Initial Receiver Tests - Mercury HPSDR vs: FT-1000D

[KM1H]

Yes, several have made their own coax loops using copper pipe, fittings and wire which is all sorta getting pricey these days. Whatever is used the idea is to get the C as low as possible if you want selectivity. The 2 turn balanced loop with a PP Jfet preamp gives better performance than a single unbalanced turn.

Forming pipe into a 2 turn loop could be a challenge

[Steve - K4HX]

Would a multi-turn loop remove the need for copper tubing?

[kg8lb]

Copper tubing or "pipe"  is quite easily formed into loop configuration.  Using basic tools this is easily done in the home shop.

[Steve - K4HX]

Anything larger than 0.5 inch is overkill anyway, especially for RX.

[KM1H]

Multi turn open loops dont have the noise reduction or selectivity, they are OK for general purpose use and go back to the 19teens.

Multi wire shielded loops get right back to the high C issue and are fine for direction finding as done in WW2.

At least with CATV hardline you dont need a pipe bender, and other tools to be a plumber...plus its free.

My preference was the need to minimize noise bandwidth as well as offer enough selectivity to reduce QRM and other crud on 160 during pileups and contests. This also works for BCB DXing and the noise reduction is good for the 2 experimenters bands.

[K1JJ]

Dig this test:  There is a unique reason for needing a preselector on the Mercury receiver.  At night, with the triple 40M Yagi stack  connected to Mercury listening Europe on 20M, the ADC goes into overload. The noise floor goes up at least 25db. There are SW BC images all over the 20M band from 40M. This is at night when the SW BC sigs are crushing, of course, and during the day it is quiet. This is with Mercury's preamp on.   The same thing happens on the higher bands, 10-15M too.
 
This is a VERY demanding test, of course, with BC signals 60+ over. But there is still some SW 40M BC stuff in there when using the 20M stack, though very weak.  The preselector would probably cure this completely.  I think the existing Merc front end (as little as there is) is right on the brink and could be improved, especially when the Merc's preamp needs to be on for 10-20M..

With the same test, my own FT-1000D does NOT have 40M BC images on 10-20M listening on the 40M stack at night. Huge difference.

I'm not complaining - just pointing out that a preselector is a very good investment for the Merc.

I got an email from a guy who said the UK preselctor we discussed will fit the Merc to a "T".

http://www.herostechnology.co.uk/pages/tiny_SCR_preselector.html

T

[WA1GFZ]

Tom,
The Alex filter may be enough in your case. Actually the FT1000 has a filter system is similar to Alex. Look at the heros schematic. It is dirt simple and could be easily duplicated with two BB transformers , a tapped inductor and a variable cap.
The cool thing is that SCR will track Power SDR. I see it has not been updated to handle the Metis interface but that will come. It would be cool to interface 1 controller board to two filters so diversity is possible. I bet it would just take a different ribbon cable.

[Steve - K4HX]

Consider using a Taylor hybrid. It will improve things greatly. I've added one to the FT-1000. The difference is night and day.

[WA1GFZ]

Last night I checked the 10 meter sensitivity using an 80 meter dipole. When I connected the antenna the background noise came up. This tells me there is plenty of sensitivity since I run my Mercury with a 6 dB pad on the input.
Without the pad would be even better. You do need to select the preamplifier "on" though.
I didn't think to check 6 meters but the RX noise floor is sitting around -140 dBM. (-107 dBM is 1uV)

[K1JJ]

Try the Mercury on 20M with the 40M ant connected at night. Preamp on.

No preamp = quiet. With preamp on many images and noisy 40M BC crud.


I built a new QIX overload board for the 1000D and ready to test.   The LP filter controller board from TX got lost in the USPS mail. Just my luck.

Added digital readout to voltage and current on the 1000D amp.   Coming along.

T

[WA1GFZ]

I'll give that a try over the weekend.
Almost ready to wire my power supply for HPSDR Erb final. Just a few more holes. Decided to run aluminum strap across the 5 filter caps on the 45 volt supply. Man it will be a packed box but will deliver over 1KW of power with a 24 volt 3 amp supply for predriver and control. All in a 5 inch rack.

[kg8lb]

Copper tubing and/or pipe are easily worked into loops with common hand tools . Loops fabricated from tubing or pipe require minimal support from added brackets and braces.  Plywood forms are convenient fixtures for pulling the tubing into the required shape.

  The techniques are more related to Metal Model Making than the Plumbing trades.