One thing I've noticed while operating digital is that I frequently see Cuban stations operating PSK31, but I don't think I've ever seen one operating JT-65.  Just curious as to why that would be.  Is JT-65 not an allowed mode for Cuba? 

I recently bought some Hamstick antennas from Lakeview, then found they were closed and only had one band in stock.  I bought MFJ antennas for the others, and have been very pleased with them.  You can adjust them to be resonant at a certain frequency, take them apart, and then when you put them back together they are still adjusted.  Whereas the Hamstick you have to adjust every time (guess you could mark it somehow, but not as convenient as using the MFJ ones).

I got an E-mail from them on Sunday.  The E-mail said that they are indeed in the process of closing down after 35 years, and are now just selling their remaining stock.  I got a notice from UPS that my order shipped on Monday.

A week or so ago I purchased some antennas and equipment online from Hamstick.com.  I received an order number, but never heard anything after that.  So yesterday evening I sent them an E-mail inquiring about the status of my order.  When I didn't receive a reply today, I tried calling their voice number.  I get a recording saying the number has been disconnected!  I tried the number listed on their website (864-226-6990) several times to be sure I did not misdial.

Not sure what is going on.  I checked and found that my credit card has NOT been charged from the order.  I know this company does a lot at hamfests.  Maybe they are not open year round?  Still, I did get an order number when I ordered, and no indication of any delays.

Has anyone else ordered from there recently or have any further information?

I believe you have to build a special interface (basically a transistor and a resistor as I recall) and connect it directly to the key jack when using N1MM to send CW.  It does not send CW using the sound card.  And, it can't receive CW, only transmit. 

"My on-board sound card is not a 16 bit sound blaster,(no line in/out, just mic/spkr jacks)."

This is not a problem; you just need to attenuate the signal more.  You could buy attenuating patch cords (Radio Shack used to sell these; not sure if they still do).  Or you could make your own.  Try resistor values of 10 to 50 ohms across both ends of the patch cord, with about 1k between the tips of the two ends.

73
Frank KG9NZ
 

"The receiver is designed for sensitivity (or Noise Figure if you like), but at the same time to be reasonably resistant to IMD.

It is typically matched, just not a very exact match... especially in scanners.

Have you read the specs of a ham receiver? They usually specify a nominal 50 ohm input impedance, but rarely specify tolerance."

I don't typically see the nominal receiver antenna input impedance in specs for VHF ham transceivers.  For example, looking at my spec sheet for the Yaesu VX-7R, the only reference to impedance is for audio output to the speaker.  For transmit, I'm sure the assumption is that the antenna impedance is 50 ohms since that is somewhat of a standard, but for receive I was not sure.


"Did you model the 2m quarter wave on 288? What was the loss due to mismatch at the antenna terminals."

Modeling the antenna itself, at 2nd harmonic resonance the impedance is around 2700 ohms.  So indeed, if the radio is 50 ohms input, the mismatch loss will be large.  Lets see - voltage percent will be 50/2750, instead of 50/100, so power ratio is (100/2750)^2 = 0.03637.  Then 10 * Log10(0.03637) = -14dB.  

73,
Frank KG9NZ

"On receive, the gain refers to the available power when matched for maximum power transfer, ie the antenna is terminated in the conjugate of its feed point impedance."

This raises another question.  Since gain is cheap, I would think that most wideband receivers (for example say a 2 meter HT that has broadband coverage) would have a voltage follower circuit on the input so that impedance would not matter.  Just a guess on my part - hopefully educated.  Anyone know if this is the case?  Or do they try to still keep the receive impedance at 50 ohms to avoid reflection and SWR problems (not sure they would matter for receive)?  I'm curious about this.  

Frank KG9NZ

I have used NEC-2 programs such as MMANA to model gain for antennas before.  Given the specs for the antenna element lengths and positions, these programs calculate gain for the antenna and plot the gain as a function of direction.  I can understand that, if a given antenna has say a 6dB gain in a particular direction and I put 100 watts into it from a transmitter, I will be getting the equivalent of 400 watts fed to an omnidirectional antenna in that direction.  My question is - does this apply identically for receiving?  

