

You also have to consider the wires used to interface with the RA equipment and power supplies can pickup energy at non RA frequencies and get into your RA receiver.

James indicates he is operating 40 meter CW. That puts him down on the lower end of the 7 MHz band. So his multiples would be

1420/7.xx or about 200 times. That is a lot and makes me think he has other things causing his problem.  

If your transmitter antennat is near your RA receiver that make it stronger. So best to space them as far apart as you can.

You could actually measure the emitted proper from your transmitter at the RA frequencies to know what the levels are.

You can have a careful look at the RA receiver input bandwidth and understand what the lower level of sensitivity is in dB and then know exactly what you are dealing with.

By diffinition you are trying to make your RA system as sensitive as possible so this is good for RA but bad for any time of RF interference. Sensitive to signal down to -120 dB in the passband with the gain of the antenna.

On the Ham side you may use extra power amplifiers to bost you signal strength and this increases the level of any harmonics.

Some people have a lot of fun operating QRP which is low power, typically less than 5 Watts.

You could also go mobil with you ham equipment and operate from a local park. This is some special hams do. Activate a local national park for instance with you radio.

Probably way more than you wanted but I hope it helps.

The test is not to difficult but you may need to take it a couple of times just to get a feel for what is actually asked and the trick questions.

Have fun,

Bob N5BRG

[Alex P]

More Thoughts

1) The first gain stage of the LNA is ( more or less ) unfiltered and can respond to a wide frequency range and be overloaded by any strong signal levels

2) The small size of the RA Feed ( compared to amateur radio HF bands )  does, by itself,  limit  frequency range reception efficiency

3)  FCC approved radio transmission equipment must be certified to limit harmonics.

4)  A significant RFI source may be the AC<>12V Switching Power Supply

Alex KK4VB

[Lester Veenstra]

Yes, or is it RF into the ADC.   The termination should isolate the issue.  

What freq(s) are you observing that are being overloaded?

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[James Abshier]

Lester: The strong 7 MHz signal could be getting into the system almost anywhere. I figure that it is not worth trying to track it down because I don't plan on operating the radio telescope when transmitting.

Jim Abshier

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[Captain Anne Flint]

Thanks Bob. Nathan: 

I took the general radiotelephone operator’s exam in 2002. 

I believe it is the most technical exam - certainly the longest! 

I bought a study guide with sample exams and worked from that. 

You can just take the test[s] repeatedly until you pass. 

But I can’t imagine you’d have that much trouble with it. 

Wende 

[Douglas Decker]

Hi Nathan,

I have been an Amateur Radio Operator Advanced class since 1968. I also Have a FCC Commercial License since the late 70's.

I operate all hf bands and 144 and 440 fm bands and live in an 80 x 160 foot lot.

I am also running a 1.4 ghz dish and a 50 mhz meteor system. Both use SDR's and individual PC's.

So having said that I have kept some degree of separation of antennas for all systems.

To date I have not experienced any cross band interference that I am aware of. 

Some interference from LED lights and Mini Split air conditioners. I have proven the interference by just turning them off and on.

P.S when I took the exams there were no question and answer pools like today just plain old theory books.

I do not know if this helps but throwing in my 2 cents worth.

Doug K5WMT.

[Nathaniel Butts]

Thanks all,

Passed my test and waiting for my callsign.  Got a Baofeng coming this week too so I can start playing around; will also use it to check for interference on my current setup when I get the callsign and can transmit.  Don't expect much interreference from 8 watts  Not sure I'll ever have a 60 or 100 watt system here at this house so it might do for a bit.

Thanks,

Nathan Butts

Wannabe Astronomy

Bowling Green, KY