Ham College episode 100 is now available for download.

Extra Class Exam Questions – Part 38
E7H Oscillators and signal sources: types of oscillators, synthesizers and phase-locked loops,
direct digital synthesizers, stabilizing thermal drift, microphonics, high-accuracy oscillators.

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While doing a presentation about choosing the right coaxial cable, someone suggested that RG-8X (also called “Mini 8”) might be the best general-purpose cable for amateur radio. There is a lot to like about RG-8X. It is about 1/4-inch in diameter, and is flexible and affordable. This comment made me realize that I default to a larger cable (LMR-400 or RG-8) for everyday use and consider RG-8X as the cable for lightweight, portable applications (such as SOTA and POTA). But perhaps I am underestimating the capabilities of RG-8X.

So let’s take a look at the specs on RG-8X, using the DXEngineering RG-8X datasheet. Other manufacturers of RG-8X will have similar specs.

Power Rating

Most general-purpose amateur radio operation occurs at power levels of up to 100 watts for frequencies of 3 MHz to 54 MHz and up to 50 watts from 144 MHz to 450 MHz. I am thinking in terms of a station that has a 100-watt radio for HF and 6m and a typical 50-watt FM dual-band radio for 2m and 70 cm.

These power levels are easily handled by RG-8X. In fact, the cable is spec’d for over 1 kW for all of the HF bands. At 50 MHz, the power rating drops to 900 watts and further reduces to 400 watts at 150 MHz. DX Engineering does not specify the power at 440 MHz, so I looked at other websites and found that the power rating drops off to about 100 watts. So power handling is not going to be an issue.

Signal Loss

Signal loss may be a more significant limitation. How much loss are we going to be comfortable with? That is difficult to answer because each of us may make different tradeoffs to accomplish our radio operating objectives. As an upper bound, I hate to see the cable loss go as high as 3 dB, which corresponds to losing half the power in the cable! But living with 1 dB might be acceptable, which is 20% power loss. So let’s use that.

(Someone reading this is thinking: 3 dB is only half an S-unit, it won’t matter that much. To which I say: it won’t matter unless you are operating near the noise floor and 3 dB is enough loss to have your signal disappear.)

The table above shows the loss in dB per 100 feet. At 100 feet, the loss creeps up to 1.5 dB at 30 MHz. Let’s stretch our 1 dB rule of thumb to 1.5 dB, which means the loss is reasonable for all the HF bands using a 100-foot cable. At 50 MHz, the loss increases to 2.3 dB/100 feet, so to stay within 1 dB or so, we would need to limit our cable length to 50 feet. At 150 MHz, the loss rises to 3.8 dB/100 feet so we should keep our cable length less than about 25 feet. We don’t have a spec for the loss at 450 MHz but checking other websites reveals a typical loss of 6.6 dB/100 feet at 400 MHz. A 25-foot cable at 450 MHz will have a little over 1.6 dB loss.

So now the problem becomes clear: signal loss at high frequencies will be the limiting factor. (This is why I tend to grab a larger cable because I’m often operating above 50 MHz.)

Conclusions

So what can we conclude in very broad terms? Is RG-8X a good choice for a “general purpose” coaxial cable? I am going to say “Yes, But”. The key issue is signal loss and that is driven by the frequency being used and the length of the cable. So Yes, RG-8X is a good general-purpose coaxial cable but watch out for signal loss and cable length at high frequencies.

Here’s my Rules of Thumb for this cable:

For HF, RG-8X is great for all bands with cable lengths of 100 feet (maybe longer).
For 6m, RG-8X is good with a cable length of up to 50 feet.
For 2m and 70 cm, RG-8X is good with a cable length of up to 25 feet.

In all cases, checking the manufacturer’s specs and doing your own calculations is recommended. For a slightly deeper look at coaxial cables, see Hey, Which Coaxial Cable Should I Use? 

