    
Tech237
Moderator
Username: Tech237
Post Number: 883
Registered: 4-2004
| | Posted on Saturday, October 13, 2007 - 11:44 am: | 
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RM HBF 500
Complete Station Meter
Automatic Low-Pass Filter
w/Frequency, Power and SWR Meter
Microprocessor Controlled
Non - Technical Review.
By
Simon ~ Tech237 ~ N7AUS
REVIEW
I unpacked the HBF-500 Automatic Low Pass Filter and was impressed with the solid no nonsense construction and ease of setup - just two pieces of coax and a source of 12VDC.
I was further impressed when upon setting the Kenwood TS-520 to TX and the Filter started flashing and beeping an audible warning about High SWR.
The reason for that was two-fold,
#1 ~ a squirrel had dined on the coax and
#2 ~ The TS-520 was on 80m and the vertical antenna only went as low as 40m.
At least, it did show, that the system will protect you from some operator errors.
After fixing/correcting the above two errors, the display showed the frequency of cut-off, and displayed the power and swr in the system. All as it should be.
I had intended to run so lab tests to plot the actual band pass criteria and the insertion loss but unfortunately this did not eventuate.
I used the next best test available to me - empirical testing.
To do this I left the HBF-500 in line with the 520 and set the radio to mid 20m band.
Properly tuned up this radio produces around 120W PEP.
Next I set my 10m radio to twice the frequency of the 520. With the filter switched off I keyed up the 520.
To say the 10m radio went crazy, full scale on the meter, distorted but extremely strong audio, would be an understatement.
I should point out that my HF and 10m verticals are only about 8ft apart.
Now I set the HBF-500 to the 15MHz range and re-transmitted.
The 10m radios displayed no effects what so ever, no needle movement, no squelch opening, and no audio. It was just like I was not transmitting.
I am not sure how much attention that really represents but the result was certainly outstanding.
Just image a Field Day setup with each of the multiple transmitters working on one band and fitted with one of these filters??
With that in mind, I reversed the procedure and listened on 20m while I transmitted on 10.
With the filter off, the 520 produced some random bursts of audio and certainly enough noise and interference to make working a weak
station difficult.
Turning the filter on (set to 15MHz) removed that little amount of interference.
Final Comment's,
In short - this filter work and works rather well, and it is with regret that I'll be packing up the test unit and shipping it back to Copper, when I'd much rather it stay in my shack.
Yes this item is at the top of my "To Be
Purchased" list just as soon as possible. 
Respectfully Submitted,
Simon
Tech237
N7AUS
Simon
Tech237
N7AUS
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