The reason I ask this has to do with the type of system I am trying to model.  I am using a 2-meter antenna on top of my car to receive other bands with a scanner.  Lets say I am receiving at 900 MHz.  Although the pattern is going to be really weird, this antenna will have gain over an isotropic antenna and even over a dipole.  But will it also have additional gain over the dB figure a simulation shows, due to the fact that it has a larger aperture than an isotropic antenna?  Obviously if I were transmitting, there would be no gain (except directionally), since I would be putting in the same amount of power regardless of antenna size.  But receiving, shouldn't a larger antenna also intercept more power regardless of its radiation pattern?  I'm trying to figure out how much I lose (or gain) using a 2m antenna for receiving on all bands vs. using an antenna cut for each band.

Thanks,
Frank KG9NZ

In the past two months, I have placed two orders with Ham Radio Outlet.  In both cases my radios shipped (free shipping) within a day after I ordered them, and everything was fine when I received them a few days later.  These were shipped from the New Hampshire store.

I also recently ordered a preamp from Hamtronics.  I ordered over the weekend and received it on Tuesday (I am in the same state).  

All three of these experiences were positive.

73,
Frank KG9NZ

I have one of the little Pinnacle Pro USB HTDV adapters.  These connect to a small antenna and then connect to a computer using USB2.  Apparently the USB stick does RF sampling and the computer's CPU is used to do DSP to decode the TV signal.  Sounds to me like this device might be useful to make a SDR, especially given that it covers all VHF and UHF TV channels in both analog and digital mode.  They are certainly inexpensive enough(list price under $100, I paid under $60 on sale).  Any thoughts?

73
Frank KG9NZ

Thanks for all the replies.  This confirmed my thoughts that RF doesn't just magically dissipate in space as a function of the number of wavelengths it has traveled.

It also raises other questions about how well an antenna that is "too long" for resonance capture the power intercepted by its aperture (i.e. do I gain anything by receiving a 20m signal with a 40m dipole and tuner vs just a 20m resonant dipole).  But that is a different topic, one which I can presumably investigate myself using an NEC2 simulation.

Thanks again and 73.
Frank KG9NZ

I read that path loss can be calculated from:

Path Loss (dB) = 20 * log10(4 * pi * distance / wavelength).

I can see where part of this formula must come from.  The area covered by the sphere of diameter distance is 4 * pi * distance squared.  In logs, squaring can be done by multiplying by 2, and the 10 factor is since the result is in dB instead of B.  But what I don't understand is how the wavelength comes into play.  Why would a shorter wavelength have a higher loss?  My guess is that there is some type of assumption about the antenna built into this formula.  At a shorter wavelength, a given type of antenna is going to be smaller.  This would not mean that power is lost more rapidly with distance at shorter wavelengths, but simply that the antenna is smaller at shorter wavelengths and therefore intercepts less area.  Is this correct?  If so, what type of antenna is implicitly assumed by this formula?  

Also, assume that the receiving antenna is kept the same physical size for receiving all wavelengths, and a (lossless) matching network is used to match impedance at the receiving end.  Would the path loss then be the same regardless of wavelength?

Thanks,
Frank KG9NZ

I have successfully run Echolink in sysop mode using a Rigblaster NoMic (which I normally use with my HF rig for PSK).  You will need to configure the Rigblaster for your particular HT.  Here is a link to the microphone connection setup:
http://www.westmountainradio.com/supportno.htm
Of course, you could build your own equivalent circuit if you wish.

You will need a serial port on your computer for controlling transmit keying.  If you have a newer computer without a serial port, you can use a USB to serial converter (available cheap on E-Bay).  The Rigblaster has the built in serial port circuit for keying.  Or you can build one yourself - as I recall it just takes a few diodes and resistors.

Hope this helps.

73,
Frank KG9NZ

Congratulations!  I'm considering building that $50 circuit winner from QST as well some time.

When I first got my license in the late 1990's, I built a kit radio (40m QRP from Ramsey and 5W QRP amplifier) and had QSOs using this and a commercial SW radio as the receiver.  Never have had QSOs with the receiver being homebuilt though.

73
Frank KG9NZ