73 Bob K0NR

The post Is RG-8X the General Purpose Coaxial Cable? appeared first on The KØNR Radio Site.

Morse Code Day on April 27 (every year) honors one of the inventers of the Morse code, Samuel Morse, who was born on this day in 1791.

Happy Morse Code Day, April 27 (every year).

Samuel Finley Breese Morse (April 27, 1791 – April 2, 1872) was an American inventor and painter. After having established his reputation as a portrait painter, in his middle age Morse contributed to the invention of a single-wire telegraph system based on European telegraphs. He was a co-developer of Morse code and helped to develop the commercial use of telegraphy.

Alfred Vail developed the dot-dash structure, and Leonard Gale along with Vail was instrumental in developing the mechanical receiving apparatus for code.

Samuel Morse gets most of the credit because of his work in promoting this code as a viable means of communication. Morse code is still used now. Amateur radio is one of the communities in which Morse code is popular and in daily use.

73 de NW7US dit dit
https://NW7US.us

..

Way back on April 20th late in the afternoon, I checked my go-to DX cluster DX heat to see what was happening on the bands. I saw VU2TMP from India spotted and I have seen this station in the past but never heard him just the pileup. 

This time he was spotted on 15m and out my way in the afternoon 15m can do some very surprising things. I flipped on the Icom 7610 and spun over to 21.001 CW and low and behold there was VU2TMP at about S5! I put the radio in split and Dual receive and to my surprise there was not much action happening. I dropped my call a few times but he went back to other stations I could not hear most in Europe. I thought to myself the only time I hear him he can’t hear me, but I am only running 100 watts into a Hustler 4BTV. 

I dropped my call again a few times and low and behold I hear “VE9?” now I am thinking it’s one of my fellow VE9’s also calling him. I tried again and heard “VE9K?” well know things are getting serious and to top it off he is now fading!! I sent “VE9KK…KK…KK” and his reply was “VE9KK 5NN” Well hot dog I am in the log. I sent my exchange and all was good.

 TX Relay, Power and TX REQ IN

Wiring the Break Out Box and TX-REQ-IN

So I used my last spare plastic project box, some female phono jacks and found a push-button that I'd cut off of some other project in my junk box and went to work.

I used some shrink wrap for the momentary switch for the TX-REQ-IN pin.

I wired up 3 phono jacks... One for the TX relay, another for the +12v out, and one for the ALC control in case I ever do get an amp.  I safed the other wires for future use inside the project box.

Partial Success

Unfortunately, the TX-REQ-IN does NOT do what it does with other Yaesu transceivers.  Pressing the button grounds the TX-REQ-IN - the radio does transmit a carrier in any mode (here I tested with LSB) but rather than transmitted a reduced power carrier as it's supposed to, it just transmits at whatever wattage the mode is currently set to.  In this case I had the power set to 50w into a dummy load and it transmitted the full 50w rather than a reduced power 10w or 20w carrier for tuning.  See the power out on the radio's display

April 29 at our Training Site

5746 142 Street, Surrey

Surrey Amateur Radio Communications will be holding a parking lot sale next Saturday April 29th (weather permitting) to dispose of a large quantity of surplus ham equipment. 

Lots to choose from!

 
Items for sale include HF and mobile transmitters, receivers, transceivers, antennas, rotators, test instruments, coax and other cable, swr and power meters, power supplies, tuners, scopes, dummy loads, misc. accessories etc. We also have a utility trailer for sale. 
 
The sale is at our Ops & Training Centre 5756 142 St. Surrey, BC. from 11 am to 2 pm.  No early birds please (Map link: : https://what3words.com/daunted.rarity.parrot)

 
SARC/SEPAR members and non-members are also invited to set up a table or sell personal items from their vehicles. There is no charge for this.
 
Before the event, you may also wish to join us for our club breakfast at Denny’s Restaurant 6850 King George Blvd between 7:30 and 9:00 am.
 
Questions? [email protected]

Here is a partial list

See you there.

 

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