Thursday, March 19, 2009

Still oogling the VP8

I heard VP8KF on last night and decided to try out Dual Diversity and the tightest filters

here is a shot of the radio setup

He was very weak, and the band was somewhat noisy. The antennas are my two 80M verticals

Here is an an MP3 of the encounter. It starts with DD active and then it is switched on and off several times. The times you hear best are with both RX's active. In really weak situations DD makes a difference. The filters are 25hz and the sample rate is 48K and 4096 in the DSP. To change to 48K you enter setup/audio and switch to 48K, easy! This is the highest performance. At this sample rate the 25hz filters become laser sharp. I was reading the Flex reflector and a ham was talking about revisiting 48khz sampling. I usually run 96khz. The trade off is lag. You get superior performance at 48k but there is more lag. In the old days the lag was considerably more. In the latest iteration it is barely noticeable. Where lag really shows up is in the side tone on TX and I really can't perceive a difference. With the advent of all the recent upgrades in receiver performance, I thought I'd give 48 a whirl. I was amazed. The filters are good at 96k, super good, but the filters at 48 are laser sharp. The VP8 gave me a good chance to put the radio through its paces. You will need headphones to review these clips.


I was using every trick I had to copy. The new code in the RX has improved overall performance. In addition to the now adaptive nature of image rejection (that is the RX maximizes the image rejection on an ongoing basis by an algorithm that is active in the background as you use the radio. It adapts itself to its best performance all the time), the NR and ANF have been much improved. Also BIN which is the binaural audio simulation now works great It works better than advertised. When I have used bin in the past in other receivers and in outboard DSP filters, it has always been ho hum. In this case it really makes the signal stand out. I also had dual diversity turned on, this meant I could change filters in both receivers independently. That also gave an interesting effect. I run through various scenarios in this clip. When you hear the VP8 best I have 25hz in each RX, BIN on in RX1. There is BIN in RX2 but that tends to cancel the BIN effect. With these filters you need to be on frequency, period. 5 hz makes a difference. In this instance skimmer helps. The way Skimmer does frequency, it is always exactly on freq. There is a little circle next to the bit stream and if you click that you are dead on period. It is a great help for tuning these sharp filters.

Here is an example of a QSO on 80M this morning I move 45Hz up on their center freq. I start at 100hz filter and you can hear the filter as I move up. Then I switch to 50hz and then to 25. I am in dual diversity mode. I then open up the filters and move back to the center freq.

80m 3 filters dual diversity

These stations are about S9 on 3520.00 I tune up the band from center freq by 45hz to 3520.045. I am at 100hz in both receivers and you can easily hear the decrease in signal strength as I descend the upper slope of the 100hz filter. Next I switch to 50hz so the edge of my filter are centered at +25 and -25 hz around 3520.045. You can hear the result. Next I switch to 25hz bandwidth. Now the filter is + 13 -12 at 3520.045. You can hear the result. Except for the guy's keyclix he is NOT in the pass band. I could easily work a less than s1 station in this mode, only 45hz from an S9 station.

Here is an Israel station last night, Dual diversity and 3 filters switched in and out


When the station becomes best audible is when I am perfectly tuned with 25hz filters and dual diversity any reduction in filtering or diversity results in no copy


Here is a JA4 station from this morning. Again with the kitchen sink thrown at him. He starts about 40 sec into the clip and I slowly bring him out of the noise by narrowing filters and playing with BIN and NR

This performance is ahead of what it was just 6 months ago, in fact it is ahead of what it was last week.

On another note my friend Tim W4TME has decided to chronicle his F3K experience in his own blog. He said he was going to announce his blog today so I will give you a preview

Where I consider myself a close in outsider in the Flex world, Tim is a true insider, (he has an email address that has @flexradio in it and one of those natty powder blue golf shirts) very hooked in, and should give a really interesting insiders view of the new radio. Tim manages the information systems on the Flex site and the knowledge base. He is one smart cookie. Should be a good read.