FTV1000 RX SENSITIVITY TESTS by K1SIX 05 Feb 2003

Serious 6M Dxers often rely on out of band indicators to give them a "feel" for conditions that may soon give them an early warning that 50 Mhz propagation may be favorable for them.

This series of tests was conducted on the FTV1000 Transverter with all the "bias" expected from an avid 6M Dxer that has been using propagation "indicators" to full advantage for many years. These tests are OBJECTIVE but DO NOT comply with the standard method of MDS measurements with a characterized square law detector! The tests utilize Joe Taylor's (K1JT) WSJT "MEASUREMENT MODE" and an RF Signal Generator with calibrated attenuator to estimate MDS. The tests should be reproducible by others for comparison purposes provided the WSJT Measure Mode is tested for calibration. My calibration tests reveal that when a weak signal (-124 dBm) is set to exactly 0 dB in the Measure Mode and dropped exactly 3 dB (-127 dBm), the WSJT Measure Mode also drops 3 dB to a new reading of -3 dB. Therefore, in these tests the non-signal noise is set for a WSJT Measure Mode reading of -3 dB and the RF level recorded that produces a WSJT Measure Mode reading of exactly 0 dB. The WSJT application requires a sound card and may be downloaded for free via the Internet. These are the conditions under which these MDS were conducted:

1-CW Mode, dual 500 Hz Filters in the IFs of the FT1000MP Mark V
2-Mark V IPO ON, AGC OFF, Transverter receive to Mark V RX IN jack
3-CW Mode, AGC OFF, 500Hz single IF Filter for the existing R9000 system
4-3' 1/4" Super flex jumper to signal generator.
5-WSJT 0 dB reading to determine MDS (see diagram for sig. gen. injection point)

Here's the results (settings refer to FTV1000 settings):

CONCLUSIONS (based upon 50.110 baseline):

1. Little difference in loss as low as the 48.250 video indicator band

2. Adequate sensitivity at 48.250 to show indication WELL PRIOR to 6M opening

3. Average 3.5 dB loss at 46.172 (Still adequate)

4. Average 4.5 dB loss at 45.250 (Still adequate)

5. Bench tests are great but do NOT account for external noise contribution when antenna is connected!

6. External noise contribution is a FACT OF LIFE on 6 meters and below. There will always be some degradation from external sources whether they are cosmic or manmade

7. The external noise contribution will be HIGHER at lower frequencies

8. BUT the external noise pickup from a high Q 50 Mhz antenna will be LESS at the lower frequencies because it is not optimized there!!

9. The above tests indicate a very capable receive system at lower "indicator" frequencies for the FTV1000.

Although the FTV1000 provides adequate sensitivity on video carrier frequencies to warn the 6M Op that an in-band opening is about to occur, I find it lacking the extreme out of band sensitivity required for maximum advance notice. To compensate, I use a second receiver and a multiple receiver distribution system. The newly constructed "K1SIX Magic Box" was completed and first air tested on 17 January 2003 and includes all the bells and whistles required at this particular station. This actually adds a "new" selectable front end to the FTV1000 depending upon the position of the THRU switch, S2. When S2 is in the THRU position, a red LED illuminates as a warning. Therefore, by utilizing the "Magic Box", the following front end combinations are possible:

1- THRU Switch= Normal, FTV1000 in IPO ON position: Provides GAASFET front end optimized near 45 MHz and up to four receiver multicoupling.
2- THRU Switch to THRU position: The FTV front end selections of IPO ON, Preamp#1 and Preamp#2 operate as normal (the input to the 4 receiver multicoupling system is disconnected).

NOTE: An ARB-702Y is used to interface the PTT (pin 2) and LINEAR (pin 8) FTV1000 signals. This buffer is connected to the LIN BAND DATA connector on the rear of the FTV1000. In order to prevent HOT SWITCHING of the T/R relay, a 10k pull-up resistor to 13 VDC must be added to the HANDSHAKING jack inside the ARB-702 and the HANDSHAKING connection must be connected to either Sequencer section C or D. Thus, when the sequencer relay is open a current source through the 10k pull-up resistor will INHIBIT RF TRANSMISSION until such time as the sequencer C or D relay grounds. This delayed ground will then enable RF transmission.

Click Here for a schematic of the "Magic Box"
 

The tables below show comparative sensitivity tests of the new receiver distribution system and two ARR preamps. These tests were accomplished in an identical manner as those described earlier. Note that all tests utilized FTV1000 preamp #2 which will always show the best sensitivity on the bench but using this front end is a poor choice in series with the outboard GAASFET preamp and an antenna connected due to the excessive gain. With the outboard preamp inline, the most sensitive practical choice is shown in (brackets) consistent with the lowest possible gain. For example, at 50.110 MHz a choice of IPO ON results is only a 2.3 dB sensitivity reduction versus Preamp #2 while Preamp #1 shows only a .5 dB sensitivity reduction versus Preamp #2. The new system now offers many front end gain/NF choices including using only the FTV1000 mixer as a front end and with these choices the overall sensitivity across all regions of interest can be greatly improved- IF NEEDED.

 

Note: 50.110 is the 6M DX calling frequency, 49.750 is the center of the East Europe/ Asian TV video carrier band, 48.250 is the center of the West Europe video carrier band, 46.172 is the high ERP video carrier frequency for Australia (46.240 is also a good VK indicator) and 45.250 is the center of the New Zealand video carrier frequency band. Most video carrier frequency bands are only 20 kHz wide with a center (0) offset, a minus 10 kHz and a plus 10 kHz offset for video carriers which are AM and for all practical purposes (with a narrowband IF filter choice)- a pure CW note.

Some notes on NOISE BLANKER settings (for 6m):
Living in a rural area, I am plagued by power line noise problems. From this hilltop I am LOS to many noisy insulators. Each direction exhibits a different noise characteristic. For me the Mark V settings of A14, B13 and B15 work best and must be customized for each direction. Unfortunately IF Noise Blankers will exhibit overload from strong signals so keep the gain setting to as minimal as possible and if you can operate with the NB off- then do so!A 20 over S9 "local" wipes out +/- 15 kHz here with his continuous CQs when I have the blanker ON and set for A14 (My NE optimized setting). USE S-METER LITE freeware to determine best noise reduction setting in a wide ssb bandwidth. Adjust the gain to MINIMUM required to do the job! Use FAST and NB button combined to make quick adjustments. In this programming mode, as you change settings and/or turn the blanker on/off: S-METER LITE and the Mark V will remain ACTIVE so you can see the dynamic results of your settings! Once happy- simply hit the ENT button to store the setting. It is likely that POWER LINE noise characteristics will change with temperature and humidity so be prepared to reprogram your settings "on the fly" by familiarization with the procedure. GL with IF Blanking as it is a battle against physical limitations. In order for a blanker to be effective, it's "detection bandwidth" must be relatively wide so that the blanking pulses are not distorted by the stretching that would occur with narrow detection bandwidths. This is an inherent problem with IF BLANKING. I'll bet that the most effective blankers are the worst when it comes to adjacent channel overload. This is The Nature of This Beast.

I hope some find these data of use 73 de K1SIX